/*

Copyright (c) 2015, Mikhail Titov
Copyright (c) 2004-2020, Arvid Norberg
Copyright (c) 2016-2017, Steven Siloti
Copyright (c) 2016, Pavel Pimenov
Copyright (c) 2016-2018, 2020, Alden Torres
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of the author nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#include <cctype>
#include <functional>
#include <tuple>

#include "libtorrent/parse_url.hpp"
#include "libtorrent/udp_tracker_connection.hpp"
#include "libtorrent/hex.hpp"
#include "libtorrent/random.hpp"
#include "libtorrent/aux_/session_settings.hpp"
#include "libtorrent/aux_/resolver_interface.hpp"
#include "libtorrent/ip_filter.hpp"
#include "libtorrent/aux_/time.hpp"
#include "libtorrent/aux_/io.hpp"
#include "libtorrent/aux_/ip_helpers.hpp" // for is_v6
#include "libtorrent/peer.hpp"
#include "libtorrent/error_code.hpp"

#ifndef TORRENT_DISABLE_LOGGING
#include "libtorrent/socket_io.hpp"
#endif

namespace libtorrent {

	std::map<address, udp_tracker_connection::connection_cache_entry>
		udp_tracker_connection::m_connection_cache;

	std::mutex udp_tracker_connection::m_cache_mutex;

	udp_tracker_connection::udp_tracker_connection(
		io_context& ios
		, tracker_manager& man
		, tracker_request const& req
		, std::weak_ptr<request_callback> c)
		: tracker_connection(man, req, ios, std::move(c))
		, m_transaction_id(0)
		, m_attempts(0)
		, m_state(action_t::error)
		, m_abort(false)
	{
		update_transaction_id();
	}

	void udp_tracker_connection::start()
	{
		// TODO: 2 support authentication here. tracker_req().auth
		std::string hostname;
		std::string protocol;
		int port;
		error_code ec;

		std::tie(protocol, std::ignore, hostname, port, std::ignore)
			= parse_url_components(tracker_req().url, ec);
		if (port == -1) port = protocol == "http" ? 80 : 443;

		if (ec)
		{
			tracker_connection::fail(ec, operation_t::parse_address);
			return;
		}

		aux::session_settings const& settings = m_man.settings();

		int const proxy_type = settings.get_int(settings_pack::proxy_type);

		if (settings.get_bool(settings_pack::proxy_hostnames)
			&& (proxy_type == settings_pack::socks5
				|| proxy_type == settings_pack::socks5_pw))
		{
			m_hostname = hostname;
			m_target.port(std::uint16_t(port));
			start_announce();
		}
		else
		{
			using namespace std::placeholders;
			ADD_OUTSTANDING_ASYNC("udp_tracker_connection::name_lookup");
			// when stopping, pass in the cache-only flag, because we
			// don't want to get stuck on DNS lookups when shutting down
			m_man.host_resolver().async_resolve(hostname
				, (tracker_req().event == event_t::stopped
					? aux::resolver_interface::cache_only : aux::resolver_flags{})
					| aux::resolver_interface::abort_on_shutdown
				, std::bind(&udp_tracker_connection::name_lookup
					, shared_from_this(), _1, _2, port));

#ifndef TORRENT_DISABLE_LOGGING
			std::shared_ptr<request_callback> cb = requester();
			if (cb) cb->debug_log("*** UDP_TRACKER [ initiating name lookup: \"%s\" ]"
				, hostname.c_str());
#endif
		}

		set_timeout(tracker_req().event == event_t::stopped
			? settings.get_int(settings_pack::stop_tracker_timeout)
			: settings.get_int(settings_pack::tracker_completion_timeout)
			, settings.get_int(settings_pack::tracker_receive_timeout));
	}

	void udp_tracker_connection::fail(error_code const& ec, operation_t const op
		, char const* msg, seconds32 const interval, seconds32 const min_interval)
	{
		// m_target failed. remove it from the endpoint list
		auto const i = std::find(m_endpoints.begin()
			, m_endpoints.end(), make_tcp(m_target));

		if (i != m_endpoints.end()) m_endpoints.erase(i);

