Add forwarding cache (#1204)

Fixes #51.

.gitignore

@@ -5,6 +5,7 @@
 .cache
 .vscode
 .python-version
+.DS_Store
 CMakeUserPresets.json
 config.json
 src/main/impl/Build.cpp

CMakeLists.txt

@@ -102,6 +102,7 @@ target_sources(
           src/etl/LoadBalancer.cpp
           src/etl/CacheLoaderSettings.cpp
           src/etl/Source.cpp
+          src/etl/impl/ForwardingCache.cpp
           src/etl/impl/ForwardingSource.cpp
           src/etl/impl/GrpcSource.cpp
           src/etl/impl/SubscriptionSource.cpp
@@ -191,28 +192,51 @@ if (tests)
     # Common
     unittests/ConfigTests.cpp
     unittests/data/BackendCountersTests.cpp
+    unittests/data/BackendCountersTests.cpp
+    unittests/data/BackendFactoryTests.cpp
     unittests/data/BackendFactoryTests.cpp
     unittests/data/cassandra/AsyncExecutorTests.cpp
     # Webserver
+    unittests/data/cassandra/AsyncExecutorTests.cpp
+    # Webserver
+    unittests/data/cassandra/BackendTests.cpp
     unittests/data/cassandra/BackendTests.cpp
     unittests/data/cassandra/BaseTests.cpp
+    unittests/data/cassandra/BaseTests.cpp
+    unittests/data/cassandra/ExecutionStrategyTests.cpp
     unittests/data/cassandra/ExecutionStrategyTests.cpp
     unittests/data/cassandra/RetryPolicyTests.cpp
+    unittests/data/cassandra/RetryPolicyTests.cpp
+    unittests/data/cassandra/SettingsProviderTests.cpp
     unittests/data/cassandra/SettingsProviderTests.cpp
     unittests/DOSGuardTests.cpp
     unittests/etl/AmendmentBlockHandlerTests.cpp
+    unittests/etl/AmendmentBlockHandlerTests.cpp
     unittests/etl/CacheLoaderSettingsTests.cpp
     unittests/etl/CacheLoaderTests.cpp
+    unittests/etl/CacheLoaderTests.cpp
     unittests/etl/CursorProviderTests.cpp
     unittests/etl/ETLStateTests.cpp
+    unittests/etl/ETLStateTests.cpp
+    unittests/etl/ExtractionDataPipeTests.cpp
     unittests/etl/ExtractionDataPipeTests.cpp
     unittests/etl/ExtractorTests.cpp
+    unittests/etl/ExtractorTests.cpp
+    unittests/etl/ForwardingCacheTests.cpp
+    unittests/etl/ForwardingSourceTests.cpp
     unittests/etl/ForwardingSourceTests.cpp
     unittests/etl/GrpcSourceTests.cpp
+    unittests/etl/GrpcSourceTests.cpp
+    unittests/etl/LedgerPublisherTests.cpp
     unittests/etl/LedgerPublisherTests.cpp
     unittests/etl/SourceTests.cpp
+    unittests/etl/SourceTests.cpp
+    unittests/etl/SubscriptionSourceDependenciesTests.cpp
     unittests/etl/SubscriptionSourceDependenciesTests.cpp
     unittests/etl/SubscriptionSourceTests.cpp
+    unittests/etl/SubscriptionSourceTests.cpp
+    unittests/etl/TransformerTests.cpp
+    # RPC
     unittests/etl/TransformerTests.cpp
     # RPC
     unittests/feed/BookChangesFeedTests.cpp
@@ -229,48 +253,92 @@ if (tests)
     unittests/Playground.cpp
     unittests/ProfilerTests.cpp
     unittests/rpc/AmendmentsTests.cpp
+    unittests/rpc/AmendmentsTests.cpp
+    unittests/rpc/APIVersionTests.cpp
     unittests/rpc/APIVersionTests.cpp
     unittests/rpc/BaseTests.cpp
+    unittests/rpc/BaseTests.cpp
+    unittests/rpc/CountersTests.cpp
     unittests/rpc/CountersTests.cpp
     unittests/rpc/ErrorTests.cpp
+    unittests/rpc/ErrorTests.cpp
+    unittests/rpc/ForwardingProxyTests.cpp
     unittests/rpc/ForwardingProxyTests.cpp
     unittests/rpc/handlers/AccountChannelsTests.cpp
+    unittests/rpc/handlers/AccountChannelsTests.cpp
+    unittests/rpc/handlers/AccountCurrenciesTests.cpp
     unittests/rpc/handlers/AccountCurrenciesTests.cpp
