Add the missing input check for "diff" field of "ledger" (#643)

Fixes #644

.clang-format

@@ -34,7 +34,7 @@ BreakBeforeBinaryOperators: false
 BreakBeforeBraces: Custom
 BreakBeforeTernaryOperators: true
 BreakConstructorInitializersBeforeComma: true
-ColumnLimit:     80
+ColumnLimit:     120
 CommentPragmas:  '^ IWYU pragma:'
 ConstructorInitializerAllOnOneLineOrOnePerLine: true
 ConstructorInitializerIndentWidth: 4

.dockerignore

@@ -0,0 +1 @@
+build/

.git-blame-ignore-revs

@@ -7,3 +7,4 @@
 # clang-format
 e41150248a97e4bdc1cf21b54650c4bb7c63928e
 2e542e7b0d94451a933c88778461cc8d3d7e6417
+d816ef54abd8e8e979b9c795bdb657a8d18f5e95

.githooks/ensure_release_tag

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+# Pushing a release branch requires an annotated tag at the released commit
+branch=$(git rev-parse --abbrev-ref HEAD)
+
+if [[ $branch =~ master ]]; then
+  # check if HEAD commit is tagged
+  if ! git describe --exact-match HEAD; then
+    echo "Commits to master must be tagged"
+    exit 1
+  fi
+elif [[ $branch =~ release/* ]]; then
+  IFS=/ read -r branch rel_ver <<< ${branch}
+  tag=$(git describe --tags --abbrev=0)
+  if [[ "${rel_ver}" != "${tag}" ]]; then
+    echo "release/${rel_ver} branches must have annotated tag ${rel_ver}"
+    echo "git tag -am\"${rel_ver}\" ${rel_ver}"
+    exit 1
+  fi
+fi

.githooks/pre-commit

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+exec 1>&2
+
+# paths to check and re-format
+sources="src unittests"
+formatter="clang-format-11 -i"
+
+first=$(git diff $sources)
+find $sources -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 $formatter
+second=$(git diff $sources)
+changes=$(diff <(echo "$first") <(echo "$second") | wc -l | sed -e 's/^[[:space:]]*//')
+
+if [ "$changes" != "0" ]; then
+    cat <<\EOF
+
+                                   WARNING
+-----------------------------------------------------------------------------
+  Automatically re-formatted code with `clang-format` - commit was aborted.
+  Please manually add any updated files and commit again.
+-----------------------------------------------------------------------------
+
+EOF
+    exit 1
+fi
+
+.githooks/ensure_release_tag

.github/actions/lint/action.yml

@@ -0,0 +1,13 @@
+runs:
+  using: composite
+  steps:
+    # Github's ubuntu-20.04 image already has clang-format-11 installed
+    - run: |
+        find src unittests -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format-11 -i
+      shell: bash
+
+    - name: Check for differences
+      id: assert
+      shell: bash
+      run: |
+        git diff --color --exit-code | tee "clang-format.patch"

.github/actions/test/Dockerfile

@@ -0,0 +1,6 @@
+FROM cassandra:4.0.4
+
+RUN apt-get update && apt-get install -y postgresql
+COPY entrypoint.sh /entrypoint.sh
+
+ENTRYPOINT ["/entrypoint.sh"]

.github/actions/test/entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+pg_ctlcluster 12 main start
+su postgres -c"psql -c\"alter user postgres with password 'postgres'\""
+su cassandra -c "/opt/cassandra/bin/cassandra -R"
+sleep 90
+chmod +x ./clio_tests
+./clio_tests

.github/workflows/build.yml

@@ -1,9 +1,9 @@
 name: Build Clio
 on:
   push:
-    branches:  [master, release, develop, develop-next]
+    branches: [master, release/*, develop, develop-next]
   pull_request:
-    branches:  [master, release, develop, develop-next]
+    branches: [master, release/*, develop, develop-next]
   workflow_dispatch:
 
 jobs:
@@ -11,94 +11,202 @@ jobs:
     name: Lint
     runs-on: ubuntu-20.04
     steps:
-      - name: Get source
-        uses: actions/checkout@v3
-
+      - uses: actions/checkout@v3
       - name: Run clang-format
-        uses: XRPLF/clio-gha/lint@main
+        uses: ./.github/actions/lint
 
   build_clio:
     name: Build Clio
-    runs-on: [self-hosted, Linux]
+    runs-on: [self-hosted, heavy]
+    needs: lint
+    strategy:
+      fail-fast: false
+      matrix:
+        type:
+          - suffix: deb
+            image: rippleci/clio-dpkg-builder:2022-09-17
+            script: dpkg
+          - suffix: rpm
+            image: rippleci/clio-rpm-builder:2022-09-17
+            script: rpm
+
+    container:
+      image: ${{ matrix.type.image }}
     steps:
+      - uses: actions/checkout@v3
+        with:
+          path: clio
+          fetch-depth: 0
 
-      - name: Clone Clio repo
+      - name: Clone Clio packaging repo
         uses: actions/checkout@v3
         with:
-          path: clio_src
-
-      - name: Clone Clio CI repo
-        uses: actions/checkout@v3
-        with:
-          path: clio_ci
-          repository: 'XRPLF/clio-ci'
+          path: clio-packages
+          repository: XRPLF/clio-packages
+          ref: main
 
       - name: Build
-        uses: XRPLF/clio-gha/build@main
-
+        shell: bash
+        run: |
+          export CLIO_ROOT=$(realpath clio)
+          if [ ${{ matrix.type.suffix }} == "rpm" ]; then
+            source /opt/rh/devtoolset-11/enable
+          fi
+          cmake -S clio-packages -B clio-packages/build -DCLIO_ROOT=$CLIO_ROOT
+          cmake --build clio-packages/build --parallel $(nproc)
+          cp ./clio-packages/build/clio-prefix/src/clio-build/clio_tests .
+          mv ./clio-packages/build/*.${{ matrix.type.suffix }} .
       - name: Artifact packages
         uses: actions/upload-artifact@v3
         with:
-          name: clio_packages
-          path: ${{ github.workspace }}/*.deb
+          name: clio_${{ matrix.type.suffix }}_packages
+          path: ${{ github.workspace }}/*.${{ matrix.type.suffix }}
 
       - name: Artifact clio_tests
         uses: actions/upload-artifact@v3
         with:
-          name: clio_tests
-          path: clio_tests
+          name: clio_tests-${{ matrix.type.suffix }}
+          path: ${{ github.workspace }}/clio_tests
 
-  sign:
-    name: Sign packages
-    needs: build_clio
-    runs-on: ubuntu-20.04
-    if: github.ref == 'refs/heads/master' || github.ref == 'refs/heads/release' || github.ref == 'refs/heads/develop'
-    env:
-      GPG_KEY_B64: ${{ secrets.GPG_KEY_B64 }}
-      GPG_KEY_PASS_B64: ${{ secrets.GPG_KEY_PASS_B64 }}
+  build_dev:
+    name: Build on Mac/Clang14 and run tests
+    needs: lint
+    continue-on-error: false
+    runs-on: [self-hosted, macOS]
 
     steps:
-      - name: Get package artifact
-        uses: actions/download-artifact@v3
+      - uses: actions/checkout@v3
         with:
-          name: clio_packages
+          path: clio
 
-      - name: find packages
-        run: find . -name "*.deb"
-
-      - name: Install dpkg-sig
-        run: |
-          sudo apt-get update && sudo apt-get install -y dpkg-sig
-
-      - name: Sign Debian packages
-        uses: XRPLF/clio-gha/sign@main
-
-      - name: Verify the signature
-        run: |
-          set -e
-          for PKG in $(ls *.deb); do
-            gpg --verify "${PKG}"
-          done
-
-      - name: Get short SHA
-        id: shortsha
-        run: echo "::set-output name=sha8::$(echo ${GITHUB_SHA} | cut -c1-8)"
-
-      - name: Artifact Debian package
-        uses: actions/upload-artifact@v2
+      - name: Check Boost cache
+        id: boost
+        uses: actions/cache@v3
         with:
-          name: clio-deb-packages-${{ steps.shortsha.outputs.sha8 }}
-          path: ${{ github.workspace }}/*.deb
+          path: boost_1_77_0
+          key: ${{ runner.os }}-boost
+
+      - name: Build Boost
+        if: ${{ steps.boost.outputs.cache-hit != 'true' }}
+        run: |
+          rm -rf boost_1_77_0.tar.gz boost_1_77_0 # cleanup if needed first
+          curl -s -fOJL "https://boostorg.jfrog.io/artifactory/main/release/1.77.0/source/boost_1_77_0.tar.gz"
+          tar zxf boost_1_77_0.tar.gz
+          cd boost_1_77_0
+          ./bootstrap.sh
+          ./b2 define=BOOST_ASIO_HAS_STD_INVOKE_RESULT cxxflags="-std=c++20"
+
+      - name: Install dependencies
+        run: |
+          brew install llvm@14 pkg-config protobuf openssl ninja cassandra-cpp-driver bison cmake
+
+      - name: Setup environment for llvm-14
+        run: |
+          export PATH="/usr/local/opt/llvm@14/bin:$PATH"
+          export LDFLAGS="-L/usr/local/opt/llvm@14/lib -L/usr/local/opt/llvm@14/lib/c++ -Wl,-rpath,/usr/local/opt/llvm@14/lib/c++"
+          export CPPFLAGS="-I/usr/local/opt/llvm@14/include"
+
+      - name: Build clio
+        run: |
+          export BOOST_ROOT=$(pwd)/boost_1_77_0
+          cd clio
+          cmake -B build -DCMAKE_C_COMPILER='/usr/local/opt/llvm@14/bin/clang' -DCMAKE_CXX_COMPILER='/usr/local/opt/llvm@14/bin/clang++'
+          if ! cmake --build build -j; then
+            echo '# 🔥🔥 MacOS AppleClang build failed!💥' >> $GITHUB_STEP_SUMMARY
+            exit 1
+          fi
+      - name: Run Test
+        run: |
+          cd clio/build
+          ./clio_tests --gtest_filter="-BackendTest*:BackendCassandraBaseTest*:BackendCassandraTest*"
 
   test_clio:
     name: Test Clio
     runs-on: [self-hosted, Linux]
     needs: build_clio
+    strategy:
+      fail-fast: false
+      matrix:
+        suffix: [rpm, deb]
     steps:
+      - uses: actions/checkout@v3
+
       - name: Get clio_tests artifact
         uses: actions/download-artifact@v3
         with:
-          name: clio_tests
+          name: clio_tests-${{ matrix.suffix }}
 
       - name: Run tests
-        uses: XRPLF/clio-gha/test@main
+        timeout-minutes: 10
+        uses: ./.github/actions/test
+
+  code_coverage:
+    name: Build on Linux and code coverage
+    needs: lint
+    continue-on-error: false
+    runs-on: ubuntu-22.04
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          path: clio
+
+      - name: Check Boost cache
+        id: boost
+        uses: actions/cache@v3
+        with:
+          path: boost
+          key: ${{ runner.os }}-boost
+
+      - name: Build boost
+        if: steps.boost.outputs.cache-hit != 'true'
+        run: |
+          curl -s -OJL "https://boostorg.jfrog.io/artifactory/main/release/1.77.0/source/boost_1_77_0.tar.gz"
+          tar zxf boost_1_77_0.tar.gz
+          mv boost_1_77_0 boost
+          cd boost
+          ./bootstrap.sh
+          ./b2
+      - name: install deps
+        run: |
+          sudo apt-get -y install git pkg-config protobuf-compiler libprotobuf-dev libssl-dev wget build-essential doxygen bison flex autoconf clang-format gcovr
+      - name: Build clio
+        run: |
+          export BOOST_ROOT=$(pwd)/boost
+          cd clio
+          cmake -B build -DCODE_COVERAGE=on -DTEST_PARAMETER='--gtest_filter="-BackendTest*:BackendCassandraBaseTest*:BackendCassandraTest*"'
+          if ! cmake --build build -j$(nproc); then
+            echo '# 🔥Ubuntu build🔥 failed!💥' >> $GITHUB_STEP_SUMMARY
+            exit 1
+          fi
+          cd build
+          make clio_tests-ccov
+      - name: Code Coverage Summary Report
+        uses: irongut/CodeCoverageSummary@v1.2.0
+        with:
+          filename: clio/build/clio_tests-gcc-cov/out.xml
+          badge: true
+          output: both
+          format: markdown
+
+      - name: Save PR number and ccov report
+        run: |
+          mkdir -p ./UnitTestCoverage
+          echo ${{ github.event.number }} > ./UnitTestCoverage/NR
+          cp clio/build/clio_tests-gcc-cov/report.html ./UnitTestCoverage/report.html
+          cp code-coverage-results.md ./UnitTestCoverage/out.md
+          cat code-coverage-results.md > $GITHUB_STEP_SUMMARY
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          files: clio/build/clio_tests-gcc-cov/out.xml
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: UnitTestCoverage
+          path: UnitTestCoverage/
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: code_coverage_report
+          path: clio/build/clio_tests-gcc-cov/out.xml

.gitignore

@@ -1,3 +1,6 @@
 *clio*.log
-build/
+build*/
+.vscode
 .python-version
+config.json
+src/main/impl/Build.cpp

CMake/Build.cpp.in

@@ -0,0 +1,39 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <main/Build.h>
+
+namespace Build {
+static constexpr char versionString[] = "@VERSION@";
+
+std::string const&
+getClioVersionString()
+{
+    static std::string const value = versionString;
+    return value;
+}
+
+std::string const&
+getClioFullVersionString()
+{
+    static std::string const value = "clio-" + getClioVersionString();
+    return value;
+}
+
+}  // namespace Build

CMake/ClioVersion.cmake

@@ -1,15 +1,33 @@
 #[===================================================================[
-   read version from source
+   write version to source
 #]===================================================================]
 
-file (STRINGS src/main/impl/Build.cpp BUILD_INFO)
-foreach (line_ ${BUILD_INFO})
-  if (line_ MATCHES "versionString[ ]*=[ ]*\"(.+)\"")
-    set (clio_version ${CMAKE_MATCH_1})
-  endif ()
-endforeach ()
-if (clio_version)
-  message (STATUS "clio version: ${clio_version}")
-else ()
-  message (FATAL_ERROR "unable to determine clio version")
-endif ()
+find_package(Git REQUIRED)
+
+set(GIT_COMMAND rev-parse --short HEAD)
+execute_process(COMMAND ${GIT_EXECUTABLE} ${GIT_COMMAND} OUTPUT_VARIABLE REV OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+set(GIT_COMMAND branch --show-current)
+execute_process(COMMAND ${GIT_EXECUTABLE} ${GIT_COMMAND} OUTPUT_VARIABLE BRANCH OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+if(BRANCH STREQUAL "")
+  set(BRANCH "dev")
+endif()
+
+if(NOT (BRANCH MATCHES master OR BRANCH MATCHES release/*)) # for develop and any other branch name YYYYMMDDHMS-<branch>-<git-ref>
+  execute_process(COMMAND date +%Y%m%d%H%M%S OUTPUT_VARIABLE DATE OUTPUT_STRIP_TRAILING_WHITESPACE)
+  set(VERSION "${DATE}-${BRANCH}-${REV}")
+else()
+  set(GIT_COMMAND describe --tags)
+  execute_process(COMMAND ${GIT_EXECUTABLE} ${GIT_COMMAND} OUTPUT_VARIABLE TAG_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)
+  set(VERSION "${TAG_VERSION}-${REV}")
+endif()
+
+if(CMAKE_BUILD_TYPE MATCHES Debug)
+  set(VERSION "${VERSION}+DEBUG")
+endif()
+
+message(STATUS "Build version: ${VERSION}")
+set(clio_version "${VERSION}")
+
+configure_file(CMake/Build.cpp.in ${CMAKE_SOURCE_DIR}/src/main/impl/Build.cpp)

CMake/coverage.cmake

@@ -0,0 +1,126 @@
+# call add_converage(module_name) to add coverage targets for the given module
+function(add_converage module)
+  if("${CMAKE_C_COMPILER_ID}" MATCHES "(Apple)?[Cc]lang"
+     OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "(Apple)?[Cc]lang")
+    message("[Coverage] Building with llvm Code Coverage Tools")
+    # Using llvm gcov ; llvm install by xcode
+    set(LLVM_COV_PATH /Library/Developer/CommandLineTools/usr/bin)
+    if(NOT EXISTS ${LLVM_COV_PATH}/llvm-cov)
+      message(FATAL_ERROR "llvm-cov not found! Aborting.")
+    endif()
+
+    # set Flags
+    target_compile_options(${module} PRIVATE -fprofile-instr-generate
+                                             -fcoverage-mapping)
+    target_link_options(${module} PUBLIC -fprofile-instr-generate
+                        -fcoverage-mapping)
+
+    target_compile_options(clio PRIVATE -fprofile-instr-generate
+                                        -fcoverage-mapping)
+    target_link_options(clio PUBLIC -fprofile-instr-generate
+                        -fcoverage-mapping)
+
+    # llvm-cov
+    add_custom_target(
+      ${module}-ccov-preprocessing
+      COMMAND LLVM_PROFILE_FILE=${module}.profraw $<TARGET_FILE:${module}>
+      COMMAND ${LLVM_COV_PATH}/llvm-profdata merge -sparse ${module}.profraw -o
+              ${module}.profdata
+      DEPENDS ${module})
+
+    add_custom_target(
+      ${module}-ccov-show
+      COMMAND ${LLVM_COV_PATH}/llvm-cov show $<TARGET_FILE:${module}>
+              -instr-profile=${module}.profdata -show-line-counts-or-regions
+      DEPENDS ${module}-ccov-preprocessing)
+
+    # add summary for CI parse
+    add_custom_target(
+      ${module}-ccov-report
+      COMMAND
+        ${LLVM_COV_PATH}/llvm-cov report $<TARGET_FILE:${module}>
+        -instr-profile=${module}.profdata
+        -ignore-filename-regex=".*_makefiles|.*unittests|.*_deps"
+        -show-region-summary=false
+      DEPENDS ${module}-ccov-preprocessing)
+
+    # exclude libs and unittests self
+    add_custom_target(
+      ${module}-ccov
+      COMMAND
+        ${LLVM_COV_PATH}/llvm-cov show $<TARGET_FILE:${module}>
+        -instr-profile=${module}.profdata -show-line-counts-or-regions
+        -output-dir=${module}-llvm-cov -format="html"
+        -ignore-filename-regex=".*_makefiles|.*unittests|.*_deps" > /dev/null 2>&1
+      DEPENDS ${module}-ccov-preprocessing)
+
+    add_custom_command(
+      TARGET ${module}-ccov
+      POST_BUILD
+      COMMENT
+        "Open ${module}-llvm-cov/index.html in your browser to view the coverage report."
+    )
+  elseif("${CMAKE_C_COMPILER_ID}" MATCHES "GNU" OR "${CMAKE_CXX_COMPILER_ID}"
+                                                   MATCHES "GNU")
+    message("[Coverage] Building with Gcc Code Coverage Tools")
+
+    find_program(GCOV_PATH gcov)
+    if(NOT GCOV_PATH)
+      message(FATAL_ERROR "gcov not found! Aborting...")
+    endif() # NOT GCOV_PATH
+    find_program(GCOVR_PATH gcovr)
+    if(NOT GCOVR_PATH)
+      message(FATAL_ERROR "gcovr not found! Aborting...")
+    endif() # NOT GCOVR_PATH
+
+    set(COV_OUTPUT_PATH ${module}-gcc-cov)
+    target_compile_options(${module} PRIVATE -fprofile-arcs -ftest-coverage
+                                             -fPIC)
+    target_link_libraries(${module} PRIVATE gcov)
+
+    target_compile_options(clio PRIVATE -fprofile-arcs -ftest-coverage
+                                             -fPIC)
+    target_link_libraries(clio PRIVATE gcov)
+    # this target is used for CI as well generate the summary out.xml will send
+    # to github action to generate markdown, we can paste it to comments or
+    # readme
+    add_custom_target(
+      ${module}-ccov
+      COMMAND ${module} ${TEST_PARAMETER}
+      COMMAND rm -rf ${COV_OUTPUT_PATH}
+      COMMAND mkdir ${COV_OUTPUT_PATH}
+      COMMAND
+        gcovr -r ${CMAKE_SOURCE_DIR} --object-directory=${PROJECT_BINARY_DIR} -x
+        ${COV_OUTPUT_PATH}/out.xml --exclude='${CMAKE_SOURCE_DIR}/unittests/'
+        --exclude='${PROJECT_BINARY_DIR}/'
+      COMMAND
+        gcovr -r ${CMAKE_SOURCE_DIR} --object-directory=${PROJECT_BINARY_DIR}
+        --html ${COV_OUTPUT_PATH}/report.html
+        --exclude='${CMAKE_SOURCE_DIR}/unittests/'
+        --exclude='${PROJECT_BINARY_DIR}/'
+      WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
+      COMMENT "Running gcovr to produce Cobertura code coverage report.")
+
+    # generate the detail report
+    add_custom_target(
+      ${module}-ccov-report
+      COMMAND ${module} ${TEST_PARAMETER}
+      COMMAND rm -rf ${COV_OUTPUT_PATH}
+      COMMAND mkdir ${COV_OUTPUT_PATH}
+      COMMAND
+        gcovr -r ${CMAKE_SOURCE_DIR} --object-directory=${PROJECT_BINARY_DIR}
+        --html-details ${COV_OUTPUT_PATH}/index.html
+        --exclude='${CMAKE_SOURCE_DIR}/unittests/'
+        --exclude='${PROJECT_BINARY_DIR}/'
+      WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
+      COMMENT "Running gcovr to produce Cobertura code coverage report.")
+    add_custom_command(
+      TARGET ${module}-ccov-report
+      POST_BUILD
+      COMMENT
+        "Open ${COV_OUTPUT_PATH}/index.html in your browser to view the coverage report."
+    )
+  else()
+    message(FATAL_ERROR "Complier not support yet")
+  endif()
+endfunction()

CMake/deps/Postgres.cmake

@@ -1,31 +0,0 @@
-set(POSTGRES_INSTALL_DIR ${CMAKE_BINARY_DIR}/postgres)
-set(POSTGRES_LIBS pq pgcommon pgport)
-ExternalProject_Add(postgres
-    GIT_REPOSITORY https://github.com/postgres/postgres.git
-    GIT_TAG REL_14_1
-    GIT_SHALLOW 1
-    LOG_CONFIGURE 1
-    LOG_BUILD 1
-    CONFIGURE_COMMAND ./configure --prefix ${POSTGRES_INSTALL_DIR} --without-readline --verbose
-    BUILD_COMMAND ${CMAKE_COMMAND} -E env --unset=MAKELEVEL make VERBOSE=${CMAKE_VERBOSE_MAKEFILE} -j32
-    BUILD_IN_SOURCE 1
-    INSTALL_COMMAND  ${CMAKE_COMMAND} -E env make -s --no-print-directory install
-    UPDATE_COMMAND ""
-    BUILD_BYPRODUCTS
-        ${POSTGRES_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}pq${CMAKE_STATIC_LIBRARY_SUFFIX}}
-        ${POSTGRES_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}pgcommon${CMAKE_STATIC_LIBRARY_SUFFIX}}
-        ${POSTGRES_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}pgport${CMAKE_STATIC_LIBRARY_SUFFIX}}
-        )
-ExternalProject_Get_Property (postgres BINARY_DIR)
-
-foreach(_lib ${POSTGRES_LIBS})
-    add_library(${_lib} STATIC IMPORTED GLOBAL)
-    add_dependencies(${_lib} postgres)
-    set_target_properties(${_lib} PROPERTIES
-        IMPORTED_LOCATION ${POSTGRES_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}${_lib}.a)
-    set_target_properties(${_lib} PROPERTIES
-        INTERFACE_INCLUDE_DIRECTORIES ${POSTGRES_INSTALL_DIR}/include)
-    target_link_libraries(clio PUBLIC ${POSTGRES_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}${_lib}${CMAKE_STATIC_LIBRARY_SUFFIX})
-endforeach()
-add_dependencies(clio postgres)
-target_include_directories(clio PUBLIC ${POSTGRES_INSTALL_DIR}/include)

CMake/deps/SourceLocation.cmake

@@ -0,0 +1,11 @@
+include(CheckIncludeFileCXX)
+
+check_include_file_cxx("source_location" SOURCE_LOCATION_AVAILABLE)
+if(SOURCE_LOCATION_AVAILABLE) 
+    target_compile_definitions(clio PUBLIC "HAS_SOURCE_LOCATION")
+endif()
+
+check_include_file_cxx("experimental/source_location" EXPERIMENTAL_SOURCE_LOCATION_AVAILABLE)
+if(EXPERIMENTAL_SOURCE_LOCATION_AVAILABLE)     
+    target_compile_definitions(clio PUBLIC "HAS_EXPERIMENTAL_SOURCE_LOCATION")
+endif()

CMake/deps/cassandra.cmake

@@ -144,8 +144,10 @@ if(NOT cassandra)
 else()
     message("Found system installed cassandra cpp driver")
     message(${cassandra})
-
     find_path(cassandra_includes NAMES cassandra.h REQUIRED)
+    message(${cassandra_includes})
+    get_filename_component(CASSANDRA_HEADER ${cassandra_includes}/cassandra.h REALPATH)
+    get_filename_component(CASSANDRA_HEADER_DIR ${CASSANDRA_HEADER} DIRECTORY)
     target_link_libraries (clio PUBLIC ${cassandra})
-    target_include_directories(clio INTERFACE ${cassandra_includes})
+    target_include_directories(clio PUBLIC ${CASSANDRA_HEADER_DIR})
 endif()

CMake/deps/gtest.cmake

@@ -10,7 +10,8 @@ if(NOT googletest_POPULATED)
   add_subdirectory(${googletest_SOURCE_DIR} ${googletest_BINARY_DIR} EXCLUDE_FROM_ALL)
 endif()
 
-target_link_libraries(clio_tests PUBLIC clio gtest_main)
+target_link_libraries(clio_tests PUBLIC clio gmock_main)
+target_include_directories(clio_tests PRIVATE unittests)
 
 enable_testing()
 

CMake/deps/libfmt.cmake

@@ -0,0 +1,14 @@
+FetchContent_Declare(
+  libfmt
+  URL https://github.com/fmtlib/fmt/releases/download/9.1.0/fmt-9.1.0.zip
+)
+
+FetchContent_GetProperties(libfmt)
+
+if(NOT libfmt_POPULATED)
+  FetchContent_Populate(libfmt)
+  add_subdirectory(${libfmt_SOURCE_DIR} ${libfmt_BINARY_DIR} EXCLUDE_FROM_ALL)
+endif()
+
+target_link_libraries(clio PUBLIC fmt)
+

CMake/install/clio.service.in

@@ -11,6 +11,7 @@ ExecStart=@CLIO_INSTALL_DIR@/bin/clio_server @CLIO_INSTALL_DIR@/etc/config.json
 Restart=on-failure
 User=clio
 Group=clio
+LimitNOFILE=65536
 
 [Install]
-WantedBy=multi-user.target
+WantedBy=multi-user.target

CMake/settings.cmake

@@ -1 +1,6 @@
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-narrowing -Wall -Werror -Wno-dangling-else")
+target_compile_options(clio  
+  PUBLIC -Wall
+         -Werror 
+         -Wno-narrowing
+         -Wno-deprecated-declarations 
+         -Wno-dangling-else)

CMakeLists.txt

@@ -14,21 +14,13 @@ if(VERBOSE)
   set(FETCHCONTENT_QUIET FALSE CACHE STRING "Verbose FetchContent()")
 endif()
 
-if(NOT GIT_COMMIT_HASH)
-  if(VERBOSE)
-    message("GIT_COMMIT_HASH not provided...looking for git")
-  endif()
-  find_package(Git)
-  if(Git_FOUND)
-      execute_process(COMMAND ${GIT_EXECUTABLE} describe --always --abbrev=8
-          OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE gch)
-      if(gch)
-          set(GIT_COMMIT_HASH "${gch}")
-          message(STATUS "Git commit: ${GIT_COMMIT_HASH}")
-          add_definitions(-DCLIO_GIT_COMMIT_HASH="${GIT_COMMIT_HASH}")
-      endif()
-  endif()
-endif() #git
+
+if(PACKAGING)
+  add_definitions(-DPKG=1)
+endif()
+
+#c++20 removed std::result_of but boost 1.75 is still using it.
+add_definitions(-DBOOST_ASIO_HAS_STD_INVOKE_RESULT=1)
 
 add_library(clio)
 target_compile_features(clio PUBLIC cxx_std_20)
@@ -39,9 +31,10 @@ include(ExternalProject)
 include(CMake/settings.cmake)
 include(CMake/ClioVersion.cmake)
 include(CMake/deps/rippled.cmake)
+include(CMake/deps/libfmt.cmake)
 include(CMake/deps/Boost.cmake)
 include(CMake/deps/cassandra.cmake)
-include(CMake/deps/Postgres.cmake)
+include(CMake/deps/SourceLocation.cmake)
 
 target_sources(clio PRIVATE
   ## Main
@@ -49,61 +42,131 @@ target_sources(clio PRIVATE
   ## Backend
   src/backend/BackendInterface.cpp
   src/backend/CassandraBackend.cpp
-  src/backend/Pg.cpp
-  src/backend/PostgresBackend.cpp
   src/backend/SimpleCache.cpp
+  ## NextGen Backend
+  src/backend/cassandra/impl/Future.cpp
+  src/backend/cassandra/impl/Cluster.cpp
+  src/backend/cassandra/impl/Batch.cpp
+  src/backend/cassandra/impl/Result.cpp
+  src/backend/cassandra/impl/Tuple.cpp
+  src/backend/cassandra/impl/SslContext.cpp
+  src/backend/cassandra/Handle.cpp
+  src/backend/cassandra/SettingsProvider.cpp
   ## ETL
   src/etl/ETLSource.cpp
+  src/etl/ProbingETLSource.cpp
   src/etl/NFTHelpers.cpp
   src/etl/ReportingETL.cpp
   ## Subscriptions
   src/subscriptions/SubscriptionManager.cpp
   ## RPC
-  src/rpc/RPC.cpp
+  src/rpc/Errors.cpp
+  src/rpc/Factories.cpp
   src/rpc/RPCHelpers.cpp
   src/rpc/Counters.cpp
   src/rpc/WorkQueue.cpp
-  ## RPC Methods
-  # Account
+  src/rpc/common/Specs.cpp
+  src/rpc/common/Validators.cpp
+  # RPC impl
+  src/rpc/common/impl/HandlerProvider.cpp
+  ## RPC handler
   src/rpc/handlers/AccountChannels.cpp
   src/rpc/handlers/AccountCurrencies.cpp
   src/rpc/handlers/AccountInfo.cpp
   src/rpc/handlers/AccountLines.cpp
-  src/rpc/handlers/AccountOffers.cpp
+  src/rpc/handlers/AccountNFTs.cpp
   src/rpc/handlers/AccountObjects.cpp
+  src/rpc/handlers/AccountOffers.cpp
+  src/rpc/handlers/AccountTx.cpp
+  src/rpc/handlers/BookChanges.cpp
+  src/rpc/handlers/BookOffers.cpp
   src/rpc/handlers/GatewayBalances.cpp
-  src/rpc/handlers/NoRippleCheck.cpp
-  # NFT
-  src/rpc/handlers/NFTInfo.cpp
-  # Ledger
   src/rpc/handlers/Ledger.cpp
   src/rpc/handlers/LedgerData.cpp
   src/rpc/handlers/LedgerEntry.cpp
   src/rpc/handlers/LedgerRange.cpp
-  # Transaction
-  src/rpc/handlers/Tx.cpp
+  src/rpc/handlers/NFTBuyOffers.cpp
+  src/rpc/handlers/NFTHistory.cpp
+  src/rpc/handlers/NFTInfo.cpp
+  src/rpc/handlers/NFTOffersCommon.cpp
+  src/rpc/handlers/NFTSellOffers.cpp
+  src/rpc/handlers/NoRippleCheck.cpp
+  src/rpc/handlers/Random.cpp
   src/rpc/handlers/TransactionEntry.cpp
-  src/rpc/handlers/AccountTx.cpp
-  # Dex
-  src/rpc/handlers/BookOffers.cpp
-  # NFT
-  src/rpc/handlers/NFTOffers.cpp
-  # Payment Channel
-  src/rpc/handlers/ChannelAuthorize.cpp
-  src/rpc/handlers/ChannelVerify.cpp
-  # Subscribe
-  src/rpc/handlers/Subscribe.cpp
-  # Server
-  src/rpc/handlers/ServerInfo.cpp
-  # Utility
-  src/rpc/handlers/Random.cpp)
+  src/rpc/handlers/Tx.cpp
+  ## Util
+  src/config/Config.cpp
+  src/log/Logger.cpp
+  src/util/Taggable.cpp)
 
 add_executable(clio_server src/main/main.cpp)
 target_link_libraries(clio_server PUBLIC clio)
 
 if(BUILD_TESTS)
-  add_executable(clio_tests unittests/main.cpp)
+  set(TEST_TARGET clio_tests)
+  add_executable(${TEST_TARGET}
+    unittests/Playground.cpp
+    unittests/Backend.cpp
+    unittests/Logger.cpp
+    unittests/Config.cpp
+    unittests/ProfilerTest.cpp
+    unittests/DOSGuard.cpp
+    unittests/SubscriptionTest.cpp
+    unittests/SubscriptionManagerTest.cpp
+    unittests/util/TestObject.cpp
+    # RPC
+    unittests/rpc/ErrorTests.cpp
+    unittests/rpc/BaseTests.cpp
+    unittests/rpc/RPCHelpersTest.cpp
+    unittests/rpc/CountersTest.cpp
+    unittests/rpc/AdminVerificationTest.cpp
+    ## RPC handlers
+    unittests/rpc/handlers/DefaultProcessorTests.cpp
+    unittests/rpc/handlers/TestHandlerTests.cpp
+    unittests/rpc/handlers/AccountCurrenciesTest.cpp
+    unittests/rpc/handlers/AccountLinesTest.cpp
+    unittests/rpc/handlers/AccountTxTest.cpp
+    unittests/rpc/handlers/AccountOffersTest.cpp
+    unittests/rpc/handlers/AccountInfoTest.cpp
+    unittests/rpc/handlers/AccountChannelsTest.cpp
+    unittests/rpc/handlers/AccountNFTsTest.cpp
+    unittests/rpc/handlers/BookOffersTest.cpp
+    unittests/rpc/handlers/GatewayBalancesTest.cpp
+    unittests/rpc/handlers/TxTest.cpp
+    unittests/rpc/handlers/TransactionEntryTest.cpp
+    unittests/rpc/handlers/LedgerEntryTest.cpp
+    unittests/rpc/handlers/LedgerRangeTest.cpp
+    unittests/rpc/handlers/NoRippleCheckTest.cpp
+    unittests/rpc/handlers/ServerInfoTest.cpp
+    unittests/rpc/handlers/PingTest.cpp
+    unittests/rpc/handlers/RandomTest.cpp
+    unittests/rpc/handlers/NFTInfoTest.cpp
+    unittests/rpc/handlers/NFTBuyOffersTest.cpp
+    unittests/rpc/handlers/NFTSellOffersTest.cpp
+    unittests/rpc/handlers/NFTHistoryTest.cpp
+    unittests/rpc/handlers/SubscribeTest.cpp
+    unittests/rpc/handlers/UnsubscribeTest.cpp
+    unittests/rpc/handlers/LedgerDataTest.cpp
+    unittests/rpc/handlers/AccountObjectsTest.cpp
+    unittests/rpc/handlers/BookChangesTest.cpp
+    unittests/rpc/handlers/LedgerTest.cpp
+    # Backend
+    unittests/backend/cassandra/BaseTests.cpp
+    unittests/backend/cassandra/BackendTests.cpp
+    unittests/backend/cassandra/RetryPolicyTests.cpp
+    unittests/backend/cassandra/SettingsProviderTests.cpp
+    unittests/backend/cassandra/ExecutionStrategyTests.cpp
+    unittests/backend/cassandra/AsyncExecutorTests.cpp)
   include(CMake/deps/gtest.cmake)
+
+  # test for dwarf5 bug on ci 
+  target_compile_options(clio PUBLIC -gdwarf-4)
+
+  # if CODE_COVERAGE enable, add clio_test-ccov
+  if(CODE_COVERAGE)
+    include(CMake/coverage.cmake)
+    add_converage(${TEST_TARGET})
+  endif()
 endif()
 
 include(CMake/install/install.cmake)

CONTRIBUTING.md

@@ -0,0 +1,134 @@
+# Contributing
+Thank you for your interest in contributing to the `clio` project 🙏
+
+To contribute, please:
+1. Fork the repository under your own user.
+2. Create a new branch on which to commit/push your changes.
+3. Write and test your code.
+4. Ensure that your code compiles with the provided build engine and update the provided build engine as part of your PR where needed and where appropriate.
+5. Where applicable, write test cases for your code and include those in `unittests`.
+6. Ensure your code passes automated checks (e.g. clang-format)
+7. Squash your commits (i.e. rebase) into as few commits as is reasonable to describe your changes at a high level (typically a single commit for a small change). See below for more details.
+8. Open a PR to the main repository onto the _develop_ branch, and follow the provided template.
+
+> **Note:** Please read the [Style guide](#style-guide).
+
+## Install git hooks
+Please run the following command in order to use git hooks that are helpful for `clio` development.
+
+``` bash
+git config --local core.hooksPath .githooks
+```
+
+## Git commands
+This sections offers a detailed look at the git commands you will need to use to get your PR submitted. 
+Please note that there are more than one way to do this and these commands are provided for your convenience.
+At this point it's assumed that you have already finished working on your feature/bug.
+
+> **Important:** Before you issue any of the commands below, please hit the `Sync fork` button and make sure your fork's `develop` branch is up-to-date with the main `clio` repository.
+
+``` bash
+# Create a backup of your branch
+git branch <your feature branch>_bk
+
+# Rebase and squash commits into one
+git checkout develop
+git pull origin develop
+git checkout <your feature branch>
+git rebase -i develop
+```
+For each commit in the list other than the first one, enter `s` to squash.
+After this is done, you will have the opportunity to write a message for the squashed commit.
+
+> **Hint:** Please use **imperative mood** in the commit message, and capitalize the first word.
+
+``` bash
+# You should now have a single commit on top of a commit in `develop`
+git log
+```
+> **Note:** If there are merge conflicts, please resolve them now.
+
+``` bash
+# Use the same commit message as you did above
+git commit -m 'Your message'
+git rebase --continue
+```
+
+> **Important:** If you have no GPG keys set up, please follow [this tutorial](https://docs.github.com/en/authentication/managing-commit-signature-verification/adding-a-gpg-key-to-your-github-account)
+
+``` bash
+# Sign the commit with your GPG key, and push your changes
+git commit --amend -S
+git push --force
+```
+
+## Fixing issues found during code review
+While your code is in review, it's possible that some changes will be requested by reviewer(s).
+This section describes the process of adding your fixes.
+
+We assume that you already made the required changes on your feature branch.
+
+``` bash
+# Add the changed code
+git add <paths to add>
+
+# Add a [FOLD] commit message (so you remember to squash it later)
+# while also signing it with your GPG key
+git commit -S -m "[FOLD] Your commit message"
+
+# And finally push your changes
+git push
+```
+
+## After code review
+When your PR is approved and ready to merge, use `Squash and merge`.
+The button for that is near the bottom of the PR's page on GitHub.
+
+> **Important:** Please leave the automatically-generated mention/link to the PR in the subject line **and** in the description field add `"Fix #ISSUE_ID"` (replacing `ISSUE_ID` with yours) if the PR fixes an issue.
+> **Note:** See [issues](https://github.com/XRPLF/clio/issues) to find the `ISSUE_ID` for the feature/bug you were working on.
+
+# Style guide
+This is a non-exhaustive list of recommended style guidelines. These are not always strictly enforced and serve as a way to keep the codebase coherent.
+
+## Formatting
+Code must conform to `clang-format` version 10, unless the result would be unreasonably difficult to read or maintain.
+To change your code to conform use `clang-format -i <your changed files>`.
+
+## Avoid
+* Proliferation of nearly identical code.
+* Proliferation of new files and classes unless it improves readability or/and compilation time.
+* Unmanaged memory allocation and raw pointers.
+* Macros (unless they add significant value.)
+* Lambda patterns (unless these add significant value.)
+* CPU or architecture-specific code unless there is a good reason to include it, and where it is used guard it with macros and provide explanatory comments.
+* Importing new libraries unless there is a very good reason to do so.
+
+## Seek to
+* Extend functionality of existing code rather than creating new code.
+* Prefer readability over terseness where important logic is concerned.
+* Inline functions that are not used or are not likely to be used elsewhere in the codebase.
+* Use clear and self-explanatory names for functions, variables, structs and classes.
+* Use TitleCase for classes, structs and filenames, camelCase for function and variable names, lower case for namespaces and folders.
+* Provide as many comments as you feel that a competent programmer would need to understand what your code does.
+
+# Maintainers
+Maintainers are ecosystem participants with elevated access to the repository. They are able to push new code, make decisions on when a release should be made, etc.
+
+## Code Review
+A PR must be reviewed and approved by at least one of the maintainers before it can be merged.
+
+## Adding and Removing
+New maintainers can be proposed by two existing maintainers, subject to a vote by a quorum of the existing maintainers. A minimum of 50% support and a 50% participation is required. In the event of a tie vote, the addition of the new maintainer will be rejected.
+
+Existing maintainers can resign, or be subject to a vote for removal at the behest of two existing maintainers. A minimum of 60% agreement and 50% participation are required. The XRP Ledger Foundation will have the ability, for cause, to remove an existing maintainer without a vote.
+
+## Existing Maintainers
+
+* [cindyyan317](https://github.com/cindyyan317) (Ripple)
+* [godexsoft](https://github.com/godexsoft) (Ripple)
+* [legleux](https://github.com/legleux) (Ripple)
+
+## Honorable ex-Maintainers
+
+* [cjcobb23](https://github.com/cjcobb23) (ex-Ripple)
+* [natenichols](https://github.com/natenichols) (ex-Ripple)

Doxyfile

@@ -0,0 +1,3 @@
+PROJECT_NAME           = "Clio"
+INPUT                  = src
+RECURSIVE              = YES

README.md

@@ -22,13 +22,15 @@ from which data can be extracted. The rippled node does not need to be running o
 
 ## Building
 
-Clio is built with CMake. Clio requires at least GCC-11 (C++20), and Boost 1.75.0 or later.
+Clio is built with CMake. Clio requires at least GCC-11/clang-14.0.0 (C++20), and Boost 1.75.0.
 