		// if that was the last one, or the listen socket was closed
		// fail the whole announce
		if (m_endpoints.empty() || !tracker_req().outgoing_socket)
		{
			tracker_connection::fail(ec, op, msg, interval, min_interval);
			return;
		}

#ifndef TORRENT_DISABLE_LOGGING
		std::shared_ptr<request_callback> cb = requester();
		if (cb && cb->should_log())
		{
			cb->debug_log(R"(*** UDP_TRACKER [ host: "%s" ip: "%s" | ERROR: "%s" ])"
				, m_hostname.c_str(), print_endpoint(m_target).c_str(), ec.message().c_str());
		}
#endif

		// pick another target endpoint and try again
		m_target = make_udp(m_endpoints.front());

#ifndef TORRENT_DISABLE_LOGGING
		if (cb && cb->should_log())
		{
			cb->debug_log(R"(*** UDP_TRACKER trying next IP [ host: "%s" ip: "%s" ])"
				, m_hostname.c_str(), print_endpoint(m_target).c_str());
		}
#endif
		post(get_executor(), std::bind(
			&udp_tracker_connection::start_announce, shared_from_this()));

		aux::session_settings const& settings = m_man.settings();
		set_timeout(tracker_req().event == event_t::stopped
			? settings.get_int(settings_pack::stop_tracker_timeout)
			: settings.get_int(settings_pack::tracker_completion_timeout)
			, settings.get_int(settings_pack::tracker_receive_timeout));
	}

	void udp_tracker_connection::name_lookup(error_code const& error
		, std::vector<address> const& addresses, int port)
	{
		COMPLETE_ASYNC("udp_tracker_connection::name_lookup");
		if (m_abort) return;
		if (error == boost::asio::error::operation_aborted) return;
		if (error || addresses.empty())
		{
			fail(error, operation_t::hostname_lookup);
			return;
		}

		std::shared_ptr<request_callback> cb = requester();
#ifndef TORRENT_DISABLE_LOGGING
		if (cb) cb->debug_log("*** UDP_TRACKER [ name lookup successful ]");
#endif
		if (cancelled())
		{
			fail(error_code(errors::torrent_aborted), operation_t::hostname_lookup);
			return;
		}

		restart_read_timeout();

		if (!tracker_req().outgoing_socket)
		{
			fail(error_code(errors::invalid_listen_socket), operation_t::hostname_lookup);
			return;
		}

		auto const listen_socket = bind_socket();

		// filter all endpoints we cannot reach from this listen socket, which may
		// be all of them, in which case we should not announce this listen socket
		// to this tracker
		for (auto const& addr : addresses)
		{
			if (!listen_socket.can_route(addr)) continue;
			m_endpoints.emplace_back(addr, std::uint16_t(port));
		}

		if (m_endpoints.empty())
		{
			fail(error_code(boost::system::errc::host_unreachable, generic_category())
				, operation_t::hostname_lookup);
			return;
		}

		if (tracker_req().filter)
		{
			// remove endpoints that are filtered by the IP filter
			for (auto k = m_endpoints.begin(); k != m_endpoints.end();)
			{
				if (tracker_req().filter->access(k->address()) == ip_filter::blocked)
				{
#ifndef TORRENT_DISABLE_LOGGING
					if (cb && cb->should_log())
					{
						cb->debug_log("*** UDP_TRACKER [ IP blocked by filter: %s ]"
							, print_address(k->address()).c_str());
					}
#endif
					k = m_endpoints.erase(k);
				}
				else
					++k;
			}
		}