     unittests/rpc/handlers/AccountInfoTests.cpp
+    unittests/rpc/handlers/AccountInfoTests.cpp
+    unittests/rpc/handlers/AccountLinesTests.cpp
     unittests/rpc/handlers/AccountLinesTests.cpp
     unittests/rpc/handlers/AccountNFTsTests.cpp
+    unittests/rpc/handlers/AccountNFTsTests.cpp
+    unittests/rpc/handlers/AccountObjectsTests.cpp
     unittests/rpc/handlers/AccountObjectsTests.cpp
     unittests/rpc/handlers/AccountOffersTests.cpp
+    unittests/rpc/handlers/AccountOffersTests.cpp
+    unittests/rpc/handlers/AccountTxTests.cpp
     unittests/rpc/handlers/AccountTxTests.cpp
     unittests/rpc/handlers/AMMInfoTests.cpp
     # Backend
+    unittests/rpc/handlers/AMMInfoTests.cpp
+    # Backend
+    unittests/rpc/handlers/BookChangesTests.cpp
     unittests/rpc/handlers/BookChangesTests.cpp
     unittests/rpc/handlers/BookOffersTests.cpp
+    unittests/rpc/handlers/BookOffersTests.cpp
+    unittests/rpc/handlers/DefaultProcessorTests.cpp
     unittests/rpc/handlers/DefaultProcessorTests.cpp
     unittests/rpc/handlers/DepositAuthorizedTests.cpp
+    unittests/rpc/handlers/DepositAuthorizedTests.cpp
+    unittests/rpc/handlers/GatewayBalancesTests.cpp
     unittests/rpc/handlers/GatewayBalancesTests.cpp
     unittests/rpc/handlers/LedgerDataTests.cpp
+    unittests/rpc/handlers/LedgerDataTests.cpp
+    unittests/rpc/handlers/LedgerEntryTests.cpp
     unittests/rpc/handlers/LedgerEntryTests.cpp
     unittests/rpc/handlers/LedgerRangeTests.cpp
+    unittests/rpc/handlers/LedgerRangeTests.cpp
+    unittests/rpc/handlers/LedgerTests.cpp
     unittests/rpc/handlers/LedgerTests.cpp
     unittests/rpc/handlers/NFTBuyOffersTests.cpp
+    unittests/rpc/handlers/NFTBuyOffersTests.cpp
+    unittests/rpc/handlers/NFTHistoryTests.cpp
     unittests/rpc/handlers/NFTHistoryTests.cpp
     unittests/rpc/handlers/NFTInfoTests.cpp
+    unittests/rpc/handlers/NFTInfoTests.cpp
+    unittests/rpc/handlers/NFTsByIssuerTest.cpp
     unittests/rpc/handlers/NFTsByIssuerTest.cpp
     unittests/rpc/handlers/NFTSellOffersTests.cpp
+    unittests/rpc/handlers/NFTSellOffersTests.cpp
+    unittests/rpc/handlers/NoRippleCheckTests.cpp
     unittests/rpc/handlers/NoRippleCheckTests.cpp
     unittests/rpc/handlers/PingTests.cpp
+    unittests/rpc/handlers/PingTests.cpp
+    unittests/rpc/handlers/RandomTests.cpp
     unittests/rpc/handlers/RandomTests.cpp
     unittests/rpc/handlers/ServerInfoTests.cpp
+    unittests/rpc/handlers/ServerInfoTests.cpp
+    unittests/rpc/handlers/SubscribeTests.cpp
     unittests/rpc/handlers/SubscribeTests.cpp
     unittests/rpc/handlers/TestHandlerTests.cpp
+    unittests/rpc/handlers/TestHandlerTests.cpp
+    unittests/rpc/handlers/TransactionEntryTests.cpp
     unittests/rpc/handlers/TransactionEntryTests.cpp
     unittests/rpc/handlers/TxTests.cpp
+    unittests/rpc/handlers/TxTests.cpp
     unittests/rpc/handlers/UnsubscribeTests.cpp
+    unittests/rpc/handlers/UnsubscribeTests.cpp
+    unittests/rpc/handlers/VersionHandlerTests.cpp
     unittests/rpc/handlers/VersionHandlerTests.cpp
     unittests/rpc/JsonBoolTests.cpp
     # RPC handlers
+    unittests/rpc/JsonBoolTests.cpp
+    # RPC handlers
     unittests/rpc/RPCHelpersTests.cpp
+    unittests/rpc/RPCHelpersTests.cpp
+    unittests/rpc/WorkQueueTests.cpp
     unittests/rpc/WorkQueueTests.cpp
     unittests/util/AssertTests.cpp
     unittests/util/async/AnyExecutionContextTests.cpp

