mqtt5/include/async_mqtt5/impl/replies.hpp

#ifndef ASYNC_MQTT5_REPLIES_HPP
#define ASYNC_MQTT5_REPLIES_HPP

#include <boost/asio/any_completion_handler.hpp>
#include <boost/asio/any_io_executor.hpp>
#include <boost/asio/consign.hpp>
#include <boost/asio/dispatch.hpp>
#include <boost/asio/error.hpp>
#include <boost/asio/post.hpp>
#include <boost/asio/prepend.hpp>

#include <async_mqtt5/detail/control_packet.hpp>
#include <async_mqtt5/detail/internal_types.hpp>

namespace async_mqtt5::detail {

namespace asio = boost::asio;

class replies {
public:
	using executor_type = asio::any_io_executor;
private:
	using Signature = void (error_code, byte_citer, byte_citer);

	static constexpr auto max_reply_time = std::chrono::seconds(20);

	class reply_handler {
		asio::any_completion_handler<Signature> _handler;
		control_code_e _code;
		uint16_t _packet_id;
		std::chrono::time_point<std::chrono::system_clock> _ts;
	public:
		template <typename H>
		reply_handler(control_code_e code, uint16_t pid, H&& handler) :
			_handler(std::forward<H>(handler)), _code(code), _packet_id(pid),
			_ts(std::chrono::system_clock::now())
		{}

		void complete(
			error_code ec,
			byte_citer first = byte_citer {}, byte_citer last = byte_citer {}
		) {
			asio::dispatch(asio::prepend(std::move(_handler), ec, first, last));
		}

		void complete_post(const executor_type& ex, error_code ec) {
			asio::post(
				ex,
				asio::prepend(
					std::move(_handler), ec, byte_citer {}, byte_citer {}
				)
			);
		}

		uint16_t packet_id() const noexcept {
			return _packet_id;
		}

		control_code_e code() const noexcept {
			return _code;
		}

		auto time() const noexcept {
			return _ts;
		}
	};

	executor_type _ex;

	using handlers = std::vector<reply_handler>;
	handlers _handlers;

	struct fast_reply {
		control_code_e code;
		uint16_t packet_id;
		std::unique_ptr<std::string> packet;
	};
	using fast_replies = std::vector<fast_reply>;
	fast_replies _fast_replies;

public:
	template <typename Executor>
	replies(const Executor& ex) : _ex(ex) {}

	template <typename CompletionToken>
	decltype(auto) async_wait_reply(
		control_code_e code, uint16_t packet_id, CompletionToken&& token
	) {
		auto dup_handler_ptr = find_handler(code, packet_id);
		if (dup_handler_ptr != _handlers.end()) {
			dup_handler_ptr->complete_post(_ex, asio::error::operation_aborted);
			_handlers.erase(dup_handler_ptr);
		}

		auto freply = find_fast_reply(code, packet_id);

		if (freply == _fast_replies.end()) {
			auto initiation = [](
				auto handler, replies& self,
				control_code_e code, uint16_t packet_id
			) {
				self._handlers.emplace_back(
					code, packet_id, std::move(handler)
				);
			};
			return asio::async_initiate<CompletionToken, Signature>(
				initiation, token, std::ref(*this), code, packet_id
			);
		}

		auto fdata = std::move(*freply);
		_fast_replies.erase(freply);

		auto initiation = [](
			auto handler, std::unique_ptr<std::string> packet,
			const executor_type& ex
		) {
			byte_citer first = packet->cbegin();
			byte_citer last = packet->cend();

			asio::post(
				ex,
				asio::consign(
					asio::prepend(
						std::move(handler), error_code {}, first, last
					),
					std::move(packet)
				)
			);
		};

		return asio::async_initiate<CompletionToken, Signature>(
			initiation, token, std::move(fdata.packet), _ex
		);
	}

	void dispatch(
		error_code ec, control_code_e code, uint16_t packet_id,
		byte_citer first, byte_citer last
	) {
		auto handler_ptr = find_handler(code, packet_id);

		if (handler_ptr == _handlers.end()) {
			_fast_replies.push_back({
				code, packet_id,
				std::make_unique<std::string>(first, last)
			});
			return;
		}

		auto handler = std::move(*handler_ptr);
		_handlers.erase(handler_ptr);
		handler.complete(ec, first, last);
	}

	void resend_unanswered() {
		auto ua = std::move(_handlers);
		for (auto& h : ua)
			h.complete(asio::error::try_again);
	}

	void cancel_unanswered() {
		auto ua = std::move(_handlers);
		for (auto& h : ua)
			h.complete(asio::error::operation_aborted);
	}

	bool any_expired() {
		auto now = std::chrono::system_clock::now();
		return std::any_of(
			_handlers.begin(), _handlers.end(),
			[now](const auto& h) {
				return now - h.time() > max_reply_time;
			}
		);
	}

	void clear_fast_replies() {
		_fast_replies.clear();
	}

	void clear_pending_pubrels() {
		for (auto it = _handlers.begin(); it != _handlers.end();) {
			if (it->code() == control_code_e::pubrel) {
				it->complete(asio::error::operation_aborted);
				it = _handlers.erase(it);
			}
			else
				++it;
		}
	}

private:
	handlers::iterator find_handler(control_code_e code, uint16_t packet_id) {
		return std::find_if(
			_handlers.begin(), _handlers.end(),
			[code, packet_id](const auto& h) {
				return h.code() == code && h.packet_id() == packet_id;
			}
		);
	}

	fast_replies::iterator find_fast_reply(
		control_code_e code, uint16_t packet_id
	) {
		return std::find_if(
			_fast_replies.begin(), _fast_replies.end(),
			[code, packet_id](const auto& f) {
				return f.code == code && f.packet_id == packet_id;
			}
		);
	}

};

} // end namespace async_mqtt5::detail

#endif // !ASYNC_MQTT5_REPLIES_HPP