construct/include/ircd/net/resolver.h

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_NET_RESOLVER_H

// This file is not included with the IRCd standard include stack because
// it requires symbols we can't forward declare without boost headers. It
// is part of the <ircd/asio.h> stack which can be included in your
// definition file if you need low level access to this resolver API.

/// Internal resolver service
struct ircd::net::dns::resolver
{
	struct tag;
	using header = rfc1035::header;

	static constexpr const size_t &MAX_COUNT{64};
	static conf::item<milliseconds> timeout;
	static conf::item<milliseconds> send_rate;

	std::vector<ip::udp::endpoint> server;       // The list of active servers
	size_t server_next{0};                       // Round-robin state to hit servers
	void init_servers();

	ctx::dock dock;
	std::map<uint16_t, tag> tags;                // The active requests
	steady_point send_last;                      // Time of last send
	using queued = std::pair<uint16_t, std::string>;
	std::deque<queued> sendq;                    // Queue of frames for rate-limiting

	ip::udp::socket ns;                          // A pollable activity object
	ip::udp::endpoint reply_from;                // Remote addr of recv
	char reply[64_KiB] alignas(16);              // Buffer for recv

	bool handle_error(const error_code &ec) const;
	bool handle_error(const header &, const rfc1035::question &, const dns::opts &);
	void handle_reply(const header &, const const_buffer &body, tag &);
	void handle_reply(const header &, const const_buffer &body);
	void handle(const error_code &ec, const size_t &) noexcept;
	void set_handle();

	void queue_query(const const_buffer &, tag &);
	void send_query(const ip::udp::endpoint &, const const_buffer &, tag &);
	void send_query(const const_buffer &, tag &);
	void submit(const const_buffer &, tag &);

	tag &set_tag(tag &&);
	const_buffer make_query(const mutable_buffer &buf, const tag &) const;
	void operator()(const hostport &, const opts &, callback);

	bool check_timeout(const uint16_t &id, tag &, const steady_point &expired);
	void check_timeouts(const milliseconds &timeout);
	void timeout_worker();
	ctx::context timeout_context;

	void flush(const queued &);
	void sendq_worker();
	ctx::context sendq_context;

	resolver();
	~resolver() noexcept;
};

struct ircd::net::dns::resolver::tag
{
	uint16_t id {0};
	hostport hp;          // note: invalid after query sent
	dns::opts opts;       // note: invalid after query sent
	callback cb;
	steady_point last;
	uint8_t tries {0};

	tag(const hostport &, const dns::opts &, callback);
};

inline
ircd::net::dns::resolver::tag::tag(const hostport &hp,
                                   const dns::opts &opts,
                                   callback cb)
:hp{hp}
,opts{opts}
,cb{std::move(cb)}
{}