docs/configure-clio.md

@@ -83,3 +83,17 @@ By default Clio checks admin privileges by IP address from requests (only `127.0
 
 If the password is presented in the config, Clio will check the Authorization header (if any) in each request for the password. The Authorization header should contain the type `Password`, and the password from the config (e.g. `Password secret`).
 Exactly equal password gains admin rights for the request or a websocket connection.
+
+## ETL sources forwarding cache
+
+Clio can cache requests to ETL sources to reduce the load on the ETL source.
+Only following commands are cached: `server_info`, `server_state`, `server_definitions`, `fee`, `ledger_closed`.
+By default the forwarding cache is off.
+To enable the caching for a source, `forwarding_cache_timeout` value should be added to the configuration file, e.g.:
+
+```json
+"forwarding_cache_timeout": 0.250,
+```
+
+`forwarding_cache_timeout` defines for how long (in seconds) a cache entry will be valid after being placed into the cache.
+Zero value turns off the cache feature.

docs/examples/config/example-config.json

@@ -35,6 +35,7 @@
             "grpc_port": "50051"
         }
     ],
+    "forwarding_cache_timeout": 0.250, // in seconds, could be 0, which means no cache
     "dos_guard": {
         // Comma-separated list of IPs to exclude from rate limiting
         "whitelist": [

src/etl/ETLState.hpp

@@ -44,7 +44,7 @@ struct ETLState {
      */
     template <typename Forward>
     static std::optional<ETLState>
-    fetchETLStateFromSource(Forward const& source) noexcept
+    fetchETLStateFromSource(Forward& source) noexcept
     {
         auto const serverInfoRippled = data::synchronous([&source](auto yield) {
             return source.forwardToRippled({{"command", "server_info"}}, std::nullopt, yield);

src/etl/LoadBalancer.cpp

@@ -70,6 +70,13 @@ LoadBalancer::LoadBalancer(
     std::shared_ptr<NetworkValidatedLedgers> validatedLedgers
 )
 {
+    auto const forwardingCacheTimeout = config.valueOr<float>("forwarding_cache_timeout", 0.f);
+    if (forwardingCacheTimeout > 0.f) {
+        forwardingCache_ = impl::ForwardingCache{
+            std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::duration<float>{forwardingCacheTimeout})
+        };
+    }
+
     static constexpr std::uint32_t MAX_DOWNLOAD = 256;
     if (auto value = config.maybeValue<uint32_t>("num_markers"); value) {
         downloadRanges_ = std::clamp(*value, 1u, MAX_DOWNLOAD);
@@ -99,7 +106,8 @@ LoadBalancer::LoadBalancer(
                 if (not hasForwardingSource_)
                     chooseForwardingSource();
             },
-            [this]() { chooseForwardingSource(); }
+            [this]() { chooseForwardingSource(); },
+            [this]() { forwardingCache_->invalidate(); }
         );
 
         // checking etl node validity
@@ -193,22 +201,34 @@ LoadBalancer::forwardToRippled(
     boost::json::object const& request,
     std::optional<std::string> const& clientIp,
     boost::asio::yield_context yield
-) const
+)
 {
+    if (forwardingCache_) {
+        if (auto cachedResponse = forwardingCache_->get(request); cachedResponse) {
+            return cachedResponse;
+        }
+    }
+
     std::size_t sourceIdx = 0;
     if (!sources_.empty())
         sourceIdx = util::Random::uniform(0ul, sources_.size() - 1);
 
     auto numAttempts = 0u;
 
+    std::optional<boost::json::object> response;
     while (numAttempts < sources_.size()) {
-        if (auto res = sources_[sourceIdx].forwardToRippled(request, clientIp, yield))
+        if (auto res = sources_[sourceIdx].forwardToRippled(request, clientIp, yield)) {
-            return res;
+            response = std::move(res);
+            break;
+        }
 
         sourceIdx = (sourceIdx + 1) % sources_.size();
         ++numAttempts;
     }
 
+    if (response and forwardingCache_ and not response->contains("error"))
+        forwardingCache_->put(request, *response);
+
     return {};
 }
 

src/etl/LoadBalancer.hpp

@@ -23,6 +23,7 @@
 #include "etl/ETLHelpers.hpp"
 #include "etl/ETLState.hpp"
 #include "etl/Source.hpp"
+#include "etl/impl/ForwardingCache.hpp"
 #include "feed/SubscriptionManager.hpp"
 #include "util/config/Config.hpp"
 #include "util/log/Logger.hpp"
@@ -72,10 +73,12 @@ private:
     static constexpr std::uint32_t DEFAULT_DOWNLOAD_RANGES = 16;
 
     util::Logger log_{"ETL"};
+    // Forwarding cache must be destroyed after sources because sources have a callnack to invalidate cache
+    std::optional<impl::ForwardingCache> forwardingCache_;
     std::vector<Source> sources_;
     std::optional<ETLState> etlState_;
     std::uint32_t downloadRanges_ =
-        DEFAULT_DOWNLOAD_RANGES; /*< The number of markers to use when downloading intial ledger */
+        DEFAULT_DOWNLOAD_RANGES; /*< The number of markers to use when downloading initial ledger */
     std::atomic_bool hasForwardingSource_{false};
 
 public:
@@ -164,7 +167,7 @@ public:
         boost::json::object const& request,
         std::optional<std::string> const& clientIp,
         boost::asio::yield_context yield
-    ) const;
+    );
 
     /**
      * @brief Return state of ETL nodes.

src/etl/Source.cpp

@@ -26,7 +26,9 @@
 
 #include <boost/asio/io_context.hpp>
 
+#include <chrono>
 #include <memory>
+#include <optional>
 #include <string>
 #include <utility>
 