		// if all endpoints were filtered by the IP filter, we can't connect
		if (m_endpoints.empty())
		{
			fail(error_code(errors::banned_by_ip_filter), operation_t::hostname_lookup);
			return;
		}

		m_target = make_udp(m_endpoints.front());

		start_announce();
	}

	void udp_tracker_connection::start_announce()
	{
		std::unique_lock<std::mutex> l(m_cache_mutex);
		auto const cc = m_connection_cache.find(m_target.address());
		if (cc != m_connection_cache.end())
		{
			// we found a cached entry! Now, we can only
			// use if if it hasn't expired
			if (aux::time_now() < cc->second.expires)
			{
				if (tracker_req().kind & tracker_request::scrape_request)
					send_udp_scrape();
				else
					send_udp_announce();
				return;
			}
			// if it expired, remove it from the cache
			m_connection_cache.erase(cc);
		}
		l.unlock();

		send_udp_connect();
	}

	void udp_tracker_connection::on_timeout(error_code const& ec)
	{
		if (ec)
		{
			fail(ec, operation_t::timer);
			return;
		}

#ifndef TORRENT_DISABLE_LOGGING
		std::shared_ptr<request_callback> cb = requester();
		if (cb) cb->debug_log("*** UDP_TRACKER [ timed out url: %s ]", tracker_req().url.c_str());
#endif
		fail(error_code(errors::timed_out), operation_t::timer);
	}

	void udp_tracker_connection::close()
	{
		cancel();
		m_man.remove_request(this);
	}

	bool udp_tracker_connection::on_receive_hostname(char const* hostname
		, span<char const> buf)
	{
		TORRENT_UNUSED(hostname);
		// just ignore the hostname this came from, pretend that
		// it's from the same endpoint we sent it to (i.e. the same
		// port). We have so many other ways of confirming this packet
		// comes from the tracker anyway, so it's not a big deal
		return on_receive(m_target, buf);
	}

	bool udp_tracker_connection::on_receive(udp::endpoint const& ep
		, span<char const> const buf)
	{
#ifndef TORRENT_DISABLE_LOGGING
		std::shared_ptr<request_callback> cb = requester();
#endif

		// ignore responses before we've sent any requests
		if (m_state == action_t::error)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb) cb->debug_log("<== UDP_TRACKER [ m_action == error ]");
#endif
			return false;
		}

		if (m_abort)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb) cb->debug_log("<== UDP_TRACKER [ aborted]");
#endif
			return false;
		}

		// ignore packet not sent from the tracker
		// if m_target is inaddr_any, it suggests that we
		// sent the packet through a proxy only knowing
		// the hostname, in which case this packet might be for us
		if (!m_target.address().is_unspecified() && m_target != ep)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb && cb->should_log())
			{
				cb->debug_log("<== UDP_TRACKER [ unexpected source IP: %s "
					"expected: %s ]"
					, print_endpoint(ep).c_str()
					, print_endpoint(m_target).c_str());
			}
#endif
			return false;
		}

#ifndef TORRENT_DISABLE_LOGGING
		if (cb) cb->debug_log("<== UDP_TRACKER_PACKET [ size: %d ]"
			, int(buf.size()));
#endif

		// ignore packets smaller than 8 bytes
		if (buf.size() < 8) return false;

		span<const char> ptr = buf;
		auto const action = static_cast<action_t>(aux::read_int32(ptr));
		std::uint32_t const transaction = aux::read_uint32(ptr);

#ifndef TORRENT_DISABLE_LOGGING
		if (cb) cb->debug_log("*** UDP_TRACKER_PACKET [ action: %d ]"
			, static_cast<int>(action));
#endif

		// ignore packets with incorrect transaction id
		if (m_transaction_id != transaction)
		{
#ifndef TORRENT_DISABLE_LOGGING
		if (cb) cb->debug_log("*** UDP_TRACKER_PACKET [ tid: %x ]"
				, int(transaction));
#endif
			return false;
		}

		if (action == action_t::error)
		{
			fail(error_code(errors::tracker_failure), operation_t::bittorrent
				, std::string(buf.data(), static_cast<std::size_t>(buf.size())).c_str());
			return true;
		}