 Use these instructions to build a Clio executable from the source. These instructions were tested on Ubuntu 20.04 LTS.
 
 ```sh
 # Install dependencies
-  sudo apt-get -y install git pkg-config protobuf-compiler libprotobuf-dev libssl-dev wget build-essential bison flex autoconf cmake
+  sudo apt-get -y install git pkg-config protobuf-compiler libprotobuf-dev libssl-dev wget build-essential bison flex autoconf cmake clang-format
+# Install gcovr to run code coverage
+  sudo apt-get -y install gcovr
 
 # Compile Boost
   wget -O $HOME/boost_1_75_0.tar.gz https://boostorg.jfrog.io/artifactory/main/release/1.75.0/source/boost_1_75_0.tar.gz
@@ -72,6 +74,36 @@ server is running
 to the IP of your Clio server. This entry can take the form of a comma-separated list if
 you are running multiple Clio nodes.
 
+
+In addition, the parameter `start_sequence` can be included and configured within the top level of the config file. This parameter specifies the sequence of first ledger to extract if the database is empty. Note that ETL extracts ledgers in order and that no backfilling functionality currently exists, meaning Clio will not retroactively learn ledgers older than the one you specify. Choosing to specify this or not will yield the following behavior:
+- If this setting is absent and the database is empty, ETL will start with the next ledger validated by the network. 
+- If this setting is present and the database is not empty, an exception is thrown.
+
+In addition, the optional parameter `finish_sequence` can be added to the json file as well, specifying where the ledger can stop.
+
+To add `start_sequence` and/or `finish_sequence` to the config.json file appropriately, they will be on the same top level of precedence as other parameters (such as `database`, `etl_sources`, `read_only`, etc.) and be specified with an integer. Here is an example snippet from the config file:
+
+```json
+"start_sequence": 12345,
+"finish_sequence": 54321
+```
+
+The parameters `ssl_cert_file` and `ssl_key_file` can also be added to the top level of precedence of our Clio config. `ssl_cert_file` specifies the filepath for your SSL cert while `ssl_key_file` specifies the filepath for your SSL key. It is up to you how to change ownership of these folders for your designated Clio user. Your options include:
+- Copying the two files as root somewhere that's accessible by the Clio user, then running `sudo chown` to your user
+- Changing the permissions directly so it's readable by your Clio user
+- Running Clio as root (strongly discouraged)
+
+An example of how to specify `ssl_cert_file` and `ssl_key_file` in the config:
+
+```json
+"server":{
+    "ip": "0.0.0.0",
+    "port": 51233
+},
+"ssl_cert_file" : "/full/path/to/cert.file",
+"ssl_key_file" : "/full/path/to/key.file"
+```
+
 Once your config files are ready, start rippled and Clio. It doesn't matter which you
 start first, and it's fine to stop one or the other and restart at any given time.
 
@@ -152,24 +184,53 @@ You must:
 ## Logging
 Clio provides several logging options, all are configurable via the config file and are detailed below.
 
-`log_level`: The minimum level of severity at which the log message will be outputted.
-Severity options are `trace`, `debug`, `info`, `warning`, `error`, `fatal`.
+`log_level`: The minimum level of severity at which the log message will be outputted by default.
+Severity options are `trace`, `debug`, `info`, `warning`, `error`, `fatal`. Defaults to `info`.
+
+`log_format`: The format of log lines produced by clio. Defaults to `"%TimeStamp% (%SourceLocation%) [%ThreadID%] %Channel%:%Severity% %Message%"`.
+Each of the variables expands like so
+- `TimeStamp`: The full date and time of the log entry
+- `SourceLocation`: A partial path to the c++ file and the line number in said file (`source/file/path:linenumber`)  
+- `ThreadID`: The ID of the thread the log entry is written from
+- `Channel`: The channel that this log entry was sent to
+- `Severity`: The severity (aka log level) the entry was sent at
+- `Message`: The actual log message
+
+`log_channels`: An array of json objects, each overriding properties for a logging `channel`. 
+At the moment of writing, only `log_level` can be overriden using this mechanism.
+
+Each object is of this format:
+```json
+{
+    "channel": "Backend",
+    "log_level": "fatal"
+}
+``` 
+If no override is present for a given channel, that channel will log at the severity specified by the global `log_level`.
+Overridable log channels: `Backend`, `WebServer`, `Subscriptions`, `RPC`, `ETL` and `Performance`.
+
+> **Note:** See `example-config.json` for more details. 
 
 `log_to_console`: Enable/disable log output to console. Options are `true`/`false`. Defaults to true.
 
 `log_directory`: Path to the directory where log files are stored. If such directory doesn't exist, Clio will create it. If not specified, logs are not written to a file.
 
-`log_rotation_size`: The max size of the log file in **megabytes** before it will rotate into a smaller file.
+`log_rotation_size`: The max size of the log file in **megabytes** before it will rotate into a smaller file. Defaults to 2GB.
 
 `log_directory_max_size`: The max size of the log directory in **megabytes** before old log files will be
-deleted to free up space.
+deleted to free up space. Defaults to 50GB.
 
 `log_rotation_hour_interval`: The time interval in **hours** after the last log rotation to automatically
-rotate the current log file.
+rotate the current log file. Defaults to 12 hours.
 
 Note, time-based log rotation occurs dependently on size-based log rotation, where if a
 size-based log rotation occurs, the timer for the time-based rotation will reset.
 
+`log_tag_style`: Tag implementation to use. Must be one of:
+- `uint`: Lock free and threadsafe but outputs just a simple unsigned integer 
+- `uuid`: Threadsafe and outputs a UUID tag
+- `none`: Don't use tagging at all
+
 ## Cassandra / Scylla Administration
 
 Since Clio relies on either Cassandra or Scylla for its database backend, here are some important considerations:

REVIEW.md

@@ -1,121 +0,0 @@
-# How to review clio
-Clio is a massive project, and thus I don't expect the code to be reviewed the
-way a normal PR would. So I put this guide together to help reviewers look at
-the relevant pieces of code without getting lost in the weeds.
-
-One thing reviewers should keep in mind is that most of clio is designed to be
-lightweight and simple. We try not to introduce any uneccessary complexity and
-keep the code as simple and straightforward as possible. Sometimes complexity is
-unavoidable, but simplicity is the goal.
-
-## Order of review
-The code is organized into 4 main components, each with their own folder. The
-code in each folder is as self contained as possible. A good way to approach
-the review would be to review one folder at a time.
-
-### backend
-The code in the backend folder is the heart of the project, and reviewers should
-start here. This is the most complex part of the code, as well as the most
-performance sensitive. clio does not keep any data in memory, so performance
-generally depends on the data model and the way we talk to the database.
-
-Reviewers should start with the README in this folder to get a high level idea
-of the data model and to review the data model itself. Then, reviewers should
-dive into the implementation. The table schemas and queries for Cassandra are 
-defined in `CassandraBackend::open()`. The table schemas for Postgres are defined
-in Pg.cpp. The queries for Postgres are defined in each of the functions of `PostgresBackend`.
-A good way to approach the implementation would be to look at the table schemas,
-and then go through the functions declared in `BackendInterface`. Reviewers could
-also branch out to the rest of the code by looking at where these functions are
-called from.
-
-### webserver
-The code in the webserver folder implements the web server for handling RPC requests.
-This code was mostly copied and pasted from boost beast example code, so I would
-really appreciate review here.
-
-### rpc
-The rpc folder contains all of the handlers and any helper functions they need.
-This code is not too complicated, so reviewers don't need to dwell long here.
-
-### etl
-The etl folder contains all of the code for extracting data from rippled. This
-code is complex and important, but most of this code was just copied from rippled
-reporting mode, and thus has already been reviewed and is being used in prod.
-
-## Design decisions that should be reviewed
-
-### Data model
-Reviewers should review the general data model. The data model itself is described
-at a high level in the README in the backend folder. The table schemas and queries
-for Cassandra are defined in the `open()` function of `CassandraBackend`. The table
-schemas for Postgres are defined in Pg.cpp. 
-
-Particular attention should be paid to the keys table, and the problem that solves
-(successor/upper bound). I originally was going to have a special table for book_offers,
-but then I decided that we could use the keys table itself for that and save space.
-This makes book_offers somewhat slow compared to rippled, though still very usable.
-
-### Large rows
-I did some tricks with Cassandra to deal with very large rows in the keys and account_tx
-tables. For each of these, the partition key (the first component of the primary
-key) is a compound key. This is meant to break large rows into smaller rows. This
-is done to avoid hotspots. Data is sharded in Cassandra, and if some rows get very
-large, some nodes can have a lot more data than others.
-
-For account_tx, this has performance implications when iterating very far back
-in time. Refer to the `fetchAccountTransactions()` function in `CassandraBackend`.
-
-It is unclear if this needs to be done for other tables.
-
-### Postgres table partitioning
-Originally, Postgres exhibited performance problems when the dataset approach 1
-TB. This was solved by table partitioning.
-
-### Threading
-I used asio for multithreading. There are a lot of different io_contexts lying
-around the code. This needs to be cleaned up a bit. Most of these are really
-just ways to submit an async job to a single thread. I don't think it makes
-sense to have one io_context for the whole application, but some of the threading
-is a bit opaque and could be cleaned up.
-
-### Boost Json
-I used boost json for serializing data to json.
-
-### No cache
-As of now, there is no cache. I am not sure if a cache is even worth it. A
-transaction cache would not be hard, but a cache for ledger data will be hard.
-While a cache would improve performance, it would increase memory usage. clio
-is designed to be lightweight. Also, I've reached thousands of requests per
-second with a single clio node, so I'm not sure performance is even an issue.
-
-## Things I'm less than happy about
-
-#### BackendIndexer
-This is a particularly hairy piece of code that handles writing to the keys table.
-I am not too happy with this code. Parts of it need to execute in real time as
-part of ETL, and other parts are allowed to run in the background. There is also
-code that detects if a previous background job failed to complete before the
-server shutdown, and thus tries to rerun that job. The code feels tacked on, and
-I would like it to be more cleanly integrated with the rest of the code.
-
-#### Shifting
-There is some bit shifting going on with the keys table and the account_tx table.
-The keys table is written to every 2^20 ledgers. Maybe it would be better to just
-write every 1 million ledgers. 
-
-#### performance of book_offers
-book_offers is a bit slow. It could be sped up in a variety of ways. One is to
-keep a separate book_offers table. However, this is not straightforward and will
-use more space. Another is to keep a cache of book_offers for the most recent ledger
-(or few ledgers). I am not sure if this is worth it
-
-#### account_tx in Cassandra
-After the fix to deal with large rows, account_tx can be slow at times when using
-Cassandra. Specifically, if there are large gaps in time where the account was
-not affected by any transactions, the code will be reading empty records. I would
-like to sidestep this issue if possible.
-
-#### Implementation of fetchLedgerPage
-`fetchLedgerPage()` is rather complex. Part of this seems unavoidable, since this
-code is dealing with the keys table.

docker/centos/Dockerfile

@@ -0,0 +1,49 @@
+# FROM centos:7 as deps
+FROM centos:7 as build
+
+ENV CLIO_DIR=/opt/clio/
+# ENV OPENSSL_DIR=/opt/openssl
+
+RUN yum -y install git epel-release centos-release-scl perl-IPC-Cmd openssl
+RUN yum install -y devtoolset-11
+ENV version=3.16
+ENV build=3
+# RUN curl -OJL https://cmake.org/files/v$version/cmake-$version.$build.tar.gz
+COPY docker/shared/install_cmake.sh /install_cmake.sh
+RUN /install_cmake.sh 3.16.3 /usr/local
+RUN source /opt/rh/devtoolset-11/enable
+WORKDIR /tmp
+# RUN mkdir $OPENSSL_DIR && cd $OPENSSL_DIR
+COPY docker/centos/build_git_centos7.sh build_git_centos7.sh
+
+RUN ./build_git_centos7.sh
+RUN git clone https://github.com/openssl/openssl
+WORKDIR /tmp/openssl
+RUN git checkout OpenSSL_1_1_1q
+#--prefix=/usr --openssldir=/etc/ssl --libdir=lib no-shared zlib-dynamic
+RUN SSLDIR=$(openssl version -d | cut -d: -f2 | tr -d [:space:]\") && ./config -fPIC --prefix=/usr --openssldir=${SSLDIR} zlib shared && \
+    make -j $(nproc) && \
+    make install_sw
+WORKDIR /tmp
+# FROM centos:7 as build
+
+RUN git clone https://github.com/xrplf/clio.git
+COPY docker/shared/build_boost.sh build_boost.sh
+ENV OPENSSL_ROOT=/opt/local/openssl
+ENV BOOST_ROOT=/boost
+RUN source scl_source enable devtoolset-11 && /tmp/build_boost.sh 1.75.0
+RUN yum install -y bison flex
+RUN yum install -y rpmdevtools rpmlint
+RUN source /opt/rh/devtoolset-11/enable && cd /tmp/clio && \
+    cmake -B build -DBUILD_TESTS=1 && \
+    cmake --build build --parallel $(nproc)
+RUN mkdir output
+RUN strip clio/build/clio_server && strip clio/build/clio_tests
+RUN cp clio/build/clio_tests output/ && cp clio/build/clio_server output/
+RUN cp clio/example-config.json output/example-config.json
+
+FROM centos:7
+COPY --from=build /tmp/output /clio
+RUN mkdir -p /opt/clio/etc && mv /clio/example-config.json /opt/clio/etc/config.json
+
+CMD ["/clio/clio_server", "/opt/clio/etc/config.json"]

docker/centos/build_git_centos7.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -ex
+GIT_VERSION="2.37.1"
+curl -OJL https://github.com/git/git/archive/refs/tags/v${GIT_VERSION}.tar.gz
+tar zxvf git-${GIT_VERSION}.tar.gz
+cd git-${GIT_VERSION}
+
+yum install -y centos-release-scl epel-release
+yum update -y
+yum install -y devtoolset-11 autoconf gnu-getopt gettext zlib-devel  libcurl-devel
+
+source /opt/rh/devtoolset-11/enable
+make configure
+./configure
+make git -j$(nproc)
+make install git
+git  --version | cut -d ' ' -f3

docker/centos/install_cmake.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+set -eo pipefail
+
+CMAKE_VERSION=${1:-"3.16.3"}
+cd /tmp
+URL="https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/cmake-${CMAKE_VERSION}-linux-x86_64.tar.gz"
+curl -OJLs $URL
+tar xzvf cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz
+mv cmake-${CMAKE_VERSION}-Linux-x86_64 /opt/
+ln -s /opt/cmake-${CMAKE_VERSION}-Linux-x86_64/bin/cmake /usr/local/bin/cmake

docker/clio_docker/centos/build_boost.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -exu
+
+#yum install wget lz4 lz4-devel git llvm13-static.x86_64 llvm13-devel.x86_64 devtoolset-11-binutils zlib-static
+# it's either those or link=static that halves the failures. probably link=static
+BOOST_VERSION=$1
+BOOST_VERSION_=$(echo ${BOOST_VERSION} | tr . _)
+echo "BOOST_VERSION: ${BOOST_VERSION}"
+echo "BOOST_VERSION_: ${BOOST_VERSION_}"
+curl -OJLs "https://boostorg.jfrog.io/artifactory/main/release/${BOOST_VERSION}/source/boost_${BOOST_VERSION_}.tar.gz"
+tar zxf "boost_${BOOST_VERSION_}.tar.gz"
+cd boost_${BOOST_VERSION_} && ./bootstrap.sh && ./b2 --without-python link=static -j$(nproc)
+mkdir -p /boost && mv boost /boost && mv stage /boost

docker/clio_docker/centos/build_git_centos7.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -ex
+GIT_VERSION="2.37.1"
+curl -OJL https://github.com/git/git/archive/refs/tags/v${GIT_VERSION}.tar.gz
+tar zxvf git-${GIT_VERSION}.tar.gz
+cd git-${GIT_VERSION}
+
+yum install -y centos-release-scl epel-release
+yum update -y
+yum install -y devtoolset-11 autoconf gnu-getopt gettext zlib-devel  libcurl-devel
+
+source /opt/rh/devtoolset-11/enable
+make configure
+./configure
+make git -j$(nproc)
+make install git
+git  --version | cut -d ' ' -f3

docker/clio_docker/centos/dockerfile

@@ -0,0 +1,34 @@
+FROM centos:7
+
+ENV CLIO_DIR=/opt/clio/
+# ENV OPENSSL_DIR=/opt/openssl
+
+RUN yum -y install git epel-release centos-release-scl perl-IPC-Cmd openssl
+RUN yum install -y devtoolset-11
+ENV version=3.16
+ENV build=3
+# RUN curl -OJL https://cmake.org/files/v$version/cmake-$version.$build.tar.gz
+COPY install_cmake.sh /install_cmake.sh
+RUN /install_cmake.sh 3.16.3 /usr/local
+RUN source /opt/rh/devtoolset-11/enable
+WORKDIR /tmp
+# RUN mkdir $OPENSSL_DIR && cd $OPENSSL_DIR
+COPY build_git_centos7.sh build_git_centos7.sh
+
+RUN ./build_git_centos7.sh
+RUN git clone https://github.com/openssl/openssl
+WORKDIR /tmp/openssl
+RUN git checkout OpenSSL_1_1_1q
+#--prefix=/usr --openssldir=/etc/ssl --libdir=lib no-shared zlib-dynamic
+RUN SSLDIR=$(openssl version -d | cut -d: -f2 | tr -d [:space:]\") && ./config -fPIC --prefix=/usr --openssldir=${SSLDIR} zlib shared && \
+    make -j $(nproc) && \
+    make install_sw
+WORKDIR /tmp
+RUN git clone https://github.com/xrplf/clio.git
+COPY build_boost.sh build_boost.sh
+ENV OPENSSL_ROOT=/opt/local/openssl
+ENV BOOST_ROOT=/boost
+RUN source scl_source enable devtoolset-11 && /tmp/build_boost.sh 1.75.0
+RUN yum install -y bison flex
+RUN source /opt/rh/devtoolset-11/enable && \
+    cd /tmp/clio && cmake -B build -Dtests=0 -Dlocal_libarchive=1 -Dunity=0 -DBUILD_TESTS=0 && cmake --build build --parallel $(nproc)

docker/clio_docker/centos/install_cmake.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+set -eo pipefail
+
+CMAKE_VERSION=${1:-"3.16.3"}
+cd /tmp
+URL="https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/cmake-${CMAKE_VERSION}-linux-x86_64.tar.gz"
+curl -OJLs $URL
+tar xzvf cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz
+mv cmake-${CMAKE_VERSION}-Linux-x86_64 /opt/
+ln -s /opt/cmake-${CMAKE_VERSION}-Linux-x86_64/bin/cmake /usr/local/bin/cmake

docker/shared/build_boost.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -exu
+
+#yum install wget lz4 lz4-devel git llvm13-static.x86_64 llvm13-devel.x86_64 devtoolset-11-binutils zlib-static
+# it's either those or link=static that halves the failures. probably link=static
+BOOST_VERSION=$1
+BOOST_VERSION_=$(echo ${BOOST_VERSION} | tr . _)
+echo "BOOST_VERSION: ${BOOST_VERSION}"
+echo "BOOST_VERSION_: ${BOOST_VERSION_}"
+curl -OJLs "https://boostorg.jfrog.io/artifactory/main/release/${BOOST_VERSION}/source/boost_${BOOST_VERSION_}.tar.gz"
+tar zxf "boost_${BOOST_VERSION_}.tar.gz"
+cd boost_${BOOST_VERSION_} && ./bootstrap.sh && ./b2 --without-python link=static -j$(nproc)
+mkdir -p /boost && mv boost /boost && mv stage /boost

docker/shared/install_cmake.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+set -eo pipefail
+
+CMAKE_VERSION=${1:-"3.16.3"}
+cd /tmp
+URL="https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/cmake-${CMAKE_VERSION}-linux-x86_64.tar.gz"
+curl -OJLs $URL
+tar xzvf cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz
+mv cmake-${CMAKE_VERSION}-Linux-x86_64 /opt/
+ln -s /opt/cmake-${CMAKE_VERSION}-Linux-x86_64/bin/cmake /usr/local/bin/cmake

docker/shared/install_openssl.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+set -e

docker/ubuntu/Dockerfile

@@ -0,0 +1,24 @@
+FROM ubuntu:20.04 AS boost
+
+RUN apt-get update && apt-get install -y build-essential
+ARG BOOST_VERSION_=1_75_0
+ARG BOOST_VERSION=1.75.0
+COPY docker/shared/build_boost.sh .
+RUN apt install -y curl
+RUN ./build_boost.sh ${BOOST_VERSION}
+ENV BOOST_ROOT=/boost
+
+FROM ubuntu:20.04 AS build
+ENV BOOST_ROOT=/boost
+COPY --from=boost /boost /boost
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && apt-get install --no-install-recommends -y build-essential software-properties-common pkg-config libssl-dev wget curl gpg git zlib1g-dev bison flex autoconf lsb-release
+RUN apt install -y gpg-agent
+RUN wget https://apt.llvm.org/llvm.sh
+RUN chmod +x llvm.sh && ./llvm.sh 14 && ./llvm.sh 15
+# COPY . /clio
+## Install cmake
+ARG CMAKE_VERSION=3.16.3
+COPY docker/shared/install_cmake.sh .
+RUN ./install_cmake.sh ${CMAKE_VERSION}
+ENV PATH="/opt/local/cmake/bin:$PATH"

example-config.json

@@ -1,42 +1,93 @@
 {
-    "database":
-    {
-        "type":"cassandra",
-        "cassandra":
-        {
-            "contact_points":"127.0.0.1",
-            "port":9042,
-            "keyspace":"clio",
-            "replication_factor":1,
-            "table_prefix":"",
-            "max_requests_outstanding":25000,
-            "threads":8
+    "database": {
+        "type": "cassandra",
+        "cassandra": {
+            "contact_points": "127.0.0.1",
+            "port": 9042,
+            "keyspace": "clio",
+            "replication_factor": 1,
+            "table_prefix": "",
+            "max_write_requests_outstanding": 25000,
+            "max_read_requests_outstanding": 30000,
+            "threads": 8
         }
     },
-    "etl_sources":
-    [
+    "etl_sources": [
         {
-            "ip":"127.0.0.1",
-            "ws_port":"6006",
-            "grpc_port":"50051"
+            "ip": "127.0.0.1",
+            "ws_port": "6006",
+            "grpc_port": "50051"
         }
     ],
-    "dos_guard":
-    {
-        "whitelist":["127.0.0.1"]
+    "dos_guard": {
+        "whitelist": [
+            "127.0.0.1"
+        ], // comma-separated list of ips to exclude from rate limiting
+        /* The below values are the default values and are only specified here
+         * for documentation purposes. The rate limiter currently limits
+         * connections and bandwidth per ip. The rate limiter looks at the raw
+         * ip of a client connection, and so requests routed through a load
+         * balancer will all have the same ip and be treated as a single client
+         */
+        "max_fetches": 1000000, // max bytes per ip per sweep interval
+        "max_connections": 20, // max connections per ip
+        "max_requests": 20, // max connections per ip
+        "sweep_interval": 1 // time in seconds before resetting bytes per ip count
     },
-    "server":{
-        "ip":"0.0.0.0",
-        "port":51233
+    "cache": {
+        "peers": [
+            {
+                "ip": "127.0.0.1",
+                "port": 51234
+            }
+        ]
     },
-    "log_level":"debug",
+    "server": {
+        "ip": "0.0.0.0",
+        "port": 51233,
+        /* Max number of requests to queue up before rejecting further requests.
+        * Defaults to 0, which disables the limit
+        */
+        "max_queue_size": 500
+    },
+    "log_channels": [
+        {
+            "channel": "Backend",
+            "log_level": "fatal"
+        },
+        {
+            "channel": "WebServer",
+            "log_level": "info"
+        },
+        {
+            "channel": "Subscriptions",
+            "log_level": "info"
+        },
+        {
+            "channel": "RPC",
+            "log_level": "error"
+        },
+        {
+            "channel": "ETL",
+            "log_level": "debug"
+        },
+        {
+            "channel": "Performance",
+            "log_level": "trace"
+        }
+    ],
+    "log_level": "info",
+    "log_format": "%TimeStamp% (%SourceLocation%) [%ThreadID%] %Channel%:%Severity% %Message%", // This is the default format
     "log_to_console": true,
-    "log_to_file": true,
-    "log_directory":"./clio_log",
+    "log_directory": "./clio_log",
     "log_rotation_size": 2048,
     "log_directory_max_size": 51200,
     "log_rotation_hour_interval": 12,
-    "online_delete":0,
-    "extractor_threads":8,
-    "read_only":false
+    "log_tag_style": "uint",
+    "extractor_threads": 8,
+    "read_only": false,
+    //"start_sequence": [integer] the ledger index to start from,
+    //"finish_sequence": [integer] the ledger index to finish at,
+    //"ssl_cert_file" : "/full/path/to/cert.file",
+    //"ssl_key_file" : "/full/path/to/key.file"
 }

src/backend/BackendFactory.h

@@ -1,47 +1,55 @@
-#ifndef RIPPLE_APP_REPORTING_BACKENDFACTORY_H_INCLUDED
-#define RIPPLE_APP_REPORTING_BACKENDFACTORY_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
-#include <boost/algorithm/string.hpp>
 #include <backend/BackendInterface.h>
 #include <backend/CassandraBackend.h>
-#include <backend/PostgresBackend.h>
+#include <backend/CassandraBackendNew.h>
+#include <config/Config.h>
+#include <log/Logger.h>
+
+#include <boost/algorithm/string.hpp>
 
 namespace Backend {
 std::shared_ptr<BackendInterface>
-make_Backend(boost::asio::io_context& ioc, boost::json::object const& config)
+make_Backend(boost::asio::io_context& ioc, clio::Config const& config)
 {
-    BOOST_LOG_TRIVIAL(info) << __func__ << ": Constructing BackendInterface";
-
-    boost::json::object dbConfig = config.at("database").as_object();
-
-    bool readOnly = false;
-    if (config.contains("read_only"))
-        readOnly = config.at("read_only").as_bool();
-
-    auto type = dbConfig.at("type").as_string();
+    static clio::Logger log{"Backend"};
+    log.info() << "Constructing BackendInterface";
 
+    auto readOnly = config.valueOr("read_only", false);
+    auto type = config.value<std::string>("database.type");
     std::shared_ptr<BackendInterface> backend = nullptr;
 
     if (boost::iequals(type, "cassandra"))
     {
-        if (config.contains("online_delete"))
-            dbConfig.at(type).as_object()["ttl"] =
-                config.at("online_delete").as_int64() * 4;
-        backend = std::make_shared<CassandraBackend>(
-            ioc, dbConfig.at(type).as_object());
+        auto cfg = config.section("database." + type);
+        auto ttl = config.valueOr<uint32_t>("online_delete", 0) * 4;
+        backend = std::make_shared<CassandraBackend>(ioc, cfg, ttl);
     }
-    else if (boost::iequals(type, "postgres"))
+    else if (boost::iequals(type, "cassandra-new"))
     {
-        if (dbConfig.contains("experimental") &&
-            dbConfig.at("experimental").is_bool() &&
-            dbConfig.at("experimental").as_bool())
-            backend = std::make_shared<PostgresBackend>(
-                ioc, dbConfig.at(type).as_object());
-        else
-            BOOST_LOG_TRIVIAL(fatal)
-                << "Postgres support is experimental at this time. "
-                << "If you would really like to use Postgres, add "
-                   "\"experimental\":true to your database config";
+        auto cfg = config.section("database." + type);
+        auto ttl = config.valueOr<uint16_t>("online_delete", 0) * 4;
+        backend =
+            std::make_shared<Backend::Cassandra::CassandraBackend>(Backend::Cassandra::SettingsProvider{cfg, ttl});
     }
 
     if (!backend)
@@ -55,11 +63,8 @@ make_Backend(boost::asio::io_context& ioc, boost::json::object const& config)
         backend->updateRange(rng->maxSequence);
     }
 
-    BOOST_LOG_TRIVIAL(info)
-        << __func__ << ": Constructed BackendInterface Successfully";
+    log.info() << "Constructed BackendInterface Successfully";
 
     return backend;
 }
 }  // namespace Backend
-
-#endif  // RIPPLE_REPORTING_BACKEND_FACTORY

src/backend/BackendInterface.cpp

@@ -1,33 +1,58 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
 #include <ripple/protocol/Indexes.h>
 #include <ripple/protocol/STLedgerEntry.h>
 #include <backend/BackendInterface.h>
+#include <log/Logger.h>
+
+using namespace clio;
+
+// local to compilation unit loggers
+namespace {
+clio::Logger gLog{"Backend"};
+}  // namespace
+
 namespace Backend {
 bool
 BackendInterface::finishWrites(std::uint32_t const ledgerSequence)
 {
+    gLog.debug() << "Want finish writes for " << ledgerSequence;
     auto commitRes = doFinishWrites();
     if (commitRes)
     {
+        gLog.debug() << "Successfully commited. Updating range now to " << ledgerSequence;
         updateRange(ledgerSequence);
     }
     return commitRes;
 }
 void
-BackendInterface::writeLedgerObject(
-    std::string&& key,
-    std::uint32_t const seq,
-    std::string&& blob)
+BackendInterface::writeLedgerObject(std::string&& key, std::uint32_t const seq, std::string&& blob)
 {
     assert(key.size() == sizeof(ripple::uint256));
-    ripple::uint256 key256 = ripple::uint256::fromVoid(key.data());
     doWriteLedgerObject(std::move(key), seq, std::move(blob));
 }
 
 std::optional<LedgerRange>
-BackendInterface::hardFetchLedgerRangeNoThrow(
-    boost::asio::yield_context& yield) const
+BackendInterface::hardFetchLedgerRangeNoThrow(boost::asio::yield_context& yield) const
 {
-    BOOST_LOG_TRIVIAL(debug) << __func__;
+    gLog.trace() << "called";
     while (true)
     {
         try
@@ -44,7 +69,7 @@ BackendInterface::hardFetchLedgerRangeNoThrow(
 std::optional<LedgerRange>
 BackendInterface::hardFetchLedgerRangeNoThrow() const
 {
-    BOOST_LOG_TRIVIAL(debug) << __func__;
+    gLog.trace() << "called";
     return retryOnTimeout([&]() { return hardFetchLedgerRange(); });
 }
 
@@ -58,21 +83,17 @@ BackendInterface::fetchLedgerObject(
     auto obj = cache_.get(key, sequence);
     if (obj)
     {
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << " - cache hit - " << ripple::strHex(key);
+        gLog.trace() << "Cache hit - " << ripple::strHex(key);
         return *obj;
     }
     else
     {
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << " - cache miss - " << ripple::strHex(key);
+        gLog.trace() << "Cache miss - " << ripple::strHex(key);
         auto dbObj = doFetchLedgerObject(key, sequence, yield);
         if (!dbObj)
-            BOOST_LOG_TRIVIAL(trace)
-                << __func__ << " - missed cache and missed in db";
+            gLog.trace() << "Missed cache and missed in db";
         else
-            BOOST_LOG_TRIVIAL(trace)
-                << __func__ << " - missed cache but found in db";
+            gLog.trace() << "Missed cache but found in db";
         return dbObj;
     }
 }
@@ -94,9 +115,7 @@ BackendInterface::fetchLedgerObjects(
         else
             misses.push_back(keys[i]);
     }
-    BOOST_LOG_TRIVIAL(trace)
-        << __func__ << " - cache hits = " << keys.size() - misses.size()
-        << " - cache misses = " << misses.size();
+    gLog.trace() << "Cache hits = " << keys.size() - misses.size() << " - cache misses = " << misses.size();
 
     if (misses.size())
     {
@@ -122,11 +141,9 @@ BackendInterface::fetchSuccessorKey(
 {
     auto succ = cache_.getSuccessor(key, ledgerSequence);
     if (succ)
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << " - cache hit - " << ripple::strHex(key);
+        gLog.trace() << "Cache hit - " << ripple::strHex(key);
     else
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << " - cache miss - " << ripple::strHex(key);
+        gLog.trace() << "Cache miss - " << ripple::strHex(key);
     return succ ? succ->key : doFetchSuccessorKey(key, ledgerSequence, yield);
 }
 
@@ -153,7 +170,6 @@ BackendInterface::fetchBookOffers(
     ripple::uint256 const& book,
     std::uint32_t const ledgerSequence,
     std::uint32_t const limit,
-    std::optional<ripple::uint256> const& cursor,
     boost::asio::yield_context& yield) const
 {
     // TODO try to speed this up. This can take a few seconds. The goal is
@@ -162,10 +178,7 @@ BackendInterface::fetchBookOffers(
     const ripple::uint256 bookEnd = ripple::getQualityNext(book);
     ripple::uint256 uTipIndex = book;
     std::vector<ripple::uint256> keys;
-    auto getMillis = [](auto diff) {
-        return std::chrono::duration_cast<std::chrono::milliseconds>(diff)
-            .count();
-    };
+    auto getMillis = [](auto diff) { return std::chrono::duration_cast<std::chrono::milliseconds>(diff).count(); };
     auto begin = std::chrono::system_clock::now();
     std::uint32_t numSucc = 0;
     std::uint32_t numPages = 0;
@@ -180,30 +193,24 @@ BackendInterface::fetchBookOffers(
         succMillis += getMillis(mid2 - mid1);
         if (!offerDir || offerDir->key >= bookEnd)
         {
-            BOOST_LOG_TRIVIAL(trace) << __func__ << " - offerDir.has_value() "
-                                     << offerDir.has_value() << " breaking";
+            gLog.trace() << "offerDir.has_value() " << offerDir.has_value() << " breaking";
             break;
         }
         uTipIndex = offerDir->key;
         while (keys.size() < limit)
         {
             ++numPages;
-            ripple::STLedgerEntry sle{
-                ripple::SerialIter{
-                    offerDir->blob.data(), offerDir->blob.size()},
-                offerDir->key};
+            ripple::STLedgerEntry sle{ripple::SerialIter{offerDir->blob.data(), offerDir->blob.size()}, offerDir->key};
             auto indexes = sle.getFieldV256(ripple::sfIndexes);
             keys.insert(keys.end(), indexes.begin(), indexes.end());
             auto next = sle.getFieldU64(ripple::sfIndexNext);
             if (!next)
             {
-                BOOST_LOG_TRIVIAL(trace)
-                    << __func__ << " next is empty. breaking";
+                gLog.trace() << "Next is empty. breaking";
                 break;
             }
             auto nextKey = ripple::keylet::page(uTipIndex, next);
-            auto nextDir =
-                fetchLedgerObject(nextKey.key, ledgerSequence, yield);
+            auto nextDir = fetchLedgerObject(nextKey.key, ledgerSequence, yield);
             assert(nextDir);
             offerDir->blob = *nextDir;
             offerDir->key = nextKey.key;
@@ -215,29 +222,21 @@ BackendInterface::fetchBookOffers(
     auto objs = fetchLedgerObjects(keys, ledgerSequence, yield);
     for (size_t i = 0; i < keys.size() && i < limit; ++i)
     {
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << " key = " << ripple::strHex(keys[i])
-            << " blob = " << ripple::strHex(objs[i])
-            << " ledgerSequence = " << ledgerSequence;
+        gLog.trace() << "Key = " << ripple::strHex(keys[i]) << " blob = " << ripple::strHex(objs[i])
+                     << " ledgerSequence = " << ledgerSequence;
         assert(objs[i].size());
         page.offers.push_back({keys[i], objs[i]});
     }
     auto end = std::chrono::system_clock::now();
-    BOOST_LOG_TRIVIAL(debug)
-        << __func__ << " "
-        << "Fetching " << std::to_string(keys.size()) << " offers took "
-        << std::to_string(getMillis(mid - begin))
-        << " milliseconds. Fetching next dir took "
-        << std::to_string(succMillis) << " milliseonds. Fetched next dir "
-        << std::to_string(numSucc) << " times"
-        << " Fetching next page of dir took " << std::to_string(pageMillis)
-        << " milliseconds"
-        << ". num pages = " << std::to_string(numPages)
-        << ". Fetching all objects took "
-        << std::to_string(getMillis(end - mid))
-        << " milliseconds. total time = "
-        << std::to_string(getMillis(end - begin)) << " milliseconds"
-        << " book = " << ripple::strHex(book);
+    gLog.debug() << "Fetching " << std::to_string(keys.size()) << " offers took "
+                 << std::to_string(getMillis(mid - begin)) << " milliseconds. Fetching next dir took "
+                 << std::to_string(succMillis) << " milliseonds. Fetched next dir " << std::to_string(numSucc)
+                 << " times"
+                 << " Fetching next page of dir took " << std::to_string(pageMillis) << " milliseconds"
+                 << ". num pages = " << std::to_string(numPages) << ". Fetching all objects took "
+                 << std::to_string(getMillis(end - mid))
+                 << " milliseconds. total time = " << std::to_string(getMillis(end - begin)) << " milliseconds"
+                 << " book = " << ripple::strHex(book);
 
     return page;
 }
@@ -256,11 +255,8 @@ BackendInterface::fetchLedgerPage(
     bool reachedEnd = false;
     while (keys.size() < limit && !reachedEnd)
     {
-        ripple::uint256 const& curCursor = keys.size() ? keys.back()
-            : cursor                                   ? *cursor
-                                                       : firstKey;
-        std::uint32_t const seq =
-            outOfOrder ? range->maxSequence : ledgerSequence;
+        ripple::uint256 const& curCursor = keys.size() ? keys.back() : cursor ? *cursor : firstKey;
+        std::uint32_t const seq = outOfOrder ? range->maxSequence : ledgerSequence;
         auto succ = fetchSuccessorKey(curCursor, seq, yield);
         if (!succ)
             reachedEnd = true;
@@ -275,16 +271,14 @@ BackendInterface::fetchLedgerPage(
             page.objects.push_back({std::move(keys[i]), std::move(objects[i])});
         else if (!outOfOrder)
         {
-            BOOST_LOG_TRIVIAL(error)
-                << __func__
-                << " deleted or non-existent object in successor table. key = "
-                << ripple::strHex(keys[i]) << " - seq = " << ledgerSequence;
+            gLog.error() << "Deleted or non-existent object in successor table. key = " << ripple::strHex(keys[i])
+                         << " - seq = " << ledgerSequence;
             std::stringstream msg;
             for (size_t j = 0; j < objects.size(); ++j)
             {
                 msg << " - " << ripple::strHex(keys[j]);
             }
-            BOOST_LOG_TRIVIAL(error) << __func__ << msg.str();
+            gLog.error() << msg.str();
         }
     }
     if (keys.size() && !reachedEnd)
@@ -294,9 +288,7 @@ BackendInterface::fetchLedgerPage(
 }
 
 std::optional<ripple::Fees>
-BackendInterface::fetchFees(
-    std::uint32_t const seq,
-    boost::asio::yield_context& yield) const
+BackendInterface::fetchFees(std::uint32_t const seq, boost::asio::yield_context& yield) const
 {
     ripple::Fees fees;
 
@@ -305,7 +297,7 @@ BackendInterface::fetchFees(
 
     if (!bytes)
     {
-        BOOST_LOG_TRIVIAL(error) << __func__ << " - could not find fees";
+        gLog.error() << "Could not find fees";
         return {};
     }
 

src/backend/BackendInterface.h

@@ -1,16 +1,48 @@
-#ifndef RIPPLE_APP_REPORTING_BACKENDINTERFACE_H_INCLUDED
-#define RIPPLE_APP_REPORTING_BACKENDINTERFACE_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
 #include <ripple/ledger/ReadView.h>
-#include <boost/asio.hpp>
 #include <backend/DBHelpers.h>
 #include <backend/SimpleCache.h>
 #include <backend/Types.h>
+#include <config/Config.h>
+#include <log/Logger.h>
+
+#include <boost/asio/spawn.hpp>
+#include <boost/json.hpp>
+
 #include <thread>
 #include <type_traits>
+
 namespace Backend {
 
+/**
+ * @brief Throws an error when database read time limit is exceeded.
+ *
+ * This class is throws an error when read time limit is exceeded but
+ * is also paired with a separate class to retry the connection.
+ */
 class DatabaseTimeout : public std::exception
 {
+public:
     const char*
     what() const throw() override
     {
@@ -18,10 +50,20 @@ class DatabaseTimeout : public std::exception
     }
 };
 
+/**
+ * @brief Separate class that reattempts connection after time limit.
+ *
+ * @tparam F Represents a class of handlers for Cassandra database.
+ * @param func Instance of Cassandra database handler class.
+ * @param waitMs Is the arbitrary time limit of 500ms.
+ * @return auto
+ */
 template <class F>
 auto
 retryOnTimeout(F func, size_t waitMs = 500)
 {
+    static clio::Logger log{"Backend"};
+
     while (true)
     {
         try
@@ -30,48 +72,82 @@ retryOnTimeout(F func, size_t waitMs = 500)
         }
         catch (DatabaseTimeout& t)
         {
+            log.error() << "Database request timed out. Sleeping and retrying ... ";
             std::this_thread::sleep_for(std::chrono::milliseconds(waitMs));
-            BOOST_LOG_TRIVIAL(error)
-                << __func__ << " function timed out. Retrying ... ";
         }
     }
 }
 
+/**
+ * @brief Passes in serialized handlers in an asynchronous fashion.
+ *
+ * Note that the synchronous auto passes handlers critical to supporting
+ * the Clio backend. The coroutine types are checked if same/different.
+ *
+ * @tparam F Represents a class of handlers for Cassandra database.
+ * @param f R-value instance of Cassandra handler class.
+ * @return auto
+ */
 template <class F>
 auto
 synchronous(F&& f)
 {
+    /** @brief Serialized handlers and their execution.
+     *
+     * The ctx class is converted into a serialized handler, also named
+     * ctx, and is used to pass a stream of data into the method.
+     */
     boost::asio::io_context ctx;
     boost::asio::io_context::strand strand(ctx);
     std::optional<boost::asio::io_context::work> work;
 
+    /*! @brief Place the ctx within the vector of serialized handlers. */
     work.emplace(ctx);
 
-    using R = typename std::result_of<F(boost::asio::yield_context&)>::type;
+    /**
+     * @brief If/else statements regarding coroutine type matching.
+     *
+     * R is the currently executing coroutine that is about to get passed.
+     * If corountine types do not match, the current one's type is stored.
+     */
+    using R = typename boost::result_of<F(boost::asio::yield_context&)>::type;
     if constexpr (!std::is_same<R, void>::value)
     {
+        /**
+         * @brief When the coroutine type is the same
+         *
+         * The spawn function enables programs to implement asynchronous logic
+         * in a synchronous manner. res stores the instance of the currently
+         * executing coroutine, yield. The different type is returned.
+         */
         R res;
-        boost::asio::spawn(
-            strand, [&f, &work, &res](boost::asio::yield_context yield) {
-                res = f(yield);
-                work.reset();
-            });
+        boost::asio::spawn(strand, [&f, &work, &res](boost::asio::yield_context yield) {
+            res = f(yield);
+            work.reset();
+        });
 
         ctx.run();
         return res;
     }
     else
     {
-        boost::asio::spawn(
-            strand, [&f, &work](boost::asio::yield_context yield) {
-                f(yield);
-                work.reset();
-            });
+        /*! @brief When the corutine type is different, run as normal. */
+        boost::asio::spawn(strand, [&f, &work](boost::asio::yield_context yield) {
+            f(yield);
+            work.reset();
+        });
 
         ctx.run();
     }
 }
 
+/**
+ * @brief Reestablishes synchronous connection on timeout.
+ *
+ * @tparam Represents a class of handlers for Cassandra database.
+ * @param f R-value instance of Cassandra database handler class.
+ * @return auto
+ */
 template <class F>
 auto
 synchronousAndRetryOnTimeout(F&& f)
@@ -79,32 +155,43 @@ synchronousAndRetryOnTimeout(F&& f)
     return retryOnTimeout([&]() { return synchronous(f); });
 }
 
+/*! @brief Handles ledger and transaction backend data. */
 class BackendInterface
 {
+    /**
+     * @brief Shared mutexes and a cache for the interface.
+     *
+     * rngMutex is a shared mutex. Shared mutexes prevent shared data
+     * from being accessed by multiple threads and has two levels of
+     * access: shared and exclusive.
+     */
 protected:
     mutable std::shared_mutex rngMtx_;
     std::optional<LedgerRange> range;
     SimpleCache cache_;
 
-    // mutex used for open() and close()
-    mutable std::mutex mutex_;
+    /**
+     * @brief Public read methods
+     *
+     * All of these reads methods can throw DatabaseTimeout. When writing
+     * code in an RPC handler, this exception does not need to be caught:
+     * when an RPC results in a timeout, an error is returned to the client.
+     */
 
 public:
-    BackendInterface(boost::json::object const& config)
-    {
-    }
-    virtual ~BackendInterface()
-    {
-    }
+    BackendInterface() = default;
+    virtual ~BackendInterface() = default;
 
-    // *** public read methods ***
-    // All of these reads methods can throw DatabaseTimeout. When writing code
-    // in an RPC handler, this exception does not need to be caught: when an RPC
-    // results in a timeout, an error is returned to the client
+    /*! @brief LEDGER METHODS */
 public:
-    // *** ledger methods
-    //
-
+    /**
+     * @brief Cache that holds states of the ledger
+     *
+     * const version holds the original cache state; the other tracks
+     * historical changes.
+     *
+     * @return SimpleCache const&
+     */
     SimpleCache const&
     cache() const
     {
@@ -117,19 +204,19 @@ public:
         return cache_;
     }
 
+    /*! @brief Fetches a specific ledger by sequence number. */
     virtual std::optional<ripple::LedgerInfo>
-    fetchLedgerBySequence(
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const = 0;
+    fetchLedgerBySequence(std::uint32_t const sequence, boost::asio::yield_context& yield) const = 0;
 
+    /*! @brief Fetches a specific ledger by hash. */
     virtual std::optional<ripple::LedgerInfo>
-    fetchLedgerByHash(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const = 0;
+    fetchLedgerByHash(ripple::uint256 const& hash, boost::asio::yield_context& yield) const = 0;
 
+    /*! @brief Fetches the latest ledger sequence. */
     virtual std::optional<std::uint32_t>
     fetchLatestLedgerSequence(boost::asio::yield_context& yield) const = 0;
 
+    /*! @brief Fetches the current ledger range while locking that process */
     std::optional<LedgerRange>
     fetchLedgerRange() const
     {
@@ -137,10 +224,18 @@ public:
         return range;
     }
 
+    /**
+     * @brief Updates the range of sequences to be tracked.
+     *
+     * Function that continues updating the range sliding window or creates
+     * a new sliding window once the maxSequence limit has been reached.
+     *
+     * @param newMax Unsigned 32-bit integer representing new max of range.
+     */
     void
     updateRange(uint32_t newMax)
     {
-        std::unique_lock lck(rngMtx_);
+        std::scoped_lock lck(rngMtx_);
         assert(!range || newMax >= range->maxSequence);
         if (!range)
             range = {newMax, newMax};
@@ -148,20 +243,49 @@ public:
             range->maxSequence = newMax;
     }
 
+    /**
+     * @brief Returns the fees for specific transactions.
+     *
+     * @param seq Unsigned 32-bit integer reprsenting sequence.
+     * @param yield The currently executing coroutine.
+     * @return std::optional<ripple::Fees>
+     */
     std::optional<ripple::Fees>
     fetchFees(std::uint32_t const seq, boost::asio::yield_context& yield) const;
 
-    // *** transaction methods
+    /*! @brief TRANSACTION METHODS */
+    /**
+     * @brief Fetches a specific transaction.
+     *
+     * @param hash Unsigned 256-bit integer representing hash.
+     * @param yield The currently executing coroutine.
+     * @return std::optional<TransactionAndMetadata>
+     */
     virtual std::optional<TransactionAndMetadata>
-    fetchTransaction(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const = 0;
+    fetchTransaction(ripple::uint256 const& hash, boost::asio::yield_context& yield) const = 0;
 
+    /**
+     * @brief Fetches multiple transactions.
+     *
+     * @param hashes Unsigned integer value representing a hash.
+     * @param yield The currently executing coroutine.
+     * @return std::vector<TransactionAndMetadata>
+     */
     virtual std::vector<TransactionAndMetadata>
-    fetchTransactions(
-        std::vector<ripple::uint256> const& hashes,
-        boost::asio::yield_context& yield) const = 0;
+    fetchTransactions(std::vector<ripple::uint256> const& hashes, boost::asio::yield_context& yield) const = 0;
 
+    /**
+     * @brief Fetches all transactions for a specific account
+     *
+     * @param account A specific XRPL Account, speciifed by unique type
+     * accountID.
+     * @param limit Paging limit for how many transactions can be returned per
+     * page.
+     * @param forward Boolean whether paging happens forwards or backwards.
+     * @param cursor Important metadata returned every time paging occurs.
+     * @param yield Currently executing coroutine.
+     * @return TransactionsAndCursor
+     */
     virtual TransactionsAndCursor
     fetchAccountTransactions(
         ripple::AccountID const& account,
@@ -170,23 +294,50 @@ public:
         std::optional<TransactionsCursor> const& cursor,
         boost::asio::yield_context& yield) const = 0;
 
+    /**
+     * @brief Fetches all transactions from a specific ledger.
+     *
+     * @param ledgerSequence Unsigned 32-bit integer for latest total
+     * transactions.
+     * @param yield Currently executing coroutine.
+     * @return std::vector<TransactionAndMetadata>
+     */
     virtual std::vector<TransactionAndMetadata>
-    fetchAllTransactionsInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const = 0;
+    fetchAllTransactionsInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const = 0;
 
+    /**
+     * @brief Fetches all transaction hashes from a specific ledger.
+     *
+     * @param ledgerSequence Standard unsigned integer.
+     * @param yield Currently executing coroutine.
+     * @return std::vector<ripple::uint256>
+     */
     virtual std::vector<ripple::uint256>
-    fetchAllTransactionHashesInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const = 0;
+    fetchAllTransactionHashesInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const = 0;
 
-    // *** NFT methods
+    /*! @brief NFT methods */
+    /**
+     * @brief Fetches a specific NFT
+     *
+     * @param tokenID Unsigned 256-bit integer.
+     * @param ledgerSequence Standard unsigned integer.
+     * @param yield Currently executing coroutine.
+     * @return std::optional<NFT>
+     */
     virtual std::optional<NFT>
-    fetchNFT(
-        ripple::uint256 const& tokenID,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const = 0;
+    fetchNFT(ripple::uint256 const& tokenID, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const = 0;
 
+    /**
+     * @brief Fetches all transactions for a specific NFT.
+     *
+     * @param tokenID Unsigned 256-bit integer.
+     * @param limit Paging limit as to how many transactions return per page.
+     * @param forward Boolean whether paging happens forwards or backwards.
+     * @param cursorIn Represents transaction number and ledger sequence.
+     * @param yield Currently executing coroutine is passed in as input.
+     * @return TransactionsAndCursor
+     */
     virtual TransactionsAndCursor
     fetchNFTTransactions(
         ripple::uint256 const& tokenID,
@@ -195,38 +346,68 @@ public:
         std::optional<TransactionsCursor> const& cursorIn,
         boost::asio::yield_context& yield) const = 0;
 
-    // *** state data methods
+    /*! @brief STATE DATA METHODS */
+    /**
+     * @brief Fetches a specific ledger object: vector of unsigned chars
+     *
+     * @param key Unsigned 256-bit integer.
+     * @param sequence Unsigned 32-bit integer.
+     * @param yield Currently executing coroutine.
+     * @return std::optional<Blob>
+     */
     std::optional<Blob>
-    fetchLedgerObject(
-        ripple::uint256 const& key,
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const;
+    fetchLedgerObject(ripple::uint256 const& key, std::uint32_t const sequence, boost::asio::yield_context& yield)
+        const;
 
+    /**
+     * @brief Fetches all ledger objects: a vector of vectors of unsigned chars.
+     *
+     * @param keys Unsigned 256-bit integer.
+     * @param sequence Unsigned 32-bit integer.
+     * @param yield Currently executing coroutine.
+     * @return std::vector<Blob>
+     */
     std::vector<Blob>
     fetchLedgerObjects(
         std::vector<ripple::uint256> const& keys,
         std::uint32_t const sequence,
         boost::asio::yield_context& yield) const;
 
+    /*! @brief Virtual function version of fetchLedgerObject */
     virtual std::optional<Blob>
-    doFetchLedgerObject(
-        ripple::uint256 const& key,
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const = 0;
+    doFetchLedgerObject(ripple::uint256 const& key, std::uint32_t const sequence, boost::asio::yield_context& yield)
+        const = 0;
 
+    /*! @brief Virtual function version of fetchLedgerObjects */
     virtual std::vector<Blob>
     doFetchLedgerObjects(
         std::vector<ripple::uint256> const& keys,
         std::uint32_t const sequence,
         boost::asio::yield_context& yield) const = 0;
 
+    /**
+     * @brief Returns the difference between ledgers: vector of objects
+     *
+     * Objects are made of a key value, vector of unsigned chars (blob),
+     * and a boolean detailing whether keys and blob match.
+     *
+     * @param ledgerSequence Standard unsigned integer.
+     * @param yield Currently executing coroutine.
+     * @return std::vector<LedgerObject>
+     */
     virtual std::vector<LedgerObject>
-    fetchLedgerDiff(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const = 0;
+    fetchLedgerDiff(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const = 0;
 
-    // Fetches a page of ledger objects, ordered by key/index.
-    // Used by ledger_data
+    /**
+     * @brief Fetches a page of ledger objects, ordered by key/index.
+     *
+     * @param cursor Important metadata returned every time paging occurs.
+     * @param ledgerSequence Standard unsigned integer.
+     * @param limit Paging limit as to how many transactions returned per page.
+     * @param outOfOrder Boolean on whether ledger page is out of order.
+     * @param yield Currently executing coroutine.
+     * @return LedgerPage
+     */
     LedgerPage
     fetchLedgerPage(
         std::optional<ripple::uint256> const& cursor,
@@ -235,63 +416,94 @@ public:
         bool outOfOrder,
         boost::asio::yield_context& yield) const;
 
-    // Fetches the successor to key/index
+    /*! @brief Fetches successor object from key/index. */
     std::optional<LedgerObject>
-    fetchSuccessorObject(
-        ripple::uint256 key,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const;
+    fetchSuccessorObject(ripple::uint256 key, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const;
 
+    /*! @brief Fetches successor key from key/index. */
     std::optional<ripple::uint256>
-    fetchSuccessorKey(
-        ripple::uint256 key,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const;
-    // Fetches the successor to key/index
+    fetchSuccessorKey(ripple::uint256 key, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const;
 
+    /*! @brief Virtual function version of fetchSuccessorKey. */
     virtual std::optional<ripple::uint256>
-    doFetchSuccessorKey(
-        ripple::uint256 key,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const = 0;
+    doFetchSuccessorKey(ripple::uint256 key, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const = 0;
 
+    /**
+     * @brief Fetches book offers.
+     *
+     * @param book Unsigned 256-bit integer.
+     * @param ledgerSequence Standard unsigned integer.
+     * @param limit Pagaing limit as to how many transactions returned per page.
+     * @param cursor Important metadata returned every time paging occurs.
+     * @param yield Currently executing coroutine.
+     * @return BookOffersPage
+     */
     BookOffersPage
     fetchBookOffers(
         ripple::uint256 const& book,
         std::uint32_t const ledgerSequence,
         std::uint32_t const limit,
-        std::optional<ripple::uint256> const& cursor,
         boost::asio::yield_context& yield) const;
 
+    /**
+     * @brief Returns a ledger range
+     *
+     * Ledger range is a struct of min and max sequence numbers). Due to
+     * the use of [&], which denotes a special case of a lambda expression
+     * where values found outside the scope are passed by reference, wrt the
+     * currently executing coroutine.
+     *
+     * @return std::optional<LedgerRange>
+     */
     std::optional<LedgerRange>
     hardFetchLedgerRange() const
     {
-        return synchronous([&](boost::asio::yield_context yield) {
-            return hardFetchLedgerRange(yield);
-        });
+        return synchronous([&](boost::asio::yield_context yield) { return hardFetchLedgerRange(yield); });
     }
 
+    /*! @brief Virtual function equivalent of hardFetchLedgerRange. */
     virtual std::optional<LedgerRange>
     hardFetchLedgerRange(boost::asio::yield_context& yield) const = 0;
 
-    // Doesn't throw DatabaseTimeout. Should be used with care.
+    /*! @brief Fetches ledger range but doesn't throw timeout. Use with care. */
     std::optional<LedgerRange>
     hardFetchLedgerRangeNoThrow() const;
-    // Doesn't throw DatabaseTimeout. Should be used with care.
+    /*! @brief Fetches ledger range but doesn't throw timeout. Use with care. */
     std::optional<LedgerRange>
     hardFetchLedgerRangeNoThrow(boost::asio::yield_context& yield) const;
 
+    /**
+     * @brief Writes to a specific ledger.
+     *
+     * @param ledgerInfo Const on ledger information.
+     * @param ledgerHeader r-value string representing ledger header.
+     */
     virtual void
-    writeLedger(
-        ripple::LedgerInfo const& ledgerInfo,
-        std::string&& ledgerHeader) = 0;
+    writeLedger(ripple::LedgerInfo const& ledgerInfo, std::string&& ledgerHeader) = 0;
 
+    /**
+     * @brief Writes a new ledger object.
+     *
+     * The key and blob are r-value references and do NOT have memory addresses.
+     *
+     * @param key String represented as an r-value.
+     * @param seq Unsigned integer representing a sequence.
+     * @param blob r-value vector of unsigned characters (blob).
+     */
     virtual void
-    writeLedgerObject(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& blob);
+    writeLedgerObject(std::string&& key, std::uint32_t const seq, std::string&& blob);
 
+    /**
+     * @brief Writes a new transaction.
+     *
+     * @param hash r-value reference. No memory address.
+     * @param seq Unsigned 32-bit integer.