@@ -42,13 +44,15 @@ make_Source(
     std::shared_ptr<feed::SubscriptionManager> subscriptions,
     std::shared_ptr<NetworkValidatedLedgers> validatedLedgers,
     Source::OnDisconnectHook onDisconnect,
-    Source::OnConnectHook onConnect
+    Source::OnConnectHook onConnect,
+    Source::OnLedgerClosedHook onLedgerClosed
 )
 {
     auto const ip = config.valueOr<std::string>("ip", {});
     auto const wsPort = config.valueOr<std::string>("ws_port", {});
     auto const grpcPort = config.valueOr<std::string>("grpc_port", {});
 
+    impl::ForwardingSource forwardingSource{ip, wsPort};
     impl::GrpcSource grpcSource{ip, grpcPort, std::move(backend)};
     auto subscriptionSource = std::make_unique<impl::SubscriptionSource>(
         ioc,
@@ -57,9 +61,9 @@ make_Source(
         std::move(validatedLedgers),
         std::move(subscriptions),
         std::move(onConnect),
-        std::move(onDisconnect)
+        std::move(onDisconnect),
+        std::move(onLedgerClosed)
     );
-    impl::ForwardingSource forwardingSource{ip, wsPort};
 
     return Source{
         ip, wsPort, grpcPort, std::move(grpcSource), std::move(subscriptionSource), std::move(forwardingSource)

src/etl/Source.hpp

@@ -68,6 +68,7 @@ class SourceImpl {
 public:
     using OnConnectHook = impl::SubscriptionSource::OnConnectHook;
     using OnDisconnectHook = impl::SubscriptionSource::OnDisconnectHook;
+    using OnLedgerClosedHook = impl::SubscriptionSource::OnLedgerClosedHook;
 
     /**
      * @brief Construct a new SourceImpl object
@@ -80,7 +81,7 @@ public:
      * @param forwardingSource The forwarding source
      */
     template <typename SomeGrpcSourceType, typename SomeForwardingSourceType>
-        requires std::is_same_v<GrpcSourceType, SomeGrpcSourceType> &&
+        requires std::is_same_v<GrpcSourceType, SomeGrpcSourceType> and
                      std::is_same_v<ForwardingSourceType, SomeForwardingSourceType>
     SourceImpl(
         std::string ip,
@@ -250,7 +251,8 @@ make_Source(
     std::shared_ptr<feed::SubscriptionManager> subscriptions,
     std::shared_ptr<NetworkValidatedLedgers> validatedLedgers,
     Source::OnDisconnectHook onDisconnect,
-    Source::OnConnectHook onConnect
+    Source::OnConnectHook onConnect,
+    Source::OnLedgerClosedHook onLedgerClosed
 );
 
 }  // namespace etl

src/etl/impl/ForwardingCache.cpp

@@ -0,0 +1,134 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, 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/impl/ForwardingCache.hpp"
+
+#include "util/Assert.hpp"
+
+#include <boost/json/object.hpp>
+#include <boost/json/value_to.hpp>
+
+#include <chrono>
+#include <mutex>
+#include <optional>
+#include <shared_mutex>
+#include <string>
+#include <unordered_set>
+#include <utility>
+
+namespace etl::impl {
+
+namespace {
+
+std::optional<std::string>
+getCommand(boost::json::object const& request)
+{
+    if (not request.contains("command")) {
+        return std::nullopt;
+    }
+    return boost::json::value_to<std::string>(request.at("command"));
+}
+
+}  // namespace
+
+void
+CacheEntry::put(boost::json::object response)
+{
+    response_ = std::move(response);
+    lastUpdated_ = std::chrono::steady_clock::now();
+}
+
+std::optional<boost::json::object>
+CacheEntry::get() const
+{
+    return response_;
+}
+
+std::chrono::steady_clock::time_point
+CacheEntry::lastUpdated() const
+{
+    return lastUpdated_;
+}
+
+void
+CacheEntry::invalidate()
+{
+    response_.reset();
+}
+
+std::unordered_set<std::string> const
+    ForwardingCache::CACHEABLE_COMMANDS{"server_info", "server_state", "server_definitions", "fee", "ledger_closed"};
+
+ForwardingCache::ForwardingCache(std::chrono::steady_clock::duration const cacheTimeout) : cacheTimeout_{cacheTimeout}
+{
+    for (auto const& command : CACHEABLE_COMMANDS) {
+        cache_.emplace(command, CacheEntry{});
+    }
+}
+
+bool
+ForwardingCache::shouldCache(boost::json::object const& request)
+{
+    auto const command = getCommand(request);
+    return command.has_value() and CACHEABLE_COMMANDS.contains(*command);
+}
+
+std::optional<boost::json::object>
+ForwardingCache::get(boost::json::object const& request) const
+{
+    auto const command = getCommand(request);
+
+    if (not command.has_value()) {
+        return std::nullopt;
+    }
+
+    auto it = cache_.find(*command);
+    if (it == cache_.end())
+        return std::nullopt;
+
+    auto const& entry = it->second.lock<std::shared_lock>();
+    if (std::chrono::steady_clock::now() - entry->lastUpdated() > cacheTimeout_)
+        return std::nullopt;
+
+    return entry->get();
+}
+
+void
+ForwardingCache::put(boost::json::object const& request, boost::json::object const& response)
+{
+    auto const command = getCommand(request);
+    if (not command.has_value() or not shouldCache(request))
+        return;
+
+    ASSERT(cache_.contains(*command), "Command is not in the cache: {}", *command);
+
+    auto entry = cache_[*command].lock<std::unique_lock>();
+    entry->put(response);
+}
+
+void
+ForwardingCache::invalidate()
+{
+    for (auto& [_, entry] : cache_) {
+        auto entryLock = entry.lock<std::unique_lock>();
+        entryLock->invalidate();
+    }
+}
+
+}  // namespace etl::impl