		// ignore packets that's not a response to our message
		if (action != m_state)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb) cb->debug_log("*** UDP_TRACKER_PACKET [ unexpected action: %d "
				" expected: %d ]", static_cast<int>(action), static_cast<int>(m_state));
#endif
			return false;
		}

		restart_read_timeout();

#ifndef TORRENT_DISABLE_LOGGING
		if (cb)
			cb->debug_log("*** UDP_TRACKER_RESPONSE [ tid: %x ]"
				, int(transaction));
#endif

		switch (m_state)
		{
			case action_t::connect:
				return on_connect_response(buf);
			case action_t::announce:
				return on_announce_response(buf);
			case action_t::scrape:
				return on_scrape_response(buf);
			case action_t::error:
				return false;
		}
		return false;
	}

	void udp_tracker_connection::update_transaction_id()
	{
		// don't use 0, because that has special meaning (uninitialized)
		std::uint32_t const new_tid = random(0xfffffffe) + 1;

		if (m_transaction_id != 0)
			m_man.update_transaction_id(shared_from_this(), new_tid);
		m_transaction_id = new_tid;
	}

	bool udp_tracker_connection::on_connect_response(span<char const> buf)
	{
		// ignore packets smaller than 16 bytes
		if (buf.size() < 16) return false;

		restart_read_timeout();

		// skip header
		buf = buf.subspan(8);

		// reset transaction
		update_transaction_id();
		std::int64_t const connection_id = aux::read_int64(buf);

		std::lock_guard<std::mutex> l(m_cache_mutex);
		connection_cache_entry& cce = m_connection_cache[m_target.address()];
		cce.connection_id = connection_id;
		cce.expires = aux::time_now() + seconds(m_man.settings().get_int(settings_pack::udp_tracker_token_expiry));

		if (!(tracker_req().kind & tracker_request::scrape_request))
			send_udp_announce();
		else if (tracker_req().kind & tracker_request::scrape_request)
			send_udp_scrape();
		return true;
	}

	void udp_tracker_connection::send_udp_connect()
	{
#ifndef TORRENT_DISABLE_LOGGING
		std::shared_ptr<request_callback> cb = requester();
#endif

		if (m_abort)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb) cb->debug_log("==> UDP_TRACKER_CONNECT [ skipped, m_abort ]");
#endif
			return;
		}

		std::size_t const connect_packet_size = 16;
		std::array<char, connect_packet_size> buf;
		span<char> view = buf;

		TORRENT_ASSERT(m_transaction_id != 0);

		aux::write_uint32(0x417, view);
		aux::write_uint32(0x27101980, view); // connection_id
		aux::write_int32(action_t::connect, view); // action (connect)
		aux::write_int32(m_transaction_id, view); // transaction_id
		TORRENT_ASSERT(view.empty());

		error_code ec;
		if (!m_hostname.empty())
		{
			m_man.send_hostname(bind_socket(), m_hostname.c_str()
				, m_target.port(), buf, ec
				, udp_socket::tracker_connection);
		}
		else
		{
			m_man.send(bind_socket(), m_target, buf, ec
				, udp_socket::tracker_connection);
		}

		++m_attempts;
		if (ec)
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (cb && cb->should_log())
			{
				cb->debug_log("==> UDP_TRACKER_CONNECT [ failed: %s ]"
					, ec.message().c_str());
			}
#endif
			fail(ec, operation_t::sock_write);
			return;
		}

#ifndef TORRENT_DISABLE_LOGGING
		if (cb && cb->should_log())
		{
			cb->debug_log("==> UDP_TRACKER_CONNECT [ to: %s ih: %s ]"
				, m_hostname.empty()
					? print_endpoint(m_target).c_str()
					: (m_hostname + ":" + to_string(m_target.port()).data()).c_str()
				, aux::to_hex(tracker_req().info_hash).c_str());
		}
#endif

		m_state = action_t::connect;
		sent_bytes(16 + 28); // assuming UDP/IP header
	}

	void udp_tracker_connection::send_udp_scrape()
	{
		if (m_abort) return;

