mqtt5/include/async_mqtt5/detail/channel_traits.hpp

#ifndef ASYNC_MQTT5_CHANNEL_TRAITS_HPP
#define ASYNC_MQTT5_CHANNEL_TRAITS_HPP

#include <deque>

#include <boost/asio/error.hpp>

namespace async_mqtt5::detail {

namespace asio = boost::asio;
using error_code = boost::system::error_code;

template <typename Element>
class bounded_deque {
	std::deque<Element> _buffer;
	static constexpr size_t MAX_SIZE = 65535;

public:
	bounded_deque() = default;
	bounded_deque(size_t n) : _buffer(n) {}

	size_t size() const { return _buffer.size(); }

	template <typename E>
	void push_back(E&& e) {
		if (_buffer.size() == MAX_SIZE)
			_buffer.pop_front();
		_buffer.push_back(std::forward<E>(e));
	}

	void pop_front() { _buffer.pop_front(); }

	void clear() { _buffer.clear(); }

	const auto& front() const noexcept { return _buffer.front(); }

	auto& front() noexcept { return _buffer.front(); }
};

template <typename... Signatures>
struct channel_traits {
	template <typename... NewSignatures>
	struct rebind {
		using other = channel_traits<NewSignatures...>;
	};
};

template <typename R, typename... Args>
struct channel_traits<R(error_code, Args...)> {
	static_assert(sizeof...(Args) > 0);
	template <typename... NewSignatures>
	struct rebind {
		using other = channel_traits<NewSignatures...>;
	};

	template <typename Element>
	struct container {
		using type = bounded_deque<Element>;
	};

	using receive_cancelled_signature = R(error_code, Args...);

	template <typename F>
	static void invoke_receive_cancelled(F f) {
		std::forward<F>(f)(
			asio::error::operation_aborted,
			typename std::decay_t<Args>()...
		);
	}

	using receive_closed_signature = R(error_code, Args...);

	template <typename F>
	static void invoke_receive_closed(F f) {
		std::forward<F>(f)(
			asio::error::operation_aborted,
			typename std::decay_t<Args>()...
		);
	}
};

} // namespace async_mqtt5::detail

#endif // !ASYNC_MQTT5_CHANNEL_TRAITS_HPP