src/etl/impl/ForwardingCache.hpp

@@ -0,0 +1,125 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, 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/Mutex.hpp"
+
+#include <boost/json/object.hpp>
+
+#include <chrono>
+#include <optional>
+#include <shared_mutex>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+
+namespace etl::impl {
+
+/**
+ * @brief A class to store a cache entry.
+ */
+class CacheEntry {
+    std::chrono::steady_clock::time_point lastUpdated_;
+    std::optional<boost::json::object> response_;
+
+public:
+    /**
+     * @brief Put a response into the cache
+     *
+     * @param response The response to store
+     */
+    void
+    put(boost::json::object response);
+
+    /**
+     * @brief Get the response from the cache
+     *
+     * @return The response
+     */
+    std::optional<boost::json::object>
+    get() const;
+
+    /**
+     * @brief Get the last time the cache was updated
+     *
+     * @return The last time the cache was updated
+     */
+    std::chrono::steady_clock::time_point
+    lastUpdated() const;
+
+    /**
+     * @brief Invalidate the cache entry
+     */
+    void
+    invalidate();
+};
+
+/**
+ * @brief A class to store a cache of forwarding responses
+ */
+class ForwardingCache {
+    std::chrono::steady_clock::duration cacheTimeout_;
+    std::unordered_map<std::string, util::Mutex<CacheEntry, std::shared_mutex>> cache_;
+
+public:
+    static std::unordered_set<std::string> const CACHEABLE_COMMANDS;
+
+    /**
+     * @brief Construct a new Forwarding Cache object
+     *
+     * @param cacheTimeout The time for cache entries to expire
+     */
+    ForwardingCache(std::chrono::steady_clock::duration cacheTimeout);
+
+    /**
+     * @brief Check if a request should be cached
+     *
+     * @param request The request to check
+     * @return true if the request should be cached and false otherwise
+     */
+    [[nodiscard]] static bool
+    shouldCache(boost::json::object const& request);
+
+    /**
+     * @brief Get a response from the cache
+     *
+     * @param request The request to get the response for
+     * @return The response if it exists or std::nullopt otherwise
+     */
+    [[nodiscard]] std::optional<boost::json::object>
+    get(boost::json::object const& request) const;
+
+    /**
+     * @brief Put a response into the cache if the request should be cached
+     *
+     * @param request The request to store the response for
+     * @param response The response to store
+     */
+    void
+    put(boost::json::object const& request, boost::json::object const& response);
+
+    /**
+     * @brief Invalidate all entries in the cache
+     */
+    void
+    invalidate();
+};
+
+}  // namespace etl::impl

src/etl/impl/ForwardingSource.cpp

@@ -92,6 +92,7 @@ ForwardingSource::forwardToRippled(
 
     auto responseObject = parsedResponse.as_object();
     responseObject["forwarded"] = true;
+
     return responseObject;
 }
 

src/etl/impl/ForwardingSource.hpp

@@ -34,6 +34,7 @@ namespace etl::impl {
 class ForwardingSource {
     util::Logger log_;
     util::requests::WsConnectionBuilder connectionBuilder_;
+
     static constexpr std::chrono::seconds CONNECTION_TIMEOUT{3};
 
 public:

src/etl/impl/SubscriptionSource.cpp

@@ -197,6 +197,8 @@ SubscriptionSource::handleMessage(std::string const& message)
                 auto validatedLedgers = boost::json::value_to<std::string>(object.at(JS(validated_ledgers)));
                 setValidatedRange(std::move(validatedLedgers));
             }
+            if (isForwarding_)
+                onLedgerClosed_();
 
         } else {
             if (isForwarding_) {

src/etl/impl/SubscriptionSource.hpp

@@ -52,6 +52,7 @@ class SubscriptionSource {
 public:
     using OnConnectHook = std::function<void()>;
     using OnDisconnectHook = std::function<void()>;
+    using OnLedgerClosedHook = std::function<void()>;
 
 private:
     util::Logger log_;
@@ -72,6 +73,7 @@ private:
 