		auto const i = m_connection_cache.find(m_target.address());
		// this isn't really supposed to happen
		TORRENT_ASSERT(i != m_connection_cache.end());
		if (i == m_connection_cache.end()) return;

		char buf[8 + 4 + 4 + 20];
		span<char> view = buf;

		aux::write_int64(i->second.connection_id, view); // connection_id
		aux::write_int32(action_t::scrape, view); // action (scrape)
		aux::write_int32(m_transaction_id, view); // transaction_id
		// info_hash
		std::copy(tracker_req().info_hash.begin(), tracker_req().info_hash.end()
			, view.data());
#if TORRENT_USE_ASSERTS
		TORRENT_ASSERT(view.size() == 20);
#endif

		error_code ec;
		if (!m_hostname.empty())
		{
			m_man.send_hostname(bind_socket(), m_hostname.c_str(), m_target.port()
				, buf, ec, udp_socket::tracker_connection);
		}
		else
		{
			m_man.send(bind_socket(), m_target, buf, ec
				, udp_socket::tracker_connection);
		}
		m_state = action_t::scrape;
		sent_bytes(sizeof(buf) + 28); // assuming UDP/IP header
		++m_attempts;
		if (ec)
		{
			fail(ec, operation_t::sock_write);
			return;
		}
	}

	bool udp_tracker_connection::on_announce_response(span<char const> buf)
	{
		if (buf.size() < 20) return false;

		buf = buf.subspan(8);
		restart_read_timeout();

		tracker_response resp;

		resp.interval = seconds32(aux::read_int32(buf));
		resp.min_interval = seconds32(60);
		resp.incomplete = aux::read_int32(buf);
		resp.complete = aux::read_int32(buf);

		int const ip_stride = aux::is_v6(m_target) ? 18 : 6;
		auto const num_peers = buf.size() / ip_stride;
		if (buf.size() % ip_stride != 0)
		{
			fail(error_code(errors::invalid_tracker_response_length), operation_t::bittorrent);
			return false;
		}

		std::shared_ptr<request_callback> cb = requester();
#ifndef TORRENT_DISABLE_LOGGING
		if (cb)
		{
			cb->debug_log("<== UDP_TRACKER_RESPONSE [ url: %s ]", tracker_req().url.c_str());
		}
#endif

		if (!cb)
		{
			close();
			return true;
		}

		if (aux::is_v6(m_target))
		{
			resp.peers6.reserve(static_cast<std::size_t>(num_peers));
			for (int i = 0; i < num_peers; ++i)
			{
				ipv6_peer_entry e{};
				std::memcpy(e.ip.data(), buf.data(), 16);
				buf = buf.subspan(16);
				e.port = aux::read_uint16(buf);
				resp.peers6.push_back(e);
			}
		}
		else
		{
			resp.peers4.reserve(static_cast<std::size_t>(num_peers));
			for (int i = 0; i < num_peers; ++i)
			{
				ipv4_peer_entry e{};
				std::memcpy(e.ip.data(), buf.data(), 4);
				buf = buf.subspan(4);
				e.port = aux::read_uint16(buf);
				resp.peers4.push_back(e);
			}
		}

		// TODO: why is this a linked list?
		std::list<address> ip_list;
		std::transform(m_endpoints.begin(), m_endpoints.end(), std::back_inserter(ip_list)
			, [](tcp::endpoint const& ep) { return ep.address(); } );

		cb->tracker_response(tracker_req(), m_target.address(), ip_list, resp);

		close();
		return true;
	}

	bool udp_tracker_connection::on_scrape_response(span<char const> buf)
	{
		restart_read_timeout();
		auto const action = static_cast<action_t>(aux::read_int32(buf));
		std::uint32_t const transaction = aux::read_uint32(buf);

		if (transaction != m_transaction_id)
		{
			fail(error_code(errors::invalid_tracker_transaction_id), operation_t::bittorrent);
			return false;
		}