+     * @param date Unsigned 32-bit integer.
+     * @param transaction r-value reference. No memory address.
+     * @param metadata r-value refrence. No memory address.
+     */
     virtual void
     writeTransaction(
         std::string&& hash,
@@ -300,55 +512,98 @@ public:
         std::string&& transaction,
         std::string&& metadata) = 0;
 
+    /**
+     * @brief Write a new NFT.
+     *
+     * @param data Passed in as an r-value reference.
+     */
     virtual void
     writeNFTs(std::vector<NFTsData>&& data) = 0;
 
+    /**
+     * @brief Write a new set of account transactions.
+     *
+     * @param data Passed in as an r-value reference.
+     */
     virtual void
     writeAccountTransactions(std::vector<AccountTransactionsData>&& data) = 0;
 
+    /**
+     * @brief Write a new transaction for a specific NFT.
+     *
+     * @param data Passed in as an r-value reference.
+     */
     virtual void
     writeNFTTransactions(std::vector<NFTTransactionsData>&& data) = 0;
 
+    /**
+     * @brief Write a new successor.
+     *
+     * @param key Passed in as an r-value reference.
+     * @param seq Unsigned 32-bit integer.
+     * @param successor Passed in as an r-value reference.
+     */
     virtual void
-    writeSuccessor(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& successor) = 0;
+    writeSuccessor(std::string&& key, std::uint32_t const seq, std::string&& successor) = 0;
 
-    // Tell the database we are about to begin writing data for a particular
-    // ledger.
+    /*! @brief Tells database we will write data for a specific ledger. */
     virtual void
     startWrites() const = 0;
 
-    // Tell the database we have finished writing all data for a particular
-    // ledger
-    // TODO change the return value to represent different results. committed,
-    // write conflict, errored, successful but not committed
+    /**
+     * @brief Tells database we finished writing all data for a specific ledger.
+     *
+     * TODO: change the return value to represent different results:
+     * Committed, write conflict, errored, successful but not committed
+     *
+     * @param ledgerSequence Const unsigned 32-bit integer on ledger sequence.
+     * @return true
+     * @return false
+     */
     bool
     finishWrites(std::uint32_t const ledgerSequence);
 
+    /**
+     * @brief Selectively delets parts of the database.
+     *
+     * @param numLedgersToKeep Unsigned 32-bit integer on number of ledgers to
+     * keep.
+     * @param yield Currently executing coroutine.
+     * @return true
+     * @return false
+     */
     virtual bool
-    doOnlineDelete(
-        std::uint32_t numLedgersToKeep,
-        boost::asio::yield_context& yield) const = 0;
+    doOnlineDelete(std::uint32_t numLedgersToKeep, boost::asio::yield_context& yield) const = 0;
 
-    // Open the database. Set up all of the necessary objects and
-    // datastructures. After this call completes, the database is ready for
-    // use.
+    /**
+     * @brief Opens the database
+     *
+     * Open the database. Set up all of the necessary objects and
+     * datastructures. After this call completes, the database is
+     * ready for use.
+     *
+     * @param readOnly Boolean whether ledger is read only.
+     */
     virtual void
     open(bool readOnly) = 0;
 
-    // Close the database, releasing any resources
+    /*! @brief Closes the database, releasing any resources. */
     virtual void
     close(){};
 
-    // *** private helper methods
+    virtual bool
+    isTooBusy() const = 0;
+
 private:
+    /**
+     * @brief Private helper method to write ledger object
+     *
+     * @param key r-value string representing key.
+     * @param seq Unsigned 32-bit integer representing sequence.
+     * @param blob r-value vector of unsigned chars.
+     */
     virtual void
-    doWriteLedgerObject(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& blob) = 0;
+    doWriteLedgerObject(std::string&& key, std::uint32_t const seq, std::string&& blob) = 0;
 
     virtual bool
     doFinishWrites() = 0;
@@ -356,4 +611,3 @@ private:
 
 }  // namespace Backend
 using BackendInterface = Backend::BackendInterface;
-#endif

src/backend/CassandraBackend.h

@@ -1,28 +1,52 @@
-#ifndef RIPPLE_APP_REPORTING_CASSANDRABACKEND_H_INCLUDED
-#define RIPPLE_APP_REPORTING_CASSANDRABACKEND_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
 #include <ripple/basics/base_uint.h>
+#include <backend/BackendInterface.h>
+#include <backend/DBHelpers.h>
+#include <log/Logger.h>
+
+#include <cassandra.h>
+
 #include <boost/asio.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/spawn.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/json.hpp>
-#include <boost/log/trivial.hpp>
+
 #include <atomic>
-#include <backend/BackendInterface.h>
-#include <backend/DBHelpers.h>
-#include <cassandra.h>
 #include <cstddef>
 #include <iostream>
 #include <memory>
 #include <mutex>
 #include <thread>
 
+#include <config/Config.h>
+
 namespace Backend {
 
 class CassandraPreparedStatement
 {
 private:
+    clio::Logger log_{"Backend"};
     CassPrepared const* prepared_ = nullptr;
 
 public:
@@ -61,9 +85,9 @@ public:
         else
         {
             std::stringstream ss;
-            ss << "nodestore: Error preparing statement : " << rc << ", "
-               << cass_error_desc(rc) << ". query : " << query;
-            BOOST_LOG_TRIVIAL(error) << ss.str();
+            ss << "nodestore: Error preparing statement : " << rc << ", " << cass_error_desc(rc)
+               << ". query : " << query;
+            log_.error() << ss.str();
         }
         cass_future_free(prepareFuture);
         return rc == CASS_OK;
@@ -71,7 +95,7 @@ public:
 
     ~CassandraPreparedStatement()
     {
-        BOOST_LOG_TRIVIAL(trace) << __func__;
+        log_.trace() << "called";
         if (prepared_)
         {
             cass_prepared_free(prepared_);
@@ -84,6 +108,7 @@ class CassandraStatement
 {
     CassStatement* statement_ = nullptr;
     size_t curBindingIndex_ = 0;
+    clio::Logger log_{"Backend"};
 
 public:
     CassandraStatement(CassandraPreparedStatement const& prepared)
@@ -112,16 +137,13 @@ public:
     bindNextBoolean(bool val)
     {
         if (!statement_)
-            throw std::runtime_error(
-                "CassandraStatement::bindNextBoolean - statement_ is null");
-        CassError rc = cass_statement_bind_bool(
-            statement_, curBindingIndex_, static_cast<cass_bool_t>(val));
+            throw std::runtime_error("CassandraStatement::bindNextBoolean - statement_ is null");
+        CassError rc = cass_statement_bind_bool(statement_, curBindingIndex_, static_cast<cass_bool_t>(val));
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding boolean to statement: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding boolean to statement: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         curBindingIndex_++;
@@ -165,19 +187,14 @@ public:
     bindNextBytes(const unsigned char* data, std::uint32_t const size)
     {
         if (!statement_)
-            throw std::runtime_error(
-                "CassandraStatement::bindNextBytes - statement_ is null");
-        CassError rc = cass_statement_bind_bytes(
-            statement_,
-            curBindingIndex_,
-            static_cast<cass_byte_t const*>(data),
-            size);
+            throw std::runtime_error("CassandraStatement::bindNextBytes - statement_ is null");
+        CassError rc =
+            cass_statement_bind_bytes(statement_, curBindingIndex_, static_cast<cass_byte_t const*>(data), size);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding bytes to statement: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding bytes to statement: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         curBindingIndex_++;
@@ -187,18 +204,14 @@ public:
     bindNextUInt(std::uint32_t const value)
     {
         if (!statement_)
-            throw std::runtime_error(
-                "CassandraStatement::bindNextUInt - statement_ is null");
-        BOOST_LOG_TRIVIAL(trace)
-            << std::to_string(curBindingIndex_) << " " << std::to_string(value);
-        CassError rc =
-            cass_statement_bind_int32(statement_, curBindingIndex_, value);
+            throw std::runtime_error("CassandraStatement::bindNextUInt - statement_ is null");
+        log_.trace() << std::to_string(curBindingIndex_) << " " << std::to_string(value);
+        CassError rc = cass_statement_bind_int32(statement_, curBindingIndex_, value);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding uint to statement: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding uint to statement: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         curBindingIndex_++;
@@ -214,16 +227,13 @@ public:
     bindNextInt(int64_t value)
     {
         if (!statement_)
-            throw std::runtime_error(
-                "CassandraStatement::bindNextInt - statement_ is null");
-        CassError rc =
-            cass_statement_bind_int64(statement_, curBindingIndex_, value);
+            throw std::runtime_error("CassandraStatement::bindNextInt - statement_ is null");
+        CassError rc = cass_statement_bind_int64(statement_, curBindingIndex_, value);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding int to statement: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding int to statement: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         curBindingIndex_++;
@@ -237,27 +247,24 @@ public:
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding int to tuple: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding int to tuple: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         rc = cass_tuple_set_int64(tuple, 1, second);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding int to tuple: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding int to tuple: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         rc = cass_statement_bind_tuple(statement_, curBindingIndex_, tuple);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "Error binding tuple to statement: " << rc << ", "
-               << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << __func__ << " : " << ss.str();
+            ss << "Error binding tuple to statement: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << ss.str();
             throw std::runtime_error(ss.str());
         }
         cass_tuple_free(tuple);
@@ -273,6 +280,7 @@ public:
 
 class CassandraResult
 {
+    clio::Logger log_{"Backend"};
     CassResult const* result_ = nullptr;
     CassRow const* row_ = nullptr;
     CassIterator* iter_ = nullptr;
@@ -356,14 +364,12 @@ public:
             throw std::runtime_error("CassandraResult::getBytes - no result");
         cass_byte_t const* buf;
         std::size_t bufSize;
-        CassError rc = cass_value_get_bytes(
-            cass_row_get_column(row_, curGetIndex_), &buf, &bufSize);
+        CassError rc = cass_value_get_bytes(cass_row_get_column(row_, curGetIndex_), &buf, &bufSize);
         if (rc != CASS_OK)
         {
             std::stringstream msg;
-            msg << "CassandraResult::getBytes - error getting value: " << rc
-                << ", " << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << msg.str();
+            msg << "CassandraResult::getBytes - error getting value: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << msg.str();
             throw std::runtime_error(msg.str());
         }
         curGetIndex_++;
@@ -377,14 +383,12 @@ public:
             throw std::runtime_error("CassandraResult::uint256 - no result");
         cass_byte_t const* buf;
         std::size_t bufSize;
-        CassError rc = cass_value_get_bytes(
-            cass_row_get_column(row_, curGetIndex_), &buf, &bufSize);
+        CassError rc = cass_value_get_bytes(cass_row_get_column(row_, curGetIndex_), &buf, &bufSize);
         if (rc != CASS_OK)
         {
             std::stringstream msg;
-            msg << "CassandraResult::getuint256 - error getting value: " << rc
-                << ", " << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << msg.str();
+            msg << "CassandraResult::getuint256 - error getting value: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << msg.str();
             throw std::runtime_error(msg.str());
         }
         curGetIndex_++;
@@ -397,14 +401,12 @@ public:
         if (!row_)
             throw std::runtime_error("CassandraResult::getInt64 - no result");
         cass_int64_t val;
-        CassError rc =
-            cass_value_get_int64(cass_row_get_column(row_, curGetIndex_), &val);
+        CassError rc = cass_value_get_int64(cass_row_get_column(row_, curGetIndex_), &val);
         if (rc != CASS_OK)
         {
             std::stringstream msg;
-            msg << "CassandraResult::getInt64 - error getting value: " << rc
-                << ", " << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << msg.str();
+            msg << "CassandraResult::getInt64 - error getting value: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << msg.str();
             throw std::runtime_error(msg.str());
         }
         ++curGetIndex_;
@@ -421,8 +423,7 @@ public:
     getInt64Tuple()
     {
         if (!row_)
-            throw std::runtime_error(
-                "CassandraResult::getInt64Tuple - no result");
+            throw std::runtime_error("CassandraResult::getInt64Tuple - no result");
 
         CassValue const* tuple = cass_row_get_column(row_, curGetIndex_);
         CassIterator* tupleIter = cass_iterator_from_tuple(tuple);
@@ -430,8 +431,7 @@ public:
         if (!cass_iterator_next(tupleIter))
         {
             cass_iterator_free(tupleIter);
-            throw std::runtime_error(
-                "CassandraResult::getInt64Tuple - failed to iterate tuple");
+            throw std::runtime_error("CassandraResult::getInt64Tuple - failed to iterate tuple");
         }
 
         CassValue const* value = cass_iterator_get_value(tupleIter);
@@ -440,8 +440,7 @@ public:
         if (!cass_iterator_next(tupleIter))
         {
             cass_iterator_free(tupleIter);
-            throw std::runtime_error(
-                "CassandraResult::getInt64Tuple - failed to iterate tuple");
+            throw std::runtime_error("CassandraResult::getInt64Tuple - failed to iterate tuple");
         }
 
         value = cass_iterator_get_value(tupleIter);
@@ -460,20 +459,17 @@ public:
         std::size_t bufSize;
 
         if (!row_)
-            throw std::runtime_error(
-                "CassandraResult::getBytesTuple - no result");
+            throw std::runtime_error("CassandraResult::getBytesTuple - no result");
         CassValue const* tuple = cass_row_get_column(row_, curGetIndex_);
         CassIterator* tupleIter = cass_iterator_from_tuple(tuple);
         if (!cass_iterator_next(tupleIter))
-            throw std::runtime_error(
-                "CassandraResult::getBytesTuple - failed to iterate tuple");
+            throw std::runtime_error("CassandraResult::getBytesTuple - failed to iterate tuple");
         CassValue const* value = cass_iterator_get_value(tupleIter);
         cass_value_get_bytes(value, &buf, &bufSize);
         Blob first{buf, buf + bufSize};
 
         if (!cass_iterator_next(tupleIter))
-            throw std::runtime_error(
-                "CassandraResult::getBytesTuple - failed to iterate tuple");
+            throw std::runtime_error("CassandraResult::getBytesTuple - failed to iterate tuple");
         value = cass_iterator_get_value(tupleIter);
         cass_value_get_bytes(value, &buf, &bufSize);
         Blob second{buf, buf + bufSize};
@@ -488,20 +484,17 @@ public:
     {
         if (!row_)
         {
-            std::stringstream msg;
-            msg << __func__ << " - no result";
-            BOOST_LOG_TRIVIAL(error) << msg.str();
-            throw std::runtime_error(msg.str());
+            std::string msg{"No result"};
+            log_.error() << msg;
+            throw std::runtime_error(msg);
         }
         cass_bool_t val;
-        CassError rc =
-            cass_value_get_bool(cass_row_get_column(row_, curGetIndex_), &val);
+        CassError rc = cass_value_get_bool(cass_row_get_column(row_, curGetIndex_), &val);
         if (rc != CASS_OK)
         {
             std::stringstream msg;
-            msg << __func__ << " - error getting value: " << rc << ", "
-                << cass_error_desc(rc);
-            BOOST_LOG_TRIVIAL(error) << msg.str();
+            msg << "Error getting value: " << rc << ", " << cass_error_desc(rc);
+            log_.error() << msg.str();
             throw std::runtime_error(msg.str());
         }
         ++curGetIndex_;
@@ -516,13 +509,12 @@ public:
             cass_iterator_free(iter_);
     }
 };
+
 inline bool
 isTimeout(CassError rc)
 {
-    if (rc == CASS_ERROR_LIB_NO_HOSTS_AVAILABLE or
-        rc == CASS_ERROR_LIB_REQUEST_TIMED_OUT or
-        rc == CASS_ERROR_SERVER_UNAVAILABLE or
-        rc == CASS_ERROR_SERVER_OVERLOADED or
+    if (rc == CASS_ERROR_LIB_NO_HOSTS_AVAILABLE or rc == CASS_ERROR_LIB_REQUEST_TIMED_OUT or
+        rc == CASS_ERROR_SERVER_UNAVAILABLE or rc == CASS_ERROR_SERVER_OVERLOADED or
         rc == CASS_ERROR_SERVER_READ_TIMEOUT)
         return true;
     return false;
@@ -533,8 +525,7 @@ CassError
 cass_future_error_code(CassFuture* fut, CompletionToken&& token)
 {
     using function_type = void(boost::system::error_code, CassError);
-    using result_type =
-        boost::asio::async_result<CompletionToken, function_type>;
+    using result_type = boost::asio::async_result<CompletionToken, function_type>;
     using handler_type = typename result_type::completion_handler_type;
 
     handler_type handler(std::forward<decltype(token)>(token));
@@ -553,12 +544,10 @@ cass_future_error_code(CassFuture* fut, CompletionToken&& token)
         HandlerWrapper* hw = (HandlerWrapper*)data;
 
         boost::asio::post(
-            boost::asio::get_associated_executor(hw->handler),
-            [fut, hw, handler = std::move(hw->handler)]() mutable {
+            boost::asio::get_associated_executor(hw->handler), [fut, hw, handler = std::move(hw->handler)]() mutable {
                 delete hw;
 
-                handler(
-                    boost::system::error_code{}, cass_future_error_code(fut));
+                handler(boost::system::error_code{}, cass_future_error_code(fut));
             });
     };
 
@@ -583,29 +572,27 @@ private:
     makeStatement(char const* query, std::size_t params)
     {
         CassStatement* ret = cass_statement_new(query, params);
-        CassError rc =
-            cass_statement_set_consistency(ret, CASS_CONSISTENCY_QUORUM);
+        CassError rc = cass_statement_set_consistency(ret, CASS_CONSISTENCY_QUORUM);
         if (rc != CASS_OK)
         {
             std::stringstream ss;
-            ss << "nodestore: Error setting query consistency: " << query
-               << ", result: " << rc << ", " << cass_error_desc(rc);
+            ss << "nodestore: Error setting query consistency: " << query << ", result: " << rc << ", "
+               << cass_error_desc(rc);
             throw std::runtime_error(ss.str());
         }
         return ret;
     }
 
+    clio::Logger log_{"Backend"};
     std::atomic<bool> open_{false};
 
-    std::unique_ptr<CassSession, void (*)(CassSession*)> session_{
-        nullptr,
-        [](CassSession* session) {
-            // Try to disconnect gracefully.
-            CassFuture* fut = cass_session_close(session);
-            cass_future_wait(fut);
-            cass_future_free(fut);
-            cass_session_free(session);
-        }};
+    std::unique_ptr<CassSession, void (*)(CassSession*)> session_{nullptr, [](CassSession* session) {
+                                                                      // Try to disconnect gracefully.
+                                                                      CassFuture* fut = cass_session_close(session);
+                                                                      cass_future_wait(fut);
+                                                                      cass_future_free(fut);
+                                                                      cass_session_free(session);
+                                                                  }};
 
     // Database statements cached server side. Using these is more efficient
     // than making a new statement
@@ -629,6 +616,8 @@ private:
     CassandraPreparedStatement insertNFT_;
     CassandraPreparedStatement selectNFT_;
     CassandraPreparedStatement insertIssuerNFT_;
+    CassandraPreparedStatement insertNFTURI_;
+    CassandraPreparedStatement selectNFTURI_;
     CassandraPreparedStatement insertNFTTx_;
     CassandraPreparedStatement selectNFTTx_;
     CassandraPreparedStatement selectNFTTxForward_;
@@ -645,16 +634,18 @@ private:
     uint32_t syncInterval_ = 1;
     uint32_t lastSync_ = 0;
 
-    // maximum number of concurrent in flight requests. New requests will wait
-    // for earlier requests to finish if this limit is exceeded
-    std::uint32_t maxRequestsOutstanding = 10000;
-    // we keep this small because the indexer runs in the background, and we
-    // don't want the database to be swamped when the indexer is running
-    std::uint32_t indexerMaxRequestsOutstanding = 10;
-    mutable std::atomic_uint32_t numRequestsOutstanding_ = 0;
+    // maximum number of concurrent in flight write requests. New requests will
+    // wait for earlier requests to finish if this limit is exceeded
+    std::uint32_t maxWriteRequestsOutstanding = 10000;
+    mutable std::atomic_uint32_t numWriteRequestsOutstanding_ = 0;
+
+    // maximum number of concurrent in flight read requests. isTooBusy() will
+    // return true if the number of in flight read requests exceeds this limit
+    std::uint32_t maxReadRequestsOutstanding = 100000;
+    mutable std::atomic_uint32_t numReadRequestsOutstanding_ = 0;
 
     // mutex and condition_variable to limit the number of concurrent in flight
-    // requests
+    // write requests
     mutable std::mutex throttleMutex_;
     mutable std::condition_variable throttleCv_;
 
@@ -668,15 +659,14 @@ private:
     std::optional<boost::asio::io_context::work> work_;
     std::thread ioThread_;
 
-    boost::json::object config_;
+    clio::Config config_;
+    uint32_t ttl_ = 0;
 
     mutable std::uint32_t ledgerSequence_ = 0;
 
 public:
-    CassandraBackend(
-        boost::asio::io_context& ioc,
-        boost::json::object const& config)
-        : BackendInterface(config), config_(config)
+    CassandraBackend(boost::asio::io_context& ioc, clio::Config const& config, uint32_t ttl)
+        : config_(config), ttl_(ttl)
     {
         work_.emplace(ioContext_);
         ioThread_ = std::thread([this]() { ioContext_.run(); });
@@ -745,13 +735,10 @@ public:
         statement.bindNextInt(ledgerSequence_ - 1);
         if (!executeSyncUpdate(statement))
         {
-            BOOST_LOG_TRIVIAL(warning)
-                << __func__ << " Update failed for ledger "
-                << std::to_string(ledgerSequence_) << ". Returning";
+            log_.warn() << "Update failed for ledger " << std::to_string(ledgerSequence_) << ". Returning";
             return false;
         }
-        BOOST_LOG_TRIVIAL(info) << __func__ << " Committed ledger "
-                                << std::to_string(ledgerSequence_);
+        log_.info() << "Committed ledger " << std::to_string(ledgerSequence_);
         return true;
     }
 
@@ -762,8 +749,7 @@ public:
         // if db is empty, sync. if sync interval is 1, always sync.
         // if we've never synced, sync. if its been greater than the configured
         // sync interval since we last synced, sync.
-        if (!range || lastSync_ == 0 ||
-            ledgerSequence_ - syncInterval_ >= lastSync_)
+        if (!range || lastSync_ == 0 || ledgerSequence_ - syncInterval_ >= lastSync_)
         {
             // wait for all other writes to finish
             sync();
@@ -785,22 +771,16 @@ public:
                 statement.bindNextInt(lastSync_);
             if (!executeSyncUpdate(statement))
             {
-                BOOST_LOG_TRIVIAL(warning)
-                    << __func__ << " Update failed for ledger "
-                    << std::to_string(ledgerSequence_) << ". Returning";
+                log_.warn() << "Update failed for ledger " << std::to_string(ledgerSequence_) << ". Returning";
                 return false;
             }
-            BOOST_LOG_TRIVIAL(info) << __func__ << " Committed ledger "
-                                    << std::to_string(ledgerSequence_);
+            log_.info() << "Committed ledger " << std::to_string(ledgerSequence_);
             lastSync_ = ledgerSequence_;
         }
         else
         {
-            BOOST_LOG_TRIVIAL(info)
-                << __func__ << " Skipping commit. sync interval is "
-                << std::to_string(syncInterval_) << " - last sync is "
-                << std::to_string(lastSync_) << " - ledger sequence is "
-                << std::to_string(ledgerSequence_);
+            log_.info() << "Skipping commit. sync interval is " << std::to_string(syncInterval_) << " - last sync is "
+                        << std::to_string(lastSync_) << " - ledger sequence is " << std::to_string(ledgerSequence_);
         }
         return true;
     }
@@ -814,36 +794,32 @@ public:
             return doFinishWritesAsync();
     }
     void
-    writeLedger(ripple::LedgerInfo const& ledgerInfo, std::string&& header)
-        override;
+    writeLedger(ripple::LedgerInfo const& ledgerInfo, std::string&& header) override;
 
     std::optional<std::uint32_t>
     fetchLatestLedgerSequence(boost::asio::yield_context& yield) const override
     {
-        BOOST_LOG_TRIVIAL(trace) << __func__;
+        log_.trace() << "called";
         CassandraStatement statement{selectLatestLedger_};
         CassandraResult result = executeAsyncRead(statement, yield);
         if (!result.hasResult())
         {
-            BOOST_LOG_TRIVIAL(error)
-                << "CassandraBackend::fetchLatestLedgerSequence - no rows";
+            log_.error() << "CassandraBackend::fetchLatestLedgerSequence - no rows";
             return {};
         }
         return result.getUInt32();
     }
 
     std::optional<ripple::LedgerInfo>
-    fetchLedgerBySequence(
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const override
+    fetchLedgerBySequence(std::uint32_t const sequence, boost::asio::yield_context& yield) const override
     {
-        BOOST_LOG_TRIVIAL(trace) << __func__;
+        log_.trace() << "called";
         CassandraStatement statement{selectLedgerBySeq_};
         statement.bindNextInt(sequence);
         CassandraResult result = executeAsyncRead(statement, yield);
         if (!result)
         {
-            BOOST_LOG_TRIVIAL(error) << __func__ << " - no rows";
+            log_.error() << "No rows";
             return {};
         }
         std::vector<unsigned char> header = result.getBytes();
@@ -851,9 +827,7 @@ public:
     }
 
     std::optional<ripple::LedgerInfo>
-    fetchLedgerByHash(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const override
+    fetchLedgerByHash(ripple::uint256 const& hash, boost::asio::yield_context& yield) const override
     {
         CassandraStatement statement{selectLedgerByHash_};
 
@@ -863,7 +837,7 @@ public:
 
         if (!result.hasResult())
         {
-            BOOST_LOG_TRIVIAL(debug) << __func__ << " - no rows returned";
+            log_.debug() << "No rows returned";
             return {};
         }
 
@@ -876,20 +850,15 @@ public:
     hardFetchLedgerRange(boost::asio::yield_context& yield) const override;
 
     std::vector<TransactionAndMetadata>
-    fetchAllTransactionsInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
+    fetchAllTransactionsInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const override;
 
     std::vector<ripple::uint256>
-    fetchAllTransactionHashesInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
+    fetchAllTransactionHashesInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override;
 
     std::optional<NFT>
-    fetchNFT(
-        ripple::uint256 const& tokenID,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
+    fetchNFT(ripple::uint256 const& tokenID, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override;
 
     TransactionsAndCursor
     fetchNFTTransactions(
@@ -902,64 +871,31 @@ public:
     // Synchronously fetch the object with key key, as of ledger with sequence
     // sequence
     std::optional<Blob>
-    doFetchLedgerObject(
-        ripple::uint256 const& key,
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::optional<int64_t>
-    getToken(void const* key, boost::asio::yield_context& yield) const
-    {
-        BOOST_LOG_TRIVIAL(trace) << "Fetching from cassandra";
-        CassandraStatement statement{getToken_};
-        statement.bindNextBytes(key, 32);
-
-        CassandraResult result = executeAsyncRead(statement, yield);
-
-        if (!result)
-        {
-            BOOST_LOG_TRIVIAL(error) << __func__ << " - no rows";
-            return {};
-        }
-        int64_t token = result.getInt64();
-        if (token == INT64_MAX)
-            return {};
-        else
-            return token + 1;
-    }
+    doFetchLedgerObject(ripple::uint256 const& key, std::uint32_t const sequence, boost::asio::yield_context& yield)
+        const override;
 
     std::optional<TransactionAndMetadata>
-    fetchTransaction(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const override
+    fetchTransaction(ripple::uint256 const& hash, boost::asio::yield_context& yield) const override
     {
-        BOOST_LOG_TRIVIAL(trace) << __func__;
+        log_.trace() << "called";
         CassandraStatement statement{selectTransaction_};
         statement.bindNextBytes(hash);
         CassandraResult result = executeAsyncRead(statement, yield);
 
         if (!result)
         {
-            BOOST_LOG_TRIVIAL(error) << __func__ << " - no rows";
+            log_.error() << "No rows";
             return {};
         }
-        return {
-            {result.getBytes(),
-             result.getBytes(),
-             result.getUInt32(),
-             result.getUInt32()}};
+        return {{result.getBytes(), result.getBytes(), result.getUInt32(), result.getUInt32()}};
     }
 
     std::optional<ripple::uint256>
-    doFetchSuccessorKey(
-        ripple::uint256 key,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
+    doFetchSuccessorKey(ripple::uint256 key, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override;
 
     std::vector<TransactionAndMetadata>
-    fetchTransactions(
-        std::vector<ripple::uint256> const& hashes,
-        boost::asio::yield_context& yield) const override;
+    fetchTransactions(std::vector<ripple::uint256> const& hashes, boost::asio::yield_context& yield) const override;
 
     std::vector<Blob>
     doFetchLedgerObjects(
@@ -968,25 +904,16 @@ public:
         boost::asio::yield_context& yield) const override;
 
     std::vector<LedgerObject>
-    fetchLedgerDiff(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
+    fetchLedgerDiff(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const override;
 
     void
-    doWriteLedgerObject(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& blob) override;
+    doWriteLedgerObject(std::string&& key, std::uint32_t const seq, std::string&& blob) override;
 
     void
-    writeSuccessor(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& successor) override;
+    writeSuccessor(std::string&& key, std::uint32_t const seq, std::string&& successor) override;
 
     void
-    writeAccountTransactions(
-        std::vector<AccountTransactionsData>&& data) override;
+    writeAccountTransactions(std::vector<AccountTransactionsData>&& data) override;
 
     void
     writeNFTTransactions(std::vector<NFTTransactionsData>&& data) override;
@@ -1016,37 +943,36 @@ public:
     }
 
     bool
-    doOnlineDelete(
-        std::uint32_t const numLedgersToKeep,
-        boost::asio::yield_context& yield) const override;
+    doOnlineDelete(std::uint32_t const numLedgersToKeep, boost::asio::yield_context& yield) const override;
+
+    bool
+    isTooBusy() const override;
 
     inline void
-    incremementOutstandingRequestCount() const
+    incrementOutstandingRequestCount() const
     {
         {
             std::unique_lock<std::mutex> lck(throttleMutex_);
             if (!canAddRequest())
             {
-                BOOST_LOG_TRIVIAL(info)
-                    << __func__ << " : "
-                    << "Max outstanding requests reached. "
-                    << "Waiting for other requests to finish";
+                log_.debug() << "Max outstanding requests reached. "
+                             << "Waiting for other requests to finish";
                 throttleCv_.wait(lck, [this]() { return canAddRequest(); });
             }
         }
-        ++numRequestsOutstanding_;
+        ++numWriteRequestsOutstanding_;
     }
 
     inline void
     decrementOutstandingRequestCount() const
     {
         // sanity check
-        if (numRequestsOutstanding_ == 0)
+        if (numWriteRequestsOutstanding_ == 0)
         {
             assert(false);
             throw std::runtime_error("decrementing num outstanding below 0");
         }
-        size_t cur = (--numRequestsOutstanding_);
+        size_t cur = (--numWriteRequestsOutstanding_);
         {
             // mutex lock required to prevent race condition around spurious
             // wakeup
@@ -1065,12 +991,13 @@ public:
     inline bool
     canAddRequest() const
     {
-        return numRequestsOutstanding_ < maxRequestsOutstanding;
+        return numWriteRequestsOutstanding_ < maxWriteRequestsOutstanding;
     }
+
     inline bool
     finishedAllRequests() const
     {
-        return numRequestsOutstanding_ == 0;
+        return numWriteRequestsOutstanding_ == 0;
     }
 
     void
@@ -1081,38 +1008,27 @@ public:
 
     template <class T, class S>
     void
-    executeAsyncHelper(
-        CassandraStatement const& statement,
-        T callback,
-        S& callbackData) const
+    executeAsyncHelper(CassandraStatement const& statement, T callback, S& callbackData) const
     {
         CassFuture* fut = cass_session_execute(session_.get(), statement.get());
 
-        cass_future_set_callback(
-            fut, callback, static_cast<void*>(&callbackData));
+        cass_future_set_callback(fut, callback, static_cast<void*>(&callbackData));
 
         cass_future_free(fut);
     }
 
     template <class T, class S>
     void
-    executeAsyncWrite(
-        CassandraStatement const& statement,
-        T callback,
-        S& callbackData,
-        bool isRetry) const
+    executeAsyncWrite(CassandraStatement const& statement, T callback, S& callbackData, bool isRetry) const
     {
         if (!isRetry)
-            incremementOutstandingRequestCount();
+            incrementOutstandingRequestCount();
         executeAsyncHelper(statement, callback, callbackData);
     }
 
     template <class T, class S>
     void
-    executeAsyncRead(
-        CassandraStatement const& statement,
-        T callback,
-        S& callbackData) const
+    executeAsyncRead(CassandraStatement const& statement, T callback, S& callbackData) const
     {
         executeAsyncHelper(statement, callback, callbackData);
     }
@@ -1132,7 +1048,7 @@ public:
                 ss << "Cassandra sync write error";
                 ss << ", retrying";
                 ss << ": " << cass_error_desc(rc);
-                BOOST_LOG_TRIVIAL(warning) << ss.str();
+                log_.warn() << ss.str();
                 std::this_thread::sleep_for(std::chrono::milliseconds(5));
             }
         } while (rc != CASS_OK);
@@ -1156,7 +1072,7 @@ public:
                 ss << "Cassandra sync update error";
                 ss << ", retrying";
                 ss << ": " << cass_error_desc(rc);
-                BOOST_LOG_TRIVIAL(warning) << ss.str();
+                log_.warn() << ss.str();
                 std::this_thread::sleep_for(std::chrono::milliseconds(5));
             }
         } while (rc != CASS_OK);
@@ -1166,7 +1082,7 @@ public:
         CassRow const* row = cass_result_first_row(res);
         if (!row)
         {
-            BOOST_LOG_TRIVIAL(error) << "executeSyncUpdate - no rows";
+            log_.error() << "executeSyncUpdate - no rows";
             cass_result_free(res);
             return false;
         }
@@ -1175,16 +1091,13 @@ public:
         if (rc != CASS_OK)
         {
             cass_result_free(res);
-            BOOST_LOG_TRIVIAL(error)
-                << "executeSyncUpdate - error getting result " << rc << ", "
-                << cass_error_desc(rc);
+            log_.error() << "executeSyncUpdate - error getting result " << rc << ", " << cass_error_desc(rc);
             return false;
         }
         cass_result_free(res);
         if (success != cass_true && timedOut)
         {
-            BOOST_LOG_TRIVIAL(warning)
-                << __func__ << " Update failed, but timedOut is true";
+            log_.warn() << "Update failed, but timedOut is true";
             // if there was a timeout, the update may have succeeded in the
             // background on the first attempt. To determine if this happened,
             // we query the range from the db, making sure the range is what
@@ -1199,34 +1112,32 @@ public:
     }
 
     CassandraResult
-    executeAsyncRead(
-        CassandraStatement const& statement,
-        boost::asio::yield_context& yield) const
+    executeAsyncRead(CassandraStatement const& statement, boost::asio::yield_context& yield) const
     {
-        using result = boost::asio::async_result<
-            boost::asio::yield_context,
-            void(boost::system::error_code, CassError)>;
+        using result =
+            boost::asio::async_result<boost::asio::yield_context, void(boost::system::error_code, CassError)>;
 
         CassFuture* fut;
         CassError rc;
         do
         {
+            ++numReadRequestsOutstanding_;
             fut = cass_session_execute(session_.get(), statement.get());
 
             boost::system::error_code ec;
             rc = cass_future_error_code(fut, yield[ec]);
+            --numReadRequestsOutstanding_;
 
             if (ec)
             {
-                BOOST_LOG_TRIVIAL(error)
-                    << "Cannot read async cass_future_error_code";
+                log_.error() << "Cannot read async cass_future_error_code";
             }
             if (rc != CASS_OK)
             {
                 std::stringstream ss;
                 ss << "Cassandra executeAsyncRead error";
                 ss << ": " << cass_error_desc(rc);
-                BOOST_LOG_TRIVIAL(error) << ss.str();
+                log_.error() << ss.str();
             }
             if (isTimeout(rc))
             {
@@ -1249,4 +1160,3 @@ public:
 };
 
 }  // namespace Backend
-#endif

src/backend/CassandraBackendNew.h

@@ -0,0 +1,851 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/BackendInterface.h>
+#include <backend/cassandra/Concepts.h>
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/Schema.h>
+#include <backend/cassandra/SettingsProvider.h>
+#include <backend/cassandra/impl/ExecutionStrategy.h>
+#include <log/Logger.h>
+#include <util/Profiler.h>
+
+#include <ripple/app/tx/impl/details/NFTokenUtils.h>
+#include <boost/asio/spawn.hpp>
+
+namespace Backend::Cassandra {
+
+/**
+ * @brief Implements @ref BackendInterface for Cassandra/Scylladb
+ *
+ * Note: this is a safer and more correct rewrite of the original implementation
+ * of the backend. We deliberately did not change the interface for now so that
+ * other parts such as ETL do not have to change at all.
+ * Eventually we should change the interface so that it does not have to know
+ * about yield_context.
+ */
+template <SomeSettingsProvider SettingsProviderType, SomeExecutionStrategy ExecutionStrategy>
+class BasicCassandraBackend : public BackendInterface
+{
+    clio::Logger log_{"Backend"};
+
+    SettingsProviderType settingsProvider_;
+    Schema<SettingsProviderType> schema_;
+    Handle handle_;
+
+    // have to be mutable because BackendInterface constness :(
+    mutable ExecutionStrategy executor_;
+
+    std::atomic_uint32_t ledgerSequence_ = 0u;
+
+public:
+    /**
+     * @brief Create a new cassandra/scylla backend instance.
+     *
+     * @param settingsProvider
+     */
+    BasicCassandraBackend(SettingsProviderType settingsProvider)
+        : settingsProvider_{std::move(settingsProvider)}
+        , schema_{settingsProvider_}
+        , handle_{settingsProvider_.getSettings()}
+        , executor_{settingsProvider_.getSettings(), handle_}
+    {
+        if (auto const res = handle_.connect(); not res)
+            throw std::runtime_error("Could not connect to Cassandra: " + res.error());
+
+        if (auto const res = handle_.execute(schema_.createKeyspace); not res)
+        {
+            // on datastax, creation of keyspaces can be configured to only be done thru the admin interface.
+            // this does not mean that the keyspace does not already exist tho.
+            if (res.error().code() != CASS_ERROR_SERVER_UNAUTHORIZED)
+                throw std::runtime_error("Could not create keyspace: " + res.error());
+        }
+
+        if (auto const res = handle_.executeEach(schema_.createSchema); not res)
+            throw std::runtime_error("Could not create schema: " + res.error());
+
+        schema_.prepareStatements(handle_);
+        log_.info() << "Created (revamped) CassandraBackend";
+    }
+
+    /*! Not used in this implementation */
+    void
+    open([[maybe_unused]] bool readOnly) override
+    {
+    }
+
+    /*! Not used in this implementation */
+    void
+    close() override
+    {
+    }
+
+    TransactionsAndCursor
+    fetchAccountTransactions(
+        ripple::AccountID const& account,
+        std::uint32_t const limit,
+        bool forward,
+        std::optional<TransactionsCursor> const& cursorIn,
+        boost::asio::yield_context& yield) const override
+    {
+        auto rng = fetchLedgerRange();
+        if (!rng)
+            return {{}, {}};
+
+        Statement statement = [this, forward, &account]() {
+            if (forward)
+                return schema_->selectAccountTxForward.bind(account);
+            else
+                return schema_->selectAccountTx.bind(account);
+        }();
+
+        auto cursor = cursorIn;
+        if (cursor)
+        {
+            statement.bindAt(1, cursor->asTuple());
+            log_.debug() << "account = " << ripple::strHex(account) << " tuple = " << cursor->ledgerSequence
+                         << cursor->transactionIndex;
+        }
+        else
+        {
+            auto const seq = forward ? rng->minSequence : rng->maxSequence;
+            auto const placeHolder = forward ? 0u : std::numeric_limits<std::uint32_t>::max();
+
+            statement.bindAt(1, std::make_tuple(placeHolder, placeHolder));
+            log_.debug() << "account = " << ripple::strHex(account) << " idx = " << seq << " tuple = " << placeHolder;
+        }
+
+        // FIXME: Limit is a hack to support uint32_t properly for the time
+        // being. Should be removed later and schema updated to use proper
+        // types.
+        statement.bindAt(2, Limit{limit});
+        auto const res = executor_.read(yield, statement);
+        auto const& results = res.value();
+        if (not results.hasRows())
+        {
+            log_.debug() << "No rows returned";
+            return {};
+        }
+
+        std::vector<ripple::uint256> hashes = {};
+        auto numRows = results.numRows();
+        log_.info() << "num_rows = " << numRows;
+
+        for (auto [hash, data] : extract<ripple::uint256, std::tuple<uint32_t, uint32_t>>(results))
+        {
+            hashes.push_back(hash);
+            if (--numRows == 0)
+            {
+                log_.debug() << "Setting cursor";
+                cursor = data;
+
+                // forward queries by ledger/tx sequence `>=`
+                // so we have to advance the index by one
+                if (forward)
+                    ++cursor->transactionIndex;
+            }
+        }
+
+        auto const txns = fetchTransactions(hashes, yield);
+        log_.debug() << "Txns = " << txns.size();
+
+        if (txns.size() == limit)
+        {
+            log_.debug() << "Returning cursor";
+            return {txns, cursor};
+        }
+
+        return {txns, {}};
+    }
+
+    bool
+    doFinishWrites() override
+    {
+        // wait for other threads to finish their writes
+        executor_.sync();
+
+        if (!range)
+        {
+            executor_.writeSync(schema_->updateLedgerRange, ledgerSequence_, false, ledgerSequence_);
+        }
+
+        if (not executeSyncUpdate(schema_->updateLedgerRange.bind(ledgerSequence_, true, ledgerSequence_ - 1)))
+        {
+            log_.warn() << "Update failed for ledger " << ledgerSequence_;
+            return false;
+        }
+
+        log_.info() << "Committed ledger " << ledgerSequence_;
+        return true;
+    }
+
+    void
+    writeLedger(ripple::LedgerInfo const& ledgerInfo, std::string&& header) override
+    {
+        executor_.write(schema_->insertLedgerHeader, ledgerInfo.seq, std::move(header));
+
+        executor_.write(schema_->insertLedgerHash, ledgerInfo.hash, ledgerInfo.seq);
+
+        ledgerSequence_ = ledgerInfo.seq;
+    }
+
+    std::optional<std::uint32_t>
+    fetchLatestLedgerSequence(boost::asio::yield_context& yield) const override
+    {
+        if (auto const res = executor_.read(yield, schema_->selectLatestLedger); res)
+        {
+            if (auto const& result = res.value(); result)
+            {
+                if (auto const maybeValue = result.template get<uint32_t>(); maybeValue)
+                    return maybeValue;
+
+                log_.error() << "Could not fetch latest ledger - no rows";
+                return std::nullopt;
+            }
+
+            log_.error() << "Could not fetch latest ledger - no result";
+        }
+        else
+        {
+            log_.error() << "Could not fetch latest ledger: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::optional<ripple::LedgerInfo>
+    fetchLedgerBySequence(std::uint32_t const sequence, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call for seq " << sequence;
+
+        auto const res = executor_.read(yield, schema_->selectLedgerBySeq, sequence);
+        if (res)
+        {
+            if (auto const& result = res.value(); result)
+            {
+                if (auto const maybeValue = result.template get<std::vector<unsigned char>>(); maybeValue)
+                {
+                    return deserializeHeader(ripple::makeSlice(*maybeValue));
+                }
+
+                log_.error() << "Could not fetch ledger by sequence - no rows";
+                return std::nullopt;
+            }
+
+            log_.error() << "Could not fetch ledger by sequence - no result";
+        }
+        else
+        {
+            log_.error() << "Could not fetch ledger by sequence: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::optional<ripple::LedgerInfo>
+    fetchLedgerByHash(ripple::uint256 const& hash, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (auto const res = executor_.read(yield, schema_->selectLedgerByHash, hash); res)
+        {
+            if (auto const& result = res.value(); result)
+            {
+                if (auto const maybeValue = result.template get<uint32_t>(); maybeValue)
+                    return fetchLedgerBySequence(*maybeValue, yield);
+
+                log_.error() << "Could not fetch ledger by hash - no rows";
+                return std::nullopt;
+            }
+
+            log_.error() << "Could not fetch ledger by hash - no result";
+        }
+        else
+        {
+            log_.error() << "Could not fetch ledger by hash: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::optional<LedgerRange>
+    hardFetchLedgerRange(boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (auto const res = executor_.read(yield, schema_->selectLedgerRange); res)
+        {
+            auto const& results = res.value();
+            if (not results.hasRows())
+            {
+                log_.debug() << "Could not fetch ledger range - no rows";
+                return std::nullopt;
+            }
+
+            // TODO: this is probably a good place to use user type in
+            // cassandra instead of having two rows with bool flag. or maybe at
+            // least use tuple<int, int>?
+            LedgerRange range;
+            std::size_t idx = 0;
+            for (auto [seq] : extract<uint32_t>(results))
+            {
+                if (idx == 0)
+                    range.maxSequence = range.minSequence = seq;
+                else if (idx == 1)
+                    range.maxSequence = seq;
+
+                ++idx;
+            }
+
+            if (range.minSequence > range.maxSequence)
+                std::swap(range.minSequence, range.maxSequence);
+
+            log_.debug() << "After hardFetchLedgerRange range is " << range.minSequence << ":" << range.maxSequence;
+            return range;
+        }
+        else
+        {
+            log_.error() << "Could not fetch ledger range: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::vector<TransactionAndMetadata>
+    fetchAllTransactionsInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+        auto hashes = fetchAllTransactionHashesInLedger(ledgerSequence, yield);
+        return fetchTransactions(hashes, yield);
+    }
+
+    std::vector<ripple::uint256>
+    fetchAllTransactionHashesInLedger(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override
+    {
+        log_.trace() << __func__ << " call";
+        auto start = std::chrono::system_clock::now();
+        auto const res = executor_.read(yield, schema_->selectAllTransactionHashesInLedger, ledgerSequence);
+
+        if (not res)
+        {
+            log_.error() << "Could not fetch all transaction hashes: " << res.error();
+            return {};
+        }
+
+        auto const& result = res.value();
+        if (not result.hasRows())
+        {
+            log_.error() << "Could not fetch all transaction hashes - no rows; ledger = "
+                         << std::to_string(ledgerSequence);
+            return {};
+        }
+
+        std::vector<ripple::uint256> hashes;
+        for (auto [hash] : extract<ripple::uint256>(result))
+            hashes.push_back(std::move(hash));
+
+        auto end = std::chrono::system_clock::now();
+        log_.debug() << "Fetched " << hashes.size() << " transaction hashes from Cassandra in "
+                     << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count() << " milliseconds";
+
+        return hashes;
+    }
+
+    std::optional<NFT>
+    fetchNFT(ripple::uint256 const& tokenID, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override
+    {
+        log_.trace() << __func__ << " call";
+
+        auto const res = executor_.read(yield, schema_->selectNFT, tokenID, ledgerSequence);
+        if (not res)
+            return std::nullopt;
+
+        if (auto const maybeRow = res->template get<uint32_t, ripple::AccountID, bool>(); maybeRow)
+        {
+            auto [seq, owner, isBurned] = *maybeRow;
+            auto result = std::make_optional<NFT>(tokenID, seq, owner, isBurned);
+
+            // now fetch URI. Usually we will have the URI even for burned NFTs,
+            // but if the first ledger on this clio included NFTokenBurn
+            // transactions we will not have the URIs for any of those tokens.
+            // In any other case not having the URI indicates something went
+            // wrong with our data.
+            //
+            // TODO - in the future would be great for any handlers that use
+            // this could inject a warning in this case (the case of not having
+            // a URI because it was burned in the first ledger) to indicate that
+            // even though we are returning a blank URI, the NFT might have had
+            // one.
+            auto uriRes = executor_.read(yield, schema_->selectNFTURI, tokenID, ledgerSequence);
+            if (uriRes)
+            {
+                if (auto const maybeUri = uriRes->template get<ripple::Blob>(); maybeUri)
+                    result->uri = *maybeUri;
+            }
+
+            return result;
+        }
+
+        log_.error() << "Could not fetch NFT - no rows";
+        return std::nullopt;
+    }
+
+    TransactionsAndCursor
+    fetchNFTTransactions(
+        ripple::uint256 const& tokenID,
+        std::uint32_t const limit,
+        bool const forward,
+        std::optional<TransactionsCursor> const& cursorIn,
+        boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        auto rng = fetchLedgerRange();
+        if (!rng)
+            return {{}, {}};
+
+        Statement statement = [this, forward, &tokenID]() {
+            if (forward)
+                return schema_->selectNFTTxForward.bind(tokenID);
+            else
+                return schema_->selectNFTTx.bind(tokenID);
+        }();
+
+        auto cursor = cursorIn;
+        if (cursor)
+        {
+            statement.bindAt(1, cursor->asTuple());
+            log_.debug() << "token_id = " << ripple::strHex(tokenID) << " tuple = " << cursor->ledgerSequence
+                         << cursor->transactionIndex;
+        }
+        else
+        {
+            auto const seq = forward ? rng->minSequence : rng->maxSequence;
+            auto const placeHolder = forward ? 0 : std::numeric_limits<std::uint32_t>::max();
+
+            statement.bindAt(1, std::make_tuple(placeHolder, placeHolder));
+            log_.debug() << "token_id = " << ripple::strHex(tokenID) << " idx = " << seq << " tuple = " << placeHolder;
+        }
+
+        statement.bindAt(2, Limit{limit});
+
+        auto const res = executor_.read(yield, statement);
+        auto const& results = res.value();
+        if (not results.hasRows())
+        {
+            log_.debug() << "No rows returned";
+            return {};
+        }
+
+        std::vector<ripple::uint256> hashes = {};
+        auto numRows = results.numRows();
+        log_.info() << "num_rows = " << numRows;
+
+        for (auto [hash, data] : extract<ripple::uint256, std::tuple<uint32_t, uint32_t>>(results))
+        {
+            hashes.push_back(hash);
+            if (--numRows == 0)
+            {
+                log_.debug() << "Setting cursor";
+                cursor = data;
+
+                // forward queries by ledger/tx sequence `>=`
+                // so we have to advance the index by one
+                if (forward)
+                    ++cursor->transactionIndex;
+            }
+        }
+
+        auto const txns = fetchTransactions(hashes, yield);
+        log_.debug() << "NFT Txns = " << txns.size();
+
+        if (txns.size() == limit)
+        {
+            log_.debug() << "Returning cursor";
+            return {txns, cursor};
+        }
+
+        return {txns, {}};
+    }
+
+    std::optional<Blob>
+    doFetchLedgerObject(ripple::uint256 const& key, std::uint32_t const sequence, boost::asio::yield_context& yield)
+        const override
+    {
+        log_.debug() << "Fetching ledger object for seq " << sequence << ", key = " << ripple::to_string(key);
+        if (auto const res = executor_.read(yield, schema_->selectObject, key, sequence); res)
+        {
+            if (auto const result = res->template get<Blob>(); result)
+            {
+                if (result->size())
+                    return *result;
+            }
+            else
+            {
+                log_.debug() << "Could not fetch ledger object - no rows";
+            }
+        }
+        else
+        {
+            log_.error() << "Could not fetch ledger object: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::optional<TransactionAndMetadata>
+    fetchTransaction(ripple::uint256 const& hash, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (auto const res = executor_.read(yield, schema_->selectTransaction, hash); res)
+        {
+            if (auto const maybeValue = res->template get<Blob, Blob, uint32_t, uint32_t>(); maybeValue)
+            {
+                auto [transaction, meta, seq, date] = *maybeValue;
+                return std::make_optional<TransactionAndMetadata>(transaction, meta, seq, date);
+            }
+            else
+            {
+                log_.debug() << "Could not fetch transaction - no rows";
+            }
+        }
+        else
+        {
+            log_.error() << "Could not fetch transaction: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::optional<ripple::uint256>
+    doFetchSuccessorKey(ripple::uint256 key, std::uint32_t const ledgerSequence, boost::asio::yield_context& yield)
+        const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (auto const res = executor_.read(yield, schema_->selectSuccessor, key, ledgerSequence); res)
+        {
+            if (auto const result = res->template get<ripple::uint256>(); result)
+            {
+                if (*result == lastKey)
+                    return std::nullopt;
+                return *result;
+            }
+            else
+            {
+                log_.debug() << "Could not fetch successor - no rows";
+            }
+        }
+        else
+        {
+            log_.error() << "Could not fetch successor: " << res.error();
+        }
+
+        return std::nullopt;
+    }
+
+    std::vector<TransactionAndMetadata>
+    fetchTransactions(std::vector<ripple::uint256> const& hashes, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (hashes.size() == 0)
+            return {};
+
+        auto const numHashes = hashes.size();
+        std::vector<TransactionAndMetadata> results;
+        results.reserve(numHashes);
+
+        std::vector<Statement> statements;