     OnConnectHook onConnect_;
     OnDisconnectHook onDisconnect_;
+    OnLedgerClosedHook onLedgerClosed_;
 
     std::atomic_bool isConnected_{false};
     std::atomic_bool stop_{false};
@@ -97,6 +99,9 @@ public:
      * @param validatedLedgers The network validated ledgers object
      * @param subscriptions The subscription manager object
      * @param onDisconnect The onDisconnect hook. Called when the connection is lost
+     * @param onNewLedger The onNewLedger hook. Called when a new ledger is received
+     * @param onLedgerClosed The onLedgerClosed hook. Called when the ledger is closed but only if the source is
+     * forwarding
      * @param connectionTimeout The connection timeout. Defaults to 30 seconds
      * @param retryDelay The retry delay. Defaults to 1 second
      */
@@ -109,6 +114,7 @@ public:
         std::shared_ptr<SubscriptionManagerType> subscriptions,
         OnConnectHook onConnect,
         OnDisconnectHook onDisconnect,
+        OnLedgerClosedHook onLedgerClosed,
         std::chrono::steady_clock::duration const connectionTimeout = CONNECTION_TIMEOUT,
         std::chrono::steady_clock::duration const retryDelay = RETRY_DELAY
     )
@@ -119,6 +125,7 @@ public:
         , retry_(util::makeRetryExponentialBackoff(retryDelay, RETRY_MAX_DELAY, strand_))
         , onConnect_(std::move(onConnect))
         , onDisconnect_(std::move(onDisconnect))
+        , onLedgerClosed_(std::move(onLedgerClosed))
     {
         wsConnectionBuilder_.addHeader({boost::beast::http::field::user_agent, "clio-client"})
             .addHeader({"X-User", "clio-client"})

src/util/Mutex.hpp

@@ -24,17 +24,19 @@
 
 namespace util {
 
-template <typename ProtectedDataType>
+template <typename ProtectedDataType, typename MutextType>
 class Mutex;
 
 /**
  * @brief A lock on a mutex that provides access to the protected data.
  *
  * @tparam ProtectedDataType data type to hold
+ * @tparam LockType type of lock
+ * @tparam MutexType type of mutex
  */
-template <typename ProtectedDataType>
+template <typename ProtectedDataType, template <typename> typename LockType, typename MutexType>
 class Lock {
-    std::scoped_lock<std::mutex> lock_;
+    LockType<MutexType> lock_;
     ProtectedDataType& data_;
 
 public:
@@ -77,9 +79,9 @@ public:
     /** @endcond */
 
 private:
-    friend class Mutex<std::remove_const_t<ProtectedDataType>>;
+    friend class Mutex<std::remove_const_t<ProtectedDataType>, MutexType>;
 
-    explicit Lock(std::mutex& mutex, ProtectedDataType& data) : lock_(mutex), data_(data)
+    Lock(MutexType& mutex, ProtectedDataType& data) : lock_(mutex), data_(data)
     {
     }
 };
@@ -88,10 +90,11 @@ private:
  * @brief A container for data that is protected by a mutex. Inspired by Mutex in Rust.
  *
  * @tparam ProtectedDataType data type to hold
+ * @tparam MutexType type of mutex
  */
-template <typename ProtectedDataType>
+template <typename ProtectedDataType, typename MutexType = std::mutex>
 class Mutex {
-    mutable std::mutex mutex_;
+    mutable MutexType mutex_;
     ProtectedDataType data_;
 
 public:
@@ -123,23 +126,27 @@ public:
     /**
      * @brief Lock the mutex and get a lock object allowing access to the protected data
      *
+     * @tparam LockType The type of lock to use
      * @return A lock on the mutex and a reference to the protected data
      */
-    Lock<ProtectedDataType const>
+    template <template <typename> typename LockType = std::lock_guard>
+    Lock<ProtectedDataType const, LockType, MutexType>
     lock() const
     {
-        return Lock<ProtectedDataType const>{mutex_, data_};
+        return {mutex_, data_};
     }
 
     /**
      * @brief Lock the mutex and get a lock object allowing access to the protected data
      *
+     * @tparam LockType The type of lock to use
      * @return A lock on the mutex and a reference to the protected data
      */
-    Lock<ProtectedDataType>
+    template <template <typename> typename LockType = std::lock_guard>
+    Lock<ProtectedDataType, LockType, MutexType>
     lock()
     {
-        return Lock<ProtectedDataType>{mutex_, data_};
+        return {mutex_, data_};
     }
 };
 

unittests/etl/ETLStateTests.cpp

@@ -32,7 +32,7 @@ using namespace util;
 using namespace testing;
 
 struct ETLStateTest : public NoLoggerFixture {
-    MockSource const source = MockSource{};
+    MockSource source = MockSource{};
 };
 