		if (action == action_t::error)
		{
			fail(error_code(errors::tracker_failure), operation_t::bittorrent
				, std::string(buf.data(), static_cast<std::size_t>(buf.size())).c_str());
			return true;
		}

		if (action != action_t::scrape)
		{
			fail(error_code(errors::invalid_tracker_action), operation_t::bittorrent);
			return true;
		}

		if (buf.size() < 12)
		{
			fail(error_code(errors::invalid_tracker_response_length), operation_t::bittorrent);
			return true;
		}

		int const complete = aux::read_int32(buf);
		int const downloaded = aux::read_int32(buf);
		int const incomplete = aux::read_int32(buf);

		std::shared_ptr<request_callback> cb = requester();
		if (!cb)
		{
			close();
			return true;
		}

		cb->tracker_scrape_response(tracker_req()
			, complete, incomplete, downloaded, -1);

		close();
		return true;
	}

	void udp_tracker_connection::send_udp_announce()
	{
		if (m_abort) return;

		char buf[800];
		span<char> out = buf;

		tracker_request const& req = tracker_req();
		aux::session_settings const& settings = m_man.settings();

		auto const i = m_connection_cache.find(m_target.address());
		// this isn't really supposed to happen
		TORRENT_ASSERT(i != m_connection_cache.end());
		if (i == m_connection_cache.end()) return;

		aux::write_int64(i->second.connection_id, out); // connection_id
		aux::write_int32(action_t::announce, out); // action (announce)
		aux::write_int32(m_transaction_id, out); // transaction_id
		std::copy(req.info_hash.begin(), req.info_hash.end(), out.data()); // info_hash
		out = out.subspan(20);
		std::copy(req.pid.begin(), req.pid.end(), out.data()); // peer_id
		out = out.subspan(20);
		aux::write_int64(req.downloaded, out); // downloaded
		aux::write_int64(req.left, out); // left
		aux::write_int64(req.uploaded, out); // uploaded
		aux::write_int32(req.event, out); // event
		// ip address
		address_v4 announce_ip;

		if (!settings.get_bool(settings_pack::anonymous_mode)
			&& !settings.get_str(settings_pack::announce_ip).empty())
		{
			error_code ec;
			address ip = make_address(settings.get_str(settings_pack::announce_ip).c_str(), ec);
			if (!ec && ip.is_v4()) announce_ip = ip.to_v4();
		}
		aux::write_uint32(announce_ip.to_uint(), out);
		aux::write_int32(req.key, out); // key
		aux::write_int32(req.num_want, out); // num_want
		aux::write_uint16(req.listen_port, out); // port

		std::string request_string;
		error_code ec;
		using std::ignore;
		std::tie(ignore, ignore, ignore, ignore, request_string)
			= parse_url_components(req.url, ec);
		if (ec) request_string.clear();

		if (!request_string.empty())
		{
			std::size_t str_len = std::min(request_string.size(), std::size_t(255));
			request_string.resize(str_len);

			aux::write_uint8(2, out);
			aux::write_uint8(str_len, out);
			aux::write_string(request_string, out);
		}

#ifndef TORRENT_DISABLE_LOGGING
		std::shared_ptr<request_callback> cb = requester();
		if (cb && cb->should_log())
		{
			cb->debug_log("==> UDP_TRACKER_ANNOUNCE [%s]", aux::to_hex(req.info_hash).c_str());
		}
#endif

		if (!m_hostname.empty())
		{
			m_man.send_hostname(bind_socket(), m_hostname.c_str()
				, m_target.port(), {buf, int(sizeof(buf)) - out.size()}, ec
				, udp_socket::tracker_connection);
		}
		else
		{
			m_man.send(bind_socket(), m_target, {buf, int(sizeof(buf)) - out.size()}, ec
				, udp_socket::tracker_connection);
		}
		m_state = action_t::announce;
		sent_bytes(int(sizeof(buf)) - int(out.size()) + 28); // assuming UDP/IP header
		++m_attempts;
		if (ec)
		{
			fail(ec, operation_t::sock_write);
			return;
		}
	}

}
