refactor: Coroutine based webserver (#1699)

Code of new coroutine-based web server. The new server is not connected
to Clio and not ready to use yet.
For #919.

src/web/ng/impl/ConnectionHandler.hpp

@@ -0,0 +1,130 @@
+//------------------------------------------------------------------------------
+/*
+    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/log/Logger.hpp"
+#include "web/ng/Connection.hpp"
+#include "web/ng/Error.hpp"
+#include "web/ng/MessageHandler.hpp"
+#include "web/ng/Request.hpp"
+#include "web/ng/Response.hpp"
+
+#include <boost/asio/spawn.hpp>
+#include <boost/signals2/signal.hpp>
+#include <boost/signals2/variadic_signal.hpp>
+
+#include <cstddef>
+#include <functional>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+
+namespace web::ng::impl {
+
+class ConnectionHandler {
+public:
+    enum class ProcessingPolicy { Sequential, Parallel };
+
+    struct StringHash {
+        using hash_type = std::hash<std::string_view>;
+        using is_transparent = void;
+
+        std::size_t
+        operator()(char const* str) const;
+        std::size_t
+        operator()(std::string_view str) const;
+        std::size_t
+        operator()(std::string const& str) const;
+    };
+
+    using TargetToHandlerMap = std::unordered_map<std::string, MessageHandler, StringHash, std::equal_to<>>;
+
+private:
+    util::Logger log_{"WebServer"};
+    util::Logger perfLog_{"Performance"};
+
+    ProcessingPolicy processingPolicy_;
+    std::optional<size_t> maxParallelRequests_;
+
+    TargetToHandlerMap getHandlers_;
+    TargetToHandlerMap postHandlers_;
+    std::optional<MessageHandler> wsHandler_;
+
+    boost::signals2::signal<void()> onStop_;
+
+public:
+    ConnectionHandler(ProcessingPolicy processingPolicy, std::optional<size_t> maxParallelRequests);
+
+    void
+    onGet(std::string const& target, MessageHandler handler);
+
+    void
+    onPost(std::string const& target, MessageHandler handler);
+
+    void
+    onWs(MessageHandler handler);
+
+    void
+    processConnection(ConnectionPtr connection, boost::asio::yield_context yield);
+
+    void
+    stop();
+
+private:
+    /**
+     * @brief Handle an error.
+     *
+     * @param error The error to handle.
+     * @param connection The connection that caused the error.
+     * @return True if the connection should be gracefully closed, false otherwise.
+     */
+    bool
+    handleError(Error const& error, Connection const& connection) const;
+
+    /**
+     * @brief The request-response loop.
+     *
+     * @param connection The connection to handle.
+     * @param yield The yield context.
+     * @return True if the connection should be gracefully closed, false otherwise.
+     */
+    bool
+    sequentRequestResponseLoop(Connection& connection, boost::asio::yield_context yield);
+
+    bool
+    parallelRequestResponseLoop(Connection& connection, boost::asio::yield_context yield);
+
+    std::optional<bool>
+    processRequest(Connection& connection, Request const& request, boost::asio::yield_context yield);
+
+    /**
+     * @brief Handle a request.
+     *
+     * @param connectionContext The connection context.
+     * @param request The request to handle.
+     * @param yield The yield context.
+     * @return The response to send.
+     */
+    Response
+    handleRequest(ConnectionContext const& connectionContext, Request const& request, boost::asio::yield_context yield);
+};
+
+}  // namespace web::ng::impl