 TEST_F(ETLStateTest, Error)

unittests/etl/ForwardingCacheTests.cpp

@@ -0,0 +1,133 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, 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/impl/ForwardingCache.hpp"
+
+#include <boost/json/object.hpp>
+#include <gtest/gtest.h>
+
+#include <chrono>
+#include <thread>
+
+using namespace etl::impl;
+
+struct CacheEntryTests : public ::testing::Test {
+    CacheEntry entry_;
+    boost::json::object const object_ = {{"key", "value"}};
+};
+
+TEST_F(CacheEntryTests, PutAndGet)
+{
+    EXPECT_FALSE(entry_.get());
+
+    entry_.put(object_);
+    auto result = entry_.get();
+
+    ASSERT_TRUE(result);
+    EXPECT_EQ(*result, object_);
+}
+
+TEST_F(CacheEntryTests, LastUpdated)
+{
+    EXPECT_EQ(entry_.lastUpdated().time_since_epoch().count(), 0);
+
+    entry_.put(object_);
+    auto const lastUpdated = entry_.lastUpdated();
+
+    EXPECT_GE(
+        std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - lastUpdated).count(), 0
+    );
+
+    entry_.put(boost::json::object{{"key", "new value"}});
+    auto const newLastUpdated = entry_.lastUpdated();
+    EXPECT_GT(newLastUpdated, lastUpdated);
+    EXPECT_GE(
+        std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - newLastUpdated)
+            .count(),
+        0
+    );
+}
+
+TEST_F(CacheEntryTests, Invalidate)
+{
+    entry_.put(object_);
+    entry_.invalidate();
+    EXPECT_FALSE(entry_.get());
+}
+
+TEST(ForwardingCacheTests, ShouldCache)
+{
+    for (auto const& command : ForwardingCache::CACHEABLE_COMMANDS) {
+        auto const request = boost::json::object{{"command", command}};
+        EXPECT_TRUE(ForwardingCache::shouldCache(request));
+    }
+    auto const request = boost::json::object{{"command", "tx"}};
+    EXPECT_FALSE(ForwardingCache::shouldCache(request));
+
+    auto const requestWithoutCommand = boost::json::object{{"key", "value"}};
+    EXPECT_FALSE(ForwardingCache::shouldCache(requestWithoutCommand));
+}
+
+TEST(ForwardingCacheTests, Get)
+{
+    ForwardingCache cache{std::chrono::seconds{100}};
+    auto const request = boost::json::object{{"command", "server_info"}};
+    auto const response = boost::json::object{{"key", "value"}};
+
+    cache.put(request, response);
+    auto const result = cache.get(request);
+
+    ASSERT_TRUE(result);
+    EXPECT_EQ(*result, response);
+}
+
+TEST(ForwardingCacheTests, GetExpired)
+{
+    ForwardingCache cache{std::chrono::milliseconds{1}};
+    auto const request = boost::json::object{{"command", "server_info"}};
+    auto const response = boost::json::object{{"key", "value"}};
+
+    cache.put(request, response);
+    std::this_thread::sleep_for(std::chrono::milliseconds{2});
+
+    auto const result = cache.get(request);
+    EXPECT_FALSE(result);
+}
+
+TEST(ForwardingCacheTests, GetAndPutNotCommand)
+{
+    ForwardingCache cache{std::chrono::seconds{100}};
+    auto const request = boost::json::object{{"key", "value"}};
+    auto const response = boost::json::object{{"key", "value"}};
+    cache.put(request, response);
+    auto const result = cache.get(request);
+    EXPECT_FALSE(result);
+}
+
+TEST(ForwardingCache, Invalidate)
+{
+    ForwardingCache cache{std::chrono::seconds{100}};
+    auto const request = boost::json::object{{"command", "server_info"}};
+    auto const response = boost::json::object{{"key", "value"}};
+
+    cache.put(request, response);
+    cache.invalidate();
+
+    EXPECT_FALSE(cache.get(request));
+}

unittests/etl/ForwardingSourceTests.cpp

@@ -28,6 +28,7 @@
 #include <gtest/gtest.h>
 
 #include <chrono>
+#include <optional>
 #include <string>
 #include <utility>
 
@@ -47,7 +48,7 @@ TEST_F(ForwardingSourceTests, ConnectionFailed)
 }
 
 struct ForwardingSourceOperationsTests : ForwardingSourceTests {
-    std::string const message_ = R"({"data":"some_data"})";
+    std::string const message_ = R"({"data": "some_data"})";
     boost::json::object const reply_ = {{"reply", "some_reply"}};
 
     TestWsConnection
@@ -83,7 +84,7 @@ TEST_F(ForwardingSourceOperationsTests, ParseFailed)
 
         auto receivedMessage = connection.receive(yield);
         [&]() { ASSERT_TRUE(receivedMessage); }();
-        EXPECT_EQ(*receivedMessage, message_);
+        EXPECT_EQ(boost::json::parse(*receivedMessage), boost::json::parse(message_)) << *receivedMessage;
 
         auto sendError = connection.send("invalid_json", yield);
         [&]() { ASSERT_FALSE(sendError) << *sendError; }();
@@ -97,6 +98,28 @@ TEST_F(ForwardingSourceOperationsTests, ParseFailed)
     });
 }
 