+        statements.reserve(numHashes);
+
+        auto const timeDiff = util::timed([this, &yield, &results, &hashes, &statements]() {
+            // TODO: seems like a job for "hash IN (list of hashes)" instead?
+            std::transform(
+                std::cbegin(hashes), std::cend(hashes), std::back_inserter(statements), [this](auto const& hash) {
+                    return schema_->selectTransaction.bind(hash);
+                });
+
+            auto const entries = executor_.readEach(yield, statements);
+            std::transform(
+                std::cbegin(entries),
+                std::cend(entries),
+                std::back_inserter(results),
+                [](auto const& res) -> TransactionAndMetadata {
+                    if (auto const maybeRow = res.template get<Blob, Blob, uint32_t, uint32_t>(); maybeRow)
+                        return *maybeRow;
+                    else
+                        return {};
+                });
+        });
+
+        assert(numHashes == results.size());
+        log_.debug() << "Fetched " << numHashes << " transactions from Cassandra in " << timeDiff << " milliseconds";
+        return results;
+    }
+
+    std::vector<Blob>
+    doFetchLedgerObjects(
+        std::vector<ripple::uint256> const& keys,
+        std::uint32_t const sequence,
+        boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        if (keys.size() == 0)
+            return {};
+
+        auto const numKeys = keys.size();
+        log_.trace() << "Fetching " << numKeys << " objects";
+
+        std::vector<Blob> results;
+        results.reserve(numKeys);
+
+        std::vector<Statement> statements;
+        statements.reserve(numKeys);
+
+        // TODO: seems like a job for "key IN (list of keys)" instead?
+        std::transform(
+            std::cbegin(keys), std::cend(keys), std::back_inserter(statements), [this, &sequence](auto const& key) {
+                return schema_->selectObject.bind(key, sequence);
+            });
+
+        auto const entries = executor_.readEach(yield, statements);
+        std::transform(
+            std::cbegin(entries), std::cend(entries), std::back_inserter(results), [](auto const& res) -> Blob {
+                if (auto const maybeValue = res.template get<Blob>(); maybeValue)
+                    return *maybeValue;
+                else
+                    return {};
+            });
+
+        log_.trace() << "Fetched " << numKeys << " objects";
+        return results;
+    }
+
+    std::vector<LedgerObject>
+    fetchLedgerDiff(std::uint32_t const ledgerSequence, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+
+        auto const [keys, timeDiff] = util::timed([this, &ledgerSequence, &yield]() -> std::vector<ripple::uint256> {
+            auto const res = executor_.read(yield, schema_->selectDiff, ledgerSequence);
+            if (not res)
+            {
+                log_.error() << "Could not fetch ledger diff: " << res.error() << "; ledger = " << ledgerSequence;
+                return {};
+            }
+
+            auto const& results = res.value();
+            if (not results)
+            {
+                log_.error() << "Could not fetch ledger diff - no rows; ledger = " << ledgerSequence;
+                return {};
+            }
+
+            std::vector<ripple::uint256> keys;
+            for (auto [key] : extract<ripple::uint256>(results))
+                keys.push_back(key);
+
+            return keys;
+        });
+
+        // one of the above errors must have happened
+        if (keys.empty())
+            return {};
+
+        log_.debug() << "Fetched " << keys.size() << " diff hashes from Cassandra in " << timeDiff << " milliseconds";
+
+        auto const objs = fetchLedgerObjects(keys, ledgerSequence, yield);
+        std::vector<LedgerObject> results;
+        results.reserve(keys.size());
+
+        std::transform(
+            std::cbegin(keys),
+            std::cend(keys),
+            std::cbegin(objs),
+            std::back_inserter(results),
+            [](auto const& key, auto const& obj) {
+                return LedgerObject{key, obj};
+            });
+
+        return results;
+    }
+
+    void
+    doWriteLedgerObject(std::string&& key, std::uint32_t const seq, std::string&& blob) override
+    {
+        log_.trace() << " Writing ledger object " << key.size() << ":" << seq << " [" << blob.size() << " bytes]";
+
+        if (range)
+            executor_.write(schema_->insertDiff, seq, key);
+
+        executor_.write(schema_->insertObject, std::move(key), seq, std::move(blob));
+    }
+
+    void
+    writeSuccessor(std::string&& key, std::uint32_t const seq, std::string&& successor) override
+    {
+        log_.trace() << "Writing successor. key = " << key.size() << " bytes. "
+                     << " seq = " << std::to_string(seq) << " successor = " << successor.size() << " bytes.";
+        assert(key.size() != 0);
+        assert(successor.size() != 0);
+
+        executor_.write(schema_->insertSuccessor, std::move(key), seq, std::move(successor));
+    }
+
+    void
+    writeAccountTransactions(std::vector<AccountTransactionsData>&& data) override
+    {
+        std::vector<Statement> statements;
+        statements.reserve(data.size() * 10);  // assume 10 transactions avg
+
+        for (auto& record : data)
+        {
+            std::transform(
+                std::begin(record.accounts),
+                std::end(record.accounts),
+                std::back_inserter(statements),
+                [this, &record](auto&& account) {
+                    return schema_->insertAccountTx.bind(
+                        std::move(account),
+                        std::make_tuple(record.ledgerSequence, record.transactionIndex),
+                        record.txHash);
+                });
+        }
+
+        executor_.write(std::move(statements));
+    }
+
+    void
+    writeNFTTransactions(std::vector<NFTTransactionsData>&& data) override
+    {
+        std::vector<Statement> statements;
+        statements.reserve(data.size());
+
+        std::transform(std::cbegin(data), std::cend(data), std::back_inserter(statements), [this](auto const& record) {
+            return schema_->insertNFTTx.bind(
+                record.tokenID, std::make_tuple(record.ledgerSequence, record.transactionIndex), record.txHash);
+        });
+
+        executor_.write(std::move(statements));
+    }
+
+    void
+    writeTransaction(
+        std::string&& hash,
+        std::uint32_t const seq,
+        std::uint32_t const date,
+        std::string&& transaction,
+        std::string&& metadata) override
+    {
+        log_.trace() << "Writing txn to cassandra";
+
+        executor_.write(schema_->insertLedgerTransaction, seq, hash);
+        executor_.write(
+            schema_->insertTransaction, std::move(hash), seq, date, std::move(transaction), std::move(metadata));
+    }
+
+    void
+    writeNFTs(std::vector<NFTsData>&& data) override
+    {
+        std::vector<Statement> statements;
+        statements.reserve(data.size() * 3);
+
+        for (NFTsData const& record : data)
+        {
+            statements.push_back(
+                schema_->insertNFT.bind(record.tokenID, record.ledgerSequence, record.owner, record.isBurned));
+
+            // If `uri` is set (and it can be set to an empty uri), we know this
+            // is a net-new NFT. That is, this NFT has not been seen before by
+            // us _OR_ it is in the extreme edge case of a re-minted NFT ID with
+            // the same NFT ID as an already-burned token. In this case, we need
+            // to record the URI and link to the issuer_nf_tokens table.
+            if (record.uri)
+            {
+                statements.push_back(schema_->insertIssuerNFT.bind(
+                    ripple::nft::getIssuer(record.tokenID),
+                    static_cast<uint32_t>(ripple::nft::getTaxon(record.tokenID)),
+                    record.tokenID));
+                statements.push_back(
+                    schema_->insertNFTURI.bind(record.tokenID, record.ledgerSequence, record.uri.value()));
+            }
+        }
+
+        executor_.write(std::move(statements));
+    }
+
+    void
+    startWrites() const override
+    {
+        // Note: no-op in original implementation too.
+        // probably was used in PG to start a transaction or smth.
+    }
+
+    /*! Unused in this implementation */
+    bool
+    doOnlineDelete(std::uint32_t const numLedgersToKeep, boost::asio::yield_context& yield) const override
+    {
+        log_.trace() << __func__ << " call";
+        return true;
+    }
+
+    bool
+    isTooBusy() const override
+    {
+        return executor_.isTooBusy();
+    }
+
+private:
+    bool
+    executeSyncUpdate(Statement statement)
+    {
+        auto const res = executor_.writeSync(statement);
+        auto maybeSuccess = res->template get<bool>();
+        if (not maybeSuccess)
+        {
+            log_.error() << "executeSyncUpdate - error getting result - no row";
+            return false;
+        }
+
+        if (not maybeSuccess.value())
+        {
+            log_.warn() << "Update failed. Checking if DB state is what we expect";
+
+            // error may indicate that another writer wrote something.
+            // in this case let's just compare the current state of things
+            // against what we were trying to write in the first place and
+            // use that as the source of truth for the result.
+            auto rng = hardFetchLedgerRangeNoThrow();
+            return rng && rng->maxSequence == ledgerSequence_;
+        }
+
+        return true;
+    }
+};
+
+using CassandraBackend = BasicCassandraBackend<SettingsProvider, detail::DefaultExecutionStrategy<>>;
+
+}  // namespace Backend::Cassandra

src/backend/DBHelpers.h

@@ -1,12 +1,33 @@
-#ifndef CLIO_BACKEND_DBHELPERS_H_INCLUDED
-#define CLIO_BACKEND_DBHELPERS_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
 #include <ripple/basics/Log.h>
+#include <ripple/basics/StringUtilities.h>
+#include <ripple/ledger/ReadView.h>
 #include <ripple/protocol/SField.h>
 #include <ripple/protocol/STAccount.h>
 #include <ripple/protocol/TxMeta.h>
+
 #include <boost/container/flat_set.hpp>
-#include <backend/Pg.h>
+
 #include <backend/Types.h>
 
 /// Struct used to keep track of what to write to
@@ -18,10 +39,7 @@ struct AccountTransactionsData
     std::uint32_t transactionIndex;
     ripple::uint256 txHash;
 
-    AccountTransactionsData(
-        ripple::TxMeta& meta,
-        ripple::uint256 const& txHash,
-        beast::Journal& j)
+    AccountTransactionsData(ripple::TxMeta& meta, ripple::uint256 const& txHash, beast::Journal& j)
         : accounts(meta.getAffectedAccounts())
         , ledgerSequence(meta.getLgrSeq())
         , transactionIndex(meta.getIndex())
@@ -41,14 +59,8 @@ struct NFTTransactionsData
     std::uint32_t transactionIndex;
     ripple::uint256 txHash;
 
-    NFTTransactionsData(
-        ripple::uint256 const& tokenID,
-        ripple::TxMeta const& meta,
-        ripple::uint256 const& txHash)
-        : tokenID(tokenID)
-        , ledgerSequence(meta.getLgrSeq())
-        , transactionIndex(meta.getIndex())
-        , txHash(txHash)
+    NFTTransactionsData(ripple::uint256 const& tokenID, ripple::TxMeta const& meta, ripple::uint256 const& txHash)
+        : tokenID(tokenID), ledgerSequence(meta.getLgrSeq()), transactionIndex(meta.getIndex()), txHash(txHash)
     {
     }
 };
@@ -64,16 +76,38 @@ struct NFTsData
     // final state of an NFT per ledger. Since we pull this from transactions
     // we keep track of which tx index created this so we can de-duplicate, as
     // it is possible for one ledger to have multiple txs that change the
-    // state of the same NFT.
-    std::uint32_t transactionIndex;
+    // state of the same NFT. This field is not applicable when we are loading
+    // initial NFT state via ledger objects, since we do not have to tiebreak
+    // NFT state for a given ledger in that case.
+    std::optional<std::uint32_t> transactionIndex;
     ripple::AccountID owner;
-    bool isBurned;
+    // We only set the uri if this is a mint tx, or if we are
+    // loading initial state from NFTokenPage objects. In other words,
+    // uri should only be set if the etl process believes this NFT hasn't
+    // been seen before in our local database. We do this so that we don't
+    // write to the the nf_token_uris table every
+    // time the same NFT changes hands. We also can infer if there is a URI
+    // that we need to write to the issuer_nf_tokens table.
+    std::optional<ripple::Blob> uri;
+    bool isBurned = false;
 
+    // This constructor is used when parsing an NFTokenMint tx.
+    // Unfortunately because of the extreme edge case of being able to
+    // re-mint an NFT with the same ID, we must explicitly record a null
+    // URI. For this reason, we _always_ write this field as a result of
+    // this tx.
     NFTsData(
         ripple::uint256 const& tokenID,
         ripple::AccountID const& owner,
-        ripple::TxMeta const& meta,
-        bool isBurned)
+        ripple::Blob const& uri,
+        ripple::TxMeta const& meta)
+        : tokenID(tokenID), ledgerSequence(meta.getLgrSeq()), transactionIndex(meta.getIndex()), owner(owner), uri(uri)
+    {
+    }
+
+    // This constructor is used when parsing an NFTokenBurn or
+    // NFTokenAcceptOffer tx
+    NFTsData(ripple::uint256 const& tokenID, ripple::AccountID const& owner, ripple::TxMeta const& meta, bool isBurned)
         : tokenID(tokenID)
         , ledgerSequence(meta.getLgrSeq())
         , transactionIndex(meta.getIndex())
@@ -81,6 +115,21 @@ struct NFTsData
         , isBurned(isBurned)
     {
     }
+
+    // This constructor is used when parsing an NFTokenPage directly from
+    // ledger state.
+    // Unfortunately because of the extreme edge case of being able to
+    // re-mint an NFT with the same ID, we must explicitly record a null
+    // URI. For this reason, we _always_ write this field as a result of
+    // this tx.
+    NFTsData(
+        ripple::uint256 const& tokenID,
+        std::uint32_t const ledgerSequence,
+        ripple::AccountID const& owner,
+        ripple::Blob const& uri)
+        : tokenID(tokenID), ledgerSequence(ledgerSequence), owner(owner), uri(uri)
+    {
+    }
 };
 
 template <class T>
@@ -119,8 +168,7 @@ isBookDir(T const& key, R const& object)
     if (!isDirNode(object))
         return false;
 
-    ripple::STLedgerEntry const sle{
-        ripple::SerialIter{object.data(), object.size()}, key};
+    ripple::STLedgerEntry const sle{ripple::SerialIter{object.data(), object.size()}, key};
     return !sle[~ripple::sfOwner].has_value();
 }
 
@@ -159,10 +207,8 @@ deserializeHeader(ripple::Slice data)
     info.parentHash = sit.get256();
     info.txHash = sit.get256();
     info.accountHash = sit.get256();
-    info.parentCloseTime =
-        ripple::NetClock::time_point{ripple::NetClock::duration{sit.get32()}};
-    info.closeTime =
-        ripple::NetClock::time_point{ripple::NetClock::duration{sit.get32()}};
+    info.parentCloseTime = ripple::NetClock::time_point{ripple::NetClock::duration{sit.get32()}};
+    info.closeTime = ripple::NetClock::time_point{ripple::NetClock::duration{sit.get32()}};
     info.closeTimeResolution = ripple::NetClock::duration{sit.get8()};
     info.closeFlags = sit.get8();
 
@@ -178,4 +224,3 @@ uint256ToString(ripple::uint256 const& uint)
 }
 
 static constexpr std::uint32_t rippleEpochStart = 946684800;
-#endif

src/backend/Pg.h

@@ -1,571 +0,0 @@
-#ifndef RIPPLE_CORE_PG_H_INCLUDED
-#define RIPPLE_CORE_PG_H_INCLUDED
-
-#include <ripple/basics/StringUtilities.h>
-#include <ripple/basics/chrono.h>
-#include <ripple/ledger/ReadView.h>
-#include <boost/asio/io_context.hpp>
-#include <boost/asio/ip/tcp.hpp>
-#include <boost/asio/spawn.hpp>
-#include <boost/icl/closed_interval.hpp>
-#include <boost/json.hpp>
-#include <boost/lexical_cast.hpp>
-#include <boost/log/trivial.hpp>
-#include <atomic>
-#include <chrono>
-#include <condition_variable>
-#include <functional>
-#include <libpq-fe.h>
-#include <memory>
-#include <mutex>
-#include <optional>
-#include <string>
-#include <string_view>
-#include <utility>
-#include <vector>
-
-// These postgres structs must be freed only by the postgres API.
-using pg_result_type = std::unique_ptr<PGresult, void (*)(PGresult*)>;
-using pg_connection_type = std::unique_ptr<PGconn, void (*)(PGconn*)>;
-using asio_socket_type = std::unique_ptr<
-    boost::asio::ip::tcp::socket,
-    void (*)(boost::asio::ip::tcp::socket*)>;
-
-/** first: command
- * second: parameter values
- *
- * The 2nd member takes an optional string to
- * distinguish between NULL parameters and empty strings. An empty
- * item corresponds to a NULL parameter.
- *
- * Postgres reads each parameter as a c-string, regardless of actual type.
- * Binary types (bytea) need to be converted to hex and prepended with
- * \x ("\\x").
- */
-using pg_params =
-    std::pair<char const*, std::vector<std::optional<std::string>>>;
-
-/** Parameter values for pg API. */
-using pg_formatted_params = std::vector<char const*>;
-
-/** Parameters for managing postgres connections. */
-struct PgConfig
-{
-    /** Maximum connections allowed to db. */
-    std::size_t max_connections{1000};
-    /** Close idle connections past this duration. */
-    std::chrono::seconds timeout{600};
-
-    /** Index of DB connection parameter names. */
-    std::vector<char const*> keywordsIdx;
-    /** DB connection parameter names. */
-    std::vector<std::string> keywords;
-    /** Index of DB connection parameter values. */
-    std::vector<char const*> valuesIdx;
-    /** DB connection parameter values. */
-    std::vector<std::string> values;
-};
-
-//-----------------------------------------------------------------------------
-
-/** Class that operates on postgres query results.
- *
- * The functions that return results do not check first whether the
- * expected results are actually there. Therefore, the caller first needs
- * to check whether or not a valid response was returned using the operator
- * bool() overload. If number of tuples or fields are unknown, then check
- * those. Each result field should be checked for null before attempting
- * to return results. Finally, the caller must know the type of the field
- * before calling the corresponding function to return a field. Postgres
- * internally stores each result field as null-terminated strings.
- */
-class PgResult
-{
-    // The result object must be freed using the libpq API PQclear() call.
-    pg_result_type result_{nullptr, [](PGresult* result) { PQclear(result); }};
-    std::optional<std::pair<ExecStatusType, std::string>> error_;
-
-public:
-    /** Constructor for when the process is stopping.
-     *
-     */
-    PgResult()
-    {
-    }
-
-    /** Constructor for successful query results.
-     *
-     * @param result Query result.
-     */
-    explicit PgResult(pg_result_type&& result) : result_(std::move(result))
-    {
-    }
-
-    /** Constructor for failed query results.
-     *
-     * @param result Query result that contains error information.
-     * @param conn Postgres connection that contains error information.
-     */
-    PgResult(PGresult* result, PGconn* conn)
-        : error_({PQresultStatus(result), PQerrorMessage(conn)})
-    {
-    }
-
-    /** Return field as a null-terminated string pointer.
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists, or that the row and fields exist, or that the field is
-     * not null.
-     *
-     * @param ntuple Row number.
-     * @param nfield Field number.
-     * @return Field contents.
-     */
-    char const*
-    c_str(int ntuple = 0, int nfield = 0) const
-    {
-        return PQgetvalue(result_.get(), ntuple, nfield);
-    }
-
-    std::vector<unsigned char>
-    asUnHexedBlob(int ntuple = 0, int nfield = 0) const
-    {
-        std::string_view view{c_str(ntuple, nfield) + 2};
-        auto res = ripple::strUnHex(view.size(), view.cbegin(), view.cend());
-        if (res)
-            return *res;
-        return {};
-    }
-
-    ripple::uint256
-    asUInt256(int ntuple = 0, int nfield = 0) const
-    {
-        ripple::uint256 val;
-        if (!val.parseHex(c_str(ntuple, nfield) + 2))
-            throw std::runtime_error("Pg - failed to parse hex into uint256");
-        return val;
-    }
-
-    /** Return field as equivalent to Postgres' INT type (32 bit signed).
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists, or that the row and fields exist, or that the field is
-     * not null, or that the type is that requested.
-
-     * @param ntuple Row number.
-     * @param nfield Field number.
-     * @return Field contents.
-     */
-    std::int32_t
-    asInt(int ntuple = 0, int nfield = 0) const
-    {
-        return boost::lexical_cast<std::int32_t>(
-            PQgetvalue(result_.get(), ntuple, nfield));
-    }
-
-    /** Return field as equivalent to Postgres' BIGINT type (64 bit signed).
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists, or that the row and fields exist, or that the field is
-     * not null, or that the type is that requested.
-
-     * @param ntuple Row number.
-     * @param nfield Field number.
-     * @return Field contents.
-     */
-    std::int64_t
-    asBigInt(int ntuple = 0, int nfield = 0) const
-    {
-        return boost::lexical_cast<std::int64_t>(
-            PQgetvalue(result_.get(), ntuple, nfield));
-    }
-
-    /** Returns whether the field is NULL or not.
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists, or that the row and fields exist.
-     *
-     * @param ntuple Row number.
-     * @param nfield Field number.
-     * @return Whether field is NULL.
-     */
-    bool
-    isNull(int ntuple = 0, int nfield = 0) const
-    {
-        return PQgetisnull(result_.get(), ntuple, nfield);
-    }
-
-    /** Check whether a valid response occurred.
-     *
-     * @return Whether or not the query returned a valid response.
-     */
-    operator bool() const
-    {
-        return result_ != nullptr;
-    }
-
-    /** Message describing the query results suitable for diagnostics.
-     *
-     * If error, then the postgres error type and message are returned.
-     * Otherwise, "ok"
-     *
-     * @return Query result message.
-     */
-    std::string
-    msg() const;
-
-    /** Get number of rows in result.
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists.
-     *
-     * @return Number of result rows.
-     */
-    int
-    ntuples() const
-    {
-        return PQntuples(result_.get());
-    }
-
-    /** Get number of fields in result.
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists.
-     *
-     * @return Number of result fields.
-     */
-    int
-    nfields() const
-    {
-        return PQnfields(result_.get());
-    }
-
-    /** Return result status of the command.
-     *
-     * Note that this function does not guarantee that the result struct
-     * exists.
-     *
-     * @return
-     */
-    ExecStatusType
-    status() const
-    {
-        return PQresultStatus(result_.get());
-    }
-};
-
-/* Class that contains and operates upon a postgres connection. */
-class Pg
-{
-    friend class PgPool;
-    friend class PgQuery;
-
-    PgConfig const& config_;
-    boost::asio::io_context::strand strand_;
-    bool& stop_;
-    std::mutex& mutex_;
-
-    asio_socket_type socket_{nullptr, [](boost::asio::ip::tcp::socket*) {}};
-
-    // The connection object must be freed using the libpq API PQfinish() call.
-    pg_connection_type conn_{nullptr, [](PGconn* conn) { PQfinish(conn); }};
-
-    inline asio_socket_type
-    getSocket(boost::asio::yield_context& strand);
-
-    inline PgResult
-    waitForStatus(boost::asio::yield_context& yield, ExecStatusType expected);
-
-    inline void
-    flush(boost::asio::yield_context& yield);
-
-    /** Clear results from the connection.
-     *
-     * Results from previous commands must be cleared before new commands
-     * can be processed. This function should be called on connections
-     * that weren't processed completely before being reused, such as
-     * when being checked-in.
-     *
-     * @return whether or not connection still exists.
-     */
-    bool
-    clear();
-
-    /** Connect to postgres.
-     *
-     * Idempotently connects to postgres by first checking whether an
-     * existing connection is already present. If connection is not present
-     * or in an errored state, reconnects to the database.
-     */
-    void
-    connect(boost::asio::yield_context& yield);
-
-    /** Disconnect from postgres. */
-    void
-    disconnect()
-    {
-        conn_.reset();
-        socket_.reset();
-    }
-
-    /** Execute postgres query.
-     *
-     * If parameters are included, then the command should contain only a
-     * single SQL statement. If no parameters, then multiple SQL statements
-     * delimited by semi-colons can be processed. The response is from
-     * the last command executed.
-     *
-     * @param command postgres API command string.
-     * @param nParams postgres API number of parameters.
-     * @param values postgres API array of parameter.
-     * @return Query result object.
-     */
-    PgResult
-    query(
-        char const* command,
-        std::size_t const nParams,
-        char const* const* values,
-        boost::asio::yield_context& yield);
-
-    /** Execute postgres query with no parameters.
-     *
-     * @param command Query string.
-     * @return Query result object;
-     */
-    PgResult
-    query(char const* command, boost::asio::yield_context& yield)
-    {
-        return query(command, 0, nullptr, yield);
-    }
-
-    /** Execute postgres query with parameters.
-     *
-     * @param dbParams Database command and parameter values.
-     * @return Query result object.
-     */
-    PgResult
-    query(pg_params const& dbParams, boost::asio::yield_context& yield);
-
-    /** Insert multiple records into a table using Postgres' bulk COPY.
-     *
-     * Throws upon error.
-     *
-     * @param table Name of table for import.
-     * @param records Records in the COPY IN format.
-     */
-    void
-    bulkInsert(
-        char const* table,
-        std::string const& records,
-        boost::asio::yield_context& yield);
-
-public:
-    /** Constructor for Pg class.
-     *
-     * @param config Config parameters.
-     * @param j Logger object.
-     * @param stop Reference to connection pool's stop flag.
-     * @param mutex Reference to connection pool's mutex.
-     */
-    Pg(PgConfig const& config,
-       boost::asio::io_context& ctx,
-       bool& stop,
-       std::mutex& mutex)
-        : config_(config), strand_(ctx), stop_(stop), mutex_(mutex)
-    {
-    }
-};
-
-//-----------------------------------------------------------------------------
-
-/** Database connection pool.
- *
- * Allow re-use of postgres connections. Postgres connections are created
- * as needed until configurable limit is reached. After use, each connection
- * is placed in a container ordered by time of use. Each request for
- * a connection grabs the most recently used connection from the container.
- * If none are available, a new connection is used (up to configured limit).
- * Idle connections are destroyed periodically after configurable
- * timeout duration.
- *
- * This should be stored as a shared pointer so PgQuery objects can safely
- * outlive it.
- */
-class PgPool
-{
-    friend class PgQuery;
-
-    using clock_type = std::chrono::steady_clock;
-
-    boost::asio::io_context& ioc_;
-    PgConfig config_;
-    std::mutex mutex_;
-    std::condition_variable cond_;
-    std::size_t connections_{};
-    bool stop_{false};
-
-    /** Idle database connections ordered by timestamp to allow timing out. */
-    std::multimap<std::chrono::time_point<clock_type>, std::unique_ptr<Pg>>
-        idle_;
-
-    /** Get a postgres connection object.
-     *
-     * Return the most recent idle connection in the pool, if available.
-     * Otherwise, return a new connection unless we're at the threshold.
-     * If so, then wait until a connection becomes available.
-     *
-     * @return Postgres object.
-     */
-    std::unique_ptr<Pg>
-    checkout();
-
-    /** Return a postgres object to the pool for reuse.
-     *
-     * If connection is healthy, place in pool for reuse. After calling this,
-     * the container no longer have a connection unless checkout() is called.
-     *
-     * @param pg Pg object.
-     */
-    void
-    checkin(std::unique_ptr<Pg>& pg);
-
-public:
-    /** Connection pool constructor.
-     *
-     * @param pgConfig Postgres config.
-     * @param j Logger object.
-     * @param parent Stoppable parent.
-     */
-    PgPool(boost::asio::io_context& ioc, boost::json::object const& config);
-
-    ~PgPool()
-    {
-        onStop();
-    }
-
-    PgConfig&
-    config()
-    {
-        return config_;
-    }
-
-    /** Initiate idle connection timer.
-     *
-     * The PgPool object needs to be fully constructed to support asynchronous
-     * operations.
-     */
-    void
-    setup();
-
-    /** Prepare for process shutdown. (Stoppable) */
-    void
-    onStop();
-};
-
-//-----------------------------------------------------------------------------
-
-/** Class to query postgres.
- *
- * This class should be used by functions outside of this
- * compilation unit for querying postgres. It automatically acquires and
- * relinquishes a database connection to handle each query.
- */
-class PgQuery
-{
-private:
-    std::shared_ptr<PgPool> pool_;
-    std::unique_ptr<Pg> pg_;
-
-public:
-    PgQuery() = delete;
-
-    PgQuery(std::shared_ptr<PgPool> const& pool)
-        : pool_(pool), pg_(pool->checkout())
-    {
-    }
-
-    ~PgQuery()
-    {
-        pool_->checkin(pg_);
-    }
-
-    // TODO. add sendQuery and getResult, for sending the query and getting the
-    // result asynchronously. This could be useful for sending a bunch of
-    // requests concurrently
-
-    /** Execute postgres query with parameters.
-     *
-     * @param dbParams Database command with parameters.
-     * @return Result of query, including errors.
-     */
-    PgResult
-    operator()(pg_params const& dbParams, boost::asio::yield_context& yield)
-    {
-        if (!pg_)  // It means we're stopping. Return empty result.
-            return PgResult();
-        return pg_->query(dbParams, yield);
-    }
-
-    /** Execute postgres query with only command statement.
-     *
-     * @param command Command statement.
-     * @return Result of query, including errors.
-     */
-    PgResult
-    operator()(char const* command, boost::asio::yield_context& yield)
-    {
-        return operator()(pg_params{command, {}}, yield);
-    }
-
-    /** Insert multiple records into a table using Postgres' bulk COPY.
-     *
-     * Throws upon error.
-     *
-     * @param table Name of table for import.
-     * @param records Records in the COPY IN format.
-     */
-    void
-    bulkInsert(
-        char const* table,
-        std::string const& records,
-        boost::asio::yield_context& yield)
-    {
-        pg_->bulkInsert(table, records, yield);
-    }
-};
-
-//-----------------------------------------------------------------------------
-
-/** Create Postgres connection pool manager.
- *
- * @param pgConfig Configuration for Postgres.
- * @param j Logger object.
- * @param parent Stoppable parent object.
- * @return Postgres connection pool manager
- */
-std::shared_ptr<PgPool>
-make_PgPool(boost::asio::io_context& ioc, boost::json::object const& pgConfig);
-
-/** Initialize the Postgres schema.
- *
- * This function ensures that the database is running the latest version
- * of the schema.
- *
- * @param pool Postgres connection pool manager.
- */
-void
-initSchema(std::shared_ptr<PgPool> const& pool);
-void
-initAccountTx(std::shared_ptr<PgPool> const& pool);
-
-// Load the ledger info for the specified ledger/s from the database
-// @param whichLedger specifies the ledger to load via ledger sequence, ledger
-// hash or std::monostate (which loads the most recent)
-// @return vector of LedgerInfos
-std::optional<ripple::LedgerInfo>
-getLedger(
-    std::variant<std::monostate, ripple::uint256, std::uint32_t> const&
-        whichLedger,
-    std::shared_ptr<PgPool>& pgPool);
-
-#endif  // RIPPLE_CORE_PG_H_INCLUDED

src/backend/PostgresBackend.cpp

@@ -1,895 +0,0 @@
-#include <boost/asio.hpp>
-#include <boost/format.hpp>
-#include <backend/PostgresBackend.h>
-#include <thread>
-
-namespace Backend {
-
-// Type alias for async completion handlers
-using completion_token = boost::asio::yield_context;
-using function_type = void(boost::system::error_code);
-using result_type = boost::asio::async_result<completion_token, function_type>;
-using handler_type = typename result_type::completion_handler_type;
-
-struct HandlerWrapper
-{
-    handler_type handler;
-
-    HandlerWrapper(handler_type&& handler_) : handler(std::move(handler_))
-    {
-    }
-};
-
-PostgresBackend::PostgresBackend(
-    boost::asio::io_context& ioc,
-    boost::json::object const& config)
-    : BackendInterface(config)
-    , pgPool_(make_PgPool(ioc, config))
-    , writeConnection_(pgPool_)
-{
-    if (config.contains("write_interval"))
-    {
-        writeInterval_ = config.at("write_interval").as_int64();
-    }
-}
-void
-PostgresBackend::writeLedger(
-    ripple::LedgerInfo const& ledgerInfo,
-    std::string&& ledgerHeader)
-{
-    synchronous([&](boost::asio::yield_context yield) {
-        auto cmd = boost::format(
-            R"(INSERT INTO ledgers
-            VALUES (%u,'\x%s', '\x%s',%u,%u,%u,%u,%u,'\x%s','\x%s'))");
-
-        auto ledgerInsert = boost::str(
-            cmd % ledgerInfo.seq % ripple::strHex(ledgerInfo.hash) %
-            ripple::strHex(ledgerInfo.parentHash) % ledgerInfo.drops.drops() %
-            ledgerInfo.closeTime.time_since_epoch().count() %
-            ledgerInfo.parentCloseTime.time_since_epoch().count() %
-            ledgerInfo.closeTimeResolution.count() % ledgerInfo.closeFlags %
-            ripple::strHex(ledgerInfo.accountHash) %
-            ripple::strHex(ledgerInfo.txHash));
-
-        auto res = writeConnection_(ledgerInsert.data(), yield);
-        abortWrite_ = !res;
-        inProcessLedger = ledgerInfo.seq;
-    });
-}
-
-void
-PostgresBackend::writeAccountTransactions(
-    std::vector<AccountTransactionsData>&& data)
-{
-    if (abortWrite_)
-        return;
-    PgQuery pg(pgPool_);
-    for (auto const& record : data)
-    {
-        for (auto const& a : record.accounts)
-        {
-            std::string acct = ripple::strHex(a);
-            accountTxBuffer_ << "\\\\x" << acct << '\t'
-                             << std::to_string(record.ledgerSequence) << '\t'
-                             << std::to_string(record.transactionIndex) << '\t'
-                             << "\\\\x" << ripple::strHex(record.txHash)
-                             << '\n';
-        }
-    }
-}
-
-void
-PostgresBackend::writeNFTTransactions(std::vector<NFTTransactionsData>&& data)
-{
-    throw std::runtime_error("Not implemented");
-}
-
-void
-PostgresBackend::doWriteLedgerObject(
-    std::string&& key,
-    std::uint32_t const seq,
-    std::string&& blob)
-{
-    synchronous([&](boost::asio::yield_context yield) {
-        if (abortWrite_)
-            return;
-        objectsBuffer_ << "\\\\x" << ripple::strHex(key) << '\t'
-                       << std::to_string(seq) << '\t' << "\\\\x"
-                       << ripple::strHex(blob) << '\n';
-        numRowsInObjectsBuffer_++;
-        // If the buffer gets too large, the insert fails. Not sure why. So we
-        // insert after 1 million records
-        if (numRowsInObjectsBuffer_ % writeInterval_ == 0)
-        {
-            BOOST_LOG_TRIVIAL(info)
-                << __func__ << " Flushing large buffer. num objects = "
-                << numRowsInObjectsBuffer_;
-            writeConnection_.bulkInsert("objects", objectsBuffer_.str(), yield);
-            BOOST_LOG_TRIVIAL(info) << __func__ << " Flushed large buffer";
-            objectsBuffer_.str("");
-        }
-    });
-}
-
-void
-PostgresBackend::writeSuccessor(
-    std::string&& key,
-    std::uint32_t const seq,
-    std::string&& successor)
-{
-    synchronous([&](boost::asio::yield_context yield) {
-        if (range)
-        {
-            if (successors_.count(key) > 0)
-                return;
-            successors_.insert(key);
-        }
-        successorBuffer_ << "\\\\x" << ripple::strHex(key) << '\t'
-                         << std::to_string(seq) << '\t' << "\\\\x"
-                         << ripple::strHex(successor) << '\n';
-        BOOST_LOG_TRIVIAL(trace)
-            << __func__ << ripple::strHex(key) << " - " << std::to_string(seq);
-        numRowsInSuccessorBuffer_++;
-        if (numRowsInSuccessorBuffer_ % writeInterval_ == 0)
-        {
-            BOOST_LOG_TRIVIAL(info)
-                << __func__ << " Flushing large buffer. num successors = "
-                << numRowsInSuccessorBuffer_;
-            writeConnection_.bulkInsert(
-                "successor", successorBuffer_.str(), yield);
-            BOOST_LOG_TRIVIAL(info) << __func__ << " Flushed large buffer";
-            successorBuffer_.str("");
-        }
-    });
-}
-
-void
-PostgresBackend::writeTransaction(
-    std::string&& hash,
-    std::uint32_t const seq,
-    std::uint32_t const date,
-    std::string&& transaction,
-    std::string&& metadata)
-{
-    if (abortWrite_)
-        return;
-    transactionsBuffer_ << "\\\\x" << ripple::strHex(hash) << '\t'
-                        << std::to_string(seq) << '\t' << std::to_string(date)
-                        << '\t' << "\\\\x" << ripple::strHex(transaction)
-                        << '\t' << "\\\\x" << ripple::strHex(metadata) << '\n';
-}
-
-void
-PostgresBackend::writeNFTs(std::vector<NFTsData>&& data)
-{
-    throw std::runtime_error("Not implemented");
-}
-
-std::uint32_t
-checkResult(PgResult const& res, std::uint32_t const numFieldsExpected)
-{
-    if (!res)
-    {
-        auto msg = res.msg();
-        BOOST_LOG_TRIVIAL(error) << __func__ << " - " << msg;
-        if (msg.find("statement timeout"))
-            throw DatabaseTimeout();
-        assert(false);
-        throw DatabaseTimeout();
-    }
-    if (res.status() != PGRES_TUPLES_OK)
-    {
-        std::stringstream msg;
-        msg << " : Postgres response should have been "
-               "PGRES_TUPLES_OK but instead was "
-            << res.status() << " - msg  = " << res.msg();
-        BOOST_LOG_TRIVIAL(error) << __func__ << " - " << msg.str();
-        assert(false);
-        throw DatabaseTimeout();
-    }
-
-    BOOST_LOG_TRIVIAL(trace)
-        << __func__ << " Postgres result msg  : " << res.msg();
-    if (res.isNull() || res.ntuples() == 0)
-    {
-        return 0;
-    }
-    else if (res.ntuples() > 0)
-    {
-        if (res.nfields() != numFieldsExpected)
-        {
-            std::stringstream msg;
-            msg << "Wrong number of fields in Postgres "
-                   "response. Expected "
-                << numFieldsExpected << ", but got " << res.nfields();
-            throw std::runtime_error(msg.str());
-            assert(false);
-        }
-    }
-    return res.ntuples();
-}
-
-ripple::LedgerInfo
-parseLedgerInfo(PgResult const& res)
-{
-    std::int64_t ledgerSeq = res.asBigInt(0, 0);
-    ripple::uint256 hash = res.asUInt256(0, 1);
-    ripple::uint256 prevHash = res.asUInt256(0, 2);
-    std::int64_t totalCoins = res.asBigInt(0, 3);
-    std::int64_t closeTime = res.asBigInt(0, 4);
-    std::int64_t parentCloseTime = res.asBigInt(0, 5);
-    std::int64_t closeTimeRes = res.asBigInt(0, 6);
-    std::int64_t closeFlags = res.asBigInt(0, 7);
-    ripple::uint256 accountHash = res.asUInt256(0, 8);
-    ripple::uint256 txHash = res.asUInt256(0, 9);
-
-    using time_point = ripple::NetClock::time_point;
-    using duration = ripple::NetClock::duration;
-
-    ripple::LedgerInfo info;
-    info.seq = ledgerSeq;
-    info.hash = hash;
-    info.parentHash = prevHash;
-    info.drops = totalCoins;
-    info.closeTime = time_point{duration{closeTime}};
-    info.parentCloseTime = time_point{duration{parentCloseTime}};
-    info.closeFlags = closeFlags;
-    info.closeTimeResolution = duration{closeTimeRes};
-    info.accountHash = accountHash;
-    info.txHash = txHash;
-    info.validated = true;
-    return info;
-}
-std::optional<std::uint32_t>
-PostgresBackend::fetchLatestLedgerSequence(
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    auto const query =
-        "SELECT ledger_seq FROM ledgers ORDER BY ledger_seq DESC LIMIT 1";
-
-    if (auto res = pgQuery(query, yield); checkResult(res, 1))
-        return res.asBigInt(0, 0);
-
-    return {};
-}
-
-std::optional<ripple::LedgerInfo>
-PostgresBackend::fetchLedgerBySequence(
-    std::uint32_t const sequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT * FROM ledgers WHERE ledger_seq = "
-        << std::to_string(sequence);
-
-    if (auto res = pgQuery(sql.str().data(), yield); checkResult(res, 10))
-        return parseLedgerInfo(res);
-
-    return {};
-}
-
-std::optional<ripple::LedgerInfo>
-PostgresBackend::fetchLedgerByHash(
-    ripple::uint256 const& hash,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT * FROM ledgers WHERE ledger_hash = \'\\x"
-        << ripple::to_string(hash) << "\'";
-
-    if (auto res = pgQuery(sql.str().data(), yield); checkResult(res, 10))
-        return parseLedgerInfo(res);
-
-    return {};
-}
-
-std::optional<LedgerRange>
-PostgresBackend::hardFetchLedgerRange(boost::asio::yield_context& yield) const
-{
-    auto range = PgQuery(pgPool_)("SELECT complete_ledgers()", yield);
-    if (!range)
-        return {};
-
-    std::string res{range.c_str()};
-    BOOST_LOG_TRIVIAL(debug) << "range is = " << res;
-    try
-    {
-        size_t minVal = 0;
-        size_t maxVal = 0;
-        if (res == "empty" || res == "error" || res.empty())
-            return {};
-        else if (size_t delim = res.find('-'); delim != std::string::npos)
-        {
-            minVal = std::stol(res.substr(0, delim));
-            maxVal = std::stol(res.substr(delim + 1));
-        }
-        else
-        {
-            minVal = maxVal = std::stol(res);
-        }
-        return LedgerRange{minVal, maxVal};
-    }
-    catch (std::exception&)
-    {
-        BOOST_LOG_TRIVIAL(error)
-            << __func__ << " : "
-            << "Error parsing result of getCompleteLedgers()";
-    }
-    return {};
-}
-
-std::optional<Blob>
-PostgresBackend::doFetchLedgerObject(
-    ripple::uint256 const& key,
-    std::uint32_t const sequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT object FROM objects WHERE key = "
-        << "\'\\x" << ripple::strHex(key) << "\'"
-        << " AND ledger_seq <= " << std::to_string(sequence)
-        << " ORDER BY ledger_seq DESC LIMIT 1";
-
-    if (auto res = pgQuery(sql.str().data(), yield); checkResult(res, 1))
-    {
-        auto blob = res.asUnHexedBlob(0, 0);
-        if (blob.size())
-            return blob;
-    }
-
-    return {};
-}
-
-// returns a transaction, metadata pair
-std::optional<TransactionAndMetadata>
-PostgresBackend::fetchTransaction(
-    ripple::uint256 const& hash,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT transaction,metadata,ledger_seq,date FROM transactions "
-           "WHERE hash = "
-        << "\'\\x" << ripple::strHex(hash) << "\'";
-
-    if (auto res = pgQuery(sql.str().data(), yield); checkResult(res, 4))
-    {
-        return {
-            {res.asUnHexedBlob(0, 0),
-             res.asUnHexedBlob(0, 1),
-             res.asBigInt(0, 2),
-             res.asBigInt(0, 3)}};
-    }
-
-    return {};
-}
-std::vector<TransactionAndMetadata>
-PostgresBackend::fetchAllTransactionsInLedger(
-    std::uint32_t const ledgerSequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT transaction, metadata, ledger_seq,date FROM transactions "
-           "WHERE "
-        << "ledger_seq = " << std::to_string(ledgerSequence);
-
-    auto res = pgQuery(sql.str().data(), yield);
-    if (size_t numRows = checkResult(res, 4))
-    {
-        std::vector<TransactionAndMetadata> txns;
-        for (size_t i = 0; i < numRows; ++i)
-        {
-            txns.push_back(
-                {res.asUnHexedBlob(i, 0),
-                 res.asUnHexedBlob(i, 1),
-                 res.asBigInt(i, 2),
-                 res.asBigInt(i, 3)});
-        }
-        return txns;
-    }
-    return {};
-}
-std::vector<ripple::uint256>
-PostgresBackend::fetchAllTransactionHashesInLedger(
-    std::uint32_t const ledgerSequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT hash FROM transactions WHERE "
-        << "ledger_seq = " << std::to_string(ledgerSequence);
-
-    auto res = pgQuery(sql.str().data(), yield);
-    if (size_t numRows = checkResult(res, 1))
-    {
-        std::vector<ripple::uint256> hashes;
-        for (size_t i = 0; i < numRows; ++i)
-        {
-            hashes.push_back(res.asUInt256(i, 0));
-        }
-        return hashes;
-    }
-
-    return {};
-}
-
-std::optional<NFT>
-PostgresBackend::fetchNFT(
-    ripple::uint256 const& tokenID,
-    std::uint32_t const ledgerSequence,
-    boost::asio::yield_context& yield) const
-{
-    throw std::runtime_error("Not implemented");
-}
-
-std::optional<ripple::uint256>
-PostgresBackend::doFetchSuccessorKey(
-    ripple::uint256 key,
-    std::uint32_t const ledgerSequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT next FROM successor WHERE key = "
-        << "\'\\x" << ripple::strHex(key) << "\'"
-        << " AND ledger_seq <= " << std::to_string(ledgerSequence)
-        << " ORDER BY ledger_seq DESC LIMIT 1";
-
-    if (auto res = pgQuery(sql.str().data(), yield); checkResult(res, 1))
-    {
-        auto next = res.asUInt256(0, 0);
-        if (next == lastKey)
-            return {};
-        return next;
-    }
-
-    return {};
-}
-
-std::vector<TransactionAndMetadata>
-PostgresBackend::fetchTransactions(
-    std::vector<ripple::uint256> const& hashes,
-    boost::asio::yield_context& yield) const
-{
-    if (!hashes.size())
-        return {};
-
-    std::vector<TransactionAndMetadata> results;
-    results.resize(hashes.size());
-
-    handler_type handler(std::forward<decltype(yield)>(yield));
-    result_type result(handler);
-
-    auto hw = new HandlerWrapper(std::move(handler));
-
-    auto start = std::chrono::system_clock::now();
-
-    std::atomic_uint numRemaining = hashes.size();
-    std::atomic_bool errored = false;
-
-    for (size_t i = 0; i < hashes.size(); ++i)
-    {
-        auto const& hash = hashes[i];
-        boost::asio::spawn(
-            get_associated_executor(yield),
-            [this, &hash, &results, hw, &numRemaining, &errored, i](
-                boost::asio::yield_context yield) {
-                BOOST_LOG_TRIVIAL(trace) << __func__ << " getting txn = " << i;
-
-                PgQuery pgQuery(pgPool_);
-
-                std::stringstream sql;
-                sql << "SELECT transaction,metadata,ledger_seq,date FROM "
-                       "transactions "
-                       "WHERE HASH = \'\\x"
-                    << ripple::strHex(hash) << "\'";
-
-                try
-                {
-                    if (auto const res = pgQuery(sql.str().data(), yield);
-                        checkResult(res, 4))
-                    {
-                        results[i] = {
-                            res.asUnHexedBlob(0, 0),
-                            res.asUnHexedBlob(0, 1),
-                            res.asBigInt(0, 2),
-                            res.asBigInt(0, 3)};
-                    }
-                }
-                catch (DatabaseTimeout const&)
-                {
-                    errored = true;
-                }
-
-                if (--numRemaining == 0)
-                {
-                    handler_type h(std::move(hw->handler));
-                    h(boost::system::error_code{});
-                }
-            });
-    }
-
-    // Yields the worker to the io_context until handler is called.
-    result.get();
-
-    delete hw;
-
-    auto end = std::chrono::system_clock::now();
-    auto duration =
-        std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
-
-    BOOST_LOG_TRIVIAL(info)
-        << __func__ << " fetched " << std::to_string(hashes.size())
-        << " transactions asynchronously. took "
-        << std::to_string(duration.count());
-    if (errored)
-    {
-        BOOST_LOG_TRIVIAL(error) << __func__ << " Database fetch timed out";
-        throw DatabaseTimeout();
-    }
-
-    return results;
-}
-
-std::vector<Blob>
-PostgresBackend::doFetchLedgerObjects(
-    std::vector<ripple::uint256> const& keys,
-    std::uint32_t const sequence,
-    boost::asio::yield_context& yield) const
-{
-    if (!keys.size())
-        return {};
-
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::vector<Blob> results;
-    results.resize(keys.size());
-
-    handler_type handler(std::forward<decltype(yield)>(yield));
-    result_type result(handler);
-
-    auto hw = new HandlerWrapper(std::move(handler));
-
-    std::atomic_uint numRemaining = keys.size();
-    std::atomic_bool errored = false;
-    auto start = std::chrono::system_clock::now();
-    for (size_t i = 0; i < keys.size(); ++i)
-    {
-        auto const& key = keys[i];
-        boost::asio::spawn(
-            boost::asio::get_associated_executor(yield),
-            [this, &key, &results, &numRemaining, &errored, hw, i, sequence](
-                boost::asio::yield_context yield) {
-                PgQuery pgQuery(pgPool_);
-
-                std::stringstream sql;
-                sql << "SELECT object FROM "
-                       "objects "
-                       "WHERE key = \'\\x"
-                    << ripple::strHex(key) << "\'"
-                    << " AND ledger_seq <= " << std::to_string(sequence)
-                    << " ORDER BY ledger_seq DESC LIMIT 1";
-
-                try
-                {
-                    if (auto const res = pgQuery(sql.str().data(), yield);
-                        checkResult(res, 1))
-                        results[i] = res.asUnHexedBlob();
-                }
-                catch (DatabaseTimeout const& ex)
-                {
-                    errored = true;
-                }
-
-                if (--numRemaining == 0)
-                {
-                    handler_type h(std::move(hw->handler));
-                    h(boost::system::error_code{});
-                }
-            });
-    }
-
-    // Yields the worker to the io_context until handler is called.
-    result.get();
-
-    delete hw;
-
-    auto end = std::chrono::system_clock::now();
-    auto duration =
-        std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
-
-    BOOST_LOG_TRIVIAL(info)
-        << __func__ << " fetched " << std::to_string(keys.size())
-        << " objects asynchronously. ms = " << std::to_string(duration.count());
-    if (errored)
-    {
-        BOOST_LOG_TRIVIAL(error) << __func__ << " Database fetch timed out";
-        throw DatabaseTimeout();
-    }
-
-    return results;
-}
-
-std::vector<LedgerObject>
-PostgresBackend::fetchLedgerDiff(
-    std::uint32_t const ledgerSequence,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-
-    std::stringstream sql;
-    sql << "SELECT key,object FROM objects "
-           "WHERE "
-        << "ledger_seq = " << std::to_string(ledgerSequence);
-
-    auto res = pgQuery(sql.str().data(), yield);
-    if (size_t numRows = checkResult(res, 2))
-    {
-        std::vector<LedgerObject> objects;
-        for (size_t i = 0; i < numRows; ++i)
-        {
-            objects.push_back({res.asUInt256(i, 0), res.asUnHexedBlob(i, 1)});
-        }
-        return objects;
-    }
-
-    return {};
-}
-
-// TODO this implementation and fetchAccountTransactions should be
-// generalized
-TransactionsAndCursor
-PostgresBackend::fetchNFTTransactions(
-    ripple::uint256 const& tokenID,
-    std::uint32_t const limit,
-    bool forward,
-    std::optional<TransactionsCursor> const& cursor,
-    boost::asio::yield_context& yield) const
-{
-    throw std::runtime_error("Not implemented");
-}
-
-TransactionsAndCursor
-PostgresBackend::fetchAccountTransactions(
-    ripple::AccountID const& account,
-    std::uint32_t const limit,
-    bool forward,
-    std::optional<TransactionsCursor> const& cursor,
-    boost::asio::yield_context& yield) const
-{
-    PgQuery pgQuery(pgPool_);
-    pgQuery(set_timeout, yield);
-    pg_params dbParams;
-
-    char const*& command = dbParams.first;
-    std::vector<std::optional<std::string>>& values = dbParams.second;
-    command =
-        "SELECT account_tx($1::bytea, $2::bigint, $3::bool, "
-        "$4::bigint, $5::bigint)";
-    values.resize(5);
-    values[0] = "\\x" + strHex(account);
-
-    values[1] = std::to_string(limit);
-
-    values[2] = std::to_string(forward);
-
-    if (cursor)
-    {
-        values[3] = std::to_string(cursor->ledgerSequence);
-        values[4] = std::to_string(cursor->transactionIndex);
-    }
-    for (size_t i = 0; i < values.size(); ++i)
-    {
-        BOOST_LOG_TRIVIAL(debug) << "value " << std::to_string(i) << " = "
-                                 << (values[i] ? values[i].value() : "null");
-    }
-
-    auto start = std::chrono::system_clock::now();
-    auto res = pgQuery(dbParams, yield);
-    auto end = std::chrono::system_clock::now();
-
-    auto duration = ((end - start).count()) / 1000000000.0;
-    BOOST_LOG_TRIVIAL(info)
-        << __func__ << " : executed stored_procedure in "
-        << std::to_string(duration)
-        << " num records = " << std::to_string(checkResult(res, 1));
-
-    checkResult(res, 1);
-
-    char const* resultStr = res.c_str();
-    BOOST_LOG_TRIVIAL(debug) << __func__ << " : "
-                             << "postgres result = " << resultStr
-                             << " : account = " << strHex(account);
-
-    boost::json::value raw = boost::json::parse(resultStr);
-    boost::json::object responseObj = raw.as_object();
-    BOOST_LOG_TRIVIAL(debug) << " parsed = " << responseObj;
-    if (responseObj.contains("transactions"))
-    {
-        auto txns = responseObj.at("transactions").as_array();
-        std::vector<ripple::uint256> hashes;
-        for (auto& hashHex : txns)
-        {
-            ripple::uint256 hash;
-            if (hash.parseHex(hashHex.at("hash").as_string().c_str() + 2))
-                hashes.push_back(hash);
-        }
-        if (responseObj.contains("cursor"))
-        {
-            return {
-                fetchTransactions(hashes, yield),
-                {{responseObj.at("cursor").at("ledger_sequence").as_int64(),
-                  responseObj.at("cursor")
-                      .at("transaction_index")
-                      .as_int64()}}};
-        }
-        return {fetchTransactions(hashes, yield), {}};
-    }
-    return {{}, {}};
-}  // namespace Backend
-
-void
-PostgresBackend::open(bool readOnly)
-{
-    initSchema(pgPool_);
-    initAccountTx(pgPool_);
-}
-
-void
-PostgresBackend::close()
-{
-}
-
-void
-PostgresBackend::startWrites() const
-{
-    synchronous([&](boost::asio::yield_context yield) {
-        numRowsInObjectsBuffer_ = 0;
-        abortWrite_ = false;
-        auto res = writeConnection_("BEGIN", yield);
-        if (!res || res.status() != PGRES_COMMAND_OK)
-        {
-            std::stringstream msg;
-            msg << "Postgres error creating transaction: " << res.msg();
-            throw std::runtime_error(msg.str());
-        }
-    });
-}
-
-bool
-PostgresBackend::doFinishWrites()
-{
-    synchronous([&](boost::asio::yield_context yield) {
-        if (!abortWrite_)
-        {
-            std::string txStr = transactionsBuffer_.str();
-            writeConnection_.bulkInsert("transactions", txStr, yield);
-            writeConnection_.bulkInsert(
-                "account_transactions", accountTxBuffer_.str(), yield);
-            std::string objectsStr = objectsBuffer_.str();
-            if (objectsStr.size())
-                writeConnection_.bulkInsert("objects", objectsStr, yield);
-            BOOST_LOG_TRIVIAL(debug)
-                << __func__ << " objects size = " << objectsStr.size()
-                << " txns size = " << txStr.size();
-            std::string successorStr = successorBuffer_.str();
-            if (successorStr.size())
-                writeConnection_.bulkInsert("successor", successorStr, yield);
-            if (!range)
-            {
-                std::stringstream indexCreate;
-                indexCreate
-                    << "CREATE INDEX diff ON objects USING hash(ledger_seq) "
-                       "WHERE NOT "
-                       "ledger_seq = "
-                    << std::to_string(inProcessLedger);
-                writeConnection_(indexCreate.str().data(), yield);
-            }
-        }
-        auto res = writeConnection_("COMMIT", yield);
-        if (!res || res.status() != PGRES_COMMAND_OK)
-        {
-            std::stringstream msg;
-            msg << "Postgres error committing transaction: " << res.msg();
-            throw std::runtime_error(msg.str());
-        }
-        transactionsBuffer_.str("");
-        transactionsBuffer_.clear();
-        objectsBuffer_.str("");
-        objectsBuffer_.clear();
-        successorBuffer_.str("");
-        successorBuffer_.clear();
-        successors_.clear();
-        accountTxBuffer_.str("");
-        accountTxBuffer_.clear();
-        numRowsInObjectsBuffer_ = 0;
-    });
-
-    return !abortWrite_;
-}
-
-bool
-PostgresBackend::doOnlineDelete(
-    std::uint32_t const numLedgersToKeep,
-    boost::asio::yield_context& yield) const
-{
-    auto rng = fetchLedgerRange();
-    if (!rng)
-        return false;
-    std::uint32_t minLedger = rng->maxSequence - numLedgersToKeep;
-    if (minLedger <= rng->minSequence)
-        return false;
-    PgQuery pgQuery(pgPool_);
-    pgQuery("SET statement_timeout TO 0", yield);
-    std::optional<ripple::uint256> cursor;
-    while (true)
-    {
