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/util/CoroutineGroup.hpp

@@ -0,0 +1,88 @@
+//------------------------------------------------------------------------------
+/*
+    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 <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
+
+#include <cstddef>
+#include <functional>
+#include <optional>
+
+namespace util {
+
+/**
+ * @brief CoroutineGroup is a helper class to manage a group of coroutines. It allows to spawn multiple coroutines and
+ * wait for all of them to finish.
+ */
+class CoroutineGroup {
+    boost::asio::steady_timer timer_;
+    std::optional<int> maxChildren_;
+    int childrenCounter_{0};
+
+public:
+    /**
+     * @brief Construct a new Coroutine Group object
+     *
+     * @param yield The yield context to use for the internal timer
+     * @param maxChildren The maximum number of coroutines that can be spawned at the same time. If not provided, there
+     * is no limit
+     */
+    CoroutineGroup(boost::asio::yield_context yield, std::optional<int> maxChildren = std::nullopt);
+
+    /**
+     * @brief Destroy the Coroutine Group object
+     *
+     * @note asyncWait() must be called before the object is destroyed
+     */
+    ~CoroutineGroup();
+
+    /**
+     * @brief Spawn a new coroutine in the group
+     *
+     * @param yield The yield context to use for the coroutine (it should be the same as the one used in the
+     * constructor)
+     * @param fn The function to execute
+     * @return true If the coroutine was spawned successfully. false if the maximum number of coroutines has been
+     * reached
+     */
+    bool
+    spawn(boost::asio::yield_context yield, std::function<void(boost::asio::yield_context)> fn);
+
+    /**
+     * @brief Wait for all the coroutines in the group to finish
+     *
+     * @note This method must be called before the object is destroyed
+     *
+     * @param yield The yield context to use for the internal timer
+     */
+    void
+    asyncWait(boost::asio::yield_context yield);
+
+    /**
+     * @brief Get the number of coroutines in the group
+     *
+     * @return size_t The number of coroutines in the group
+     */
+    size_t
+    size() const;
+};
+
+}  // namespace util