+TEST_F(ForwardingSourceOperationsTests, GotNotAnObject)
+{
+    boost::asio::spawn(ctx, [&](boost::asio::yield_context yield) {
+        auto connection = serverConnection(yield);
+
+        auto receivedMessage = connection.receive(yield);
+        [&]() { ASSERT_TRUE(receivedMessage); }();
+        EXPECT_EQ(boost::json::parse(*receivedMessage), boost::json::parse(message_)) << *receivedMessage;
+
+        auto sendError = connection.send(R"(["some_value"])", yield);
+
+        [&]() { ASSERT_FALSE(sendError) << *sendError; }();
+
+        connection.close(yield);
+    });
+
+    runSpawn([&](boost::asio::yield_context yield) {
+        auto result = forwardingSource.forwardToRippled(boost::json::parse(message_).as_object(), {}, yield);
+        EXPECT_FALSE(result);
+    });
+}
+
 TEST_F(ForwardingSourceOperationsTests, Success)
 {
     boost::asio::spawn(ctx, [&](boost::asio::yield_context yield) {
@@ -104,7 +127,7 @@ TEST_F(ForwardingSourceOperationsTests, Success)
 
         auto receivedMessage = connection.receive(yield);
         [&]() { ASSERT_TRUE(receivedMessage); }();
-        EXPECT_EQ(*receivedMessage, message_);
+        EXPECT_EQ(boost::json::parse(*receivedMessage), boost::json::parse(message_)) << *receivedMessage;
 
         auto sendError = connection.send(boost::json::serialize(reply_), yield);
         [&]() { ASSERT_FALSE(sendError) << *sendError; }();

unittests/etl/SourceTests.cpp

@@ -67,7 +67,8 @@ struct ForwardingSourceMock {
     MOCK_METHOD(
         ForwardToRippledReturnType,
         forwardToRippled,
-        (boost::json::object const&, ClientIpOpt const&, boost::asio::yield_context)
+        (boost::json::object const&, ClientIpOpt const&, boost::asio::yield_context),
+        (const)
     );
 };
 

unittests/etl/SubscriptionSourceTests.cpp

@@ -60,6 +60,7 @@ struct SubscriptionSourceConnectionTests : public NoLoggerFixture {
 
     StrictMock<MockFunction<void()>> onConnectHook_;
     StrictMock<MockFunction<void()>> onDisconnectHook_;
+    StrictMock<MockFunction<void()>> onLedgerClosedHook_;
 
     std::unique_ptr<SubscriptionSource> subscriptionSource_ = std::make_unique<SubscriptionSource>(
         ioContext_,
@@ -69,6 +70,7 @@ struct SubscriptionSourceConnectionTests : public NoLoggerFixture {
         subscriptionManager_,
         onConnectHook_.AsStdFunction(),
         onDisconnectHook_.AsStdFunction(),
+        onLedgerClosedHook_.AsStdFunction(),
         std::chrono::milliseconds(1),
         std::chrono::milliseconds(1)
     );
@@ -299,10 +301,37 @@ TEST_F(SubscriptionSourceReadTests, GotResultWithLedgerIndexAndValidatedLedgers)
     EXPECT_FALSE(subscriptionSource_->hasLedger(4));
 }
 
+TEST_F(SubscriptionSourceReadTests, GotLedgerClosed)
+{
+    boost::asio::spawn(ioContext_, [this](boost::asio::yield_context yield) {
+        auto connection = connectAndSendMessage(R"({"type":"ledgerClosed"})", yield);
+        connection.close(yield);
+    });
+
+    EXPECT_CALL(onConnectHook_, Call());
+    EXPECT_CALL(onDisconnectHook_, Call()).WillOnce([this]() { subscriptionSource_->stop(); });
+    ioContext_.run();
+}
+
+TEST_F(SubscriptionSourceReadTests, GotLedgerClosedForwardingIsSet)
+{
+    subscriptionSource_->setForwarding(true);
+
+    boost::asio::spawn(ioContext_, [this](boost::asio::yield_context yield) {
+        auto connection = connectAndSendMessage(R"({"type": "ledgerClosed"})", yield);
+        connection.close(yield);
+    });
+
+    EXPECT_CALL(onConnectHook_, Call());
+    EXPECT_CALL(onLedgerClosedHook_, Call());
+    EXPECT_CALL(onDisconnectHook_, Call()).WillOnce([this]() { subscriptionSource_->stop(); });
+    ioContext_.run();
+}
+
 TEST_F(SubscriptionSourceReadTests, GotLedgerClosedWithLedgerIndex)
 {
     boost::asio::spawn(ioContext_, [this](boost::asio::yield_context yield) {
-        auto connection = connectAndSendMessage(R"({"type":"ledgerClosed","ledger_index":123})", yield);
+        auto connection = connectAndSendMessage(R"({"type": "ledgerClosed","ledger_index": 123})", yield);
         connection.close(yield);
     });