-        auto [objects, curCursor] = retryOnTimeout([&]() {
-            return fetchLedgerPage(cursor, minLedger, 256, false, yield);
-        });
-        BOOST_LOG_TRIVIAL(debug) << __func__ << " fetched a page";
-        std::stringstream objectsBuffer;
-
-        for (auto& obj : objects)
-        {
-            objectsBuffer << "\\\\x" << ripple::strHex(obj.key) << '\t'
-                          << std::to_string(minLedger) << '\t' << "\\\\x"
-                          << ripple::strHex(obj.blob) << '\n';
-        }
-        pgQuery.bulkInsert("objects", objectsBuffer.str(), yield);
-        cursor = curCursor;
-        if (!cursor)
-            break;
-    }
-    BOOST_LOG_TRIVIAL(info) << __func__ << " finished inserting into objects";
-    {
-        std::stringstream sql;
-        sql << "DELETE FROM ledgers WHERE ledger_seq < "
-            << std::to_string(minLedger);
-        auto res = pgQuery(sql.str().data(), yield);
-        if (res.msg() != "ok")
-            throw std::runtime_error("Error deleting from ledgers table");
-    }
-    {
-        std::stringstream sql;
-        sql << "DELETE FROM keys WHERE ledger_seq < "
-            << std::to_string(minLedger);
-        auto res = pgQuery(sql.str().data(), yield);
-        if (res.msg() != "ok")
-            throw std::runtime_error("Error deleting from keys table");
-    }
-    {
-        std::stringstream sql;
-        sql << "DELETE FROM books WHERE ledger_seq < "
-            << std::to_string(minLedger);
-        auto res = pgQuery(sql.str().data(), yield);
-        if (res.msg() != "ok")
-            throw std::runtime_error("Error deleting from books table");
-    }
-    return true;
-}
-
-}  // namespace Backend

src/backend/PostgresBackend.h

@@ -1,165 +0,0 @@
-#ifndef RIPPLE_APP_REPORTING_POSTGRESBACKEND_H_INCLUDED
-#define RIPPLE_APP_REPORTING_POSTGRESBACKEND_H_INCLUDED
-#include <boost/json.hpp>
-#include <backend/BackendInterface.h>
-
-namespace Backend {
-class PostgresBackend : public BackendInterface
-{
-private:
-    mutable size_t numRowsInObjectsBuffer_ = 0;
-    mutable std::stringstream objectsBuffer_;
-    mutable size_t numRowsInSuccessorBuffer_ = 0;
-    mutable std::stringstream successorBuffer_;
-    mutable std::stringstream transactionsBuffer_;
-    mutable std::stringstream accountTxBuffer_;
-    std::shared_ptr<PgPool> pgPool_;
-    mutable PgQuery writeConnection_;
-    mutable bool abortWrite_ = false;
-    std::uint32_t writeInterval_ = 1000000;
-    std::uint32_t inProcessLedger = 0;
-    mutable std::unordered_set<std::string> successors_;
-
-    const char* const set_timeout = "SET statement_timeout TO 10000";
-
-public:
-    PostgresBackend(
-        boost::asio::io_context& ioc,
-        boost::json::object const& config);
-
-    std::optional<std::uint32_t>
-    fetchLatestLedgerSequence(boost::asio::yield_context& yield) const override;
-
-    std::optional<ripple::LedgerInfo>
-    fetchLedgerBySequence(
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::optional<ripple::LedgerInfo>
-    fetchLedgerByHash(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const override;
-
-    std::optional<Blob>
-    doFetchLedgerObject(
-        ripple::uint256 const& key,
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const override;
-
-    // returns a transaction, metadata pair
-    std::optional<TransactionAndMetadata>
-    fetchTransaction(
-        ripple::uint256 const& hash,
-        boost::asio::yield_context& yield) const override;
-
-    std::vector<TransactionAndMetadata>
-    fetchAllTransactionsInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::vector<ripple::uint256>
-    fetchAllTransactionHashesInLedger(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::optional<NFT>
-    fetchNFT(
-        ripple::uint256 const& tokenID,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
-
-    TransactionsAndCursor
-    fetchNFTTransactions(
-        ripple::uint256 const& tokenID,
-        std::uint32_t const limit,
-        bool const forward,
-        std::optional<TransactionsCursor> const& cursorIn,
-        boost::asio::yield_context& yield) const override;
-
-    std::vector<LedgerObject>
-    fetchLedgerDiff(
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::optional<LedgerRange>
-    hardFetchLedgerRange(boost::asio::yield_context& yield) const override;
-
-    std::optional<ripple::uint256>
-    doFetchSuccessorKey(
-        ripple::uint256 key,
-        std::uint32_t const ledgerSequence,
-        boost::asio::yield_context& yield) const override;
-
-    std::vector<TransactionAndMetadata>
-    fetchTransactions(
-        std::vector<ripple::uint256> const& hashes,
-        boost::asio::yield_context& yield) const override;
-
-    std::vector<Blob>
-    doFetchLedgerObjects(
-        std::vector<ripple::uint256> const& keys,
-        std::uint32_t const sequence,
-        boost::asio::yield_context& yield) const override;
-
-    TransactionsAndCursor
-    fetchAccountTransactions(
-        ripple::AccountID const& account,
-        std::uint32_t const limit,
-        bool forward,
-        std::optional<TransactionsCursor> const& cursor,
-        boost::asio::yield_context& yield) const override;
-
-    void
-    writeLedger(
-        ripple::LedgerInfo const& ledgerInfo,
-        std::string&& ledgerHeader) override;
-
-    void
-    doWriteLedgerObject(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& blob) override;
-
-    void
-    writeSuccessor(
-        std::string&& key,
-        std::uint32_t const seq,
-        std::string&& successor) override;
-
-    void
-    writeTransaction(
-        std::string&& hash,
-        std::uint32_t const seq,
-        std::uint32_t const date,
-        std::string&& transaction,
-        std::string&& metadata) override;
-
-    void
-    writeNFTs(std::vector<NFTsData>&& data) override;
-
-    void
-    writeAccountTransactions(
-        std::vector<AccountTransactionsData>&& data) override;
-
-    void
-    writeNFTTransactions(std::vector<NFTTransactionsData>&& data) override;
-
-    void
-    open(bool readOnly) override;
-
-    void
-    close() override;
-
-    void
-    startWrites() const override;
-
-    bool
-    doFinishWrites() override;
-
-    bool
-    doOnlineDelete(
-        std::uint32_t const numLedgersToKeep,
-        boost::asio::yield_context& yield) const override;
-};
-}  // namespace Backend
-#endif

src/backend/README.md

@@ -1,6 +1,6 @@
 # Clio Backend
 ## Background
-The backend of Clio is responsible for handling the proper reading and writing of past ledger data from and to a given database. As of right now, Cassandra is the only supported database that is production-ready. However, support for more databases like PostgreSQL and DynamoDB may be added in future versions. Support for database types can be easily extended by creating new implementations which implements the virtual methods of `BackendInterface.h`. Then, use the Factory Object Design Pattern to simply add logic statements to `BackendFactory.h` that return the new database interface for a specific `type` in Clio's configuration file. 
+The backend of Clio is responsible for handling the proper reading and writing of past ledger data from and to a given database. As of right now, Cassandra and ScyllaDB are the only supported databases that are production-ready. Support for database types can be easily extended by creating new implementations which implements the virtual methods of `BackendInterface.h`. Then, use the Factory Object Design Pattern to simply add logic statements to `BackendFactory.h` that return the new database interface for a specific `type` in Clio's configuration file. 
 
 ## Data Model
 The data model used by Clio to read and write ledger data is different from what Rippled uses. Rippled uses a novel data structure named [*SHAMap*](https://github.com/ripple/rippled/blob/master/src/ripple/shamap/README.md), which is a combination of a Merkle Tree and a Radix Trie. In a SHAMap, ledger objects are stored in the root vertices of the tree. Thus, looking up a record located at the leaf node of the SHAMap executes a tree search, where the path from the root node to the leaf node is the key of the record. Rippled nodes can also generate a proof-tree by forming a subtree with all the path nodes and their neighbors, which can then be used to prove the existnce of the leaf node data to other Rippled nodes. In short, the main purpose of the SHAMap data structure is to facilitate the fast validation of data integrity between different decentralized Rippled nodes.
@@ -129,4 +129,92 @@ In each new ledger version with sequence `n`, a ledger object `v` can either be
  2. If `v` is...
 	 1. Being **created**, add two new records of `seq=n` with one being `e` pointing to `v`, and `v` pointing to `w` (Linked List insertion operation).
 	 2. Being **modified**, do nothing.
-	 3. Being **deleted**, add a record of `seq=n` with `e` pointing to `v`'s `next` value (Linked List deletion operation).
+	 3. Being **deleted**, add a record of `seq=n` with `e` pointing to `v`'s `next` value (Linked List deletion operation).
+
+### NFT data model
+In `rippled` NFTs are stored in NFTokenPage ledger objects. This object is
+implemented to save ledger space and has the property that it gives us O(1)
+lookup time for an NFT, assuming we know who owns the NFT at a particular
+ledger. However, if we do not know who owns the NFT at a specific ledger
+height we have no alternative in rippled other than scanning the entire
+ledger. Because of this tradeoff, clio implements a special NFT indexing data
+structure that allows clio users to query NFTs quickly, while keeping
+rippled's space-saving optimizations.
+
+#### `nf_tokens`
+```
+CREATE TABLE clio.nf_tokens (
+	token_id blob,         # The NFT's ID
+	sequence bigint,       # Sequence of ledger version
+	owner blob,            # The account ID of the owner of this NFT at this ledger
+	is_burned boolean,     # True if token was burned in this ledger
+	PRIMARY KEY (token_id, sequence)
+) WITH CLUSTERING ORDER BY (sequence DESC) ...
+```
+This table indexes NFT IDs with their owner at a given ledger. So
+```
+SELECT * FROM nf_tokens
+WHERE token_id = N AND seq <= Y
+ORDER BY seq DESC LIMIT 1;
+```
+will give you the owner of token N at ledger Y and whether it was burned. If
+the token is burned, the owner field indicates the account that owned the
+token at the time it was burned; it does not indicate the person who burned
+the token, necessarily. If you need to determine who burned the token you can
+use the `nft_history` API, which will give you the NFTokenBurn transaction
+that burned this token, along with the account that submitted that
+transaction.
+
+#### `issuer_nf_tokens_v2`
+```
+CREATE TABLE clio.issuer_nf_tokens_v2 (
+	issuer blob,       # The NFT issuer's account ID
+	taxon bigint,      # The NFT's token taxon
+	token_id blob,     # The NFT's ID
+	PRIMARY KEY (issuer, taxon, token_id)
+) WITH CLUSTERING ORDER BY (taxon ASC, token_id ASC) ...
+```
+This table indexes token IDs against their issuer and issuer/taxon
+combination. This is useful for determining all the NFTs a specific account
+issued, or all the NFTs a specific account issued with a specific taxon. It is
+not useful to know all the NFTs with a given taxon while excluding issuer, since the
+meaning of a taxon is left to an issuer.
+
+#### `nf_token_uris`
+```
+CREATE TABLE clio.nf_token_uris (
+	token_id blob,    # The NFT's ID
+	sequence bigint,  # Sequence of ledger version
+	uri blob,         # The NFT's URI
+	PRIMARY KEY (token_id, sequence)
+) WITH CLUSTERING ORDER BY (sequence DESC) ...
+```
+This table is used to store an NFT's URI. Without storing this here, we would
+need to traverse the NFT owner's entire set of NFTs to find the URI, again due
+to the way that NFTs are stored in rippled. Furthermore, instead of storing
+this in the `nf_tokens` table, we store it here to save space. A given NFT
+will have only one entry in this table (see caveat below), written to this
+table as soon as clio sees the NFTokenMint transaction, or when clio loads an
+NFTokenPage from the initial ledger it downloaded. However, the `nf_tokens`
+table is written to every time an NFT changes ownership, or if it is burned.
+
+Given this, why do we have to store the sequence? Unfortunately there is an
+extreme edge case where a given NFT ID can be burned, and then re-minted with
+a different URI. This is extremely unlikely, and might be fixed in a future
+version to rippled, but just in case we can handle that edge case by allowing
+a given NFT ID to have a new URI assigned in this case, without removing the
+prior URI.
+
+#### `nf_token_transactions`
+```
+CREATE TABLE clio.nf_token_transactions (
+	token_id blob,                  # The NFT's ID
+	seq_idx tuple<bigint, bigint>,  # Tuple of (ledger_index, transaction_index)
+	hash blob,                      # Hash of the transaction
+	PRIMARY KEY (token_id, seq_idx)
+) WITH CLUSTERING ORDER BY (seq_idx DESC) ...
+```
+This table is the NFT equivalent of `account_tx`. It's motivated by the exact
+same reasons and serves the analogous purpose here. It drives the
+`nft_history` API.
+

src/backend/SimpleCache.cpp

@@ -1,3 +1,22 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
 #include <backend/SimpleCache.h>
 namespace Backend {
 
@@ -9,16 +28,13 @@ SimpleCache::latestLedgerSequence() const
 }
 
 void
-SimpleCache::update(
-    std::vector<LedgerObject> const& objs,
-    uint32_t seq,
-    bool isBackground)
+SimpleCache::update(std::vector<LedgerObject> const& objs, uint32_t seq, bool isBackground)
 {
     if (disabled_)
         return;
 
     {
-        std::unique_lock lck{mtx_};
+        std::scoped_lock lck{mtx_};
         if (seq > latestSeq_)
         {
             assert(seq == latestSeq_ + 1 || latestSeq_ == 0);
@@ -53,11 +69,13 @@ SimpleCache::getSuccessor(ripple::uint256 const& key, uint32_t seq) const
     if (!full_)
         return {};
     std::shared_lock{mtx_};
+    successorReqCounter_++;
     if (seq != latestSeq_)
         return {};
     auto e = map_.upper_bound(key);
     if (e == map_.end())
         return {};
+    successorHitCounter_++;
     return {{e->first, e->second.blob}};
 }
 
@@ -78,14 +96,16 @@ SimpleCache::getPredecessor(ripple::uint256 const& key, uint32_t seq) const
 std::optional<Blob>
 SimpleCache::get(ripple::uint256 const& key, uint32_t seq) const
 {
+    std::shared_lock lck{mtx_};
     if (seq > latestSeq_)
         return {};
-    std::shared_lock lck{mtx_};
+    objectReqCounter_++;
     auto e = map_.find(key);
     if (e == map_.end())
         return {};
     if (seq < e->second.seq)
         return {};
+    objectHitCounter_++;
     return {e->second.blob};
 }
 
@@ -102,7 +122,7 @@ SimpleCache::setFull()
         return;
 
     full_ = true;
-    std::unique_lock lck{mtx_};
+    std::scoped_lock lck{mtx_};
     deletes_.clear();
 }
 
@@ -117,4 +137,18 @@ SimpleCache::size() const
     std::shared_lock lck{mtx_};
     return map_.size();
 }
+float
+SimpleCache::getObjectHitRate() const
+{
+    if (!objectReqCounter_)
+        return 1;
+    return ((float)objectHitCounter_) / objectReqCounter_;
+}
+float
+SimpleCache::getSuccessorHitRate() const
+{
+    if (!successorReqCounter_)
+        return 1;
+    return ((float)successorHitCounter_) / successorReqCounter_;
+}
 }  // namespace Backend

src/backend/SimpleCache.h

@@ -1,5 +1,23 @@
-#ifndef CLIO_SIMPLECACHE_H_INCLUDED
-#define CLIO_SIMPLECACHE_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
 #include <ripple/basics/base_uint.h>
 #include <ripple/basics/hardened_hash.h>
@@ -18,6 +36,13 @@ class SimpleCache
         Blob blob;
     };
 
+    // counters for fetchLedgerObject(s) hit rate
+    mutable std::atomic_uint32_t objectReqCounter_ = 0;
+    mutable std::atomic_uint32_t objectHitCounter_ = 0;
+    // counters for fetchSuccessorKey hit rate
+    mutable std::atomic_uint32_t successorReqCounter_ = 0;
+    mutable std::atomic_uint32_t successorHitCounter_ = 0;
+
     std::map<ripple::uint256, CacheEntry> map_;
     mutable std::shared_mutex mtx_;
     uint32_t latestSeq_ = 0;
@@ -31,10 +56,7 @@ public:
     // Update the cache with new ledger objects
     // set isBackground to true when writing old data from a background thread
     void
-    update(
-        std::vector<LedgerObject> const& blobs,
-        uint32_t seq,
-        bool isBackground = false);
+    update(std::vector<LedgerObject> const& blobs, uint32_t seq, bool isBackground = false);
 
     std::optional<Blob>
     get(ripple::uint256 const& key, uint32_t seq) const;
@@ -62,7 +84,12 @@ public:
 
     size_t
     size() const;
+
+    float
+    getObjectHitRate() const;
+
+    float
+    getSuccessorHitRate() const;
 };
 
 }  // namespace Backend
-#endif

src/backend/Types.h

@@ -1,5 +1,24 @@
-#ifndef CLIO_TYPES_H_INCLUDED
-#define CLIO_TYPES_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
 #include <ripple/basics/base_uint.h>
 #include <ripple/protocol/AccountID.h>
 #include <optional>
@@ -37,8 +56,27 @@ struct TransactionAndMetadata
 {
     Blob transaction;
     Blob metadata;
-    std::uint32_t ledgerSequence;
-    std::uint32_t date;
+    std::uint32_t ledgerSequence = 0;
+    std::uint32_t date = 0;
+
+    TransactionAndMetadata() = default;
+    TransactionAndMetadata(
+        Blob const& transaction,
+        Blob const& metadata,
+        std::uint32_t ledgerSequence,
+        std::uint32_t date)
+        : transaction{transaction}, metadata{metadata}, ledgerSequence{ledgerSequence}, date{date}
+    {
+    }
+
+    TransactionAndMetadata(std::tuple<Blob, Blob, std::uint32_t, std::uint32_t> data)
+        : transaction{std::get<0>(data)}
+        , metadata{std::get<1>(data)}
+        , ledgerSequence{std::get<2>(data)}
+        , date{std::get<3>(data)}
+    {
+    }
+
     bool
     operator==(const TransactionAndMetadata& other) const
     {
@@ -51,6 +89,29 @@ struct TransactionsCursor
 {
     std::uint32_t ledgerSequence;
     std::uint32_t transactionIndex;
+
+    TransactionsCursor() = default;
+    TransactionsCursor(std::uint32_t ledgerSequence, std::uint32_t transactionIndex)
+        : ledgerSequence{ledgerSequence}, transactionIndex{transactionIndex}
+    {
+    }
+
+    TransactionsCursor(std::tuple<std::uint32_t, std::uint32_t> data)
+        : ledgerSequence{std::get<0>(data)}, transactionIndex{std::get<1>(data)}
+    {
+    }
+
+    TransactionsCursor&
+    operator=(TransactionsCursor const&) = default;
+
+    bool
+    operator==(TransactionsCursor const& other) const = default;
+
+    [[nodiscard]] std::tuple<std::uint32_t, std::uint32_t>
+    asTuple() const
+    {
+        return std::make_tuple(ledgerSequence, transactionIndex);
+    }
 };
 
 struct TransactionsAndCursor
@@ -64,16 +125,31 @@ struct NFT
     ripple::uint256 tokenID;
     std::uint32_t ledgerSequence;
     ripple::AccountID owner;
+    Blob uri;
     bool isBurned;
 
+    NFT() = default;
+    NFT(ripple::uint256 const& tokenID,
+        std::uint32_t ledgerSequence,
+        ripple::AccountID const& owner,
+        Blob const& uri,
+        bool isBurned)
+        : tokenID{tokenID}, ledgerSequence{ledgerSequence}, owner{owner}, uri{uri}, isBurned{isBurned}
+    {
+    }
+
+    NFT(ripple::uint256 const& tokenID, std::uint32_t ledgerSequence, ripple::AccountID const& owner, bool isBurned)
+        : NFT(tokenID, ledgerSequence, owner, {}, isBurned)
+    {
+    }
+
     // clearly two tokens are the same if they have the same ID, but this
     // struct stores the state of a given token at a given ledger sequence, so
     // we also need to compare with ledgerSequence
     bool
     operator==(NFT const& other) const
     {
-        return tokenID == other.tokenID &&
-            ledgerSequence == other.ledgerSequence;
+        return tokenID == other.tokenID && ledgerSequence == other.ledgerSequence;
     }
 };
 
@@ -82,11 +158,7 @@ struct LedgerRange
     std::uint32_t minSequence;
     std::uint32_t maxSequence;
 };
-constexpr ripple::uint256 firstKey{
-    "0000000000000000000000000000000000000000000000000000000000000000"};
-constexpr ripple::uint256 lastKey{
-    "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"};
-constexpr ripple::uint256 hi192{
-    "0000000000000000000000000000000000000000000000001111111111111111"};
+constexpr ripple::uint256 firstKey{"0000000000000000000000000000000000000000000000000000000000000000"};
+constexpr ripple::uint256 lastKey{"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"};
+constexpr ripple::uint256 hi192{"0000000000000000000000000000000000000000000000001111111111111111"};
 }  // namespace Backend
-#endif

src/backend/cassandra/Concepts.h

@@ -0,0 +1,79 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Types.h>
+
+#include <boost/asio/spawn.hpp>
+
+#include <chrono>
+#include <concepts>
+#include <optional>
+#include <string>
+
+namespace Backend::Cassandra {
+
+// clang-format off
+template <typename T>
+concept SomeSettingsProvider = requires(T a) {
+    { a.getSettings() } -> std::same_as<Settings>;
+    { a.getKeyspace() } -> std::same_as<std::string>;
+    { a.getTablePrefix() } -> std::same_as<std::optional<std::string>>;
+    { a.getReplicationFactor() } -> std::same_as<uint16_t>;
+    { a.getTtl() } -> std::same_as<uint16_t>;
+};
+// clang-format on
+
+// clang-format off
+template <typename T>
+concept SomeExecutionStrategy = requires(
+    T a, 
+    Settings settings, 
+    Handle handle, 
+    Statement statement, 
+    std::vector<Statement> statements,
+    PreparedStatement prepared,
+    boost::asio::yield_context token
+) {
+    { T(settings, handle) };
+    { a.sync() } -> std::same_as<void>;
+    { a.isTooBusy() } -> std::same_as<bool>;
+    { a.writeSync(statement) } -> std::same_as<ResultOrError>;
+    { a.writeSync(prepared) } -> std::same_as<ResultOrError>;
+    { a.write(prepared) } -> std::same_as<void>;
+    { a.write(std::move(statements)) } -> std::same_as<void>;
+    { a.read(token, prepared) } -> std::same_as<ResultOrError>;
+    { a.read(token, statement) } -> std::same_as<ResultOrError>;
+    { a.read(token, statements) } -> std::same_as<ResultOrError>;
+    { a.readEach(token, statements) } -> std::same_as<std::vector<Result>>;
+};
+// clang-format on
+
+// clang-format off
+template <typename T>
+concept SomeRetryPolicy = requires(T a, boost::asio::io_context ioc, CassandraError err, uint32_t attempt) {
+    { T(ioc) };
+    { a.shouldRetry(err) } -> std::same_as<bool>;
+    { a.retry([](){}) } -> std::same_as<void>;
+    { a.calculateDelay(attempt) } -> std::same_as<std::chrono::milliseconds>;
+};
+// clang-format on
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/Error.h

@@ -0,0 +1,99 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <cassandra.h>
+
+#include <string>
+
+namespace Backend::Cassandra {
+
+/**
+ * @brief A simple container for both error message and error code
+ */
+class CassandraError
+{
+    std::string message_;
+    uint32_t code_;
+
+public:
+    CassandraError() = default;  // default constructible required by Expected
+    CassandraError(std::string message, uint32_t code) : message_{message}, code_{code}
+    {
+    }
+
+    template <typename T>
+    friend std::string
+    operator+(T const& lhs, CassandraError const& rhs) requires std::is_convertible_v<T, std::string>
+    {
+        return lhs + rhs.message();
+    }
+
+    template <typename T>
+    friend bool
+    operator==(T const& lhs, CassandraError const& rhs) requires std::is_convertible_v<T, std::string>
+    {
+        return lhs == rhs.message();
+    }
+
+    template <std::integral T>
+    friend bool
+    operator==(T const& lhs, CassandraError const& rhs)
+    {
+        return lhs == rhs.code();
+    }
+
+    friend std::ostream&
+    operator<<(std::ostream& os, CassandraError const& err)
+    {
+        os << err.message();
+        return os;
+    }
+
+    std::string
+    message() const
+    {
+        return message_;
+    }
+
+    uint32_t
+    code() const
+    {
+        return code_;
+    }
+
+    bool
+    isTimeout() const
+    {
+        if (code_ == CASS_ERROR_LIB_NO_HOSTS_AVAILABLE or code_ == CASS_ERROR_LIB_REQUEST_TIMED_OUT or
+            code_ == CASS_ERROR_SERVER_UNAVAILABLE or code_ == CASS_ERROR_SERVER_OVERLOADED or
+            code_ == CASS_ERROR_SERVER_READ_TIMEOUT)
+            return true;
+        return false;
+    }
+
+    bool
+    isInvalidQuery() const
+    {
+        return code_ == CASS_ERROR_SERVER_INVALID_QUERY;
+    }
+};
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/Handle.cpp

@@ -0,0 +1,155 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/Handle.h>
+
+namespace Backend::Cassandra {
+
+Handle::Handle(Settings clusterSettings) : cluster_{clusterSettings}
+{
+}
+
+Handle::Handle(std::string_view contactPoints) : Handle{Settings::defaultSettings().withContactPoints(contactPoints)}
+{
+}
+
+Handle::~Handle()
+{
+    [[maybe_unused]] auto _ = disconnect();  // attempt to disconnect
+}
+
+Handle::FutureType
+Handle::asyncConnect() const
+{
+    return cass_session_connect(session_, cluster_);
+}
+
+Handle::MaybeErrorType
+Handle::connect() const
+{
+    return asyncConnect().await();
+}
+
+Handle::FutureType
+Handle::asyncConnect(std::string_view keyspace) const
+{
+    return cass_session_connect_keyspace(session_, cluster_, keyspace.data());
+}
+
+Handle::MaybeErrorType
+Handle::connect(std::string_view keyspace) const
+{
+    return asyncConnect(keyspace).await();
+}
+
+Handle::FutureType
+Handle::asyncDisconnect() const
+{
+    return cass_session_close(session_);
+}
+
+Handle::MaybeErrorType
+Handle::disconnect() const
+{
+    return asyncDisconnect().await();
+}
+
+Handle::FutureType
+Handle::asyncReconnect(std::string_view keyspace) const
+{
+    if (auto rc = asyncDisconnect().await(); not rc)  // sync
+        throw std::logic_error("Reconnect to keyspace '" + std::string{keyspace} + "' failed: " + rc.error());
+    return asyncConnect(keyspace);
+}
+
+Handle::MaybeErrorType
+Handle::reconnect(std::string_view keyspace) const
+{
+    return asyncReconnect(keyspace).await();
+}
+
+std::vector<Handle::FutureType>
+Handle::asyncExecuteEach(std::vector<Statement> const& statements) const
+{
+    std::vector<Handle::FutureType> futures;
+    for (auto const& statement : statements)
+        futures.push_back(cass_session_execute(session_, statement));
+    return futures;
+}
+
+Handle::MaybeErrorType
+Handle::executeEach(std::vector<Statement> const& statements) const
+{
+    for (auto futures = asyncExecuteEach(statements); auto const& future : futures)
+    {
+        if (auto const rc = future.await(); not rc)
+            return rc;
+    }
+
+    return {};
+}
+
+Handle::FutureType
+Handle::asyncExecute(Statement const& statement) const
+{
+    return cass_session_execute(session_, statement);
+}
+
+Handle::FutureWithCallbackType
+Handle::asyncExecute(Statement const& statement, std::function<void(Handle::ResultOrErrorType)>&& cb) const
+{
+    return Handle::FutureWithCallbackType{cass_session_execute(session_, statement), std::move(cb)};
+}
+
+Handle::ResultOrErrorType
+Handle::execute(Statement const& statement) const
+{
+    return asyncExecute(statement).get();
+}
+
+Handle::FutureType
+Handle::asyncExecute(std::vector<Statement> const& statements) const
+{
+    return cass_session_execute_batch(session_, Batch{statements});
+}
+
+Handle::MaybeErrorType
+Handle::execute(std::vector<Statement> const& statements) const
+{
+    return asyncExecute(statements).await();
+}
+
+Handle::FutureWithCallbackType
+Handle::asyncExecute(std::vector<Statement> const& statements, std::function<void(Handle::ResultOrErrorType)>&& cb)
+    const
+{
+    return Handle::FutureWithCallbackType{cass_session_execute_batch(session_, Batch{statements}), std::move(cb)};
+}
+
+Handle::PreparedStatementType
+Handle::prepare(std::string_view query) const
+{
+    Handle::FutureType future = cass_session_prepare(session_, query.data());
+    if (auto const rc = future.await(); rc)
+        return cass_future_get_prepared(future);
+    else
+        throw std::runtime_error(rc.error().message());
+}
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/Handle.h

@@ -0,0 +1,295 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Error.h>
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/Batch.h>
+#include <backend/cassandra/impl/Cluster.h>
+#include <backend/cassandra/impl/Future.h>
+#include <backend/cassandra/impl/ManagedObject.h>
+#include <backend/cassandra/impl/Result.h>
+#include <backend/cassandra/impl/Session.h>
+#include <backend/cassandra/impl/Statement.h>
+#include <util/Expected.h>
+
+#include <cassandra.h>
+
+#include <chrono>
+#include <compare>
+#include <iterator>
+#include <vector>
+
+namespace Backend::Cassandra {
+
+/**
+ * @brief Represents a handle to the cassandra database cluster
+ */
+class Handle
+{
+    detail::Cluster cluster_;
+    detail::Session session_;
+
+public:
+    using ResultOrErrorType = ResultOrError;
+    using MaybeErrorType = MaybeError;
+    using FutureWithCallbackType = FutureWithCallback;
+    using FutureType = Future;
+    using StatementType = Statement;
+    using PreparedStatementType = PreparedStatement;
+    using ResultType = Result;
+
+    /**
+     * @brief Construct a new handle from a @ref Settings object
+     */
+    explicit Handle(Settings clusterSettings = Settings::defaultSettings());
+
+    /**
+     * @brief Construct a new handle with default settings and only by setting
+     * the contact points
+     */
+    explicit Handle(std::string_view contactPoints);
+
+    /**
+     * @brief Disconnects gracefully if possible
+     */
+    ~Handle();
+
+    /**
+     * @brief Move is supported
+     */
+    Handle(Handle&&) = default;
+
+    /**
+     * @brief Connect to the cluster asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncConnect() const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncConnect() const for how this works.
+     */
+    [[nodiscard]] MaybeErrorType
+    connect() const;
+
+    /**
+     * @brief Connect to the the specified keyspace asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncConnect(std::string_view keyspace) const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncConnect(std::string_view) const for how this works.
+     */
+    [[nodiscard]] MaybeErrorType
+    connect(std::string_view keyspace) const;
+
+    /**
+     * @brief Disconnect from the cluster asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncDisconnect() const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncDisconnect() const for how this works.
+     */
+    [[maybe_unused]] MaybeErrorType
+    disconnect() const;
+
+    /**
+     * @brief Reconnect to the the specified keyspace asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncReconnect(std::string_view keyspace) const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncReconnect(std::string_view) const for how this works.
+     */
+    [[nodiscard]] MaybeErrorType
+    reconnect(std::string_view keyspace) const;
+
+    /**
+     * @brief Execute a simple query with optional args asynchronously
+     *
+     * @return A future
+     */
+    template <typename... Args>
+    [[nodiscard]] FutureType
+    asyncExecute(std::string_view query, Args&&... args) const
+    {
+        auto statement = StatementType{query, std::forward<Args>(args)...};
+        return cass_session_execute(session_, statement);
+    }
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncExecute(std::string_view, Args&&...) const for how this
+     * works.
+     */
+    template <typename... Args>
+    [[maybe_unused]] ResultOrErrorType
+    execute(std::string_view query, Args&&... args) const
+    {
+        return asyncExecute<Args...>(query, std::forward<Args>(args)...).get();
+    }
+
+    /**
+     * @brief Execute each of the statements asynchronously
+     *
+     * Batched version is not always the right option. Especially since it only
+     * supports INSERT, UPDATE and DELETE statements.
+     * This can be used as an alternative when statements need to execute in
+     * bulk.
+     *
+     * @return A vector of future objects
+     */
+    [[nodiscard]] std::vector<FutureType>
+    asyncExecuteEach(std::vector<StatementType> const& statements) const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncExecuteEach(std::vector<StatementType> const&) const for
+     * how this works.
+     */
+    [[maybe_unused]] MaybeErrorType
+    executeEach(std::vector<StatementType> const& statements) const;
+
+    /**
+     * @brief Execute a prepared statement with optional args asynchronously
+     *
+     * @return A future
+     */
+    template <typename... Args>
+    [[nodiscard]] FutureType
+    asyncExecute(PreparedStatementType const& statement, Args&&... args) const
+    {
+        auto bound = statement.bind<Args...>(std::forward<Args>(args)...);
+        return cass_session_execute(session_, bound);
+    }
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncExecute(std::vector<StatementType> const&, Args&&...) const
+     * for how this works.
+     */
+    template <typename... Args>
+    [[maybe_unused]] ResultOrErrorType
+    execute(PreparedStatementType const& statement, Args&&... args) const
+    {
+        return asyncExecute<Args...>(statement, std::forward<Args>(args)...).get();
+    }
+
+    /**
+     * @brief Execute one (bound or simple) statements asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncExecute(StatementType const& statement) const;
+
+    /**
+     * @brief Execute one (bound or simple) statements asynchronously with a
+     * callback
+     *
+     * @return A future that holds onto the callback provided
+     */
+    [[nodiscard]] FutureWithCallbackType
+    asyncExecute(StatementType const& statement, std::function<void(ResultOrErrorType)>&& cb) const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncExecute(StatementType const&) const for how this
+     * works.
+     */
+    [[maybe_unused]] ResultOrErrorType
+    execute(StatementType const& statement) const;
+
+    /**
+     * @brief Execute a batch of (bound or simple) statements asynchronously
+     *
+     * @return A future
+     */
+    [[nodiscard]] FutureType
+    asyncExecute(std::vector<StatementType> const& statements) const;
+
+    /**
+     * @brief Synchonous version of the above
+     *
+     * See @ref asyncExecute(std::vector<StatementType> const&) const for how
+     * this works.
+     */
+    [[maybe_unused]] MaybeErrorType
+    execute(std::vector<StatementType> const& statements) const;
+
+    /**
+     * @brief Execute a batch of (bound or simple) statements asynchronously
+     * with a completion callback
+     *
+     * @return A future that holds onto the callback provided
+     */
+    [[nodiscard]] FutureWithCallbackType
+    asyncExecute(std::vector<StatementType> const& statements, std::function<void(ResultOrErrorType)>&& cb) const;
+
+    /**
+     * @brief Prepare a statement
+     *
+     * @return A @ref PreparedStatementType
+     * @throws std::runtime_error with underlying error description on failure
+     */
+    [[nodiscard]] PreparedStatementType
+    prepare(std::string_view query) const;
+};
+
+/**
+ * @brief Extracts the results into series of std::tuple<Types...> by creating a
+ * simple wrapper with an STL input iterator inside.
+ *
+ * You can call .begin() and .end() in order to iterate as usual.
+ * This also means that you can use it in a range-based for or with some
+ * algorithms.
+ */
+template <typename... Types>
+[[nodiscard]] detail::ResultExtractor<Types...>
+extract(Handle::ResultType const& result)
+{
+    return {result};
+}
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/Schema.h

@@ -0,0 +1,667 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Concepts.h>
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/SettingsProvider.h>
+#include <backend/cassandra/Types.h>
+#include <config/Config.h>
+#include <log/Logger.h>
+#include <util/Expected.h>
+
+#include <fmt/compile.h>
+
+namespace Backend::Cassandra {
+
+template <SomeSettingsProvider SettingsProviderType>
+[[nodiscard]] std::string inline qualifiedTableName(SettingsProviderType const& provider, std::string_view name)
+{
+    return fmt::format("{}.{}{}", provider.getKeyspace(), provider.getTablePrefix().value_or(""), name);
+}
+
+/**
+ * @brief Manages the DB schema and provides access to prepared statements
+ */
+template <SomeSettingsProvider SettingsProviderType>
+class Schema
+{
+    // Current schema version.
+    // Update this everytime you update the schema.
+    // Migrations will be ran automatically based on this value.
+    static constexpr uint16_t version = 1u;
+
+    clio::Logger log_{"Backend"};
+    std::reference_wrapper<SettingsProviderType const> settingsProvider_;
+
+public:
+    explicit Schema(SettingsProviderType const& settingsProvider) : settingsProvider_{std::cref(settingsProvider)}
+    {
+    }
+
+    std::string createKeyspace = [this]() {
+        return fmt::format(
+            R"(
+            CREATE KEYSPACE IF NOT EXISTS {} 
+              WITH replication = {{
+                     'class': 'SimpleStrategy',
+                     'replication_factor': '{}'
+                   }} 
+               AND durable_writes = true
+            )",
+            settingsProvider_.get().getKeyspace(),
+            settingsProvider_.get().getReplicationFactor());
+    }();
+
+    // =======================
+    // Schema creation queries
+    // =======================
+
+    std::vector<Statement> createSchema = [this]() {
+        std::vector<Statement> statements;
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  (      
+                         key blob, 
+                    sequence bigint, 
+                      object blob, 
+                     PRIMARY KEY (key, sequence) 
+                  ) 
+             WITH CLUSTERING ORDER BY (sequence DESC) 
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "objects"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  (     
+                        hash blob PRIMARY KEY, 
+             ledger_sequence bigint, 
+                        date bigint,
+                 transaction blob, 
+                    metadata blob 
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "transactions"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  (     
+             ledger_sequence bigint, 
+                        hash blob, 
+                     PRIMARY KEY (ledger_sequence, hash) 
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "ledger_transactions"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  (     
+                    key blob,
+                    seq bigint, 
+                   next blob, 
+                PRIMARY KEY (key, seq) 
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "successor"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  (     
+                    seq bigint, 
+                    key blob,
+                PRIMARY KEY (seq, key) 
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "diff"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    account blob,    
+                    seq_idx tuple<bigint, bigint>, 
+                       hash blob,
+                    PRIMARY KEY (account, seq_idx) 
+                  ) 
+             WITH CLUSTERING ORDER BY (seq_idx DESC)
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "account_tx"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    sequence bigint PRIMARY KEY,
+                      header blob
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "ledgers"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    hash blob PRIMARY KEY,
+                sequence bigint
+                  ) 
+             WITH default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "ledger_hashes"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    is_latest boolean PRIMARY KEY,
+                     sequence bigint
+                  )
+            )",
+            qualifiedTableName(settingsProvider_.get(), "ledger_range")));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    token_id blob,    
+                    sequence bigint,
+                       owner blob,
+                   is_burned boolean,
+                     PRIMARY KEY (token_id, sequence) 
+                  ) 
+             WITH CLUSTERING ORDER BY (sequence DESC)
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "nf_tokens"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                      issuer blob,
+                       taxon bigint,
+                    token_id blob,
+                     PRIMARY KEY (issuer, taxon, token_id)
+                  ) 
+             WITH CLUSTERING ORDER BY (taxon ASC, token_id ASC)
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "issuer_nf_tokens_v2"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    token_id blob,
+                    sequence bigint,
+                         uri blob,
+                     PRIMARY KEY (token_id, sequence)
+                  ) 
+             WITH CLUSTERING ORDER BY (sequence DESC)
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "nf_token_uris"),
+            settingsProvider_.get().getTtl()));
+
+        statements.emplace_back(fmt::format(
+            R"(
+           CREATE TABLE IF NOT EXISTS {}
+                  ( 
+                    token_id blob,    
+                     seq_idx tuple<bigint, bigint>,
+                        hash blob,
+                     PRIMARY KEY (token_id, seq_idx) 
+                  ) 
+             WITH CLUSTERING ORDER BY (seq_idx DESC)
+              AND default_time_to_live = {}
+            )",
+            qualifiedTableName(settingsProvider_.get(), "nf_token_transactions"),
+            settingsProvider_.get().getTtl()));
+
+        return statements;
+    }();
+
+    /**
+     * @brief Prepared statements holder
+     */
+    class Statements
+    {
+        std::reference_wrapper<SettingsProviderType const> settingsProvider_;
+        std::reference_wrapper<Handle const> handle_;
+
+    public:
+        Statements(SettingsProviderType const& settingsProvider, Handle const& handle)
+            : settingsProvider_{settingsProvider}, handle_{std::cref(handle)}
+        {
+        }
+
+        //
+        // Insert queries
+        //
+
+        PreparedStatement insertObject = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (key, sequence, object)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "objects")));
+        }();
+
+        PreparedStatement insertTransaction = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (hash, ledger_sequence, date, transaction, metadata)
+                VALUES (?, ?, ?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "transactions")));
+        }();
+
+        PreparedStatement insertLedgerTransaction = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (ledger_sequence, hash)
+                VALUES (?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_transactions")));
+        }();
+
+        PreparedStatement insertSuccessor = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (key, seq, next)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "successor")));
+        }();
+
+        PreparedStatement insertDiff = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (seq, key)
+                VALUES (?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "diff")));
+        }();
+
+        PreparedStatement insertAccountTx = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (account, seq_idx, hash)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "account_tx")));
+        }();
+
+        PreparedStatement insertNFT = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (token_id, sequence, owner, is_burned)
+                VALUES (?, ?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_tokens")));
+        }();
+
+        PreparedStatement insertIssuerNFT = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (issuer, taxon, token_id)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "issuer_nf_tokens_v2")));
+        }();
+
+        PreparedStatement insertNFTURI = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (token_id, sequence, uri)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_token_uris")));
+        }();
+
+        PreparedStatement insertNFTTx = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (token_id, seq_idx, hash)
+                VALUES (?, ?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_token_transactions")));
+        }();
+
+        PreparedStatement insertLedgerHeader = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (sequence, header)
+                VALUES (?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledgers")));
+        }();
+
+        PreparedStatement insertLedgerHash = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                INSERT INTO {} 
+                       (hash, sequence)
+                VALUES (?, ?)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_hashes")));
+        }();
+
+        //
+        // Update (and "delete") queries
+        //
+
+        PreparedStatement updateLedgerRange = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                UPDATE {} 
+                   SET sequence = ?
+                 WHERE is_latest = ? 
+                    IF sequence IN (?, null)
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_range")));
+        }();
+
+        PreparedStatement deleteLedgerRange = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                UPDATE {} 
+                   SET sequence = ?
+                 WHERE is_latest = false
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_range")));
+        }();
+
+        //
+        // Select queries
+        //
+
+        PreparedStatement selectSuccessor = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT next 
+                  FROM {}               
+                 WHERE key = ?
+                   AND seq <= ?
+              ORDER BY seq DESC 
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "successor")));
+        }();
+
+        PreparedStatement selectDiff = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT key 
+                  FROM {}
+                 WHERE seq = ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "diff")));
+        }();
+
+        PreparedStatement selectObject = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT object, sequence 
+                  FROM {}               
+                 WHERE key = ?
+                   AND sequence <= ?
+              ORDER BY sequence DESC 
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "objects")));
+        }();
+
+        PreparedStatement selectTransaction = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT transaction, metadata, ledger_sequence, date 
+                  FROM {}
+                 WHERE hash = ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "transactions")));
+        }();
+
+        PreparedStatement selectAllTransactionHashesInLedger = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT hash 
+                  FROM {}               
+                 WHERE ledger_sequence = ?               
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_transactions")));
+        }();
+
+        PreparedStatement selectLedgerPageKeys = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT key 
+                  FROM {}               
+                 WHERE TOKEN(key) >= ?
+                   AND sequence <= ?
+         PER PARTITION LIMIT 1 
+                 LIMIT ?
+                 ALLOW FILTERING
+                )",
+                qualifiedTableName(settingsProvider_.get(), "objects")));
+        }();
+
+        PreparedStatement selectLedgerPage = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT object, key
+                  FROM {}
+                 WHERE TOKEN(key) >= ?
+                   AND sequence <= ?
+         PER PARTITION LIMIT 1
+                 LIMIT ?
+                 ALLOW FILTERING
+                )",
+                qualifiedTableName(settingsProvider_.get(), "objects")));
+        }();
+
+        PreparedStatement getToken = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT TOKEN(key) 
+                  FROM {}               
+                 WHERE key = ?               
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "objects")));
+        }();
+
+        PreparedStatement selectAccountTx = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT hash, seq_idx 
+                  FROM {}               
+                 WHERE account = ?
+                   AND seq_idx <= ?
+                 LIMIT ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "account_tx")));
+        }();
+
+        PreparedStatement selectAccountTxForward = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT hash, seq_idx 
+                  FROM {}               
+                 WHERE account = ?
+                   AND seq_idx >= ?
+              ORDER BY seq_idx ASC 
+                 LIMIT ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "account_tx")));
+        }();
+
+        PreparedStatement selectNFT = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT sequence, owner, is_burned
+                  FROM {}    
+                 WHERE token_id = ?
+                   AND sequence <= ?
+              ORDER BY sequence DESC
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_tokens")));
+        }();
+
+        PreparedStatement selectNFTURI = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT uri
+                  FROM {}    
+                 WHERE token_id = ?
+                   AND sequence <= ?
+              ORDER BY sequence DESC
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_token_uris")));
+        }();
+
+        PreparedStatement selectNFTTx = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT hash, seq_idx
+                  FROM {}    
+                 WHERE token_id = ?
+                   AND seq_idx < ?
+              ORDER BY seq_idx DESC
+                 LIMIT ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_token_transactions")));
+        }();
+
+        PreparedStatement selectNFTTxForward = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT hash, seq_idx
+                  FROM {}    
+                 WHERE token_id = ?
+                   AND seq_idx >= ?
+              ORDER BY seq_idx ASC
+                 LIMIT ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "nf_token_transactions")));
+        }();
+
+        PreparedStatement selectLedgerByHash = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT sequence
+                  FROM {}
+                 WHERE hash = ?     
+                 LIMIT 1
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_hashes")));
+        }();
+
+        PreparedStatement selectLedgerBySeq = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT header
+                  FROM {}
+                 WHERE sequence = ?
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledgers")));
+        }();
+
+        PreparedStatement selectLatestLedger = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT sequence
+                  FROM {}    
+                 WHERE is_latest = true               
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_range")));
+        }();
+
+        PreparedStatement selectLedgerRange = [this]() {
+            return handle_.get().prepare(fmt::format(
+                R"(
+                SELECT sequence
+                  FROM {}
+                )",
+                qualifiedTableName(settingsProvider_.get(), "ledger_range")));
+        }();
+    };
+
+    /**
+     * @brief Recreates the prepared statements
+     */
+    void
+    prepareStatements(Handle const& handle)
+    {
+        log_.info() << "Preparing cassandra statements";
+        statements_ = std::make_unique<Statements>(settingsProvider_, handle);
+        log_.info() << "Finished preparing statements";
+    }
+
+    /**
+     * @brief Provides access to statements
+     */
+    std::unique_ptr<Statements> const&
+    operator->() const
+    {
+        return statements_;
+    }
+
+private:
+    std::unique_ptr<Statements> statements_{nullptr};
+};
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/SettingsProvider.cpp

@@ -0,0 +1,125 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/SettingsProvider.h>
+#include <backend/cassandra/impl/Cluster.h>
+#include <backend/cassandra/impl/Statement.h>
+#include <config/Config.h>
+
+#include <boost/json.hpp>
+
+#include <string>
+#include <thread>
+
+namespace Backend::Cassandra {
+
+namespace detail {
+inline Settings::ContactPoints
+tag_invoke(boost::json::value_to_tag<Settings::ContactPoints>, boost::json::value const& value)
+{
+    if (not value.is_object())
+        throw std::runtime_error(
+            "Feed entire Cassandra section to parse "
+            "Settings::ContactPoints instead");
+
+    clio::Config obj{value};
+    Settings::ContactPoints out;
+
+    out.contactPoints = obj.valueOrThrow<std::string>("contact_points", "`contact_points` must be a string");
+    out.port = obj.maybeValue<uint16_t>("port");
+
+    return out;
+}
+
+inline Settings::SecureConnectionBundle
+tag_invoke(boost::json::value_to_tag<Settings::SecureConnectionBundle>, boost::json::value const& value)
+{
+    if (not value.is_string())
+        throw std::runtime_error("`secure_connect_bundle` must be a string");
+    return Settings::SecureConnectionBundle{value.as_string().data()};
+}
+}  // namespace detail
+
+SettingsProvider::SettingsProvider(clio::Config const& cfg, uint16_t ttl)
+    : config_{cfg}
+    , keyspace_{cfg.valueOr<std::string>("keyspace", "clio")}
+    , tablePrefix_{cfg.maybeValue<std::string>("table_prefix")}
+    , replicationFactor_{cfg.valueOr<uint16_t>("replication_factor", 3)}
+    , ttl_{ttl}
+    , settings_{parseSettings()}
+{
+}
+
+Settings
+SettingsProvider::getSettings() const
+{
+    return settings_;
+}
+
+std::optional<std::string>
+SettingsProvider::parseOptionalCertificate() const
+{
+    if (auto const certPath = config_.maybeValue<std::string>("certfile"); certPath)
+    {
+        auto const path = std::filesystem::path(*certPath);
+        std::ifstream fileStream(path.string(), std::ios::in);
+        if (!fileStream)
+        {
+            throw std::system_error(errno, std::generic_category(), "Opening certificate " + path.string());
+        }
+
+        std::string contents(std::istreambuf_iterator<char>{fileStream}, std::istreambuf_iterator<char>{});
+        if (fileStream.bad())
+        {
+            throw std::system_error(errno, std::generic_category(), "Reading certificate " + path.string());
+        }
+
+        return contents;
+    }
+
+    return std::nullopt;
+}
+
+Settings
+SettingsProvider::parseSettings() const
+{
+    auto settings = Settings::defaultSettings();
+    if (auto const bundle = config_.maybeValue<Settings::SecureConnectionBundle>("secure_connect_bundle"); bundle)
+    {
+        settings.connectionInfo = *bundle;
+    }
+    else
+    {
+        settings.connectionInfo =
+            config_.valueOrThrow<Settings::ContactPoints>("Missing contact_points in Cassandra config");
+    }
+
+    settings.threads = config_.valueOr<uint32_t>("threads", settings.threads);
+    settings.maxWriteRequestsOutstanding =
+        config_.valueOr<uint32_t>("max_write_requests_outstanding", settings.maxWriteRequestsOutstanding);
+    settings.maxReadRequestsOutstanding =
+        config_.valueOr<uint32_t>("max_read_requests_outstanding", settings.maxReadRequestsOutstanding);
+    settings.certificate = parseOptionalCertificate();
+    settings.username = config_.maybeValue<std::string>("username");
+    settings.password = config_.maybeValue<std::string>("password");
+
+    return settings;
+}
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/SettingsProvider.h

@@ -0,0 +1,86 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/Types.h>
+#include <config/Config.h>
+#include <log/Logger.h>
+#include <util/Expected.h>
+
+namespace Backend::Cassandra {
+
+/**
+ * @brief Provides settings for @ref CassandraBackend
+ */
+class SettingsProvider
+{
+    clio::Config config_;
+
+    std::string keyspace_;
+    std::optional<std::string> tablePrefix_;
+    uint16_t replicationFactor_;
+    uint16_t ttl_;
+    Settings settings_;
+
+public:
+    explicit SettingsProvider(clio::Config const& cfg, uint16_t ttl = 0);
+
+    /*! Get the cluster settings */
+    [[nodiscard]] Settings
+    getSettings() const;
+
+    /*! Get the specified keyspace */
+    [[nodiscard]] inline std::string
+    getKeyspace() const
+    {
+        return keyspace_;
+    }
+
+    /*! Get an optional table prefix to use in all queries */
+    [[nodiscard]] inline std::optional<std::string>
+    getTablePrefix() const
+    {
+        return tablePrefix_;
+    }
+
+    /*! Get the replication factor */
+    [[nodiscard]] inline uint16_t
+    getReplicationFactor() const
+    {
+        return replicationFactor_;
+    }
+
+    /*! Get the default time to live to use in all `create` queries */
+    [[nodiscard]] inline uint16_t
+    getTtl() const
+    {
+        return ttl_;
+    }
+
+private:
+    [[nodiscard]] std::optional<std::string>
+    parseOptionalCertificate() const;
+
+    [[nodiscard]] Settings
+    parseSettings() const;
+};
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/Types.h

@@ -0,0 +1,67 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <util/Expected.h>
+
+#include <string>
+
+namespace Backend::Cassandra {
+
+namespace detail {
+struct Settings;
+class Session;
+class Cluster;
+struct Future;
+class FutureWithCallback;
+struct Result;
+class Statement;
+class PreparedStatement;
+struct Batch;
+}  // namespace detail
+
+using Settings = detail::Settings;
+using Future = detail::Future;
+using FutureWithCallback = detail::FutureWithCallback;
+using Result = detail::Result;
+using Statement = detail::Statement;
+using PreparedStatement = detail::PreparedStatement;
+using Batch = detail::Batch;
+
+/**
+ * @brief A strong type wrapper for int32_t
+ *
+ * This is unfortunately needed right now to support uint32_t properly
+ * because clio uses bigint (int64) everywhere except for when one need
+ * to specify LIMIT, which needs an int32 :-/
+ */
+struct Limit
+{
+    int32_t limit;
+};
+
+class Handle;
+class CassandraError;
+
+using MaybeError = util::Expected<void, CassandraError>;
+using ResultOrError = util::Expected<Result, CassandraError>;
+using Error = util::Unexpected<CassandraError>;
+
+}  // namespace Backend::Cassandra

src/backend/cassandra/impl/AsyncExecutor.h

@@ -0,0 +1,119 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Concepts.h>
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/RetryPolicy.h>
+#include <log/Logger.h>
+#include <util/Expected.h>
+
+#include <boost/asio.hpp>
+
+#include <functional>
+#include <memory>
+
+namespace Backend::Cassandra::detail {
+
+/**
+ * @brief A query executor with a changable retry policy
+ *
+ * Note: this is a bit of an anti-pattern and should be done differently
+ * eventually.
+ *
+ * Currently it's basically a saner implementation of the previous design that
+ * was used in production without much issue but was using raw new/delete and
+ * could leak easily. This version is slightly better but the overall design is
+ * flawed and should be reworked.
+ */
+template <
+    typename StatementType,
+    typename HandleType = Handle,
+    SomeRetryPolicy RetryPolicyType = ExponentialBackoffRetryPolicy>
+class AsyncExecutor : public std::enable_shared_from_this<AsyncExecutor<StatementType, HandleType, RetryPolicyType>>
+{
+    using FutureWithCallbackType = typename HandleType::FutureWithCallbackType;
+    using CallbackType = std::function<void(typename HandleType::ResultOrErrorType)>;
+
+    clio::Logger log_{"Backend"};
+
+    StatementType data_;
+    RetryPolicyType retryPolicy_;
+    CallbackType onComplete_;
+
+    // does not exist during initial construction, hence optional
+    std::optional<FutureWithCallbackType> future_;
+    std::mutex mtx_;
+
+public:
+    /**
+     * @brief Create a new instance of the AsyncExecutor and execute it.
+     */
+    static void
+    run(boost::asio::io_context& ioc, HandleType const& handle, StatementType&& data, CallbackType&& onComplete)
+    {
+        // this is a helper that allows us to use std::make_shared below
+        struct EnableMakeShared : public AsyncExecutor<StatementType, HandleType, RetryPolicyType>
+        {
+            EnableMakeShared(boost::asio::io_context& ioc, StatementType&& data, CallbackType&& onComplete)
+                : AsyncExecutor(ioc, std::move(data), std::move(onComplete))
+            {
+            }
+        };
+
+        auto ptr = std::make_shared<EnableMakeShared>(ioc, std::move(data), std::move(onComplete));
+        ptr->execute(handle);
+    }
+
+private:
+    AsyncExecutor(boost::asio::io_context& ioc, StatementType&& data, CallbackType&& onComplete)
+        : data_{std::move(data)}, retryPolicy_{ioc}, onComplete_{std::move(onComplete)}
+    {
+    }
+
+    void
+    execute(HandleType const& handle)
+    {
+        auto self = this->shared_from_this();
+
+        // lifetime is extended by capturing self ptr
+        auto handler = [this, &handle, self](auto&& res) mutable {
+            if (res)
+            {
+                onComplete_(std::move(res));
+            }
+            else
+            {
+                if (retryPolicy_.shouldRetry(res.error()))
+                    retryPolicy_.retry([self, &handle]() { self->execute(handle); });
+                else
+                    onComplete_(std::move(res));  // report error
+            }
+
+            self = nullptr;  // explicitly decrement refcount
+        };
+
+        std::scoped_lock lck{mtx_};
+        future_.emplace(handle.asyncExecute(data_, std::move(handler)));
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Batch.cpp

@@ -0,0 +1,56 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/Error.h>
+#include <backend/cassandra/impl/Batch.h>
+#include <backend/cassandra/impl/Statement.h>
+#include <util/Expected.h>
+
+#include <exception>
+#include <vector>
+
+namespace {
+static constexpr auto batchDeleter = [](CassBatch* ptr) { cass_batch_free(ptr); };
+};
+
+namespace Backend::Cassandra::detail {
+
+// todo: use an appropritae value instead of CASS_BATCH_TYPE_LOGGED for
+// different use cases
+Batch::Batch(std::vector<Statement> const& statements)
+    : ManagedObject{cass_batch_new(CASS_BATCH_TYPE_LOGGED), batchDeleter}
+{
+    cass_batch_set_is_idempotent(*this, cass_true);
+
+    for (auto const& statement : statements)
+        if (auto const res = add(statement); not res)
+            throw std::runtime_error("Failed to add statement to batch: " + res.error());
+}
+
+MaybeError
+Batch::add(Statement const& statement)
+{
+    if (auto const rc = cass_batch_add_statement(*this, statement); rc != CASS_OK)
+    {
+        return Error{CassandraError{cass_error_desc(rc), rc}};
+    }
+    return {};
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Batch.h

@@ -0,0 +1,37 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/ManagedObject.h>
+
+#include <cassandra.h>
+
+namespace Backend::Cassandra::detail {
+
+struct Batch : public ManagedObject<CassBatch>
+{
+    Batch(std::vector<Statement> const& statements);
+
+    MaybeError
+    add(Statement const& statement);
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Cluster.cpp

@@ -0,0 +1,154 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/impl/Cluster.h>
+#include <backend/cassandra/impl/SslContext.h>
+#include <backend/cassandra/impl/Statement.h>
+#include <util/Expected.h>
+
+#include <exception>
+#include <vector>
+
+namespace {
+static constexpr auto clusterDeleter = [](CassCluster* ptr) { cass_cluster_free(ptr); };
+
+template <class... Ts>
+struct overloadSet : Ts...
+{
+    using Ts::operator()...;
+};
+
+// explicit deduction guide (not needed as of C++20, but clang be clang)
+template <class... Ts>
+overloadSet(Ts...) -> overloadSet<Ts...>;
+};  // namespace
+
+namespace Backend::Cassandra::detail {
+
+Cluster::Cluster(Settings const& settings) : ManagedObject{cass_cluster_new(), clusterDeleter}
+{
+    using std::to_string;
+
+    cass_cluster_set_token_aware_routing(*this, cass_true);
+    if (auto const rc = cass_cluster_set_protocol_version(*this, CASS_PROTOCOL_VERSION_V4); rc != CASS_OK)
+    {
+        throw std::runtime_error(std::string{"Error setting cassandra protocol version to v4: "} + cass_error_desc(rc));
+    }
+
+    if (auto const rc = cass_cluster_set_num_threads_io(*this, settings.threads); rc != CASS_OK)
+    {
+        throw std::runtime_error(
+            std::string{"Error setting cassandra io threads to "} + to_string(settings.threads) + ": " +
+            cass_error_desc(rc));
+    }
+
+    cass_log_set_level(settings.enableLog ? CASS_LOG_TRACE : CASS_LOG_DISABLED);
+    cass_cluster_set_connect_timeout(*this, settings.connectionTimeout.count());
+    cass_cluster_set_request_timeout(*this, settings.requestTimeout.count());
+
+    // TODO: other options to experiment with and consider later:
+    // cass_cluster_set_max_concurrent_requests_threshold(*this, 10000);
+    // cass_cluster_set_queue_size_event(*this, 100000);
+    // cass_cluster_set_queue_size_io(*this, 100000);
+    // cass_cluster_set_write_bytes_high_water_mark(*this, 16 * 1024 * 1024);  // 16mb
+    // cass_cluster_set_write_bytes_low_water_mark(*this, 8 * 1024 * 1024);  // half of allowance
+    // cass_cluster_set_pending_requests_high_water_mark(*this, 5000);
+    // cass_cluster_set_pending_requests_low_water_mark(*this, 2500);  // half
+    // cass_cluster_set_max_requests_per_flush(*this, 1000);
+    // cass_cluster_set_max_concurrent_creation(*this, 8);
+    // cass_cluster_set_max_connections_per_host(*this, 6);
+    // cass_cluster_set_core_connections_per_host(*this, 4);
+    // cass_cluster_set_constant_speculative_execution_policy(*this, 1000, 1024);
+
+    if (auto const rc = cass_cluster_set_queue_size_io(
+            *this, settings.maxWriteRequestsOutstanding + settings.maxReadRequestsOutstanding);
+        rc != CASS_OK)
+    {
+        throw std::runtime_error(std::string{"Could not set queue size for IO per host: "} + cass_error_desc(rc));
+    }
+
+    setupConnection(settings);
+    setupCertificate(settings);
+    setupCredentials(settings);
+}
+
+void
+Cluster::setupConnection(Settings const& settings)
+{
+    std::visit(
+        overloadSet{
+            [this](Settings::ContactPoints const& points) { setupContactPoints(points); },
+            [this](Settings::SecureConnectionBundle const& bundle) { setupSecureBundle(bundle); }},
+        settings.connectionInfo);
+}
+
+void
+Cluster::setupContactPoints(Settings::ContactPoints const& points)
+{
+    using std::to_string;
+    auto throwErrorIfNeeded = [](CassError rc, std::string const& label, std::string const& value) {
+        if (rc != CASS_OK)
+            throw std::runtime_error("Cassandra: Error setting " + label + " [" + value + "]: " + cass_error_desc(rc));
+    };
+
+    {
+        log_.debug() << "Attempt connection using contact points: " << points.contactPoints;
+        auto const rc = cass_cluster_set_contact_points(*this, points.contactPoints.data());
+        throwErrorIfNeeded(rc, "contact_points", points.contactPoints);
+    }
+
+    if (points.port)
+    {
+        auto const rc = cass_cluster_set_port(*this, points.port.value());
+        throwErrorIfNeeded(rc, "port", to_string(points.port.value()));
+    }
+}
+
+void
+Cluster::setupSecureBundle(Settings::SecureConnectionBundle const& bundle)
+{
+    log_.debug() << "Attempt connection using secure bundle";
+    if (auto const rc = cass_cluster_set_cloud_secure_connection_bundle(*this, bundle.bundle.data()); rc != CASS_OK)
+    {
+        throw std::runtime_error("Failed to connect using secure connection bundle" + bundle.bundle);
+    }
+}
+
+void
+Cluster::setupCertificate(Settings const& settings)
+{
+    if (not settings.certificate)
+        return;
+
+    log_.debug() << "Configure SSL context";
+    SslContext context = SslContext(*settings.certificate);
+    cass_cluster_set_ssl(*this, context);
+}
+
+void
+Cluster::setupCredentials(Settings const& settings)
+{
+    if (not settings.username || not settings.password)
+        return;
+
+    log_.debug() << "Set credentials; username: " << settings.username.value();
+    cass_cluster_set_credentials(*this, settings.username.value().c_str(), settings.password.value().c_str());
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Cluster.h

@@ -0,0 +1,99 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/impl/ManagedObject.h>
+#include <log/Logger.h>
+
+#include <cassandra.h>
+
+#include <chrono>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <thread>
+#include <variant>
+
+namespace Backend::Cassandra::detail {
+
+struct Settings
+{
+    struct ContactPoints
+    {
+        std::string contactPoints = "127.0.0.1";  // defaults to localhost
+        std::optional<uint16_t> port;
+    };
+
+    struct SecureConnectionBundle
+    {
+        std::string bundle;  // no meaningful default
+    };
+
+    bool enableLog = false;
+    std::chrono::milliseconds connectionTimeout = std::chrono::milliseconds{10000};
+    std::chrono::milliseconds requestTimeout = std::chrono::milliseconds{0};  // no timeout at all
+    std::variant<ContactPoints, SecureConnectionBundle> connectionInfo = ContactPoints{};
+    uint32_t threads = std::thread::hardware_concurrency();
+    uint32_t maxWriteRequestsOutstanding = 10'000;
+    uint32_t maxReadRequestsOutstanding = 100'000;
+    std::optional<std::string> certificate;  // ssl context
+    std::optional<std::string> username;
+    std::optional<std::string> password;
+
+    Settings
+    withContactPoints(std::string_view contactPoints)
+    {
+        auto tmp = *this;
+        tmp.connectionInfo = ContactPoints{std::string{contactPoints}};
+        return tmp;
+    }
+
+    static Settings
+    defaultSettings()
+    {
+        return Settings();
+    }
+};
+
+class Cluster : public ManagedObject<CassCluster>
+{
+    clio::Logger log_{"Backend"};
+
+public:
+    Cluster(Settings const& settings);
+
+private:
+    void
+    setupConnection(Settings const& settings);
+
+    void
+    setupContactPoints(Settings::ContactPoints const& points);
+
+    void
+    setupSecureBundle(Settings::SecureConnectionBundle const& bundle);
+
+    void
+    setupCertificate(Settings const& settings);
+
+    void
+    setupCredentials(Settings const& settings);
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/ExecutionStrategy.h

@@ -0,0 +1,443 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/AsyncExecutor.h>
+#include <log/Logger.h>
+#include <util/Expected.h>
+
+#include <boost/asio/async_result.hpp>
+#include <boost/asio/spawn.hpp>
+
+#include <atomic>
+#include <condition_variable>
+#include <functional>
+#include <memory>
+#include <mutex>
+#include <optional>
+#include <thread>
+
+namespace Backend::Cassandra::detail {
+
+/**
+ * @brief Implements async and sync querying against the cassandra DB with
+ * support for throttling.
+ *
+ * Note: A lot of the code that uses yield is repeated below. This is ok for now
+ * because we are hopefully going to be getting rid of it entirely later on.
+ */
+template <typename HandleType = Handle>
+class DefaultExecutionStrategy
+{
+    clio::Logger log_{"Backend"};
+
+    std::uint32_t maxWriteRequestsOutstanding_;
+    std::atomic_uint32_t numWriteRequestsOutstanding_ = 0;
+
+    std::uint32_t maxReadRequestsOutstanding_;
+    std::atomic_uint32_t numReadRequestsOutstanding_ = 0;
+
+    std::mutex throttleMutex_;
+    std::condition_variable throttleCv_;
+
+    std::mutex syncMutex_;
+    std::condition_variable syncCv_;
+
+    boost::asio::io_context ioc_;
+    std::optional<boost::asio::io_service::work> work_;
+
+    std::reference_wrapper<HandleType const> handle_;
+    std::thread thread_;
+
+public:
+    using ResultOrErrorType = typename HandleType::ResultOrErrorType;
+    using StatementType = typename HandleType::StatementType;
+    using PreparedStatementType = typename HandleType::PreparedStatementType;
+    using FutureType = typename HandleType::FutureType;
+    using FutureWithCallbackType = typename HandleType::FutureWithCallbackType;
+    using ResultType = typename HandleType::ResultType;
+
+    using CompletionTokenType = boost::asio::yield_context;
+    using FunctionType = void(boost::system::error_code);
+    using AsyncResultType = boost::asio::async_result<CompletionTokenType, FunctionType>;
+    using HandlerType = typename AsyncResultType::completion_handler_type;
+
+    DefaultExecutionStrategy(Settings settings, HandleType const& handle)
+        : maxWriteRequestsOutstanding_{settings.maxWriteRequestsOutstanding}
+        , maxReadRequestsOutstanding_{settings.maxReadRequestsOutstanding}
+        , work_{ioc_}
+        , handle_{std::cref(handle)}
+        , thread_{[this]() { ioc_.run(); }}
+    {
+        log_.info() << "Max write requests outstanding is " << maxWriteRequestsOutstanding_
+                    << "; Max read requests outstanding is " << maxReadRequestsOutstanding_;
+    }
+
+    ~DefaultExecutionStrategy()
+    {
+        work_.reset();
+        ioc_.stop();
+        thread_.join();
+    }
+
+    /**
+     * @brief Wait for all async writes to finish before unblocking
+     */
+    void
+    sync()
+    {
+        log_.debug() << "Waiting to sync all writes...";
+        std::unique_lock<std::mutex> lck(syncMutex_);
+        syncCv_.wait(lck, [this]() { return finishedAllWriteRequests(); });
+        log_.debug() << "Sync done.";
+    }
+
+    bool
+    isTooBusy() const
+    {
+        return numReadRequestsOutstanding_ >= maxReadRequestsOutstanding_;
+    }
+
+    /**
+     * @brief Blocking query execution used for writing data
+     *
+     * Retries forever sleeping for 5 milliseconds between attempts.
+     */
+    ResultOrErrorType
+    writeSync(StatementType const& statement)
+    {
+        while (true)
+        {
+            if (auto res = handle_.get().execute(statement); res)
+            {
+                return res;
+            }
+            else
+            {
+                log_.warn() << "Cassandra sync write error, retrying: " << res.error();
+                std::this_thread::sleep_for(std::chrono::milliseconds(5));
+            }
+        }
+    }
+
+    /**
+     * @brief Blocking query execution used for writing data
+     *
+     * Retries forever sleeping for 5 milliseconds between attempts.
+     */
+    template <typename... Args>
+    ResultOrErrorType
+    writeSync(PreparedStatementType const& preparedStatement, Args&&... args)
+    {
+        return writeSync(preparedStatement.bind(std::forward<Args>(args)...));
+    }
+
+    /**
+     * @brief Non-blocking query execution used for writing data
+     *
+     * Retries forever with retry policy specified by @ref AsyncExecutor
+     *
+     * @param prepradeStatement Statement to prepare and execute
+     * @param args Args to bind to the prepared statement
+     * @throw DatabaseTimeout on timeout
+     */
+    template <typename... Args>
+    void
+    write(PreparedStatementType const& preparedStatement, Args&&... args)
+    {
+        auto statement = preparedStatement.bind(std::forward<Args>(args)...);
+        incrementOutstandingRequestCount();
+
+        // Note: lifetime is controlled by std::shared_from_this internally
+        AsyncExecutor<std::decay_t<decltype(statement)>, HandleType>::run(
+            ioc_, handle_, std::move(statement), [this](auto const&) { decrementOutstandingRequestCount(); });
+    }
+
+    /**
+     * @brief Non-blocking batched query execution used for writing data
+     *
+     * Retries forever with retry policy specified by @ref AsyncExecutor.
+     *
+     * @param statements Vector of statements to execute as a batch
+     * @throw DatabaseTimeout on timeout
+     */
+    void
+    write(std::vector<StatementType>&& statements)
+    {
+        if (statements.empty())
+            return;
+
+        incrementOutstandingRequestCount();
+
+        // Note: lifetime is controlled by std::shared_from_this internally
+        AsyncExecutor<std::decay_t<decltype(statements)>, HandleType>::run(
+            ioc_, handle_, std::move(statements), [this](auto const&) { decrementOutstandingRequestCount(); });
+    }
+
+    /**
+     * @brief Coroutine-based query execution used for reading data.
+     *
+     * Retries forever until successful or throws an exception on timeout.
+     *
+     * @param token Completion token (yield_context)
+     * @param prepradeStatement Statement to prepare and execute
+     * @param args Args to bind to the prepared statement
+     * @throw DatabaseTimeout on timeout
+     * @return ResultType or error wrapped in Expected
+     */
+    template <typename... Args>
+    [[maybe_unused]] ResultOrErrorType
+    read(CompletionTokenType token, PreparedStatementType const& preparedStatement, Args&&... args)
+    {
+        return read(token, preparedStatement.bind(std::forward<Args>(args)...));
+    }
+
+    /**
+     * @brief Coroutine-based query execution used for reading data.
+     *
+     * Retries forever until successful or throws an exception on timeout.
+     *
+     * @param token Completion token (yield_context)
+     * @param statements Statements to execute in a batch
+     * @throw DatabaseTimeout on timeout
+     * @return ResultType or error wrapped in Expected
+     */
+    [[maybe_unused]] ResultOrErrorType
+    read(CompletionTokenType token, std::vector<StatementType> const& statements)
+    {
+        auto handler = HandlerType{token};
+        auto result = AsyncResultType{handler};
+        auto const numStatements = statements.size();
+
+        // todo: perhaps use policy instead
+        while (true)
+        {
+            numReadRequestsOutstanding_ += numStatements;
+
+            auto const future = handle_.get().asyncExecute(statements, [handler](auto&&) mutable {
+                boost::asio::post(boost::asio::get_associated_executor(handler), [handler]() mutable {
+                    handler(boost::system::error_code{});
+                });
+            });
+
+            // suspend coroutine until completion handler is called
+            result.get();
+
+            numReadRequestsOutstanding_ -= numStatements;
+
+            // it's safe to call blocking get on future here as we already
+            // waited for the coroutine to resume above.
+            if (auto res = future.get(); res)
+            {
+                return res;
+            }
+            else
+            {
+                log_.error() << "Failed batch read in coroutine: " << res.error();
+                throwErrorIfNeeded(res.error());
+            }
+        }
+    }
+
+    /**
+     * @brief Coroutine-based query execution used for reading data.
+     *
+     * Retries forever until successful or throws an exception on timeout.
+     *
+     * @param token Completion token (yield_context)
+     * @param statement Statement to execute
+     * @throw DatabaseTimeout on timeout
+     * @return ResultType or error wrapped in Expected
+     */
+    [[maybe_unused]] ResultOrErrorType
+    read(CompletionTokenType token, StatementType const& statement)
+    {
+        auto handler = HandlerType{token};
+        auto result = AsyncResultType{handler};
+
+        // todo: perhaps use policy instead
+        while (true)
+        {
+            ++numReadRequestsOutstanding_;
+
+            auto const future = handle_.get().asyncExecute(statement, [handler](auto const&) mutable {
+                boost::asio::post(boost::asio::get_associated_executor(handler), [handler]() mutable {
+                    handler(boost::system::error_code{});
+                });
+            });
+
+            // suspend coroutine until completion handler is called
+            result.get();
+
+            --numReadRequestsOutstanding_;
+
+            // it's safe to call blocking get on future here as we already
+            // waited for the coroutine to resume above.
+            if (auto res = future.get(); res)
+            {
+                return res;
+            }
+            else
+            {
+                log_.error() << "Failed read in coroutine: " << res.error();
+                throwErrorIfNeeded(res.error());
+            }
+        }
+    }
+
+    /**
+     * @brief Coroutine-based query execution used for reading data.
+     *
+     * Attempts to execute each statement. On any error the whole vector will be
+     * discarded and exception will be thrown.
+     *
+     * @param token Completion token (yield_context)
+     * @param statements Statements to execute
+     * @throw DatabaseTimeout on db error
+     * @return Vector of results
+     */
+    std::vector<ResultType>
+    readEach(CompletionTokenType token, std::vector<StatementType> const& statements)
+    {
+        auto handler = HandlerType{token};
+        auto result = AsyncResultType{handler};
+
+        std::atomic_bool hadError = false;
+        std::atomic_int numOutstanding = statements.size();
+        numReadRequestsOutstanding_ += statements.size();
+
+        auto futures = std::vector<FutureWithCallbackType>{};
+        futures.reserve(numOutstanding);
+
+        // used as the handler for each async statement individually
+        auto executionHandler = [handler, &hadError, &numOutstanding](auto const& res) mutable {
+            if (not res)
+                hadError = true;
+
+            // when all async operations complete unblock the result
+            if (--numOutstanding == 0)
+                boost::asio::post(boost::asio::get_associated_executor(handler), [handler]() mutable {
+                    handler(boost::system::error_code{});
+                });
+        };
+
+        std::transform(
+            std::cbegin(statements),
+            std::cend(statements),
+            std::back_inserter(futures),
+            [this, &executionHandler](auto const& statement) {
+                return handle_.get().asyncExecute(statement, executionHandler);
+            });
+
+        // suspend coroutine until completion handler is called
+        result.get();
+
+        numReadRequestsOutstanding_ -= statements.size();
+
+        if (hadError)
+            throw DatabaseTimeout{};
+
+        std::vector<ResultType> results;
+        results.reserve(futures.size());
+
+        // it's safe to call blocking get on futures here as we already
+        // waited for the coroutine to resume above.
+        std::transform(
+            std::make_move_iterator(std::begin(futures)),
+            std::make_move_iterator(std::end(futures)),
+            std::back_inserter(results),
+            [](auto&& future) {
+                auto entry = future.get();
+                auto&& res = entry.value();
+                return std::move(res);
+            });
+
+        assert(futures.size() == statements.size());
+        assert(results.size() == statements.size());
+        return results;
+    }
+
+private:
+    void
+    incrementOutstandingRequestCount()
+    {
+        {
+            std::unique_lock<std::mutex> lck(throttleMutex_);
+            if (!canAddWriteRequest())
+            {
+                log_.trace() << "Max outstanding requests reached. "
+                             << "Waiting for other requests to finish";
+                throttleCv_.wait(lck, [this]() { return canAddWriteRequest(); });
+            }
+        }
+        ++numWriteRequestsOutstanding_;
+    }
+
+    void
+    decrementOutstandingRequestCount()
+    {
+        // sanity check
+        if (numWriteRequestsOutstanding_ == 0)
+        {
+            assert(false);
+            throw std::runtime_error("decrementing num outstanding below 0");
+        }
+        size_t cur = (--numWriteRequestsOutstanding_);
+        {
+            // mutex lock required to prevent race condition around spurious
+            // wakeup
+            std::lock_guard lck(throttleMutex_);
+            throttleCv_.notify_one();
+        }
+        if (cur == 0)
+        {
+            // mutex lock required to prevent race condition around spurious
+            // wakeup
+            std::lock_guard lck(syncMutex_);
+            syncCv_.notify_one();
+        }
+    }
+
+    bool
+    canAddWriteRequest() const
+    {
+        return numWriteRequestsOutstanding_ < maxWriteRequestsOutstanding_;
+    }
+
+    bool
+    finishedAllWriteRequests() const
+    {
+        return numWriteRequestsOutstanding_ == 0;
+    }
+
+    void
+    throwErrorIfNeeded(CassandraError err) const
+    {
+        if (err.isTimeout())
+            throw DatabaseTimeout();
+
+        if (err.isInvalidQuery())
+            throw std::runtime_error("Invalid query");
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Future.cpp

@@ -0,0 +1,102 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/Error.h>
+#include <backend/cassandra/impl/Future.h>
+#include <backend/cassandra/impl/Result.h>
+
+#include <exception>
+#include <vector>
+
+namespace {
+static constexpr auto futureDeleter = [](CassFuture* ptr) { cass_future_free(ptr); };
+}  // namespace
+
+namespace Backend::Cassandra::detail {
+
+/* implicit */ Future::Future(CassFuture* ptr) : ManagedObject{ptr, futureDeleter}
+{
+}
+
+MaybeError
+Future::await() const
+{
+    if (auto const rc = cass_future_error_code(*this); rc)
+    {
+        auto errMsg = [this](std::string const& label) {
+            char const* message;
+            std::size_t len;
+            cass_future_error_message(*this, &message, &len);
+            return label + ": " + std::string{message, len};
+        }(cass_error_desc(rc));
+        return Error{CassandraError{errMsg, rc}};
+    }
+    return {};
+}
+
+ResultOrError
+Future::get() const
+{
+    if (auto const rc = cass_future_error_code(*this); rc)
+    {
+        auto const errMsg = [this](std::string const& label) {
+            char const* message;
+            std::size_t len;
+            cass_future_error_message(*this, &message, &len);
+            return label + ": " + std::string{message, len};
+        }("future::get()");
+        return Error{CassandraError{errMsg, rc}};
+    }
+    else
+    {
+        return Result{cass_future_get_result(*this)};
+    }
+}
+
+void
+invokeHelper(CassFuture* ptr, void* cbPtr)
+{
+    // Note: can't use Future{ptr}.get() because double free will occur :/
+    auto* cb = static_cast<FutureWithCallback::fn_t*>(cbPtr);
+    if (auto const rc = cass_future_error_code(ptr); rc)
+    {
+        auto const errMsg = [&ptr](std::string const& label) {
+            char const* message;
+            std::size_t len;
+            cass_future_error_message(ptr, &message, &len);
+            return label + ": " + std::string{message, len};
+        }("invokeHelper");
+        (*cb)(Error{CassandraError{errMsg, rc}});
+    }
+    else
+    {
+        (*cb)(Result{cass_future_get_result(ptr)});
+    }
+}
+
+/* implicit */ FutureWithCallback::FutureWithCallback(CassFuture* ptr, fn_t&& cb)
+    : Future{ptr}, cb_{std::make_unique<fn_t>(std::move(cb))}
+{
+    // Instead of passing `this` as the userdata void*, we pass the address of
+    // the callback itself which will survive std::move of the
+    // FutureWithCallback parent. Not ideal but I have no better solution atm.
+    cass_future_set_callback(*this, &invokeHelper, cb_.get());
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Future.h

@@ -0,0 +1,58 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/ManagedObject.h>
+
+#include <cassandra.h>
+
+namespace Backend::Cassandra::detail {
+
+struct Future : public ManagedObject<CassFuture>
+{
+    /* implicit */ Future(CassFuture* ptr);
+
+    MaybeError
+    await() const;
+
+    ResultOrError
+    get() const;
+};
+
+void
+invokeHelper(CassFuture* ptr, void* self);
+
+class FutureWithCallback : public Future
+{
+public:
+    using fn_t = std::function<void(ResultOrError)>;
+    using fn_ptr_t = std::unique_ptr<fn_t>;
+
+    /* implicit */ FutureWithCallback(CassFuture* ptr, fn_t&& cb);
+    FutureWithCallback(FutureWithCallback const&) = delete;
+    FutureWithCallback(FutureWithCallback&&) = default;
+
+private:
+    /*! Wrapped in a unique_ptr so it can survive std::move :/ */
+    fn_ptr_t cb_;
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/ManagedObject.h

@@ -0,0 +1,47 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <memory>
+
+namespace Backend::Cassandra::detail {
+
+template <typename Managed>
+class ManagedObject
+{
+protected:
+    std::unique_ptr<Managed, void (*)(Managed*)> ptr_;
+
+public:
+    template <typename deleterCallable>
+    ManagedObject(Managed* rawPtr, deleterCallable deleter) : ptr_{rawPtr, deleter}
+    {
+        if (rawPtr == nullptr)
+            throw std::runtime_error("Could not create DB object - got nullptr");
+    }
+    ManagedObject(ManagedObject&&) = default;
+
+    operator Managed* const() const
+    {
+        return ptr_.get();
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Result.cpp

@@ -0,0 +1,69 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/impl/Result.h>
+
+namespace {
+static constexpr auto resultDeleter = [](CassResult const* ptr) { cass_result_free(ptr); };
+static constexpr auto resultIteratorDeleter = [](CassIterator* ptr) { cass_iterator_free(ptr); };
+}  // namespace
+
+namespace Backend::Cassandra::detail {
+
+/* implicit */ Result::Result(CassResult const* ptr) : ManagedObject{ptr, resultDeleter}
+{
+}
+
+[[nodiscard]] std::size_t
+Result::numRows() const
+{
+    return cass_result_row_count(*this);
+}
+
+[[nodiscard]] bool
+Result::hasRows() const
+{
+    return numRows() > 0;
+}
+
+/* implicit */ ResultIterator::ResultIterator(CassIterator* ptr)
+    : ManagedObject{ptr, resultIteratorDeleter}, hasMore_{cass_iterator_next(ptr)}
+{
+}
+
+[[nodiscard]] ResultIterator
+ResultIterator::fromResult(Result const& result)
+{
+    return {cass_iterator_from_result(result)};
+}
+
+[[maybe_unused]] bool
+ResultIterator::moveForward()
+{
+    hasMore_ = cass_iterator_next(*this);
+    return hasMore_;
+}
+
+[[nodiscard]] bool
+ResultIterator::hasMore() const
+{
+    return hasMore_;
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Result.h

@@ -0,0 +1,257 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/impl/ManagedObject.h>
+#include <backend/cassandra/impl/Tuple.h>
+#include <util/Expected.h>
+
+#include <ripple/basics/base_uint.h>
+#include <ripple/protocol/AccountID.h>
+#include <cassandra.h>
+
+#include <compare>
+#include <iterator>
+#include <tuple>
+
+namespace Backend::Cassandra::detail {
+
+template <typename>
+static constexpr bool unsupported_v = false;
+
+template <typename Type>
+inline Type
+extractColumn(CassRow const* row, std::size_t idx)
+{
+    using std::to_string;
+    Type output;
+
+    auto throwErrorIfNeeded = [](CassError rc, std::string_view label) {
+        if (rc != CASS_OK)
+        {
+            auto const tag = '[' + std::string{label} + ']';
+            throw std::logic_error(tag + ": " + cass_error_desc(rc));
+        }
+    };
+
+    using decayed_t = std::decay_t<Type>;
+    using uint_tuple_t = std::tuple<uint32_t, uint32_t>;
+    using uchar_vector_t = std::vector<unsigned char>;
+
+    if constexpr (std::is_same_v<decayed_t, ripple::uint256>)
+    {
+        cass_byte_t const* buf;
+        std::size_t bufSize;
+        auto const rc = cass_value_get_bytes(cass_row_get_column(row, idx), &buf, &bufSize);
+        throwErrorIfNeeded(rc, "Extract ripple::uint256");
+        output = ripple::uint256::fromVoid(buf);
+    }
+    else if constexpr (std::is_same_v<decayed_t, ripple::AccountID>)
+    {
+        cass_byte_t const* buf;
+        std::size_t bufSize;
+        auto const rc = cass_value_get_bytes(cass_row_get_column(row, idx), &buf, &bufSize);
+        throwErrorIfNeeded(rc, "Extract ripple::AccountID");
+        output = ripple::AccountID::fromVoid(buf);
+    }
+    else if constexpr (std::is_same_v<decayed_t, uchar_vector_t>)
+    {
+        cass_byte_t const* buf;
+        std::size_t bufSize;
+        auto const rc = cass_value_get_bytes(cass_row_get_column(row, idx), &buf, &bufSize);
+        throwErrorIfNeeded(rc, "Extract vector<unsigned char>");
+        output = uchar_vector_t{buf, buf + bufSize};
+    }
+    else if constexpr (std::is_same_v<decayed_t, uint_tuple_t>)
+    {
+        auto const* tuple = cass_row_get_column(row, idx);
+        output = TupleIterator::fromTuple(tuple).extract<uint32_t, uint32_t>();
+    }
+    else if constexpr (std::is_convertible_v<decayed_t, std::string>)
+    {
+        char const* value;
+        std::size_t len;
+        auto const rc = cass_value_get_string(cass_row_get_column(row, idx), &value, &len);
+        throwErrorIfNeeded(rc, "Extract string");
+        output = std::string{value, len};
+    }
+    else if constexpr (std::is_same_v<decayed_t, bool>)
+    {
+        cass_bool_t flag;
+        auto const rc = cass_value_get_bool(cass_row_get_column(row, idx), &flag);
+        throwErrorIfNeeded(rc, "Extract bool");
+        output = flag ? true : false;
+    }
+    // clio only uses bigint (int64_t) so we convert any incoming type
+    else if constexpr (std::is_convertible_v<decayed_t, int64_t>)
+    {
+        int64_t out;
+        auto const rc = cass_value_get_int64(cass_row_get_column(row, idx), &out);
+        throwErrorIfNeeded(rc, "Extract int64");
+        output = static_cast<decayed_t>(out);
+    }
+    else
+    {
+        // type not supported for extraction
+        static_assert(unsupported_v<decayed_t>);
+    }
+
+    return output;
+}
+
+struct Result : public ManagedObject<CassResult const>
+{
+    /* implicit */ Result(CassResult const* ptr);
+
+    [[nodiscard]] std::size_t
+    numRows() const;
+
+    [[nodiscard]] bool
+    hasRows() const;
+
+    template <typename... RowTypes>
+    std::optional<std::tuple<RowTypes...>>
+    get() const requires(std::tuple_size<std::tuple<RowTypes...>>{} > 1)
+    {
+        // row managed internally by cassandra driver, hence no ManagedObject.
+        auto const* row = cass_result_first_row(*this);
+        if (row == nullptr)
+            return std::nullopt;
+
+        std::size_t idx = 0;
+        auto advanceId = [&idx]() { return idx++; };
+
+        return std::make_optional<std::tuple<RowTypes...>>({extractColumn<RowTypes>(row, advanceId())...});
+    }
+
+    template <typename RowType>
+    std::optional<RowType>
+    get() const
+    {
+        // row managed internally by cassandra driver, hence no ManagedObject.
+        auto const* row = cass_result_first_row(*this);
+        if (row == nullptr)
+            return std::nullopt;
+        return std::make_optional<RowType>(extractColumn<RowType>(row, 0));
+    }
+};
+
+class ResultIterator : public ManagedObject<CassIterator>
+{
+    bool hasMore_ = false;
+
+public:
+    /* implicit */ ResultIterator(CassIterator* ptr);
+
+    [[nodiscard]] static ResultIterator
+    fromResult(Result const& result);
+
+    [[maybe_unused]] bool
+    moveForward();
+
+    [[nodiscard]] bool
+    hasMore() const;
+
+    template <typename... RowTypes>
+    std::tuple<RowTypes...>
+    extractCurrentRow() const
+    {
+        // note: row is invalidated on each iteration.
+        // managed internally by cassandra driver, hence no ManagedObject.
+        auto const* row = cass_iterator_get_row(*this);
+
+        std::size_t idx = 0;
+        auto advanceId = [&idx]() { return idx++; };
+
+        return {extractColumn<RowTypes>(row, advanceId())...};
+    }
+};
+
+template <typename... Types>
+class ResultExtractor
+{
+    std::reference_wrapper<Result const> ref_;
+
+public:
+    struct Sentinel
+    {
+    };
+
+    struct Iterator
+    {
+        using iterator_category = std::input_iterator_tag;
+        using difference_type = std::size_t;  // rows count
+        using value_type = std::tuple<Types...>;
+
+        /* implicit */ Iterator(ResultIterator iterator) : iterator_{std::move(iterator)}
+        {
+        }
+
+        Iterator(Iterator const&) = delete;
+        Iterator&
+        operator=(Iterator const&) = delete;
+
+        value_type
+        operator*() const
+        {
+            return iterator_.extractCurrentRow<Types...>();
+        }
+
+        value_type
+        operator->()
+        {
+            return iterator_.extractCurrentRow<Types...>();
+        }
+
+        Iterator&
+        operator++()
+        {
+            iterator_.moveForward();
+            return *this;
+        }
+
+        bool
+        operator==(Sentinel const&) const
+        {
+            return not iterator_.hasMore();
+        }
+
+    private:
+        ResultIterator iterator_;
+    };
+
+    ResultExtractor(Result const& result) : ref_{std::cref(result)}
+    {
+    }
+
+    Iterator
+    begin()
+    {
+        return ResultIterator::fromResult(ref_);
+    }
+
+    Sentinel
+    end()
+    {
+        return {};
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/RetryPolicy.h

@@ -0,0 +1,94 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Handle.h>
+#include <backend/cassandra/Types.h>
+#include <log/Logger.h>
+#include <util/Expected.h>
+
+#include <boost/asio.hpp>
+
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+
+namespace Backend::Cassandra::detail {
+
+/**
+ * @brief A retry policy that employs exponential backoff
+ */
+class ExponentialBackoffRetryPolicy
+{
+    clio::Logger log_{"Backend"};
+
+    boost::asio::steady_timer timer_;
+    uint32_t attempt_ = 0u;
+
+public:
+    /**
+     * @brief Create a new retry policy instance with the io_context provided
+     */
+    ExponentialBackoffRetryPolicy(boost::asio::io_context& ioc) : timer_{ioc}
+    {
+    }
+
+    /**
+     * @brief Computes next retry delay and returns true unconditionally
+     *
+     * @param err The cassandra error that triggered the retry
+     */
+    [[nodiscard]] bool
+    shouldRetry([[maybe_unused]] CassandraError err)
+    {
+        auto const delay = calculateDelay(attempt_);
+        log_.error() << "Cassandra write error: " << err << ", current retries " << attempt_ << ", retrying in "
+                     << delay.count() << " milliseconds";
+
+        return true;  // keep retrying forever
+    }
+
+    /**
+     * @brief Schedules next retry
+     *
+     * @param fn The callable to execute
+     */
+    template <typename Fn>
+    void
+    retry(Fn&& fn)
+    {
+        timer_.expires_after(calculateDelay(attempt_++));
+        timer_.async_wait([fn = std::forward<Fn>(fn)]([[maybe_unused]] const auto& err) {
+            // todo: deal with cancellation (thru err)
+            fn();
+        });
+    }
+
+    /**
+     * @brief Calculates the wait time before attempting another retry
+     */
+    std::chrono::milliseconds
+    calculateDelay(uint32_t attempt)
+    {
+        return std::chrono::milliseconds{lround(std::pow(2, std::min(10u, attempt)))};
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Session.h

@@ -0,0 +1,38 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/impl/ManagedObject.h>
+
+#include <cassandra.h>
+
+namespace Backend::Cassandra::detail {
+
+class Session : public ManagedObject<CassSession>
+{
+    static constexpr auto deleter = [](CassSession* ptr) { cass_session_free(ptr); };
+
+public:
+    Session() : ManagedObject{cass_session_new(), deleter}
+    {
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/SslContext.cpp

@@ -0,0 +1,37 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/impl/SslContext.h>
+
+namespace {
+static constexpr auto contextDeleter = [](CassSsl* ptr) { cass_ssl_free(ptr); };
+}  // namespace
+
+namespace Backend::Cassandra::detail {
+
+SslContext::SslContext(std::string const& certificate) : ManagedObject{cass_ssl_new(), contextDeleter}
+{
+    cass_ssl_set_verify_flags(*this, CASS_SSL_VERIFY_NONE);
+    if (auto const rc = cass_ssl_add_trusted_cert(*this, certificate.c_str()); rc != CASS_OK)
+    {
+        throw std::runtime_error(std::string{"Error setting Cassandra SSL Context: "} + cass_error_desc(rc));
+    }
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/SslContext.h

@@ -0,0 +1,35 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/impl/ManagedObject.h>
+
+#include <cassandra.h>
+
+#include <string>
+
+namespace Backend::Cassandra::detail {
+
+struct SslContext : public ManagedObject<CassSsl>
+{
+    explicit SslContext(std::string const& certificate);
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Statement.h

@@ -0,0 +1,164 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/Types.h>
+#include <backend/cassandra/impl/ManagedObject.h>
+#include <backend/cassandra/impl/Tuple.h>
+#include <util/Expected.h>
+
+#include <ripple/basics/base_uint.h>
+#include <ripple/protocol/STAccount.h>
+#include <cassandra.h>
+#include <fmt/core.h>
+
+#include <chrono>
+#include <compare>
+#include <iterator>
+
+namespace Backend::Cassandra::detail {
+
+class Statement : public ManagedObject<CassStatement>
+{
+    static constexpr auto deleter = [](CassStatement* ptr) { cass_statement_free(ptr); };
+
+    template <typename>
+    static constexpr bool unsupported_v = false;
+
+public:
+    /**
+     * @brief Construct a new statement with optionally provided arguments
+     *
+     * Note: it's up to the user to make sure the bound parameters match
+     * the format of the query (e.g. amount of '?' matches count of args).
+     */
+    template <typename... Args>
+    explicit Statement(std::string_view query, Args&&... args)
+        : ManagedObject{cass_statement_new(query.data(), sizeof...(args)), deleter}
+    {
+        cass_statement_set_consistency(*this, CASS_CONSISTENCY_QUORUM);
+        cass_statement_set_is_idempotent(*this, cass_true);
+        bind<Args...>(std::forward<Args>(args)...);
+    }
+
+    /* implicit */ Statement(CassStatement* ptr) : ManagedObject{ptr, deleter}
+    {
+        cass_statement_set_consistency(*this, CASS_CONSISTENCY_QUORUM);
+        cass_statement_set_is_idempotent(*this, cass_true);
+    }
+
+    Statement(Statement&&) = default;
+
+    template <typename... Args>
+    void
+    bind(Args&&... args) const
+    {
+        std::size_t idx = 0;
+        (this->bindAt<Args>(idx++, std::forward<Args>(args)), ...);
+    }
+
+    template <typename Type>
+    void
+    bindAt(std::size_t const idx, Type&& value) const
+    {
+        using std::to_string;
+        auto throwErrorIfNeeded = [idx](CassError rc, std::string_view label) {
+            if (rc != CASS_OK)
+                throw std::logic_error(fmt::format("[{}] at idx {}: {}", label, idx, cass_error_desc(rc)));
+        };
+
+        auto bindBytes = [this, idx](auto const* data, size_t size) {
+            return cass_statement_bind_bytes(*this, idx, static_cast<cass_byte_t const*>(data), size);
+        };
+
+        using decayed_t = std::decay_t<Type>;
+        using uchar_vec_t = std::vector<unsigned char>;
+        using uint_tuple_t = std::tuple<uint32_t, uint32_t>;
+
+        if constexpr (std::is_same_v<decayed_t, ripple::uint256>)
+        {
+            auto const rc = bindBytes(value.data(), value.size());
+            throwErrorIfNeeded(rc, "Bind ripple::uint256");
+        }
+        else if constexpr (std::is_same_v<decayed_t, ripple::AccountID>)
+        {
+            auto const rc = bindBytes(value.data(), value.size());
+            throwErrorIfNeeded(rc, "Bind ripple::AccountID");
+        }
+        else if constexpr (std::is_same_v<decayed_t, uchar_vec_t>)
+        {
+            auto const rc = bindBytes(value.data(), value.size());
+            throwErrorIfNeeded(rc, "Bind vector<unsigned char>");
+        }
+        else if constexpr (std::is_convertible_v<decayed_t, std::string>)
+        {
+            // reinterpret_cast is needed here :'(
+            auto const rc = bindBytes(reinterpret_cast<unsigned char const*>(value.data()), value.size());
+            throwErrorIfNeeded(rc, "Bind string (as bytes)");
+        }
+        else if constexpr (std::is_same_v<decayed_t, uint_tuple_t>)
+        {
+            auto const rc = cass_statement_bind_tuple(*this, idx, Tuple{std::move(value)});
+            throwErrorIfNeeded(rc, "Bind tuple<uint32, uint32>");
+        }
+        else if constexpr (std::is_same_v<decayed_t, bool>)
+        {
+            auto const rc = cass_statement_bind_bool(*this, idx, value ? cass_true : cass_false);
+            throwErrorIfNeeded(rc, "Bind bool");
+        }
+        else if constexpr (std::is_same_v<decayed_t, Limit>)
+        {
+            auto const rc = cass_statement_bind_int32(*this, idx, value.limit);
+            throwErrorIfNeeded(rc, "Bind limit (int32)");
+        }
+        // clio only uses bigint (int64_t) so we convert any incoming type
+        else if constexpr (std::is_convertible_v<decayed_t, int64_t>)
+        {
+            auto const rc = cass_statement_bind_int64(*this, idx, value);
+            throwErrorIfNeeded(rc, "Bind int64");
+        }
+        else
+        {
+            // type not supported for binding
+            static_assert(unsupported_v<decayed_t>);
+        }
+    }
+};
+
+class PreparedStatement : public ManagedObject<CassPrepared const>
+{
+    static constexpr auto deleter = [](CassPrepared const* ptr) { cass_prepared_free(ptr); };
+
+public:
+    /* implicit */ PreparedStatement(CassPrepared const* ptr) : ManagedObject{ptr, deleter}
+    {
+    }
+
+    template <typename... Args>
+    Statement
+    bind(Args&&... args) const
+    {
+        Statement statement = cass_prepared_bind(*this);
+        statement.bind<Args...>(std::forward<Args>(args)...);
+        return statement;
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Tuple.cpp

@@ -0,0 +1,43 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <backend/cassandra/impl/Tuple.h>
+
+namespace {
+static constexpr auto tupleDeleter = [](CassTuple* ptr) { cass_tuple_free(ptr); };
+static constexpr auto tupleIteratorDeleter = [](CassIterator* ptr) { cass_iterator_free(ptr); };
+}  // namespace
+
+namespace Backend::Cassandra::detail {
+
+/* implicit */ Tuple::Tuple(CassTuple* ptr) : ManagedObject{ptr, tupleDeleter}
+{
+}
+
+/* implicit */ TupleIterator::TupleIterator(CassIterator* ptr) : ManagedObject{ptr, tupleIteratorDeleter}
+{
+}
+
+[[nodiscard]] TupleIterator
+TupleIterator::fromTuple(CassValue const* value)
+{
+    return {cass_iterator_from_tuple(value)};
+}
+
+}  // namespace Backend::Cassandra::detail

src/backend/cassandra/impl/Tuple.h

@@ -0,0 +1,149 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/cassandra/impl/ManagedObject.h>
+
+#include <cassandra.h>
+
+#include <functional>
+#include <string>
+#include <string_view>
+#include <tuple>
+
+namespace Backend::Cassandra::detail {
+
+class Tuple : public ManagedObject<CassTuple>
+{
+    static constexpr auto deleter = [](CassTuple* ptr) { cass_tuple_free(ptr); };
+
+    template <typename>
+    static constexpr bool unsupported_v = false;
+
+public:
+    /* implicit */ Tuple(CassTuple* ptr);
+
+    template <typename... Types>
+    explicit Tuple(std::tuple<Types...>&& value)
+        : ManagedObject{cass_tuple_new(std::tuple_size<std::tuple<Types...>>{}), deleter}
+    {
+        std::apply(std::bind_front(&Tuple::bind<Types...>, this), std::move(value));
+    }
+
+    template <typename... Args>
+    void
+    bind(Args&&... args) const
+    {
+        std::size_t idx = 0;
+        (this->bindAt<Args>(idx++, std::forward<Args>(args)), ...);
+    }
+
+    template <typename Type>
+    void
+    bindAt(std::size_t const idx, Type&& value) const
+    {
+        using std::to_string;
+        auto throwErrorIfNeeded = [idx](CassError rc, std::string_view label) {
+            if (rc != CASS_OK)
+            {
+                auto const tag = '[' + std::string{label} + ']';
+                throw std::logic_error(tag + " at idx " + to_string(idx) + ": " + cass_error_desc(rc));
+            }
+        };
+
+        using decayed_t = std::decay_t<Type>;
+
+        if constexpr (std::is_same_v<decayed_t, bool>)
+        {
+            auto const rc = cass_tuple_set_bool(*this, idx, value ? cass_true : cass_false);
+            throwErrorIfNeeded(rc, "Bind bool");
+        }
+        // clio only uses bigint (int64_t) so we convert any incoming type
+        else if constexpr (std::is_convertible_v<decayed_t, int64_t>)
+        {
+            auto const rc = cass_tuple_set_int64(*this, idx, value);
+            throwErrorIfNeeded(rc, "Bind int64");
+        }
+        else
+        {
+            // type not supported for binding
+            static_assert(unsupported_v<decayed_t>);
+        }
+    }
+};
+
+class TupleIterator : public ManagedObject<CassIterator>
+{
+    template <typename>
+    static constexpr bool unsupported_v = false;
+
+public:
+    /* implicit */ TupleIterator(CassIterator* ptr);
+
+    [[nodiscard]] static TupleIterator
+    fromTuple(CassValue const* value);
+
+    template <typename... Types>
+    [[nodiscard]] std::tuple<Types...>
+    extract() const
+    {
+        return {extractNext<Types>()...};
+    }
+
+private:
+    template <typename Type>
+    Type
+    extractNext() const
+    {
+        using std::to_string;
+        Type output;
+
+        if (not cass_iterator_next(*this))
+            throw std::logic_error("Could not extract next value from tuple iterator");
+
+        auto throwErrorIfNeeded = [](CassError rc, std::string_view label) {
+            if (rc != CASS_OK)
+            {
+                auto const tag = '[' + std::string{label} + ']';
+                throw std::logic_error(tag + ": " + cass_error_desc(rc));
+            }
+        };
+
+        using decayed_t = std::decay_t<Type>;
+
+        // clio only uses bigint (int64_t) so we convert any incoming type
+        if constexpr (std::is_convertible_v<decayed_t, int64_t>)
+        {
+            int64_t out;
+            auto const rc = cass_value_get_int64(cass_iterator_get_value(*this), &out);
+            throwErrorIfNeeded(rc, "Extract int64 from tuple");
+            output = static_cast<decayed_t>(out);
+        }
+        else
+        {
+            // type not supported for extraction
+            static_assert(unsupported_v<decayed_t>);
+        }
+
+        return output;
+    }
+};
+
+}  // namespace Backend::Cassandra::detail

src/config/Config.cpp

@@ -0,0 +1,183 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <config/Config.h>
+#include <log/Logger.h>
+
+#include <fstream>
+
+namespace clio {
+
+// Note: `store_(store)` MUST use `()` instead of `{}` otherwise gcc
+// picks `initializer_list` constructor and anything passed becomes an
+// array :-D
+Config::Config(boost::json::value store) : store_(std::move(store))
+{
+}
+
+Config::operator bool() const noexcept
+{
+    return not store_.is_null();
+}
+
+bool
+Config::contains(key_type key) const
+{
+    return lookup(key).has_value();
+}
+
+std::optional<boost::json::value>
+Config::lookup(key_type key) const
+{
+    if (store_.is_null())
+        return std::nullopt;
+
+    std::reference_wrapper<boost::json::value const> cur = std::cref(store_);
+    auto hasBrokenPath = false;
+    auto tokenized = detail::Tokenizer<key_type, Separator>{key};
+    std::string subkey{};
+
+    auto maybeSection = tokenized.next();
+    while (maybeSection.has_value())
+    {
+        auto section = maybeSection.value();
+        subkey += section;
+
+        if (not hasBrokenPath)
+        {
+            if (not cur.get().is_object())
+                throw detail::StoreException("Not an object at '" + subkey + "'");
+            if (not cur.get().as_object().contains(section))
+                hasBrokenPath = true;
+            else
+                cur = std::cref(cur.get().as_object().at(section));
+        }
+
+        subkey += Separator;
+        maybeSection = tokenized.next();
+    }
+
+    if (hasBrokenPath)
+        return std::nullopt;
+    return std::make_optional(cur);
+}
+
+std::optional<Config::array_type>
+Config::maybeArray(key_type key) const
+{
+    try
+    {
+        auto maybe_arr = lookup(key);
+        if (maybe_arr && maybe_arr->is_array())
+        {
+            auto& arr = maybe_arr->as_array();
+            array_type out;
+            out.reserve(arr.size());
+
+            std::transform(std::begin(arr), std::end(arr), std::back_inserter(out), [](auto&& element) {
+                return Config{std::move(element)};
+            });
+            return std::make_optional<array_type>(std::move(out));
+        }
+    }
+    catch (detail::StoreException const&)
+    {
+        // ignore store error, but rethrow key errors
+    }
+
+    return std::nullopt;
+}
+
+Config::array_type
+Config::array(key_type key) const
+{
+    if (auto maybe_arr = maybeArray(key); maybe_arr)
+        return maybe_arr.value();
+    throw std::logic_error("No array found at '" + key + "'");
+}
+
+Config::array_type
+Config::arrayOr(key_type key, array_type fallback) const
+{
+    if (auto maybe_arr = maybeArray(key); maybe_arr)
+        return maybe_arr.value();
+    return fallback;
+}
+
+Config::array_type
+Config::arrayOrThrow(key_type key, std::string_view err) const
+{
+    try
+    {
+        return maybeArray(key).value();
+    }
+    catch (std::exception const&)
+    {
+        throw std::runtime_error(err.data());
+    }
+}
+
+Config
+Config::section(key_type key) const
+{
+    auto maybe_element = lookup(key);
+    if (maybe_element && maybe_element->is_object())
+        return Config{std::move(*maybe_element)};
+    throw std::logic_error("No section found at '" + key + "'");
+}
+
+Config::array_type
+Config::array() const
+{
+    if (not store_.is_array())
+        throw std::logic_error("_self_ is not an array");
+
+    array_type out;
+    auto const& arr = store_.as_array();
+    out.reserve(arr.size());
+
+    std::transform(
+        std::cbegin(arr), std::cend(arr), std::back_inserter(out), [](auto const& element) { return Config{element}; });
+    return out;
+}
+
+Config
+ConfigReader::open(std::filesystem::path path)
+{
+    try
+    {
+        std::ifstream in(path, std::ios::in | std::ios::binary);
+        if (in)
+        {
+            std::stringstream contents;
+            contents << in.rdbuf();
+            auto opts = boost::json::parse_options{};
+            opts.allow_comments = true;
+            return Config{boost::json::parse(contents.str(), {}, opts)};
+        }
+    }
+    catch (std::exception const& e)
+    {
+        LogService::error() << "Could not read configuration file from '" << path.string() << "': " << e.what();
+    }
+
+    return Config{};
+}
+
+}  // namespace clio

src/config/Config.h

@@ -0,0 +1,401 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <config/detail/Helpers.h>
+
+#include <boost/json.hpp>
+#include <filesystem>
+#include <optional>
+#include <string>
+#include <string_view>
+
+namespace clio {
+
+/**
+ * @brief Convenience wrapper to query a JSON configuration file.
+ *
+ * Any custom data type can be supported by implementing the right `tag_invoke`
+ * for `boost::json::value_to`.
+ */
+class Config final
+{
+    boost::json::value store_;
+    static constexpr char Separator = '.';
+
+public:
+    using key_type = std::string;           /*! The type of key used */
+    using array_type = std::vector<Config>; /*! The type of array used */
+    using write_cursor_type = std::pair<std::optional<std::reference_wrapper<boost::json::value>>, key_type>;
+
+    /**
+     * @brief Construct a new Config object.
+     * @param store boost::json::value that backs this instance
+     */
+    explicit Config(boost::json::value store = {});
+
+    //
+    // Querying the store
+    //
+
+    /**
+     * @brief Checks whether underlying store is not null.
+     *
+     * @return true If the store is null
+     * @return false If the store is not null
+     */
+    operator bool() const noexcept;
+
+    /**
+     * @brief Checks whether something exists under given key.
+     *
+     * @param key The key to check
+     * @return true If something exists under key
+     * @return false If nothing exists under key
+     * @throws std::logic_error If the key is of invalid format
+     */
+    [[nodiscard]] bool
+    contains(key_type key) const;
+
+    //
+    // Key value access
+    //
+
+    /**
+     * @brief Interface for fetching values by key that returns std::optional.
+     *
+     * Will attempt to fetch the value under the desired key. If the value
+     * exists and can be represented by the desired type Result then it will be
+     * returned wrapped in an optional. If the value exists but the conversion
+     * to Result is not possible - a runtime_error will be thrown. If the value
+     * does not exist under the specified key - std::nullopt is returned.
+     *
+     * @tparam Result The desired return type
+     * @param key The key to check
+     * @return std::optional<Result> Optional value of desired type
+     * @throws std::logic_error Thrown if conversion to Result is not possible
+     * or key is of invalid format
+     */
+    template <typename Result>
+    [[nodiscard]] std::optional<Result>
+    maybeValue(key_type key) const
+    {
+        auto maybe_element = lookup(key);
+        if (maybe_element)
+            return std::make_optional<Result>(checkedAs<Result>(key, *maybe_element));
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Interface for fetching values by key.
+     *
+     * Will attempt to fetch the value under the desired key. If the value
+     * exists and can be represented by the desired type Result then it will be
+     * returned. If the value exists but the conversion
+     * to Result is not possible OR the value does not exist - a logic_error
+     * will be thrown.
+     *
+     * @tparam Result The desired return type
+     * @param key The key to check
+     * @return Result Value of desired type
+     * @throws std::logic_error Thrown if conversion to Result is not
+     * possible, value does not exist under specified key path or the key is of
+     * invalid format
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    value(key_type key) const
+    {
+        return maybeValue<Result>(key).value();
+    }
+
+    /**
+     * @brief Interface for fetching values by key with fallback.
+     *
+     * Will attempt to fetch the value under the desired key. If the value
+     * exists and can be represented by the desired type Result then it will be
+     * returned. If the value exists but the conversion
+     * to Result is not possible - a logic_error will be thrown. If the value
+     * does not exist under the specified key - user specified fallback is
+     * returned.
+     *
+     * @tparam Result The desired return type
+     * @param key The key to check
+     * @param fallback The fallback value
+     * @return Result Value of desired type
+     * @throws std::logic_error Thrown if conversion to Result is not possible
+     * or the key is of invalid format
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    valueOr(key_type key, Result fallback) const
+    {
+        try
+        {
+            return maybeValue<Result>(key).value_or(fallback);
+        }
+        catch (detail::StoreException const&)
+        {
+            return fallback;
+        }
+    }
+
+    /**
+     * @brief Interface for fetching values by key with custom error handling.
+     *
+     * Will attempt to fetch the value under the desired key. If the value
+     * exists and can be represented by the desired type Result then it will be
+     * returned. If the value exists but the conversion
+     * to Result is not possible OR the value does not exist - a runtime_error
+     * will be thrown with the user specified message.
+     *
+     * @tparam Result The desired return type
+     * @param key The key to check
+     * @param err The custom error message
+     * @return Result Value of desired type
+     * @throws std::runtime_error Thrown if conversion to Result is not possible
+     * or value does not exist under key
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    valueOrThrow(key_type key, std::string_view err) const
+    {
+        try
+        {
+            return maybeValue<Result>(key).value();
+        }
+        catch (std::exception const&)
+        {
+            throw std::runtime_error(err.data());
+        }
+    }
+
+    /**
+     * @brief Interface for fetching an array by key that returns std::optional.
+     *
+     * Will attempt to fetch an array under the desired key. If the array
+     * exists then it will be
+     * returned wrapped in an optional. If the array does not exist under the
+     * specified key - std::nullopt is returned.
+     *
+     * @param key The key to check
+     * @return std::optional<array_type> Optional array
+     * @throws std::logic_error Thrown if the key is of invalid format
+     */
+    [[nodiscard]] std::optional<array_type>
+    maybeArray(key_type key) const;
+
+    /**
+     * @brief Interface for fetching an array by key.
+     *
+     * Will attempt to fetch an array under the desired key. If the array
+     * exists then it will be
+     * returned. If the array does not exist under the
+     * specified key an std::logic_error is thrown.
+     *
+     * @param key The key to check
+     * @return array_type The array
+     * @throws std::logic_error Thrown if there is no array under the desired
+     * key or the key is of invalid format
+     */
+    [[nodiscard]] array_type
+    array(key_type key) const;
+
+    /**
+     * @brief Interface for fetching an array by key with fallback.
+     *
+     * Will attempt to fetch an array under the desired key. If the array
+     * exists then it will be returned.
+     * If the array does not exist or another type is stored under the desired
+     * key - user specified fallback is returned.
+     *
+     * @param key The key to check
+     * @param fallback The fallback array
+     * @return array_type The array
+     * @throws std::logic_error Thrown if the key is of invalid format
+     */
+    [[nodiscard]] array_type
+    arrayOr(key_type key, array_type fallback) const;
+
+    /**
+     * @brief Interface for fetching an array by key with custom error handling.
+     *
+     * Will attempt to fetch an array under the desired key. If the array
+     * exists then it will be returned.
+     * If the array does not exist or another type is stored under the desired
+     * key - std::runtime_error is thrown with the user specified error message.
+     *
+     * @param key The key to check
+     * @param err The custom error message
+     * @return array_type The array
+     * @throws std::runtime_error Thrown if there is no array under the desired
+     * key
+     */
+    [[nodiscard]] array_type
+    arrayOrThrow(key_type key, std::string_view err) const;
+
+    /**
+     * @brief Interface for fetching a sub section by key.
+     *
+     * Will attempt to fetch an entire section under the desired key and return
+     * it as a Config instance. If the section does not exist or another type is
+     * stored under the desired key - std::logic_error is thrown.
+     *
+     * @param key The key to check
+     * @return Config Section represented as a separate instance of Config
+     * @throws std::logic_error Thrown if there is no section under the
+     * desired key or the key is of invalid format
+     */
+    [[nodiscard]] Config
+    section(key_type key) const;
+
+    //
+    // Direct self-value access
+    //
+
+    /**
+     * @brief Interface for reading the value directly referred to by the
+     * instance. Wraps as std::optional.
+     *
+     * See @ref maybeValue(key_type) const for how this works.
+     */
+    template <typename Result>
+    [[nodiscard]] std::optional<Result>
+    maybeValue() const
+    {
+        if (store_.is_null())
+            return std::nullopt;
+        return std::make_optional<Result>(checkedAs<Result>("_self_", store_));
+    }
+
+    /**
+     * @brief Interface for reading the value directly referred to by the
+     * instance.
+     *
+     * See @ref value(key_type) const for how this works.
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    value() const
+    {
+        return maybeValue<Result>().value();
+    }
+
+    /**
+     * @brief Interface for reading the value directly referred to by the
+     * instance with user-specified fallback.
+     *
+     * See @ref valueOr(key_type, Result) const for how this works.
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    valueOr(Result fallback) const
+    {
+        return maybeValue<Result>().valueOr(fallback);
+    }
+
+    /**
+     * @brief Interface for reading the value directly referred to by the
+     * instance with user-specified error message.
+     *
+     * See @ref valueOrThrow(key_type, std::string_view) const for how this
+     * works.
+     */
+    template <typename Result>
+    [[nodiscard]] Result
+    valueOrThrow(std::string_view err) const
+    {
+        try
+        {
+            return maybeValue<Result>().value();
+        }
+        catch (std::exception const&)
+        {
+            throw std::runtime_error(err.data());
+        }
+    }
+
+    /**
+     * @brief Interface for reading the array directly referred to by the
+     * instance.
+     *
+     * See @ref array(key_type) const for how this works.
+     */
+    [[nodiscard]] array_type
+    array() const;
+
+private:
+    template <typename Return>
+    [[nodiscard]] Return
+    checkedAs(key_type key, boost::json::value const& value) const
+    {
+        using boost::json::value_to;
+
+        auto has_error = false;
+        if constexpr (std::is_same_v<Return, bool>)
+        {
+            if (not value.is_bool())
+                has_error = true;
+        }
+        else if constexpr (std::is_same_v<Return, std::string>)
+        {
+            if (not value.is_string())
+                has_error = true;
+        }
+        else if constexpr (std::is_same_v<Return, double>)
+        {
+            if (not value.is_number())
+                has_error = true;
+        }
+        else if constexpr (std::is_convertible_v<Return, uint64_t> || std::is_convertible_v<Return, int64_t>)
+        {
+            if (not value.is_int64() && not value.is_uint64())
+                has_error = true;
+        }
+
+        if (has_error)
+            throw std::runtime_error(
+                "Type for key '" + key + "' is '" + std::string{to_string(value.kind())} + "' in JSON but requested '" +
+                detail::typeName<Return>() + "'");
+
+        return value_to<Return>(value);
+    }
+
+    std::optional<boost::json::value>
+    lookup(key_type key) const;
+
+    write_cursor_type
+    lookupForWrite(key_type key);
+};
+
+/**
+ * @brief Simple configuration file reader.
+ *
+ * Reads the JSON file under specified path and creates a @ref Config object
+ * from its contents.
+ */
+class ConfigReader final
+{
+public:
+    static Config
+    open(std::filesystem::path path);
+};
+
+}  // namespace clio

src/config/detail/Helpers.h

@@ -0,0 +1,164 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <optional>
+#include <queue>
+#include <stdexcept>
+#include <string>
+
+namespace clio::detail {
+
+/**
+ * @brief Thrown when a KeyPath related error occurs
+ */
+struct KeyException : public ::std::logic_error
+{
+    KeyException(::std::string msg) : ::std::logic_error{msg}
+    {
+    }
+};
+
+/**
+ * @brief Thrown when a Store (config's storage) related error occurs.
+ */
+struct StoreException : public ::std::logic_error
+{
+    StoreException(::std::string msg) : ::std::logic_error{msg}
+    {
+    }
+};
+
+/**
+ * @brief Simple string tokenizer. Used by @ref Config.
+ *
+ * @tparam KeyType The type of key to use
+ * @tparam Separator The separator character
+ */
+template <typename KeyType, char Separator>
+class Tokenizer final
+{
+    using opt_key_t = std::optional<KeyType>;
+    KeyType key_;
+    KeyType token_{};
+    std::queue<KeyType> tokens_{};
+
+public:
+    explicit Tokenizer(KeyType key) : key_{key}
+    {
+        if (key.empty())
+            throw KeyException("Empty key");
+
+        for (auto const& c : key)
+        {
+            if (c == Separator)
+                saveToken();
+            else
+                token_ += c;
+        }
+
+        saveToken();
+    }
+
+    [[nodiscard]] opt_key_t
+    next()
+    {
+        if (tokens_.empty())
+            return std::nullopt;
+        auto token = tokens_.front();
+        tokens_.pop();
+        return std::make_optional(std::move(token));
+    }
+
+private:
+    void
+    saveToken()
+    {
+        if (token_.empty())
+            throw KeyException("Empty token in key '" + key_ + "'.");
+        tokens_.push(std::move(token_));
+        token_ = {};
+    }
+};
+
+template <typename T>
+static constexpr const char*
+typeName()
+{
+    return typeid(T).name();
+}
+
+template <>
+constexpr const char*
+typeName<uint64_t>()
+{
+    return "uint64_t";
+}
+
+template <>
+constexpr const char*
+typeName<int64_t>()
+{
+    return "int64_t";
+}
+
+template <>
+constexpr const char*
+typeName<uint32_t>()
+{
+    return "uint32_t";
+}
+
+template <>
+constexpr const char*
+typeName<int32_t>()
+{
+    return "int32_t";
+}
+
+template <>
+constexpr const char*
+typeName<bool>()
+{
+    return "bool";
+}
+
+template <>
+constexpr const char*
+typeName<std::string>()
+{
+    return "std::string";
+}
+
+template <>
+constexpr const char*
+typeName<const char*>()
+{
+    return "const char*";
+}
+
+template <>
+constexpr const char*
+typeName<double>()
+{
+    return "double";
+}
+
+};  // namespace clio::detail

src/etl/ETLHelpers.h

@@ -1,5 +1,24 @@
-#ifndef RIPPLE_APP_REPORTING_ETLHELPERS_H_INCLUDED
-#define RIPPLE_APP_REPORTING_ETLHELPERS_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
 #include <ripple/basics/base_uint.h>
 #include <condition_variable>
 #include <mutex>
@@ -23,8 +42,6 @@ class NetworkValidatedLedgers
 
     std::condition_variable cv_;
 
-    bool stopping_ = false;
-
 public:
     static std::shared_ptr<NetworkValidatedLedgers>
     make_ValidatedLedgers()
@@ -60,14 +77,10 @@ public:
     /// @return true if sequence was validated, false otherwise
     /// a return value of false means the datastructure has been stopped
     bool
-    waitUntilValidatedByNetwork(
-        uint32_t sequence,
-        std::optional<uint32_t> maxWaitMs = {})
+    waitUntilValidatedByNetwork(uint32_t sequence, std::optional<uint32_t> maxWaitMs = {})
     {
         std::unique_lock lck(m_);
-        auto pred = [sequence, this]() -> bool {
-            return (max_ && sequence <= *max_);
-        };
+        auto pred = [sequence, this]() -> bool { return (max_ && sequence <= *max_); };
         if (maxWaitMs)
             cv_.wait_for(lck, std::chrono::milliseconds(*maxWaitMs));
         else
@@ -142,7 +155,7 @@ public:
     std::optional<T>
     tryPop()
     {
-        std::unique_lock lck(m_);
+        std::scoped_lock lck(m_);
         if (queue_.empty())
             return {};
         T ret = std::move(queue_.front());
@@ -173,5 +186,3 @@ getMarkers(size_t numMarkers)
     }
     return markers;
 }
-
-#endif  // RIPPLE_APP_REPORTING_ETLHELPERS_H_INCLUDED

src/etl/ETLSource.h

@@ -1,5 +1,32 @@
-#ifndef RIPPLE_APP_REPORTING_ETLSOURCE_H_INCLUDED
-#define RIPPLE_APP_REPORTING_ETLSOURCE_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/BackendInterface.h>
+#include <config/Config.h>
+#include <etl/ETLHelpers.h>
+#include <log/Logger.h>
+#include <subscriptions/SubscriptionManager.h>
+
+#include "org/xrpl/rpc/v1/xrp_ledger.grpc.pb.h"
+#include <grpcpp/grpcpp.h>
 
 #include <boost/algorithm/string.hpp>
 #include <boost/asio.hpp>
@@ -7,15 +34,12 @@
 #include <boost/beast/core/string.hpp>
 #include <boost/beast/ssl.hpp>
 #include <boost/beast/websocket.hpp>
-#include <backend/BackendInterface.h>
-#include <subscriptions/SubscriptionManager.h>
-
-#include "org/xrpl/rpc/v1/xrp_ledger.grpc.pb.h"
-#include <etl/ETLHelpers.h>
-#include <grpcpp/grpcpp.h>
+#include <boost/uuid/uuid.hpp>
+#include <boost/uuid/uuid_generators.hpp>
 
 class ETLLoadBalancer;
 class ETLSource;
+class ProbingETLSource;
 class SubscriptionManager;
 
 /// This class manages a connection to a single ETL source. This is almost
@@ -29,6 +53,7 @@ class ForwardCache
 {
     using response_type = std::optional<boost::json::object>;
 
+    clio::Logger log_{"ETL"};
     mutable std::atomic_bool stopping_ = false;
     mutable std::shared_mutex mtx_;
     std::unordered_map<std::string, response_type> latestForwarded_;
@@ -42,34 +67,22 @@ class ForwardCache
     clear();
 
 public:
-    ForwardCache(
-        boost::json::object const& config,
-        boost::asio::io_context& ioc,
-        ETLSource const& source)
+    ForwardCache(clio::Config const& config, boost::asio::io_context& ioc, ETLSource const& source)
         : strand_(ioc), timer_(strand_), source_(source)
     {
-        if (config.contains("cache") && !config.at("cache").is_array())
-            throw std::runtime_error("ETLSource cache must be array");
-
-        if (config.contains("cache_duration") &&
-            !config.at("cache_duration").is_int64())
-            throw std::runtime_error(
-                "ETLSource cache_duration must be a number");
-
-        duration_ = config.contains("cache_duration")
-            ? config.at("cache_duration").as_int64()
-            : 10;
-
-        auto commands = config.contains("cache") ? config.at("cache").as_array()
-                                                 : boost::json::array{};
-
-        for (auto const& command : commands)
+        if (config.contains("cache"))
         {
-            if (!command.is_string())
-                throw std::runtime_error(
-                    "ETLSource forward command must be array of strings");
+            auto commands = config.arrayOrThrow("cache", "ETLSource cache must be array");
 
-            latestForwarded_[command.as_string().c_str()] = {};
+            if (config.contains("cache_duration"))
+                duration_ =
+                    config.valueOrThrow<uint32_t>("cache_duration", "ETLSource cache_duration must be a number");
+
+            for (auto const& command : commands)
+            {
+                auto key = command.valueOrThrow<std::string>("ETLSource forward command must be array of strings");
+                latestForwarded_[key] = {};
+            }
         }
     }
 
@@ -96,6 +109,12 @@ public:
     virtual void
     run() = 0;
 
+    virtual void
+    pause() = 0;
+
+    virtual void
+    resume() = 0;
+
     virtual std::string
     toString() const = 0;
 
@@ -103,29 +122,34 @@ public:
     hasLedger(uint32_t sequence) const = 0;
 
     virtual std::pair<grpc::Status, org::xrpl::rpc::v1::GetLedgerResponse>
-    fetchLedger(
-        uint32_t ledgerSequence,
-        bool getObjects = true,
-        bool getObjectNeighbors = false) = 0;
+    fetchLedger(uint32_t ledgerSequence, bool getObjects = true, bool getObjectNeighbors = false) = 0;
 
     virtual bool
-    loadInitialLedger(
-        uint32_t sequence,
-        std::uint32_t numMarkers,
-        bool cacheOnly = false) = 0;
+    loadInitialLedger(uint32_t sequence, std::uint32_t numMarkers, bool cacheOnly = false) = 0;
 
     virtual std::optional<boost::json::object>
-    forwardToRippled(
-        boost::json::object const& request,
-        std::string const& clientIp,
-        boost::asio::yield_context& yield) const = 0;
+    forwardToRippled(boost::json::object const& request, std::string const& clientIp, boost::asio::yield_context& yield)
+        const = 0;
+
+    virtual boost::uuids::uuid
+    token() const = 0;
 
     virtual ~ETLSource()
     {
     }
 
+    bool
+    operator==(ETLSource const& other) const
+    {
+        return token() == other.token();
+    }
+
+protected:
+    clio::Logger log_{"ETL"};
+
 private:
     friend ForwardCache;
+    friend ProbingETLSource;
 
     virtual std::optional<boost::json::object>
     requestFromRippled(
@@ -134,6 +158,14 @@ private:
         boost::asio::yield_context& yield) const = 0;
 };
 
+struct ETLSourceHooks
+{
+    enum class Action { STOP, PROCEED };
+
+    std::function<Action(boost::beast::error_code)> onConnected;
+    std::function<Action(boost::beast::error_code)> onDisconnected;
+};
+
 template <class Derived>
 class ETLSourceImpl : public ETLSource
 {
@@ -149,7 +181,7 @@ class ETLSourceImpl : public ETLSource
 
     std::vector<std::pair<uint32_t, uint32_t>> validatedLedgers_;
 
-    std::string validatedLedgersRaw_;
+    std::string validatedLedgersRaw_{"N/A"};
 
     std::shared_ptr<NetworkValidatedLedgers> networkValidatedLedgers_;
 
@@ -174,6 +206,7 @@ class ETLSourceImpl : public ETLSource
     ETLLoadBalancer& balancer_;
 
     ForwardCache forwardCache_;
+    boost::uuids::uuid uuid_;
 
     std::optional<boost::json::object>
     requestFromRippled(
@@ -199,23 +232,25 @@ protected:
 
     std::atomic_bool closing_{false};
 
+    std::atomic_bool paused_{false};
+
+    ETLSourceHooks hooks_;
+
     void
     run() override
     {
-        BOOST_LOG_TRIVIAL(trace) << __func__ << " : " << toString();
+        log_.trace() << toString();
 
         auto const host = ip_;
         auto const port = wsPort_;
 
-        resolver_.async_resolve(host, port, [this](auto ec, auto results) {
-            onResolve(ec, results);
-        });
+        resolver_.async_resolve(host, port, [this](auto ec, auto results) { onResolve(ec, results); });
     }
 
 public:
     ~ETLSourceImpl()
     {
-        close(false);
+        derived().close(false);
     }
 
     bool
@@ -224,6 +259,12 @@ public:
         return connected_;
     }
 
+    boost::uuids::uuid
+    token() const override
+    {
+        return uuid_;
+    }
+
     std::chrono::system_clock::time_point
     getLastMsgTime() const
     {
@@ -242,12 +283,49 @@ public:
     /// Fetch ledger and load initial ledger will fail for this source
     /// Primarly used in read-only mode, to monitor when ledgers are validated
     ETLSourceImpl(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioContext,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<NetworkValidatedLedgers> networkValidatedLedgers,
-        ETLLoadBalancer& balancer);
+        ETLLoadBalancer& balancer,
+        ETLSourceHooks hooks)
+        : resolver_(boost::asio::make_strand(ioContext))
+        , networkValidatedLedgers_(networkValidatedLedgers)
+        , backend_(backend)
+        , subscriptions_(subscriptions)
+        , balancer_(balancer)
+        , forwardCache_(config, ioContext, *this)
+        , ioc_(ioContext)
+        , timer_(ioContext)
+        , hooks_(hooks)
+    {
+        static boost::uuids::random_generator uuidGenerator;
+        uuid_ = uuidGenerator();
+
+        ip_ = config.valueOr<std::string>("ip", {});
+        wsPort_ = config.valueOr<std::string>("ws_port", {});
+
+        if (auto value = config.maybeValue<std::string>("grpc_port"); value)
+        {
+            grpcPort_ = *value;
+            try
+            {
+                boost::asio::ip::tcp::endpoint endpoint{boost::asio::ip::make_address(ip_), std::stoi(grpcPort_)};
+                std::stringstream ss;
+                ss << endpoint;
+                grpc::ChannelArguments chArgs;
+                chArgs.SetMaxReceiveMessageSize(-1);
+                stub_ = org::xrpl::rpc::v1::XRPLedgerAPIService::NewStub(
+                    grpc::CreateCustomChannel(ss.str(), grpc::InsecureChannelCredentials(), chArgs));
+                log_.debug() << "Made stub for remote = " << toString();
+            }
+            catch (std::exception const& e)
+            {
+                log_.debug() << "Exception while creating stub = " << e.what() << " . Remote = " << toString();
+            }
+        }
+    }
 
     /// @param sequence ledger sequence to check for
     /// @return true if this source has the desired ledger
@@ -300,9 +378,7 @@ public:
                 pairs.push_back(std::make_pair(min, max));
             }
         }
-        std::sort(pairs.begin(), pairs.end(), [](auto left, auto right) {
-            return left.first < right.first;
-        });
+        std::sort(pairs.begin(), pairs.end(), [](auto left, auto right) { return left.first < right.first; });
 
         // we only hold the lock here, to avoid blocking while string processing
         std::lock_guard lck(mtx_);
@@ -316,7 +392,6 @@ public:
     getValidatedRange() const
     {
         std::lock_guard lck(mtx_);
-
         return validatedLedgersRaw_;
     }
 
@@ -326,17 +401,13 @@ public:
     /// and the prior one
     /// @return the extracted data and the result status
     std::pair<grpc::Status, org::xrpl::rpc::v1::GetLedgerResponse>
-    fetchLedger(
-        uint32_t ledgerSequence,
-        bool getObjects = true,
-        bool getObjectNeighbors = false) override;
+    fetchLedger(uint32_t ledgerSequence, bool getObjects = true, bool getObjectNeighbors = false) override;
 
     std::string
     toString() const override
     {
-        return "{ validated_ledger : " + getValidatedRange() +
-            " , ip : " + ip_ + " , web socket port : " + wsPort_ +
-            ", grpc port : " + grpcPort_ + " }";
+        return "{validated_ledger: " + getValidatedRange() + ", ip: " + ip_ + ", web socket port: " + wsPort_ +
+            ", grpc port: " + grpcPort_ + "}";
     }
 
     boost::json::object
@@ -351,8 +422,7 @@ public:
         auto last = getLastMsgTime();
         if (last.time_since_epoch().count() != 0)
             res["last_msg_age_seconds"] = std::to_string(
-                std::chrono::duration_cast<std::chrono::seconds>(
-                    std::chrono::system_clock::now() - getLastMsgTime())
+                std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now() - getLastMsgTime())
                     .count());
         return res;
     }
@@ -362,27 +432,35 @@ public:
     /// @param writeQueue queue to push downloaded ledger objects
     /// @return true if the download was successful
     bool
-    loadInitialLedger(
-        std::uint32_t ledgerSequence,
-        std::uint32_t numMarkers,
-        bool cacheOnly = false) override;
+    loadInitialLedger(std::uint32_t ledgerSequence, std::uint32_t numMarkers, bool cacheOnly = false) override;
 
     /// Attempt to reconnect to the ETL source
     void
     reconnect(boost::beast::error_code ec);
 
+    /// Pause the source effectively stopping it from trying to reconnect
+    void
+    pause() override
+    {
+        paused_ = true;
+        derived().close(false);
+    }
+
+    /// Resume the source allowing it to reconnect again
+    void
+    resume() override
+    {
+        paused_ = false;
+        derived().close(true);
+    }
+
     /// Callback
     void
-    onResolve(
-        boost::beast::error_code ec,
-        boost::asio::ip::tcp::resolver::results_type results);
+    onResolve(boost::beast::error_code ec, boost::asio::ip::tcp::resolver::results_type results);
 
     /// Callback
     virtual void
-    onConnect(
-        boost::beast::error_code ec,
-        boost::asio::ip::tcp::resolver::results_type::endpoint_type
-            endpoint) = 0;
+    onConnect(boost::beast::error_code ec, boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint) = 0;
 
     /// Callback
     void
@@ -402,36 +480,31 @@ public:
     handleMessage();
 
     std::optional<boost::json::object>
-    forwardToRippled(
-        boost::json::object const& request,
-        std::string const& clientIp,
-        boost::asio::yield_context& yield) const override;
+    forwardToRippled(boost::json::object const& request, std::string const& clientIp, boost::asio::yield_context& yield)
+        const override;
 };
 
 class PlainETLSource : public ETLSourceImpl<PlainETLSource>
 {
-    std::unique_ptr<boost::beast::websocket::stream<boost::beast::tcp_stream>>
-        ws_;
+    std::unique_ptr<boost::beast::websocket::stream<boost::beast::tcp_stream>> ws_;
 
 public:
     PlainETLSource(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioc,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<NetworkValidatedLedgers> nwvl,
-        ETLLoadBalancer& balancer)
-        : ETLSourceImpl(config, ioc, backend, subscriptions, nwvl, balancer)
-        , ws_(std::make_unique<
-              boost::beast::websocket::stream<boost::beast::tcp_stream>>(
+        ETLLoadBalancer& balancer,
+        ETLSourceHooks hooks)
+        : ETLSourceImpl(config, ioc, backend, subscriptions, nwvl, balancer, std::move(hooks))
+        , ws_(std::make_unique<boost::beast::websocket::stream<boost::beast::tcp_stream>>(
               boost::asio::make_strand(ioc)))
     {
     }
 
     void
-    onConnect(
-        boost::beast::error_code ec,
-        boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint)
+    onConnect(boost::beast::error_code ec, boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint)
         override;
 
     /// Close the websocket
@@ -450,46 +523,39 @@ class SslETLSource : public ETLSourceImpl<SslETLSource>
 {
     std::optional<std::reference_wrapper<boost::asio::ssl::context>> sslCtx_;
 
-    std::unique_ptr<boost::beast::websocket::stream<
-        boost::beast::ssl_stream<boost::beast::tcp_stream>>>
-        ws_;
+    std::unique_ptr<boost::beast::websocket::stream<boost::beast::ssl_stream<boost::beast::tcp_stream>>> ws_;
 
 public:
     SslETLSource(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioc,
         std::optional<std::reference_wrapper<boost::asio::ssl::context>> sslCtx,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<NetworkValidatedLedgers> nwvl,
-        ETLLoadBalancer& balancer)
-        : ETLSourceImpl(config, ioc, backend, subscriptions, nwvl, balancer)
+        ETLLoadBalancer& balancer,
+        ETLSourceHooks hooks)
+        : ETLSourceImpl(config, ioc, backend, subscriptions, nwvl, balancer, std::move(hooks))
         , sslCtx_(sslCtx)
-        , ws_(std::make_unique<boost::beast::websocket::stream<
-                  boost::beast::ssl_stream<boost::beast::tcp_stream>>>(
+        , ws_(std::make_unique<boost::beast::websocket::stream<boost::beast::ssl_stream<boost::beast::tcp_stream>>>(
               boost::asio::make_strand(ioc_),
               *sslCtx_))
     {
     }
 
     void
-    onConnect(
-        boost::beast::error_code ec,
-        boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint)
+    onConnect(boost::beast::error_code ec, boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint)
         override;
 
     void
-    onSslHandshake(
-        boost::beast::error_code ec,
-        boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint);
+    onSslHandshake(boost::beast::error_code ec, boost::asio::ip::tcp::resolver::results_type::endpoint_type endpoint);
 
     /// Close the websocket
     /// @param startAgain whether to reconnect
     void
     close(bool startAgain);
 
-    boost::beast::websocket::stream<
-        boost::beast::ssl_stream<boost::beast::tcp_stream>>&
+    boost::beast::websocket::stream<boost::beast::ssl_stream<boost::beast::tcp_stream>>&
     ws()
     {
         return *ws_;
@@ -505,30 +571,27 @@ public:
 class ETLLoadBalancer
 {
 private:
+    clio::Logger log_{"ETL"};
     std::vector<std::unique_ptr<ETLSource>> sources_;
-
     std::uint32_t downloadRanges_ = 16;
 
 public:
     ETLLoadBalancer(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioContext,
-        std::optional<std::reference_wrapper<boost::asio::ssl::context>> sslCtx,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<NetworkValidatedLedgers> nwvl);
 
     static std::shared_ptr<ETLLoadBalancer>
     make_ETLLoadBalancer(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioc,
-        std::optional<std::reference_wrapper<boost::asio::ssl::context>> sslCtx,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<NetworkValidatedLedgers> validatedLedgers)
     {
-        return std::make_shared<ETLLoadBalancer>(
-            config, ioc, sslCtx, backend, subscriptions, validatedLedgers);
+        return std::make_shared<ETLLoadBalancer>(config, ioc, backend, subscriptions, validatedLedgers);
     }
 
     ~ETLLoadBalancer()
@@ -551,10 +614,7 @@ public:
     /// was found in the database or the server is shutting down, the optional
     /// will be empty
     std::optional<org::xrpl::rpc::v1::GetLedgerResponse>
-    fetchLedger(
-        uint32_t ledgerSequence,
-        bool getObjects,
-        bool getObjectNeighbors);
+    fetchLedger(uint32_t ledgerSequence, bool getObjects, bool getObjectNeighbors);
 
     /// Determine whether messages received on the transactions_proposed stream
     /// should be forwarded to subscribing clients. The server subscribes to
@@ -572,10 +632,7 @@ public:
             // We pick the first ETLSource encountered that is connected
             if (src->isConnected())
             {
-                if (src.get() == in)
-                    return true;
-                else
-                    return false;
+                return *src == *in;
             }
         }
 
@@ -598,10 +655,8 @@ public:
     /// @param request JSON-RPC request
     /// @return response received from rippled node
     std::optional<boost::json::object>
-    forwardToRippled(
-        boost::json::object const& request,
-        std::string const& clientIp,
-        boost::asio::yield_context& yield) const;
+    forwardToRippled(boost::json::object const& request, std::string const& clientIp, boost::asio::yield_context& yield)
+        const;
 
 private:
     /// f is a function that takes an ETLSource as an argument and returns a
@@ -618,5 +673,3 @@ private:
     bool
     execute(Func f, uint32_t ledgerSequence);
 };
-
-#endif

src/etl/NFTHelpers.cpp

@@ -1,4 +1,22 @@
-#include <ripple/app/tx/impl/details/NFTokenUtils.h>
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
 #include <ripple/protocol/STBase.h>
 #include <ripple/protocol/STTx.h>
 #include <ripple/protocol/TxMeta.h>
@@ -26,25 +44,18 @@ getNFTokenMintData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 
     for (ripple::STObject const& node : txMeta.getNodes())
     {
-        if (node.getFieldU16(ripple::sfLedgerEntryType) !=
-            ripple::ltNFTOKEN_PAGE)
+        if (node.getFieldU16(ripple::sfLedgerEntryType) != ripple::ltNFTOKEN_PAGE)
             continue;
 
         if (!owner)
-            owner = ripple::AccountID::fromVoid(
-                node.getFieldH256(ripple::sfLedgerIndex).data());
+            owner = ripple::AccountID::fromVoid(node.getFieldH256(ripple::sfLedgerIndex).data());
 
         if (node.getFName() == ripple::sfCreatedNode)
         {
             ripple::STArray const& toAddNFTs =
-                node.peekAtField(ripple::sfNewFields)
-                    .downcast<ripple::STObject>()
-                    .getFieldArray(ripple::sfNFTokens);
+                node.peekAtField(ripple::sfNewFields).downcast<ripple::STObject>().getFieldArray(ripple::sfNFTokens);
             std::transform(
-                toAddNFTs.begin(),
-                toAddNFTs.end(),
-                std::back_inserter(finalIDs),
-                [](ripple::STObject const& nft) {
+                toAddNFTs.begin(), toAddNFTs.end(), std::back_inserter(finalIDs), [](ripple::STObject const& nft) {
                     return nft.getFieldH256(ripple::sfNFTokenID);
                 });
         }
@@ -62,32 +73,23 @@ getNFTokenMintData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
             // as rippled outputs all fields in final fields even if they were
             // not changed.
             ripple::STObject const& previousFields =
-                node.peekAtField(ripple::sfPreviousFields)
-                    .downcast<ripple::STObject>();
+                node.peekAtField(ripple::sfPreviousFields).downcast<ripple::STObject>();
             if (!previousFields.isFieldPresent(ripple::sfNFTokens))
                 continue;
 
-            ripple::STArray const& toAddNFTs =
-                previousFields.getFieldArray(ripple::sfNFTokens);
+            ripple::STArray const& toAddNFTs = previousFields.getFieldArray(ripple::sfNFTokens);
             std::transform(
-                toAddNFTs.begin(),
-                toAddNFTs.end(),
-                std::back_inserter(prevIDs),
-                [](ripple::STObject const& nft) {
+                toAddNFTs.begin(), toAddNFTs.end(), std::back_inserter(prevIDs), [](ripple::STObject const& nft) {
                     return nft.getFieldH256(ripple::sfNFTokenID);
                 });
 
             ripple::STArray const& toAddFinalNFTs =
-                node.peekAtField(ripple::sfFinalFields)
-                    .downcast<ripple::STObject>()
-                    .getFieldArray(ripple::sfNFTokens);
+                node.peekAtField(ripple::sfFinalFields).downcast<ripple::STObject>().getFieldArray(ripple::sfNFTokens);
             std::transform(
                 toAddFinalNFTs.begin(),
                 toAddFinalNFTs.end(),
                 std::back_inserter(finalIDs),
-                [](ripple::STObject const& nft) {
-                    return nft.getFieldH256(ripple::sfNFTokenID);
-                });
+                [](ripple::STObject const& nft) { return nft.getFieldH256(ripple::sfNFTokenID); });
         }
     }
 
@@ -102,13 +104,11 @@ getNFTokenMintData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
         std::inserter(tokenIDResult, tokenIDResult.begin()));
     if (tokenIDResult.size() == 1 && owner)
         return {
-            {NFTTransactionsData(
-                tokenIDResult.front(), txMeta, sttx.getTransactionID())},
-            NFTsData(tokenIDResult.front(), *owner, txMeta, false)};
+            {NFTTransactionsData(tokenIDResult.front(), txMeta, sttx.getTransactionID())},
+            NFTsData(tokenIDResult.front(), *owner, sttx.getFieldVL(ripple::sfURI), txMeta)};
 
     std::stringstream msg;
-    msg << __func__ << " - unexpected NFTokenMint data in tx "
-        << sttx.getTransactionID();
+    msg << " - unexpected NFTokenMint data in tx " << sttx.getTransactionID();
     throw std::runtime_error(msg.str());
 }
 
@@ -116,49 +116,43 @@ std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
 getNFTokenBurnData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 {
     ripple::uint256 const tokenID = sttx.getFieldH256(ripple::sfNFTokenID);
-    std::vector<NFTTransactionsData> const txs = {
-        NFTTransactionsData(tokenID, txMeta, sttx.getTransactionID())};
+    std::vector<NFTTransactionsData> const txs = {NFTTransactionsData(tokenID, txMeta, sttx.getTransactionID())};
 
     // Determine who owned the token when it was burned by finding an
     // NFTokenPage that was deleted or modified that contains this
     // tokenID.
     for (ripple::STObject const& node : txMeta.getNodes())
     {
-        if (node.getFieldU16(ripple::sfLedgerEntryType) !=
-                ripple::ltNFTOKEN_PAGE ||
+        if (node.getFieldU16(ripple::sfLedgerEntryType) != ripple::ltNFTOKEN_PAGE ||
             node.getFName() == ripple::sfCreatedNode)
             continue;
 
         // NFT burn can result in an NFTokenPage being modified to no longer
         // include the target, or an NFTokenPage being deleted. If this is
         // modified, we want to look for the target in the fields prior to
-        // modification. If deleted, it's possible that the page was modified
-        // to remove the target NFT prior to the entire page being deleted. In
-        // this case, we need to look in the PreviousFields. Otherwise, the
-        // page was not modified prior to deleting and we need to look in the
-        // FinalFields.
+        // modification. If deleted, it's possible that the page was
+        // modified to remove the target NFT prior to the entire page being
+        // deleted. In this case, we need to look in the PreviousFields.
+        // Otherwise, the page was not modified prior to deleting and we
+        // need to look in the FinalFields.
         std::optional<ripple::STArray> prevNFTs;
 
         if (node.isFieldPresent(ripple::sfPreviousFields))
         {
             ripple::STObject const& previousFields =
-                node.peekAtField(ripple::sfPreviousFields)
-                    .downcast<ripple::STObject>();
+                node.peekAtField(ripple::sfPreviousFields).downcast<ripple::STObject>();
             if (previousFields.isFieldPresent(ripple::sfNFTokens))
                 prevNFTs = previousFields.getFieldArray(ripple::sfNFTokens);
         }
         else if (!prevNFTs && node.getFName() == ripple::sfDeletedNode)
-            prevNFTs = node.peekAtField(ripple::sfFinalFields)
-                           .downcast<ripple::STObject>()
-                           .getFieldArray(ripple::sfNFTokens);
+            prevNFTs =
+                node.peekAtField(ripple::sfFinalFields).downcast<ripple::STObject>().getFieldArray(ripple::sfNFTokens);
 
         if (!prevNFTs)
             continue;
 
-        auto const nft = std::find_if(
-            prevNFTs->begin(),
-            prevNFTs->end(),
-            [&tokenID](ripple::STObject const& candidate) {
+        auto const nft =
+            std::find_if(prevNFTs->begin(), prevNFTs->end(), [&tokenID](ripple::STObject const& candidate) {
                 return candidate.getFieldH256(ripple::sfNFTokenID) == tokenID;
             });
         if (nft != prevNFTs->end())
@@ -166,92 +160,74 @@ getNFTokenBurnData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
                 txs,
                 NFTsData(
                     tokenID,
-                    ripple::AccountID::fromVoid(
-                        node.getFieldH256(ripple::sfLedgerIndex).data()),
+                    ripple::AccountID::fromVoid(node.getFieldH256(ripple::sfLedgerIndex).data()),
                     txMeta,
                     true));
     }
 
     std::stringstream msg;
-    msg << __func__ << " - could not determine owner at burntime for tx "
-        << sttx.getTransactionID();
+    msg << " - could not determine owner at burntime for tx " << sttx.getTransactionID();
     throw std::runtime_error(msg.str());
 }
 
 std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
-getNFTokenAcceptOfferData(
-    ripple::TxMeta const& txMeta,
-    ripple::STTx const& sttx)
+getNFTokenAcceptOfferData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 {
     // If we have the buy offer from this tx, we can determine the owner
     // more easily by just looking at the owner of the accepted NFTokenOffer
     // object.
     if (sttx.isFieldPresent(ripple::sfNFTokenBuyOffer))
     {
-        auto const affectedBuyOffer = std::find_if(
-            txMeta.getNodes().begin(),
-            txMeta.getNodes().end(),
-            [&sttx](ripple::STObject const& node) {
-                return node.getFieldH256(ripple::sfLedgerIndex) ==
-                    sttx.getFieldH256(ripple::sfNFTokenBuyOffer);
+        auto const affectedBuyOffer =
+            std::find_if(txMeta.getNodes().begin(), txMeta.getNodes().end(), [&sttx](ripple::STObject const& node) {
+                return node.getFieldH256(ripple::sfLedgerIndex) == sttx.getFieldH256(ripple::sfNFTokenBuyOffer);
             });
         if (affectedBuyOffer == txMeta.getNodes().end())
         {
             std::stringstream msg;
-            msg << __func__ << " - unexpected NFTokenAcceptOffer data in tx "
-                << sttx.getTransactionID();
+            msg << " - unexpected NFTokenAcceptOffer data in tx " << sttx.getTransactionID();
             throw std::runtime_error(msg.str());
         }
 
-        ripple::uint256 const tokenID =
-            affectedBuyOffer->peekAtField(ripple::sfFinalFields)
-                .downcast<ripple::STObject>()
-                .getFieldH256(ripple::sfNFTokenID);
+        ripple::uint256 const tokenID = affectedBuyOffer->peekAtField(ripple::sfFinalFields)
+                                            .downcast<ripple::STObject>()
+                                            .getFieldH256(ripple::sfNFTokenID);
 
-        ripple::AccountID const owner =
-            affectedBuyOffer->peekAtField(ripple::sfFinalFields)
-                .downcast<ripple::STObject>()
-                .getAccountID(ripple::sfOwner);
+        ripple::AccountID const owner = affectedBuyOffer->peekAtField(ripple::sfFinalFields)
+                                            .downcast<ripple::STObject>()
+                                            .getAccountID(ripple::sfOwner);
         return {
-            {NFTTransactionsData(tokenID, txMeta, sttx.getTransactionID())},
-            NFTsData(tokenID, owner, txMeta, false)};
+            {NFTTransactionsData(tokenID, txMeta, sttx.getTransactionID())}, NFTsData(tokenID, owner, txMeta, false)};
     }
 
     // Otherwise we have to infer the new owner from the affected nodes.
-    auto const affectedSellOffer = std::find_if(
-        txMeta.getNodes().begin(),
-        txMeta.getNodes().end(),
-        [&sttx](ripple::STObject const& node) {
-            return node.getFieldH256(ripple::sfLedgerIndex) ==
-                sttx.getFieldH256(ripple::sfNFTokenSellOffer);
+    auto const affectedSellOffer =
+        std::find_if(txMeta.getNodes().begin(), txMeta.getNodes().end(), [&sttx](ripple::STObject const& node) {
+            return node.getFieldH256(ripple::sfLedgerIndex) == sttx.getFieldH256(ripple::sfNFTokenSellOffer);
         });
     if (affectedSellOffer == txMeta.getNodes().end())
     {
         std::stringstream msg;
-        msg << __func__ << " - unexpected NFTokenAcceptOffer data in tx "
-            << sttx.getTransactionID();
+        msg << " - unexpected NFTokenAcceptOffer data in tx " << sttx.getTransactionID();
         throw std::runtime_error(msg.str());
     }
 
-    ripple::uint256 const tokenID =
-        affectedSellOffer->peekAtField(ripple::sfFinalFields)
-            .downcast<ripple::STObject>()
-            .getFieldH256(ripple::sfNFTokenID);
+    ripple::uint256 const tokenID = affectedSellOffer->peekAtField(ripple::sfFinalFields)
+                                        .downcast<ripple::STObject>()
+                                        .getFieldH256(ripple::sfNFTokenID);
 
-    ripple::AccountID const seller =
-        affectedSellOffer->peekAtField(ripple::sfFinalFields)
-            .downcast<ripple::STObject>()
-            .getAccountID(ripple::sfOwner);
+    ripple::AccountID const seller = affectedSellOffer->peekAtField(ripple::sfFinalFields)
+                                         .downcast<ripple::STObject>()
+                                         .getAccountID(ripple::sfOwner);
 
     for (ripple::STObject const& node : txMeta.getNodes())
     {
-        if (node.getFieldU16(ripple::sfLedgerEntryType) !=
-                ripple::ltNFTOKEN_PAGE ||
+        if (node.getFieldU16(ripple::sfLedgerEntryType) != ripple::ltNFTOKEN_PAGE ||
             node.getFName() == ripple::sfDeletedNode)
             continue;
 
-        ripple::AccountID const nodeOwner = ripple::AccountID::fromVoid(
-            node.getFieldH256(ripple::sfLedgerIndex).data());
+        ripple::AccountID const nodeOwner =
+            ripple::AccountID::fromVoid(node.getFieldH256(ripple::sfLedgerIndex).data());
         if (nodeOwner == seller)
             continue;
 
@@ -265,12 +241,9 @@ getNFTokenAcceptOfferData(
                 .getFieldArray(ripple::sfNFTokens);
         }();
 
-        auto const nft = std::find_if(
-            nfts.begin(),
-            nfts.end(),
-            [&tokenID](ripple::STObject const& candidate) {
-                return candidate.getFieldH256(ripple::sfNFTokenID) == tokenID;
-            });
+        auto const nft = std::find_if(nfts.begin(), nfts.end(), [&tokenID](ripple::STObject const& candidate) {
+            return candidate.getFieldH256(ripple::sfNFTokenID) == tokenID;
+        });
         if (nft != nfts.end())
             return {
                 {NFTTransactionsData(tokenID, txMeta, sttx.getTransactionID())},
@@ -278,8 +251,7 @@ getNFTokenAcceptOfferData(
     }
 
     std::stringstream msg;
-    msg << __func__ << " - unexpected NFTokenAcceptOffer data in tx "
-        << sttx.getTransactionID();
+    msg << " - unexpected NFTokenAcceptOffer data in tx " << sttx.getTransactionID();
     throw std::runtime_error(msg.str());
 }
 
@@ -288,40 +260,28 @@ getNFTokenAcceptOfferData(
 // transaction using this feature. This transaction also never returns an
 // NFTsData because it does not change the state of an NFT itself.
 std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
-getNFTokenCancelOfferData(
-    ripple::TxMeta const& txMeta,
-    ripple::STTx const& sttx)
+getNFTokenCancelOfferData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 {
     std::vector<NFTTransactionsData> txs;
     for (ripple::STObject const& node : txMeta.getNodes())
     {
-        if (node.getFieldU16(ripple::sfLedgerEntryType) !=
-            ripple::ltNFTOKEN_OFFER)
+        if (node.getFieldU16(ripple::sfLedgerEntryType) != ripple::ltNFTOKEN_OFFER)
             continue;
 
-        ripple::uint256 const tokenID = node.peekAtField(ripple::sfFinalFields)
-                                            .downcast<ripple::STObject>()
-                                            .getFieldH256(ripple::sfNFTokenID);
+        ripple::uint256 const tokenID =
+            node.peekAtField(ripple::sfFinalFields).downcast<ripple::STObject>().getFieldH256(ripple::sfNFTokenID);
         txs.emplace_back(tokenID, txMeta, sttx.getTransactionID());
     }
 
     // Deduplicate any transactions based on tokenID/txIdx combo. Can't just
     // use txIdx because in this case one tx can cancel offers for several
     // NFTs.
-    std::sort(
-        txs.begin(),
-        txs.end(),
-        [](NFTTransactionsData const& a, NFTTransactionsData const& b) {
-            return a.tokenID < b.tokenID &&
-                a.transactionIndex < b.transactionIndex;
-        });
-    auto last = std::unique(
-        txs.begin(),
-        txs.end(),
-        [](NFTTransactionsData const& a, NFTTransactionsData const& b) {
-            return a.tokenID == b.tokenID &&
-                a.transactionIndex == b.transactionIndex;
-        });
+    std::sort(txs.begin(), txs.end(), [](NFTTransactionsData const& a, NFTTransactionsData const& b) {
+        return a.tokenID < b.tokenID && a.transactionIndex < b.transactionIndex;
+    });
+    auto last = std::unique(txs.begin(), txs.end(), [](NFTTransactionsData const& a, NFTTransactionsData const& b) {
+        return a.tokenID == b.tokenID && a.transactionIndex == b.transactionIndex;
+    });
     txs.erase(last, txs.end());
     return {txs, {}};
 }
@@ -329,20 +289,13 @@ getNFTokenCancelOfferData(
 // This transaction never returns an NFTokensData because it does not
 // change the state of an NFT itself.
 std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
-getNFTokenCreateOfferData(
-    ripple::TxMeta const& txMeta,
-    ripple::STTx const& sttx)
+getNFTokenCreateOfferData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 {
-    return {
-        {NFTTransactionsData(
-            sttx.getFieldH256(ripple::sfNFTokenID),
-            txMeta,
-            sttx.getTransactionID())},
-        {}};
+    return {{NFTTransactionsData(sttx.getFieldH256(ripple::sfNFTokenID), txMeta, sttx.getTransactionID())}, {}};
 }
 
 std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
-getNFTData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
+getNFTDataFromTx(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
 {
     if (txMeta.getResultTER() != ripple::tesSUCCESS)
         return {{}, {}};
@@ -368,3 +321,20 @@ getNFTData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx)
             return {{}, {}};
     }
 }
+
+std::vector<NFTsData>
+getNFTDataFromObj(std::uint32_t const seq, std::string const& key, std::string const& blob)
+{
+    std::vector<NFTsData> nfts;
+    ripple::STLedgerEntry const sle =
+        ripple::STLedgerEntry(ripple::SerialIter{blob.data(), blob.size()}, ripple::uint256::fromVoid(key.data()));
+
+    if (sle.getFieldU16(ripple::sfLedgerEntryType) != ripple::ltNFTOKEN_PAGE)
+        return nfts;
+
+    auto const owner = ripple::AccountID::fromVoid(key.data());
+    for (ripple::STObject const& node : sle.getFieldArray(ripple::sfNFTokens))
+        nfts.emplace_back(node.getFieldH256(ripple::sfNFTokenID), seq, owner, node.getFieldVL(ripple::sfURI));
+
+    return nfts;
+}

src/etl/NFTHelpers.h

@@ -0,0 +1,33 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <backend/DBHelpers.h>
+
+#include <ripple/protocol/STTx.h>
+#include <ripple/protocol/TxMeta.h>
+
+// Pulling from tx via ReportingETL
+std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
+getNFTDataFromTx(ripple::TxMeta const& txMeta, ripple::STTx const& sttx);
+
+// Pulling from ledger object via loadInitialLedger
+std::vector<NFTsData>
+getNFTDataFromObj(std::uint32_t const seq, std::string const& key, std::string const& blob);

src/etl/ProbingETLSource.cpp

@@ -0,0 +1,202 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <etl/ProbingETLSource.h>
+#include <log/Logger.h>
+
+using namespace clio;
+
+ProbingETLSource::ProbingETLSource(
+    clio::Config const& config,
+    boost::asio::io_context& ioc,
+    std::shared_ptr<BackendInterface> backend,
+    std::shared_ptr<SubscriptionManager> subscriptions,
+    std::shared_ptr<NetworkValidatedLedgers> nwvl,
+    ETLLoadBalancer& balancer,
+    boost::asio::ssl::context sslCtx)
+    : sslCtx_{std::move(sslCtx)}
+    , sslSrc_{make_shared<
+          SslETLSource>(config, ioc, std::ref(sslCtx_), backend, subscriptions, nwvl, balancer, make_SSLHooks())}
+    , plainSrc_{make_shared<PlainETLSource>(config, ioc, backend, subscriptions, nwvl, balancer, make_PlainHooks())}
+{
+}
+
+void
+ProbingETLSource::run()
+{
+    sslSrc_->run();
+    plainSrc_->run();
+}
+
+void
+ProbingETLSource::pause()
+{
+    sslSrc_->pause();
+    plainSrc_->pause();
+}
+
+void
+ProbingETLSource::resume()
+{
+    sslSrc_->resume();
+    plainSrc_->resume();
+}
+
+bool
+ProbingETLSource::isConnected() const
+{
+    return currentSrc_ && currentSrc_->isConnected();
+}
+
+bool
+ProbingETLSource::hasLedger(uint32_t sequence) const
+{
+    if (!currentSrc_)
+        return false;
+    return currentSrc_->hasLedger(sequence);
+}
+
+boost::json::object
+ProbingETLSource::toJson() const
+{
+    if (!currentSrc_)
+    {
+        boost::json::object sourcesJson = {
+            {"ws", plainSrc_->toJson()},
+            {"wss", sslSrc_->toJson()},
+        };
+
+        return {
+            {"probing", sourcesJson},
+        };
+    }
+    return currentSrc_->toJson();
+}
+
+std::string
+ProbingETLSource::toString() const
+{
+    if (!currentSrc_)
+        return "{probing... ws: " + plainSrc_->toString() + ", wss: " + sslSrc_->toString() + "}";
+    return currentSrc_->toString();
+}
+
+boost::uuids::uuid
+ProbingETLSource::token() const
+{
+    if (!currentSrc_)
+        return boost::uuids::nil_uuid();
+    return currentSrc_->token();
+}
+
+bool
+ProbingETLSource::loadInitialLedger(std::uint32_t ledgerSequence, std::uint32_t numMarkers, bool cacheOnly)
+{
+    if (!currentSrc_)
+        return false;
+    return currentSrc_->loadInitialLedger(ledgerSequence, numMarkers, cacheOnly);
+}
+
+std::pair<grpc::Status, org::xrpl::rpc::v1::GetLedgerResponse>
+ProbingETLSource::fetchLedger(uint32_t ledgerSequence, bool getObjects, bool getObjectNeighbors)
+{
+    if (!currentSrc_)
+        return {};
+    return currentSrc_->fetchLedger(ledgerSequence, getObjects, getObjectNeighbors);
+}
+
+std::optional<boost::json::object>
+ProbingETLSource::forwardToRippled(
+    boost::json::object const& request,
+    std::string const& clientIp,
+    boost::asio::yield_context& yield) const
+{
+    if (!currentSrc_)
+        return {};
+    return currentSrc_->forwardToRippled(request, clientIp, yield);
+}
+
+std::optional<boost::json::object>
+ProbingETLSource::requestFromRippled(
+    boost::json::object const& request,
+    std::string const& clientIp,
+    boost::asio::yield_context& yield) const
+{
+    if (!currentSrc_)
+        return {};
+    return currentSrc_->requestFromRippled(request, clientIp, yield);
+}
+
+ETLSourceHooks
+ProbingETLSource::make_SSLHooks() noexcept
+{
+    return {// onConnected
+            [this](auto ec) {
+                std::lock_guard lck(mtx_);
+                if (currentSrc_)
+                    return ETLSourceHooks::Action::STOP;
+
+                if (!ec)
+                {
+                    plainSrc_->pause();
+                    currentSrc_ = sslSrc_;
+                    log_.info() << "Selected WSS as the main source: " << currentSrc_->toString();
+                }
+                return ETLSourceHooks::Action::PROCEED;
+            },
+            // onDisconnected
+            [this](auto ec) {
+                std::lock_guard lck(mtx_);
+                if (currentSrc_)
+                {
+                    currentSrc_ = nullptr;
+                    plainSrc_->resume();
+                }
+                return ETLSourceHooks::Action::STOP;
+            }};
+}
+
+ETLSourceHooks
+ProbingETLSource::make_PlainHooks() noexcept
+{
+    return {// onConnected
+            [this](auto ec) {
+                std::lock_guard lck(mtx_);
+                if (currentSrc_)
+                    return ETLSourceHooks::Action::STOP;
+
+                if (!ec)
+                {
+                    sslSrc_->pause();
+                    currentSrc_ = plainSrc_;
+                    log_.info() << "Selected Plain WS as the main source: " << currentSrc_->toString();
+                }
+                return ETLSourceHooks::Action::PROCEED;
+            },
+            // onDisconnected
+            [this](auto ec) {
+                std::lock_guard lck(mtx_);
+                if (currentSrc_)
+                {
+                    currentSrc_ = nullptr;
+                    sslSrc_->resume();
+                }
+                return ETLSourceHooks::Action::STOP;
+            }};
+}

src/etl/ProbingETLSource.h

@@ -0,0 +1,106 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <boost/asio.hpp>
+#include <boost/beast/core.hpp>
+#include <boost/beast/core/string.hpp>
+#include <boost/beast/ssl.hpp>
+#include <boost/beast/websocket.hpp>
+
+#include <mutex>
+
+#include <config/Config.h>
+#include <etl/ETLSource.h>
+#include <log/Logger.h>
+
+/// This ETLSource implementation attempts to connect over both secure websocket
+/// and plain websocket. First to connect pauses the other and the probing is
+/// considered done at this point. If however the connected source loses
+/// connection the probing is kickstarted again.
+class ProbingETLSource : public ETLSource
+{
+    clio::Logger log_{"ETL"};
+
+    std::mutex mtx_;
+    boost::asio::ssl::context sslCtx_;
+    std::shared_ptr<ETLSource> sslSrc_;
+    std::shared_ptr<ETLSource> plainSrc_;
+    std::shared_ptr<ETLSource> currentSrc_;
+
+public:
+    ProbingETLSource(
+        clio::Config const& config,
+        boost::asio::io_context& ioc,
+        std::shared_ptr<BackendInterface> backend,
+        std::shared_ptr<SubscriptionManager> subscriptions,
+        std::shared_ptr<NetworkValidatedLedgers> nwvl,
+        ETLLoadBalancer& balancer,
+        boost::asio::ssl::context sslCtx = boost::asio::ssl::context{boost::asio::ssl::context::tlsv12});
+
+    ~ProbingETLSource() = default;
+
+    void
+    run() override;
+
+    void
+    pause() override;
+
+    void
+    resume() override;
+
+    bool
+    isConnected() const override;
+
+    bool
+    hasLedger(uint32_t sequence) const override;
+
+    boost::json::object
+    toJson() const override;
+
+    std::string
+    toString() const override;
+
+    bool
+    loadInitialLedger(std::uint32_t ledgerSequence, std::uint32_t numMarkers, bool cacheOnly = false) override;
+
+    std::pair<grpc::Status, org::xrpl::rpc::v1::GetLedgerResponse>
+    fetchLedger(uint32_t ledgerSequence, bool getObjects = true, bool getObjectNeighbors = false) override;
+
+    std::optional<boost::json::object>
+    forwardToRippled(boost::json::object const& request, std::string const& clientIp, boost::asio::yield_context& yield)
+        const override;
+
+    boost::uuids::uuid
+    token() const override;
+
+private:
+    std::optional<boost::json::object>
+    requestFromRippled(
+        boost::json::object const& request,
+        std::string const& clientIp,
+        boost::asio::yield_context& yield) const override;
+
+    ETLSourceHooks
+    make_SSLHooks() noexcept;
+
+    ETLSourceHooks
+    make_PlainHooks() noexcept;
+};

src/etl/README.md

@@ -22,7 +22,7 @@ read-only mode. In read-only mode, the server does not perform ETL and simply
 publishes new ledgers as they are written to the database. 
 If the database is not updated within a certain time period
 (currently hard coded at 20 seconds), clio will begin the ETL
-process and start writing to the database. Postgres will report an error when
+process and start writing to the database. The database will report an error when
 trying to write a record with a key that already exists. ETL uses this error to
 determine that another process is writing to the database, and subsequently
 falls back to a soft read-only mode. clio can also operate in strict

src/etl/ReportingETL.h

@@ -1,5 +1,23 @@
-#ifndef RIPPLE_APP_REPORTING_REPORTINGETL_H_INCLUDED
-#define RIPPLE_APP_REPORTING_REPORTINGETL_H_INCLUDED
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
 #include <ripple/ledger/ReadView.h>
 #include <boost/algorithm/string.hpp>
@@ -8,6 +26,7 @@
 #include <boost/beast/websocket.hpp>
 #include <backend/BackendInterface.h>
 #include <etl/ETLSource.h>
+#include <log/Logger.h>
 #include <subscriptions/SubscriptionManager.h>
 
 #include "org/xrpl/rpc/v1/xrp_ledger.grpc.pb.h"
@@ -19,13 +38,6 @@
 
 #include <chrono>
 
-/**
- * Helper function for the ReportingETL, implemented in NFTHelpers.cpp, to
- * pull to-write data out of a transaction that relates to NFTs.
- */
-std::pair<std::vector<NFTTransactionsData>, std::optional<NFTsData>>
-getNFTData(ripple::TxMeta const& txMeta, ripple::STTx const& sttx);
-
 struct AccountTransactionsData;
 struct NFTTransactionsData;
 struct NFTsData;
@@ -55,6 +67,8 @@ class SubscriptionManager;
 class ReportingETL
 {
 private:
+    clio::Logger log_{"ETL"};
+
     std::shared_ptr<BackendInterface> backend_;
     std::shared_ptr<SubscriptionManager> subscriptions_;
     std::shared_ptr<ETLLoadBalancer> loadBalancer_;
@@ -77,6 +91,14 @@ private:
     // thread responsible for syncing the cache on startup
     std::thread cacheDownloader_;
 
+    struct ClioPeer
+    {
+        std::string ip;
+        int port;
+    };
+
+    std::vector<ClioPeer> clioPeers;
+
     std::thread worker_;
     boost::asio::io_context& ioContext_;
 
@@ -109,18 +131,6 @@ private:
     // deletion
     std::atomic_bool deleting_ = false;
 
-    /// Used to determine when to write to the database during the initial
-    /// ledger download. By default, the software downloads an entire ledger and
-    /// then writes to the database. If flushInterval_ is non-zero, the software
-    /// will write to the database as new ledger data (SHAMap leaf nodes)
-    /// arrives. It is not neccesarily more effient to write the data as it
-    /// arrives, as different SHAMap leaf nodes share the same SHAMap inner
-    /// nodes; flushing prematurely can result in the same SHAMap inner node
-    /// being written to the database more than once. It is recommended to use
-    /// the default value of 0 for this variable; however, different values can
-    /// be experimented with if better performance is desired.
-    size_t flushInterval_ = 0;
-
     /// This variable controls the number of GetLedgerData calls that will be
     /// executed in parallel during the initial ledger download. GetLedgerData
     /// allows clients to page through a ledger over many RPC calls.
@@ -146,7 +156,6 @@ private:
     std::optional<uint32_t> startSequence_;
     std::optional<uint32_t> finishSequence_;
 
-    size_t accumTxns_ = 0;
     size_t txnThreshold_ = 0;
 
     /// The time that the most recently published ledger was published. Used by
@@ -158,7 +167,7 @@ private:
     void
     setLastPublish()
     {
-        std::unique_lock lck(publishTimeMtx_);
+        std::scoped_lock lck(publishTimeMtx_);
         lastPublish_ = std::chrono::system_clock::now();
     }
 
@@ -170,7 +179,7 @@ private:
     void
     setLastClose(std::chrono::time_point<ripple::NetClock> lastCloseTime)
     {
-        std::unique_lock lck(closeTimeMtx_);
+        std::scoped_lock lck(closeTimeMtx_);
         lastCloseTime_ = lastCloseTime;
     }
 
@@ -190,6 +199,16 @@ private:
     void
     loadCache(uint32_t seq);
 
+    void
+    loadCacheFromDb(uint32_t seq);
+
+    bool
+    loadCacheFromClioPeer(
+        uint32_t ledgerSequence,
+        std::string const& ip,
+        std::string const& port,
+        boost::asio::yield_context& yield);
+
     /// Run ETL. Extracts ledgers and writes them to the database, until a
     /// write conflict occurs (or the server shuts down).
     /// @note database must already be populated when this function is
@@ -246,9 +265,7 @@ private:
     /// (mostly transaction hashes, corresponding nodestore hashes and affected
     /// accounts)
     FormattedTransactionsData
-    insertTransactions(
-        ripple::LedgerInfo const& ledger,
-        org::xrpl::rpc::v1::GetLedgerResponse& data);
+    insertTransactions(ripple::LedgerInfo const& ledger, org::xrpl::rpc::v1::GetLedgerResponse& data);
 
     // TODO update this documentation
     /// Build the next ledger using the previous ledger and the extracted data.
@@ -257,7 +274,7 @@ private:
     /// following parent
     /// @param parent the previous ledger
     /// @param rawData data extracted from an ETL source
-    /// @return the newly built ledger and data to write to Postgres
+    /// @return the newly built ledger and data to write to the database
     std::pair<ripple::LedgerInfo, bool>
     buildNextLedger(org::xrpl::rpc::v1::GetLedgerResponse& rawData);
 
@@ -295,7 +312,7 @@ private:
     void
     run()
     {
-        BOOST_LOG_TRIVIAL(info) << "Starting reporting etl";
+        log_.info() << "Starting reporting etl";
         stopping_ = false;
 
         doWork();
@@ -306,7 +323,7 @@ private:
 
 public:
     ReportingETL(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioc,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
@@ -315,15 +332,14 @@ public:
 
     static std::shared_ptr<ReportingETL>
     make_ReportingETL(
-        boost::json::object const& config,
+        clio::Config const& config,
         boost::asio::io_context& ioc,
         std::shared_ptr<BackendInterface> backend,
         std::shared_ptr<SubscriptionManager> subscriptions,
         std::shared_ptr<ETLLoadBalancer> balancer,
         std::shared_ptr<NetworkValidatedLedgers> ledgers)
     {
-        auto etl = std::make_shared<ReportingETL>(
-            config, ioc, backend, subscriptions, balancer, ledgers);
+        auto etl = std::make_shared<ReportingETL>(config, ioc, backend, subscriptions, balancer, ledgers);
 
         etl->run();
 
@@ -332,8 +348,8 @@ public:
 
     ~ReportingETL()
     {
-        BOOST_LOG_TRIVIAL(info) << "onStop called";
-        BOOST_LOG_TRIVIAL(debug) << "Stopping Reporting ETL";
+        log_.info() << "onStop called";
+        log_.debug() << "Stopping Reporting ETL";
         stopping_ = true;
 
         if (worker_.joinable())
@@ -341,7 +357,7 @@ public:
         if (cacheDownloader_.joinable())
             cacheDownloader_.join();
 
-        BOOST_LOG_TRIVIAL(debug) << "Joined ReportingETL worker thread";
+        log_.debug() << "Joined ReportingETL worker thread";
     }
 
     boost::json::object
@@ -354,8 +370,7 @@ public:
         result["read_only"] = readOnly_;
         auto last = getLastPublish();
         if (last.time_since_epoch().count() != 0)
-            result["last_publish_age_seconds"] =
-                std::to_string(lastPublishAgeSeconds());
+            result["last_publish_age_seconds"] = std::to_string(lastPublishAgeSeconds());
         return result;
     }
 
@@ -369,8 +384,7 @@ public:
     std::uint32_t
     lastPublishAgeSeconds() const
     {
-        return std::chrono::duration_cast<std::chrono::seconds>(
-                   std::chrono::system_clock::now() - getLastPublish())
+        return std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now() - getLastPublish())
             .count();
     }
 
@@ -378,12 +392,11 @@ public:
     lastCloseAgeSeconds() const
     {
         std::shared_lock lck(closeTimeMtx_);
-        auto now = std::chrono::duration_cast<std::chrono::seconds>(
-                       std::chrono::system_clock::now().time_since_epoch())
+        auto now = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch())
                        .count();
         auto closeTime = lastCloseTime_.time_since_epoch().count();
+        if (now < (rippleEpochStart + closeTime))
+            return 0;
         return now - (rippleEpochStart + closeTime);
     }
 };
-
-#endif

src/log/Logger.cpp

@@ -0,0 +1,192 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <config/Config.h>
+#include <log/Logger.h>
+
+#include <algorithm>
+#include <array>
+#include <filesystem>
+
+namespace clio {
+
+Logger LogService::general_log_ = Logger{"General"};
+Logger LogService::alert_log_ = Logger{"Alert"};
+
+std::ostream&
+operator<<(std::ostream& stream, Severity sev)
+{
+    static constexpr std::array<const char*, 6> labels = {
+        "TRC",
+        "DBG",
+        "NFO",
+        "WRN",
+        "ERR",
+        "FTL",
+    };
+
+    return stream << labels.at(static_cast<int>(sev));
+}
+
+Severity
+tag_invoke(boost::json::value_to_tag<Severity>, boost::json::value const& value)
+{
+    if (not value.is_string())
+        throw std::runtime_error("`log_level` must be a string");
+    auto const& logLevel = value.as_string();
+
+    if (boost::iequals(logLevel, "trace"))
+        return Severity::TRC;
+    else if (boost::iequals(logLevel, "debug"))
+        return Severity::DBG;
+    else if (boost::iequals(logLevel, "info"))
+        return Severity::NFO;
+    else if (boost::iequals(logLevel, "warning") || boost::iequals(logLevel, "warn"))
+        return Severity::WRN;
+    else if (boost::iequals(logLevel, "error"))
+        return Severity::ERR;
+    else if (boost::iequals(logLevel, "fatal"))
+        return Severity::FTL;
+    else
+        throw std::runtime_error(
+            "Could not parse `log_level`: expected `trace`, `debug`, `info`, "
+            "`warning`, `error` or `fatal`");
+}
+
+void
+LogService::init(Config const& config)
+{
+    namespace src = boost::log::sources;
+    namespace keywords = boost::log::keywords;
+    namespace sinks = boost::log::sinks;
+
+    boost::log::add_common_attributes();
+    boost::log::register_simple_formatter_factory<Severity, char>("Severity");
+    auto const defaultFormat =
+        "%TimeStamp% (%SourceLocation%) [%ThreadID%] %Channel%:%Severity% "
+        "%Message%";
+    std::string format = config.valueOr<std::string>("log_format", defaultFormat);
+
+    if (config.valueOr("log_to_console", false))
+    {
+        boost::log::add_console_log(std::cout, keywords::format = format);
+    }
+
+    auto logDir = config.maybeValue<std::string>("log_directory");
+    if (logDir)
+    {
+        boost::filesystem::path dirPath{logDir.value()};
+        if (!boost::filesystem::exists(dirPath))
+            boost::filesystem::create_directories(dirPath);
+        auto const rotationSize = config.valueOr<uint64_t>("log_rotation_size", 2048u) * 1024u * 1024u;
+        auto const rotationPeriod = config.valueOr<uint32_t>("log_rotation_hour_interval", 12u);
+        auto const dirSize = config.valueOr<uint64_t>("log_directory_max_size", 50u * 1024u) * 1024u * 1024u;
+        auto fileSink = boost::log::add_file_log(
+            keywords::file_name = dirPath / "clio.log",
+            keywords::target_file_name = dirPath / "clio_%Y-%m-%d_%H-%M-%S.log",
+            keywords::auto_flush = true,
+            keywords::format = format,
+            keywords::open_mode = std::ios_base::app,
+            keywords::rotation_size = rotationSize,
+            keywords::time_based_rotation =
+                sinks::file::rotation_at_time_interval(boost::posix_time::hours(rotationPeriod)));
+        fileSink->locked_backend()->set_file_collector(
+            sinks::file::make_collector(keywords::target = dirPath, keywords::max_size = dirSize));
+        fileSink->locked_backend()->scan_for_files();
+    }
+
+    // get default severity, can be overridden per channel using
+    // the `log_channels` array
+    auto defaultSeverity = config.valueOr<Severity>("log_level", Severity::NFO);
+    static constexpr std::array<const char*, 7> channels = {
+        "General",
+        "WebServer",
+        "Backend",
+        "RPC",
+        "ETL",
+        "Subscriptions",
+        "Performance",
+    };
+
+    auto core = boost::log::core::get();
+    auto min_severity = boost::log::expressions::channel_severity_filter(log_channel, log_severity);
+
+    for (auto const& channel : channels)
+        min_severity[channel] = defaultSeverity;
+    min_severity["Alert"] = Severity::WRN;  // Channel for alerts, always warning severity
+
+    for (auto const overrides = config.arrayOr("log_channels", {}); auto const& cfg : overrides)
+    {
+        auto name = cfg.valueOrThrow<std::string>("channel", "Channel name is required");
+        if (not std::count(std::begin(channels), std::end(channels), name))
+            throw std::runtime_error("Can't override settings for log channel " + name + ": invalid channel");
+
+        min_severity[name] = cfg.valueOr<Severity>("log_level", defaultSeverity);
+    }
+
+    core->set_filter(min_severity);
+    LogService::info() << "Default log level = " << defaultSeverity;
+}
+
+Logger::Pump
+Logger::trace(source_location_t const& loc) const
+{
+    return {logger_, Severity::TRC, loc};
+};
+Logger::Pump
+Logger::debug(source_location_t const& loc) const
+{
+    return {logger_, Severity::DBG, loc};
+};
+Logger::Pump
+Logger::info(source_location_t const& loc) const
+{
+    return {logger_, Severity::NFO, loc};
+};
+Logger::Pump
+Logger::warn(source_location_t const& loc) const
+{
+    return {logger_, Severity::WRN, loc};
+};
+Logger::Pump
+Logger::error(source_location_t const& loc) const
+{
+    return {logger_, Severity::ERR, loc};
+};
+Logger::Pump
+Logger::fatal(source_location_t const& loc) const
+{
+    return {logger_, Severity::FTL, loc};
+};
+
+std::string
+Logger::Pump::pretty_path(source_location_t const& loc, size_t max_depth) const
+{
+    auto const file_path = std::string{loc.file_name()};
+    auto idx = file_path.size();
+    while (max_depth-- > 0)
+    {
+        idx = file_path.rfind('/', idx - 1);
+        if (idx == std::string::npos || idx == 0)
+            break;
+    }
+    return file_path.substr(idx == std::string::npos ? 0 : idx + 1) + ':' + std::to_string(loc.line());
+}
+
+}  // namespace clio

src/log/Logger.h

@@ -0,0 +1,306 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <boost/algorithm/string/predicate.hpp>
+#include <boost/filesystem.hpp>
+#include <boost/json.hpp>
+#include <boost/log/core/core.hpp>
+#include <boost/log/expressions/predicates/channel_severity_filter.hpp>
+#include <boost/log/sinks/unlocked_frontend.hpp>
+#include <boost/log/sources/record_ostream.hpp>
+#include <boost/log/sources/severity_channel_logger.hpp>
+#include <boost/log/sources/severity_feature.hpp>
+#include <boost/log/sources/severity_logger.hpp>
+#include <boost/log/utility/manipulators/add_value.hpp>
+#include <boost/log/utility/setup/common_attributes.hpp>
+#include <boost/log/utility/setup/console.hpp>
+#include <boost/log/utility/setup/file.hpp>
+#include <boost/log/utility/setup/formatter_parser.hpp>
+
+#if defined(HAS_SOURCE_LOCATION) && __has_builtin(__builtin_source_location)
+// this is used by fully compatible compilers like gcc
+#include <source_location>
+
+#elif defined(HAS_EXPERIMENTAL_SOURCE_LOCATION)
+// this is used by clang on linux where source_location is still not out of
+// experimental headers
+#include <experimental/source_location>
+#endif
+
+#include <optional>
+#include <string>
+
+namespace clio {
+
+class Config;
+#if defined(HAS_SOURCE_LOCATION) && __has_builtin(__builtin_source_location)
+using source_location_t = std::source_location;
+#define CURRENT_SRC_LOCATION source_location_t::current()
+
+#elif defined(HAS_EXPERIMENTAL_SOURCE_LOCATION)
+using source_location_t = std::experimental::source_location;
+#define CURRENT_SRC_LOCATION source_location_t::current()
+
+#else
+// A workaround for AppleClang that is lacking source_location atm.
+// TODO: remove this workaround when all compilers catch up to c++20
+class SourceLocation
+{
+    std::string_view file_;
+    std::size_t line_;
+
+public:
+    SourceLocation(std::string_view file, std::size_t line) : file_{file}, line_{line}
+    {
+    }
+    std::string_view
+    file_name() const
+    {
+        return file_;
+    }
+    std::size_t
+    line() const
+    {
+        return line_;
+    }
+};
+using source_location_t = SourceLocation;
+#define CURRENT_SRC_LOCATION source_location_t(__builtin_FILE(), __builtin_LINE())
+#endif
+
+/**
+ * @brief Custom severity levels for @ref Logger.
+ */
+enum class Severity {
+    TRC,
+    DBG,
+    NFO,
+    WRN,
+    ERR,
+    FTL,
+};
+
+BOOST_LOG_ATTRIBUTE_KEYWORD(log_severity, "Severity", Severity);
+BOOST_LOG_ATTRIBUTE_KEYWORD(log_channel, "Channel", std::string);
+
+/**
+ * @brief Custom labels for @ref Severity in log output.
+ *
+ * @param stream std::ostream The output stream
+ * @param sev Severity The severity to output to the ostream
+ * @return std::ostream& The same ostream we were given
+ */
+std::ostream&
+operator<<(std::ostream& stream, Severity sev);
+
+/**
+ * @brief A simple thread-safe logger for the channel specified
+ * in the constructor.
+ *
+ * This is cheap to copy and move. Designed to be used as a member variable or
+ * otherwise. See @ref LogService::init() for setup of the logging core and
+ * severity levels for each channel.
+ */
+class Logger final
+{
+    using logger_t = boost::log::sources::severity_channel_logger_mt<Severity, std::string>;
+    mutable logger_t logger_;
+
+    friend class LogService;  // to expose the Pump interface
+
+    /**
+     * @brief Helper that pumps data into a log record via `operator<<`.
+     */
+    class Pump final
+    {
+        using pump_opt_t = std::optional<boost::log::aux::record_pump<logger_t>>;
+
+        boost::log::record rec_;
+        pump_opt_t pump_ = std::nullopt;
+
+    public:
+        ~Pump() = default;
+        Pump(logger_t& logger, Severity sev, source_location_t const& loc)
+            : rec_{logger.open_record(boost::log::keywords::severity = sev)}
+        {
+            if (rec_)
+            {
+                pump_.emplace(boost::log::aux::make_record_pump(logger, rec_));
+                pump_->stream() << boost::log::add_value("SourceLocation", pretty_path(loc));
+            }
+        }
+
+        Pump(Pump&&) = delete;
+        Pump(Pump const&) = delete;
+        Pump&
+        operator=(Pump const&) = delete;
+        Pump&
+        operator=(Pump&&) = delete;
+
+        /**
+         * @brief Perfectly forwards any incoming data into the underlying
+         * boost::log pump if the pump is available. nop otherwise.
+         *
+         * @tparam T Type of data to pump
+         * @param data The data to pump
+         * @return Pump& Reference to itself for chaining
+         */
+        template <typename T>
+        [[maybe_unused]] Pump&
+        operator<<(T&& data)
+        {
+            if (pump_)
+                pump_->stream() << std::forward<T>(data);
+            return *this;
+        }
+
+    private:
+        [[nodiscard]] std::string
+        pretty_path(source_location_t const& loc, size_t max_depth = 3) const;
+
+        /**
+         * @brief Custom JSON parser for @ref Severity.
+         *
+         * @param value The JSON string to parse
+         * @return Severity The parsed severity
+         * @throws std::runtime_error Thrown if severity is not in the right format
+         */
+        friend Severity
+        tag_invoke(boost::json::value_to_tag<Severity>, boost::json::value const& value);
+    };
+
+public:
+    ~Logger() = default;
+    /**
+     * @brief Construct a new Logger object that produces loglines for the
+     * specified channel.
+     *
+     * See @ref LogService::init() for general setup and configuration of
+     * severity levels per channel.
+     *
+     * @param channel The channel this logger will report into.
+     */
+    Logger(std::string channel) : logger_{boost::log::keywords::channel = channel}
+    {
+    }
+    Logger(Logger const&) = default;
+    Logger(Logger&&) = default;
+    Logger&
+    operator=(Logger const&) = default;
+    Logger&
+    operator=(Logger&&) = default;
+
+    /*! Interface for logging at @ref Severity::TRC severity */
+    [[nodiscard]] Pump
+    trace(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+
+    /*! Interface for logging at @ref Severity::DBG severity */
+    [[nodiscard]] Pump
+    debug(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+
+    /*! Interface for logging at @ref Severity::INFO severity */
+    [[nodiscard]] Pump
+    info(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+
+    /*! Interface for logging at @ref Severity::WRN severity */
+    [[nodiscard]] Pump
+    warn(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+
+    /*! Interface for logging at @ref Severity::ERR severity */
+    [[nodiscard]] Pump
+    error(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+
+    /*! Interface for logging at @ref Severity::FTL severity */
+    [[nodiscard]] Pump
+    fatal(source_location_t const& loc = CURRENT_SRC_LOCATION) const;
+};
+
+/**
+ * @brief A global logging service.
+ *
+ * Used to initialize and setup the logging core as well as a globally available
+ * entrypoint for logging into the `General` channel as well as raising alerts.
+ */
+class LogService
+{
+    static Logger general_log_; /*! Global logger for General channel */
+    static Logger alert_log_;   /*! Global logger for Alerts channel */
+
+public:
+    LogService() = delete;
+
+    /**
+     * @brief Global log core initialization from a @ref Config
+     */
+    static void
+    init(Config const& config);
+
+    /*! Globally accesible General logger at @ref Severity::TRC severity */
+    [[nodiscard]] static Logger::Pump
+    trace(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.trace(loc);
+    }
+
+    /*! Globally accesible General logger at @ref Severity::DBG severity */
+    [[nodiscard]] static Logger::Pump
+    debug(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.debug(loc);
+    }
+
+    /*! Globally accesible General logger at @ref Severity::NFO severity */
+    [[nodiscard]] static Logger::Pump
+    info(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.info(loc);
+    }
+
+    /*! Globally accesible General logger at @ref Severity::WRN severity */
+    [[nodiscard]] static Logger::Pump
+    warn(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.warn(loc);
+    }
+
+    /*! Globally accesible General logger at @ref Severity::ERR severity */
+    [[nodiscard]] static Logger::Pump
+    error(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.error(loc);
+    }
+
+    /*! Globally accesible General logger at @ref Severity::FTL severity */
+    [[nodiscard]] static Logger::Pump
+    fatal(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return general_log_.fatal(loc);
+    }
+
+    /*! Globally accesible Alert logger */
+    [[nodiscard]] static Logger::Pump
+    alert(source_location_t const& loc = CURRENT_SRC_LOCATION)
+    {
+        return alert_log_.warn(loc);
+    }
+};
+
+};  // namespace clio

src/main/Build.h

@@ -1,5 +1,23 @@
-#ifndef CLIO_BUILD_INFO_H
-#define CLIO_BUILD_INFO_H
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
 
 #include <string>
 
@@ -12,5 +30,3 @@ std::string const&
 getClioFullVersionString();
 
 }  // namespace Build
-
-#endif  // CLIO_BUILD_INFO_H

src/main/impl/Build.cpp

@@ -1,59 +0,0 @@
-#include <ripple/beast/core/SemanticVersion.h>
-#include <boost/preprocessor/stringize.hpp>
-#include <algorithm>
-#include <main/Build.h>
-#include <optional>
-#include <stdexcept>
-
-namespace Build {
-
-//--------------------------------------------------------------------------
-//  The build version number. You must edit this for each release
-//  and follow the format described at http://semver.org/
-//------------------------------------------------------------------------------
-// clang-format off
-char const* const versionString = "1.0.2"
-// clang-format on
-
-#if defined(DEBUG) || defined(SANITIZER)
-    "+"
-#ifdef CLIO_GIT_COMMIT_HASH
-    CLIO_GIT_COMMIT_HASH
-    "."
-#endif
-#ifdef DEBUG
-    "DEBUG"
-#ifdef SANITIZER
-    "."
-#endif
-#endif
-
-#ifdef SANITIZER
-    BOOST_PP_STRINGIZE(SANITIZER)
-#endif
-#endif
-
-    //--------------------------------------------------------------------------
-    ;
-
-std::string const&
-getClioVersionString()
-{
-    static std::string const value = [] {
-        std::string const s = versionString;
-        beast::SemanticVersion v;
-        if (!v.parse(s) || v.print() != s)
-            throw std::runtime_error(s + ": Bad server version string");
-        return s;
-    }();
-    return value;
-}
-
-std::string const&
-getClioFullVersionString()
-{
-    static std::string const value = "clio-" + getClioVersionString();
-    return value;
-}
-
-}  // namespace Build

src/main/main.cpp

@@ -1,3 +1,22 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022-2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
 #include <grpc/impl/codegen/port_platform.h>
 #ifdef GRPC_TSAN_ENABLED
 #undef GRPC_TSAN_ENABLED
@@ -6,25 +25,25 @@
 #undef GRPC_ASAN_ENABLED
 #endif
 
+#include <backend/BackendFactory.h>
+#include <config/Config.h>
+#include <etl/ReportingETL.h>
+#include <log/Logger.h>
+#include <rpc/Counters.h>
+#include <rpc/RPCEngine.h>
+#include <rpc/common/impl/HandlerProvider.h>
+#include <webserver/Listener.h>
+
 #include <boost/asio/dispatch.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/beast/websocket.hpp>
 #include <boost/date_time/posix_time/posix_time_types.hpp>
+#include <boost/filesystem/path.hpp>
 #include <boost/json.hpp>
-#include <boost/log/core.hpp>
-#include <boost/log/expressions.hpp>
-#include <boost/log/sinks/text_file_backend.hpp>
-#include <boost/log/sources/record_ostream.hpp>
-#include <boost/log/sources/severity_logger.hpp>
-#include <boost/log/support/date_time.hpp>
-#include <boost/log/trivial.hpp>
-#include <boost/log/utility/setup/common_attributes.hpp>
-#include <boost/log/utility/setup/console.hpp>
-#include <boost/log/utility/setup/file.hpp>
+#include <boost/program_options.hpp>
+
 #include <algorithm>
-#include <backend/BackendFactory.h>
 #include <cstdlib>
-#include <etl/ReportingETL.h>
 #include <fstream>
 #include <functional>
 #include <iostream>
@@ -34,39 +53,66 @@
 #include <string>
 #include <thread>
 #include <vector>
-#include <webserver/Listener.h>
 
-std::optional<boost::json::object>
-parse_config(const char* filename)
+using namespace clio;
+namespace po = boost::program_options;
+
+/**
+ * @brief Parse command line and return path to configuration file
+ *
+ * @param argc
+ * @param argv
+ * @return std::string Path to configuration file
+ */
+std::string
+parseCli(int argc, char* argv[])
 {
-    try
+    static constexpr char defaultConfigPath[] = "/etc/opt/clio/config.json";
+
+    // clang-format off
+    po::options_description description("Options");
+    description.add_options()
+        ("help,h", "print help message and exit")
+        ("version,v", "print version and exit")
+        ("conf,c", po::value<std::string>()->default_value(defaultConfigPath), "configuration file")
+    ;
+    // clang-format on
+    po::positional_options_description positional;
+    positional.add("conf", 1);
+
+    po::variables_map parsed;
+    po::store(po::command_line_parser(argc, argv).options(description).positional(positional).run(), parsed);
+    po::notify(parsed);
+
+    if (parsed.count("version"))
     {
-        std::ifstream in(filename, std::ios::in | std::ios::binary);
-        if (in)
-        {
-            std::stringstream contents;
-            contents << in.rdbuf();
-            in.close();
-            std::cout << contents.str() << std::endl;
-            boost::json::value value = boost::json::parse(contents.str());
-            return value.as_object();
-        }
+        std::cout << Build::getClioFullVersionString() << '\n';
+        std::exit(EXIT_SUCCESS);
     }
-    catch (std::exception const& e)
+
+    if (parsed.count("help"))
     {
-        std::cout << e.what() << std::endl;
+        std::cout << "Clio server " << Build::getClioFullVersionString() << "\n\n" << description;
+        std::exit(EXIT_SUCCESS);
     }
-    return {};
+
+    return parsed["conf"].as<std::string>();
 }
 
+/**
+ * @brief Parse certificates from configuration file
+ *
+ * @param config The configuration
+ * @return std::optional<ssl::context> SSL context if certificates were parsed
+ */
 std::optional<ssl::context>
-parse_certs(boost::json::object const& config)
+parseCerts(Config const& config)
 {
     if (!config.contains("ssl_cert_file") || !config.contains("ssl_key_file"))
         return {};
 
-    auto certFilename = config.at("ssl_cert_file").as_string().c_str();
-    auto keyFilename = config.at("ssl_key_file").as_string().c_str();
+    auto certFilename = config.value<std::string>("ssl_cert_file");
+    auto keyFilename = config.value<std::string>("ssl_key_file");
 
     std::ifstream readCert(certFilename, std::ios::in | std::ios::binary);
     if (!readCert)
@@ -74,7 +120,6 @@ parse_certs(boost::json::object const& config)
 
     std::stringstream contents;
     contents << readCert.rdbuf();
-    readCert.close();
     std::string cert = contents.str();
 
     std::ifstream readKey(keyFilename, std::ios::in | std::ios::binary);
@@ -87,106 +132,19 @@ parse_certs(boost::json::object const& config)
     std::string key = contents.str();
 
     ssl::context ctx{ssl::context::tlsv12};
-
-    ctx.set_options(
-        boost::asio::ssl::context::default_workarounds |
-        boost::asio::ssl::context::no_sslv2);
-
+    ctx.set_options(boost::asio::ssl::context::default_workarounds | boost::asio::ssl::context::no_sslv2);
     ctx.use_certificate_chain(boost::asio::buffer(cert.data(), cert.size()));
-
-    ctx.use_private_key(
-        boost::asio::buffer(key.data(), key.size()),
-        boost::asio::ssl::context::file_format::pem);
+    ctx.use_private_key(boost::asio::buffer(key.data(), key.size()), boost::asio::ssl::context::file_format::pem);
 
     return ctx;
 }
 
-void
-initLogging(boost::json::object const& config)
-{
-    namespace src = boost::log::sources;
-    namespace keywords = boost::log::keywords;
-    namespace sinks = boost::log::sinks;
-    namespace trivial = boost::log::trivial;
-    boost::log::add_common_attributes();
-    std::string format = "[%TimeStamp%] [%ThreadID%] [%Severity%] %Message%";
-    if (!config.contains("log_to_console") ||
-        config.at("log_to_console").as_bool())
-    {
-        boost::log::add_console_log(std::cout, keywords::format = format);
-    }
-    if (config.contains("log_directory"))
-    {
-        if (!config.at("log_directory").is_string())
-            throw std::runtime_error("log directory must be a string");
-        boost::filesystem::path dirPath{
-            config.at("log_directory").as_string().c_str()};
-        if (!boost::filesystem::exists(dirPath))
-            boost::filesystem::create_directories(dirPath);
-        const int64_t rotationSize = config.contains("log_rotation_size")
-            ? config.at("log_rotation_size").as_int64() * 1024 * 1024u
-            : 2 * 1024 * 1024 * 1024u;
-        if (rotationSize <= 0)
-            throw std::runtime_error(
-                "log rotation size must be greater than 0");
-        const int64_t rotationPeriod =
-            config.contains("log_rotation_hour_interval")
-            ? config.at("log_rotation_hour_interval").as_int64()
-            : 12u;
-        if (rotationPeriod <= 0)
-            throw std::runtime_error(
-                "log rotation time interval must be greater than 0");
-        const int64_t dirSize = config.contains("log_directory_max_size")
-            ? config.at("log_directory_max_size").as_int64() * 1024 * 1024u
-            : 50 * 1024 * 1024 * 1024u;
-        if (dirSize <= 0)
-            throw std::runtime_error(
-                "log rotation directory max size must be greater than 0");
-        auto fileSink = boost::log::add_file_log(
-            keywords::file_name = dirPath / "clio.log",
-            keywords::target_file_name = dirPath / "clio_%Y-%m-%d_%H-%M-%S.log",
-            keywords::auto_flush = true,
-            keywords::format = format,
-            keywords::open_mode = std::ios_base::app,
-            keywords::rotation_size = rotationSize,
-            keywords::time_based_rotation =
-                sinks::file::rotation_at_time_interval(
-                    boost::posix_time::hours(rotationPeriod)));
-        fileSink->locked_backend()->set_file_collector(
-            sinks::file::make_collector(
-                keywords::target = dirPath, keywords::max_size = dirSize));
-        fileSink->locked_backend()->scan_for_files();
-    }
-    auto const logLevel = config.contains("log_level")
-        ? config.at("log_level").as_string()
-        : "info";
-    if (boost::iequals(logLevel, "trace"))
-        boost::log::core::get()->set_filter(
-            trivial::severity >= trivial::trace);
-    else if (boost::iequals(logLevel, "debug"))
-        boost::log::core::get()->set_filter(
-            trivial::severity >= trivial::debug);
-    else if (boost::iequals(logLevel, "info"))
-        boost::log::core::get()->set_filter(trivial::severity >= trivial::info);
-    else if (
-        boost::iequals(logLevel, "warning") || boost::iequals(logLevel, "warn"))
-        boost::log::core::get()->set_filter(
-            trivial::severity >= trivial::warning);
-    else if (boost::iequals(logLevel, "error"))
-        boost::log::core::get()->set_filter(
-            trivial::severity >= trivial::error);
-    else if (boost::iequals(logLevel, "fatal"))
-        boost::log::core::get()->set_filter(
-            trivial::severity >= trivial::fatal);
-    else
-    {
-        BOOST_LOG_TRIVIAL(warning) << "Unrecognized log level: " << logLevel
-                                   << ". Setting log level to info";
-        boost::log::core::get()->set_filter(trivial::severity >= trivial::info);
-    }
-    BOOST_LOG_TRIVIAL(info) << "Log level = " << logLevel;
-}
-
+/**
+ * @brief Start context threads
+ *
+ * @param ioc Context
+ * @param numThreads Number of worker threads to start
+ */
 void
 start(boost::asio::io_context& ioc, std::uint32_t numThreads)
 {
@@ -200,88 +158,69 @@ start(boost::asio::io_context& ioc, std::uint32_t numThreads)
 
 int
 main(int argc, char* argv[])
+try
 {
-    // Check command line arguments.
-    if (argc != 2)
-    {
-        std::cerr << "Usage: clio_server "
-                     "<config_file> \n"
-                  << "Example:\n"
-                  << "    clio_server config.json \n";
-        return EXIT_FAILURE;
-    }
-
-    if (std::string{argv[1]} == "-v" || std::string{argv[1]} == "--version")
-    {
-        std::cout << Build::getClioFullVersionString() << std::endl;
-        return EXIT_SUCCESS;
-    }
-
-    auto const config = parse_config(argv[1]);
+    auto const configPath = parseCli(argc, argv);
+    auto const config = ConfigReader::open(configPath);
     if (!config)
     {
-        std::cerr << "Couldnt parse config. Exiting..." << std::endl;
+        std::cerr << "Couldnt parse config '" << configPath << "'." << std::endl;
         return EXIT_FAILURE;
     }
 
-    initLogging(*config);
+    LogService::init(config);
+    LogService::info() << "Clio version: " << Build::getClioFullVersionString();
 
-    // Announce Clio version
-    BOOST_LOG_TRIVIAL(info)
-        << "Clio version: " << Build::getClioFullVersionString();
-
-    auto ctx = parse_certs(*config);
-    auto ctxRef = ctx
-        ? std::optional<std::reference_wrapper<ssl::context>>{ctx.value()}
-        : std::nullopt;
-
-    auto const threads = config->contains("io_threads")
-        ? config->at("io_threads").as_int64()
-        : 2;
+    auto ctx = parseCerts(config);
+    auto ctxRef = ctx ? std::optional<std::reference_wrapper<ssl::context>>{ctx.value()} : std::nullopt;
 
+    auto const threads = config.valueOr("io_threads", 2);
     if (threads <= 0)
     {
-        BOOST_LOG_TRIVIAL(fatal) << "io_threads is less than 0";
+        LogService::fatal() << "io_threads is less than 0";
         return EXIT_FAILURE;
     }
-    BOOST_LOG_TRIVIAL(info) << "Number of io threads = " << threads;
+    LogService::info() << "Number of io threads = " << threads;
 
-    // io context to handle all incoming requests, as well as other things
+    // IO context to handle all incoming requests, as well as other things
     // This is not the only io context in the application
     boost::asio::io_context ioc{threads};
 
     // Rate limiter, to prevent abuse
-    DOSGuard dosGuard{config.value(), ioc};
+    auto sweepHandler = IntervalSweepHandler{config, ioc};
+    auto dosGuard = DOSGuard{config, sweepHandler};
 
     // Interface to the database
-    std::shared_ptr<BackendInterface> backend{
-        Backend::make_Backend(ioc, *config)};
+    auto backend = Backend::make_Backend(ioc, config);
 
     // Manages clients subscribed to streams
-    std::shared_ptr<SubscriptionManager> subscriptions{
-        SubscriptionManager::make_SubscriptionManager(*config, backend)};
+    auto subscriptions = SubscriptionManager::make_SubscriptionManager(config, backend);
 
     // Tracks which ledgers have been validated by the
     // network
-    std::shared_ptr<NetworkValidatedLedgers> ledgers{
-        NetworkValidatedLedgers::make_ValidatedLedgers()};
+    auto ledgers = NetworkValidatedLedgers::make_ValidatedLedgers();
 
     // Handles the connection to one or more rippled nodes.
     // ETL uses the balancer to extract data.
     // The server uses the balancer to forward RPCs to a rippled node.
     // The balancer itself publishes to streams (transactions_proposed and
     // accounts_proposed)
-    auto balancer = ETLLoadBalancer::make_ETLLoadBalancer(
-        *config, ioc, ctxRef, backend, subscriptions, ledgers);
+    auto balancer = ETLLoadBalancer::make_ETLLoadBalancer(config, ioc, backend, subscriptions, ledgers);
 
     // ETL is responsible for writing and publishing to streams. In read-only
     // mode, ETL only publishes
-    auto etl = ReportingETL::make_ReportingETL(
-        *config, ioc, backend, subscriptions, balancer, ledgers);
+    auto etl = ReportingETL::make_ReportingETL(config, ioc, backend, subscriptions, balancer, ledgers);
+
+    auto workQueue = WorkQueue::make_WorkQueue(config);
+    auto counters = RPC::Counters::make_Counters(workQueue);
+    auto const handlerProvider =
+        std::make_shared<RPC::detail::ProductionHandlerProvider const>(backend, subscriptions, balancer, etl, counters);
+    auto const rpcEngine = RPC::RPCEngine::make_RPCEngine(
+        config, backend, subscriptions, balancer, etl, dosGuard, workQueue, counters, handlerProvider);
 
     // The server handles incoming RPCs
-    auto httpServer = Server::make_HttpServer(
-        *config, ioc, ctxRef, backend, subscriptions, balancer, etl, dosGuard);
+    auto httpServer =
+        Server::make_HttpServer(config, ioc, ctxRef, backend, rpcEngine, subscriptions, balancer, etl, dosGuard);
 
     // Blocks until stopped.
     // When stopped, shared_ptrs fall out of scope
@@ -290,3 +229,7 @@ main(int argc, char* argv[])
 
     return EXIT_SUCCESS;
 }
+catch (std::exception const& e)
+{
+    LogService::fatal() << "Exit on exception: " << e.what();
+}

src/rpc/BookChangesHelper.h

@@ -0,0 +1,235 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <rpc/RPCHelpers.h>
+
+#include <set>
+
+namespace RPC {
+
+/**
+ * @brief Represents an entry in the book_changes' changes array.
+ */
+struct BookChange
+{
+    ripple::STAmount sideAVolume;
+    ripple::STAmount sideBVolume;
+    ripple::STAmount highRate;
+    ripple::STAmount lowRate;
+    ripple::STAmount openRate;
+    ripple::STAmount closeRate;
+};
+
+/**
+ * @brief Encapsulates the book_changes computations and transformations.
+ */
+class BookChanges final
+{
+public:
+    BookChanges() = delete;  // only accessed via static handle function
+
+    /**
+     * @brief Computes all book_changes for the given transactions.
+     *
+     * @param transactions The transactions to compute book changes for
+     * @return std::vector<BookChange> Book changes
+     */
+    [[nodiscard]] static std::vector<BookChange>
+    compute(std::vector<Backend::TransactionAndMetadata> const& transactions)
+    {
+        return HandlerImpl{}(transactions);
+    }
+
+private:
+    class HandlerImpl final
+    {
+        std::map<std::string, BookChange> tally_ = {};
+        std::optional<uint32_t> offerCancel_ = {};
+
+    public:
+        [[nodiscard]] std::vector<BookChange>
+        operator()(std::vector<Backend::TransactionAndMetadata> const& transactions)
+        {
+            for (auto const& tx : transactions)
+                handleBookChange(tx);
+
+            // TODO: rewrite this with std::ranges when compilers catch up
+            std::vector<BookChange> changes;
+            std::transform(
+                std::make_move_iterator(std::begin(tally_)),
+                std::make_move_iterator(std::end(tally_)),
+                std::back_inserter(changes),
+                [](auto obj) { return obj.second; });
+            return changes;
+        }
+
+    private:
+        void
+        handleAffectedNode(ripple::STObject const& node)
+        {
+            auto const& metaType = node.getFName();
+            auto const nodeType = node.getFieldU16(ripple::sfLedgerEntryType);
+
+            // we only care about ripple::ltOFFER objects being modified or
+            // deleted
+            if (nodeType != ripple::ltOFFER || metaType == ripple::sfCreatedNode)
+                return;
+
+            // if either FF or PF are missing we can't compute
+            // but generally these are cancelled rather than crossed
+            // so skipping them is consistent
+            if (!node.isFieldPresent(ripple::sfFinalFields) || !node.isFieldPresent(ripple::sfPreviousFields))
+                return;
+
+            auto const& finalFields = node.peekAtField(ripple::sfFinalFields).downcast<ripple::STObject>();
+            auto const& previousFields = node.peekAtField(ripple::sfPreviousFields).downcast<ripple::STObject>();
+
+            // defensive case that should never be hit
+            if (!finalFields.isFieldPresent(ripple::sfTakerGets) || !finalFields.isFieldPresent(ripple::sfTakerPays) ||
+                !previousFields.isFieldPresent(ripple::sfTakerGets) ||
+                !previousFields.isFieldPresent(ripple::sfTakerPays))
+                return;
+
+            // filter out any offers deleted by explicit offer cancels
+            if (metaType == ripple::sfDeletedNode && offerCancel_ &&
+                finalFields.getFieldU32(ripple::sfSequence) == *offerCancel_)
+                return;
+
+            // compute the difference in gets and pays actually
+            // affected onto the offer
+            auto const deltaGets =
+                finalFields.getFieldAmount(ripple::sfTakerGets) - previousFields.getFieldAmount(ripple::sfTakerGets);
+            auto const deltaPays =
+                finalFields.getFieldAmount(ripple::sfTakerPays) - previousFields.getFieldAmount(ripple::sfTakerPays);
+
+            transformAndStore(deltaGets, deltaPays);
+        }
+
+        void
+        transformAndStore(ripple::STAmount const& deltaGets, ripple::STAmount const& deltaPays)
+        {
+            auto const g = to_string(deltaGets.issue());
+            auto const p = to_string(deltaPays.issue());
+
+            auto const noswap = isXRP(deltaGets) ? true : (isXRP(deltaPays) ? false : (g < p));
+
+            auto first = noswap ? deltaGets : deltaPays;
+            auto second = noswap ? deltaPays : deltaGets;
+
+            // defensively programmed, should (probably) never happen
+            if (second == beast::zero)
+                return;
+
+            auto const rate = divide(first, second, ripple::noIssue());
+
+            if (first < beast::zero)
+                first = -first;
+
+            if (second < beast::zero)
+                second = -second;
+
+            auto const key = noswap ? (g + '|' + p) : (p + '|' + g);
+            if (tally_.contains(key))
+            {
+                auto& entry = tally_.at(key);
+
+                entry.sideAVolume += first;
+                entry.sideBVolume += second;
+
+                if (entry.highRate < rate)
+                    entry.highRate = rate;
+
+                if (entry.lowRate > rate)
+                    entry.lowRate = rate;
+
+                entry.closeRate = rate;
+            }
+            else
+            {
+                // TODO: use paranthesized initialization when clang catches up
+                tally_[key] = {
+                    first,   // sideAVolume
+                    second,  // sideBVolume
+                    rate,    // highRate
+                    rate,    // lowRate
+                    rate,    // openRate
+                    rate,    // closeRate
+                };
+            }
+        }
+
+        void
+        handleBookChange(Backend::TransactionAndMetadata const& blob)
+        {
+            auto const [tx, meta] = RPC::deserializeTxPlusMeta(blob);
+            if (!tx || !meta || !tx->isFieldPresent(ripple::sfTransactionType))
+                return;
+
+            offerCancel_ = shouldCancelOffer(tx);
+            for (auto const& node : meta->getFieldArray(ripple::sfAffectedNodes))
+                handleAffectedNode(node);
+        }
+
+        std::optional<uint32_t>
+        shouldCancelOffer(std::shared_ptr<ripple::STTx const> const& tx) const
+        {
+            switch (tx->getFieldU16(ripple::sfTransactionType))
+            {
+                // in future if any other ways emerge to cancel an offer
+                // this switch makes them easy to add
+                case ripple::ttOFFER_CANCEL:
+                case ripple::ttOFFER_CREATE:
+                    if (tx->isFieldPresent(ripple::sfOfferSequence))
+                        return tx->getFieldU32(ripple::sfOfferSequence);
+                default:
+                    return std::nullopt;
+            }
+        }
+    };
+};
+
+inline void
+tag_invoke(boost::json::value_from_tag, boost::json::value& jv, BookChange const& change)
+{
+    auto amountStr = [](ripple::STAmount const& amount) -> std::string {
+        return isXRP(amount) ? to_string(amount.xrp()) : to_string(amount.iou());
+    };
+
+    auto currencyStr = [](ripple::STAmount const& amount) -> std::string {
+        return isXRP(amount) ? "XRP_drops" : to_string(amount.issue());
+    };
+
+    jv = {
+        {JS(currency_a), currencyStr(change.sideAVolume)},
+        {JS(currency_b), currencyStr(change.sideBVolume)},
+        {JS(volume_a), amountStr(change.sideAVolume)},
+        {JS(volume_b), amountStr(change.sideBVolume)},
+        {JS(high), to_string(change.highRate.iou())},
+        {JS(low), to_string(change.lowRate.iou())},
+        {JS(open), to_string(change.openRate.iou())},
+        {JS(close), to_string(change.closeRate.iou())},
+    };
+}
+
+[[nodiscard]] boost::json::object const
+computeBookChanges(ripple::LedgerInfo const& lgrInfo, std::vector<Backend::TransactionAndMetadata> const& transactions);
+
+}  // namespace RPC

src/rpc/Counters.cpp

@@ -1,47 +1,41 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
 #include <rpc/Counters.h>
-#include <rpc/RPC.h>
+#include <rpc/JS.h>
+#include <rpc/RPCHelpers.h>
 
 namespace RPC {
 
-void
-Counters::initializeCounter(std::string const& method)
-{
-    std::shared_lock lk(mutex_);
-    if (methodInfo_.count(method) == 0)
-    {
-        lk.unlock();
-        std::unique_lock ulk(mutex_);
-
-        // This calls the default constructor for methodInfo of the method.
-        methodInfo_[method];
-    }
-}
-
 void
 Counters::rpcErrored(std::string const& method)
 {
-    if (!validHandler(method))
-        return;
-
-    initializeCounter(method);
-
-    std::shared_lock lk(mutex_);
+    std::scoped_lock lk(mutex_);
     MethodInfo& counters = methodInfo_[method];
     counters.started++;
     counters.errored++;
 }
 
 void
-Counters::rpcComplete(
-    std::string const& method,
-    std::chrono::microseconds const& rpcDuration)
+Counters::rpcComplete(std::string const& method, std::chrono::microseconds const& rpcDuration)
 {
-    if (!validHandler(method))
-        return;
-
-    initializeCounter(method);
-
-    std::shared_lock lk(mutex_);
+    std::scoped_lock lk(mutex_);
     MethodInfo& counters = methodInfo_[method];
     counters.started++;
     counters.finished++;
@@ -51,35 +45,35 @@ Counters::rpcComplete(
 void
 Counters::rpcForwarded(std::string const& method)
 {
-    if (!validHandler(method))
-        return;
-
-    initializeCounter(method);
-
-    std::shared_lock lk(mutex_);
+    std::scoped_lock lk(mutex_);
     MethodInfo& counters = methodInfo_[method];
     counters.forwarded++;
 }
 
 boost::json::object
-Counters::report()
+Counters::report() const
 {
-    std::shared_lock lk(mutex_);
-    boost::json::object obj = {};
+    std::scoped_lock lk(mutex_);
+    auto obj = boost::json::object{};
+
+    obj[JS(rpc)] = boost::json::object{};
+    auto& rpc = obj[JS(rpc)].as_object();
 
     for (auto const& [method, info] : methodInfo_)
     {
-        boost::json::object counters = {};
-        counters["started"] = std::to_string(info.started);
-        counters["finished"] = std::to_string(info.finished);
-        counters["errored"] = std::to_string(info.errored);
+        auto counters = boost::json::object{};
+        counters[JS(started)] = std::to_string(info.started);
+        counters[JS(finished)] = std::to_string(info.finished);
+        counters[JS(errored)] = std::to_string(info.errored);
         counters["forwarded"] = std::to_string(info.forwarded);
-        counters["duration_us"] = std::to_string(info.duration);
+        counters[JS(duration_us)] = std::to_string(info.duration);
 
-        obj[method] = std::move(counters);
+        rpc[method] = std::move(counters);
     }
 
+    obj["work_queue"] = workQueue_.get().report();
+
     return obj;
 }
 
-}  // namespace RPC
+}  // namespace RPC

src/rpc/Counters.h

@@ -1,10 +1,30 @@
-#ifndef RPC_COUNTERS_H
-#define RPC_COUNTERS_H
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <rpc/WorkQueue.h>
 
 #include <boost/json.hpp>
+
 #include <chrono>
-#include <cstdint>
-#include <shared_mutex>
+#include <mutex>
 #include <string>
 #include <unordered_map>
 
@@ -12,42 +32,40 @@ namespace RPC {
 
 class Counters
 {
-private:
     struct MethodInfo
     {
-        MethodInfo() = default;
-
-        std::atomic_uint64_t started{0};
-        std::atomic_uint64_t finished{0};
-        std::atomic_uint64_t errored{0};
-        std::atomic_uint64_t forwarded{0};
-        std::atomic_uint64_t duration{0};
+        std::uint64_t started = 0u;
+        std::uint64_t finished = 0u;
+        std::uint64_t errored = 0u;
+        std::uint64_t forwarded = 0u;
+        std::uint64_t duration = 0u;
     };
 
-    void
-    initializeCounter(std::string const& method);
-
-    std::shared_mutex mutex_;
+    mutable std::mutex mutex_;
     std::unordered_map<std::string, MethodInfo> methodInfo_;
 
+    std::reference_wrapper<const WorkQueue> workQueue_;
+
 public:
-    Counters() = default;
+    Counters(WorkQueue const& wq) : workQueue_(std::cref(wq)){};
+
+    static Counters
+    make_Counters(WorkQueue const& wq)
+    {
+        return Counters{wq};
+    }
 
     void
     rpcErrored(std::string const& method);
 
     void
-    rpcComplete(
-        std::string const& method,
-        std::chrono::microseconds const& rpcDuration);
+    rpcComplete(std::string const& method, std::chrono::microseconds const& rpcDuration);
 
     void
     rpcForwarded(std::string const& method);
 
     boost::json::object
-    report();
+    report() const;
 };
 
 }  // namespace RPC
-
-#endif  // RPC_COUNTERS_H

src/rpc/Errors.cpp

@@ -0,0 +1,145 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2022, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <rpc/Errors.h>
+
+#include <algorithm>
+
+using namespace std;
+
+namespace {
+template <class... Ts>
+struct overloadSet : Ts...
+{
+    using Ts::operator()...;
+};
+
+// explicit deduction guide (not needed as of C++20, but clang be clang)
+template <class... Ts>
+overloadSet(Ts...) -> overloadSet<Ts...>;
+}  // namespace
+
+namespace RPC {
+
+WarningInfo const&
+getWarningInfo(WarningCode code)
+{
+    constexpr static WarningInfo infos[]{
+        {warnUNKNOWN, "Unknown warning"},
+        {warnRPC_CLIO,
+         "This is a clio server. clio only serves validated data. If you "
+         "want to talk to rippled, include 'ledger_index':'current' in your "
+         "request"},
+        {warnRPC_OUTDATED, "This server may be out of date"},
+        {warnRPC_RATE_LIMIT, "You are about to be rate limited"},
+    };
+
+    auto matchByCode = [code](auto const& info) { return info.code == code; };
+    if (auto it = find_if(begin(infos), end(infos), matchByCode); it != end(infos))
+        return *it;
+
+    throw(out_of_range("Invalid WarningCode"));
+}
+
+boost::json::object
+makeWarning(WarningCode code)
+{
+    auto json = boost::json::object{};
+    auto const& info = getWarningInfo(code);
+
+    json["id"] = code;
+    json["message"] = static_cast<string>(info.message);
+
+    return json;
+}
+
+ClioErrorInfo const&
+getErrorInfo(ClioError code)
+{
+    constexpr static ClioErrorInfo infos[]{
+        {ClioError::rpcMALFORMED_CURRENCY, "malformedCurrency", "Malformed currency."},
+        {ClioError::rpcMALFORMED_REQUEST, "malformedRequest", "Malformed request."},
+        {ClioError::rpcMALFORMED_OWNER, "malformedOwner", "Malformed owner."},
+        {ClioError::rpcMALFORMED_ADDRESS, "malformedAddress", "Malformed address."},
+    };
+
+    auto matchByCode = [code](auto const& info) { return info.code == code; };
+    if (auto it = find_if(begin(infos), end(infos), matchByCode); it != end(infos))
+        return *it;
+
+    throw(out_of_range("Invalid error code"));
+}
+
+boost::json::object
+makeError(RippledError err, optional<string_view> customError, optional<string_view> customMessage)
+{
+    boost::json::object json;
+    auto const& info = ripple::RPC::get_error_info(err);
+
+    json["error"] = customError.value_or(info.token.c_str()).data();
+    json["error_code"] = static_cast<uint32_t>(err);
+    json["error_message"] = customMessage.value_or(info.message.c_str()).data();
+    json["status"] = "error";
+    json["type"] = "response";
+
+    return json;
+}
+
+boost::json::object
+makeError(ClioError err, optional<string_view> customError, optional<string_view> customMessage)
+{
+    boost::json::object json;
+    auto const& info = getErrorInfo(err);
+
+    json["error"] = customError.value_or(info.error).data();
+    json["error_code"] = static_cast<uint32_t>(info.code);
+    json["error_message"] = customMessage.value_or(info.message).data();
+    json["status"] = "error";
+    json["type"] = "response";
+
+    return json;
+}
+
+boost::json::object
+makeError(Status const& status)
+{
+    auto wrapOptional = [](string_view const& str) { return str.empty() ? nullopt : make_optional(str); };
+
+    auto res = visit(
+        overloadSet{
+            [&status, &wrapOptional](RippledError err) {
+                if (err == ripple::rpcUNKNOWN)
+                    return boost::json::object{{"error", status.message}, {"type", "response"}, {"status", "error"}};
+
+                return makeError(err, wrapOptional(status.error), wrapOptional(status.message));
+            },
+            [&status, &wrapOptional](ClioError err) {
+                return makeError(err, wrapOptional(status.error), wrapOptional(status.message));
+            },
+        },
+        status.code);
+
+    if (status.extraInfo)
+        for (auto& [key, value] : status.extraInfo.value())
+            res[key] = value;
+
+    return res;
+}
+
+}  // namespace RPC