Add announce_port support

Author: 0xThiebaut

ChangeLog

@@ -15,6 +15,7 @@
 	* fix integer overflow in piece picker
 	* torrent_status::num_pieces counts pieces passed hash check, as documented
 	* check settings_pack::max_out_request_queue before performance alert
+	* add announce_port setting to override the port announced to trackers
 
 2.0.10 released
 

include/libtorrent/session_handle.hpp

@@ -507,6 +507,7 @@ namespace libtorrent {
 		// specified info-hash, advertising the specified port. If the port is
 		// left at its default, 0, the port will be implied by the DHT message's
 		// source port (which may improve connectivity through a NAT).
+		// ``dht_announce()`` is not affected by the ``announce_port`` override setting.
 		//
 		// Both these functions are exposed for advanced custom use of the DHT.
 		// All torrents eligible to be announce to the DHT will be automatically,

include/libtorrent/settings_pack.hpp

@@ -2068,6 +2068,20 @@ namespace aux {
 			i2p_inbound_length,
 			i2p_outbound_length,
 
+			// ``announce_port`` is the port passed along as the ``port`` parameter
+			// to remote trackers such as HTTP or DHT. This setting does not affect
+			// the effective listening port nor local service discovery announcements.
+			// If left as zero (default), the listening port value is used.
+			//
+			// .. note::
+			//    This setting is only meant for very special cases where a
+			//    seed's listening port differs from the external port. As an
+			//    example, if a local proxy is used and that the proxy supports
+			//    reverse tunnels through NAT-PMP, the tracker must connect to
+			//    the external NAT-PMP port (configured using ``announce_port``)
+			//    instead of the actual local listening port.
+			announce_port,
+
 			max_int_setting_internal
 		};
 

simulation/test_tracker.cpp

@@ -361,6 +361,90 @@ void on_alert_notify(lt::session* ses)
 	});
 }
 
+void test_announce()
+{
+	using sim::asio::ip::address_v4;
+	sim::default_config network_cfg;
+	sim::simulation sim{network_cfg};
+
+	sim::asio::io_context web_server(sim, make_address_v4("2.2.2.2"));
+
+	// listen on port 8080
+	sim::http_server http(web_server, 8080);
+
+	int announces = 0;
+
+	// expect announced IP & port
+	std::string const expect_port = "&port=1234";
+	std::string const expect_ip = "&ip=1.2.3.4";
+
+	http.register_handler("/announce"
+	, [&announces, expect_port, expect_ip](std::string method, std::string req
+		, std::map<std::string, std::string>&)
+	{
+		++announces;
+		TEST_EQUAL(method, "GET");
+		TEST_CHECK(req.find(expect_port) != std::string::npos);
+		TEST_CHECK(req.find(expect_ip) != std::string::npos);
+		char response[500];
+		int const size = std::snprintf(response, sizeof(response), "d8:intervali1800e5:peers0:e");
+		return sim::send_response(200, "OK", size) + response;
+	});
+
+	{
+		lt::session_proxy zombie;
+
+		std::vector<asio::ip::address> ips;
+		ips.push_back(make_address("123.0.0.3"));
+
+		asio::io_context ios(sim, ips);
+		lt::settings_pack sett = settings();
+		sett.set_str(settings_pack::listen_interfaces, "0.0.0.0:6881");
+		sett.set_str(settings_pack::announce_ip, "1.2.3.4");
+		sett.set_int(settings_pack::announce_port, 1234);
+
+		auto ses = std::make_unique<lt::session>(sett, ios);
+
+		ses->set_alert_notify(std::bind(&on_alert_notify, ses.get()));
+
+		lt::add_torrent_params p;
+		p.name = "test-torrent";
+		p.save_path = ".";
+		p.info_hashes.v1.assign("abababababababababab");
+
+		p.trackers.push_back("http://2.2.2.2:8080/announce");
+		ses->async_add_torrent(p);
+
+		// stop the torrent 5 seconds in
+		sim::timer t1(sim, lt::seconds(5)
+			, [&ses](boost::system::error_code const&)
+		{
+			std::vector<lt::torrent_handle> torrents = ses->get_torrents();
+			for (auto const& t : torrents)
+			{
+				t.pause();
+			}
+		});
+
+		// then shut down 10 seconds in
+		sim::timer t2(sim, lt::seconds(10)
+			, [&ses,&zombie](boost::system::error_code const&)
+		{
+			zombie = ses->abort();
+			ses.reset();
+		});
+
+		sim.run();
+	}
+
+	TEST_EQUAL(announces, 2);
+}
+
+// this test makes sure that a seed can overwrite its announced IP & port
+TORRENT_TEST(announce_ip_port) {
+	test_announce();
+}
+
 static const int num_interfaces = 3;
 
 void test_ipv6_support(char const* listen_interfaces

src/session_impl.cpp

@@ -1301,9 +1301,11 @@ namespace {
 #endif
 			req.ssl_ctx = &m_ssl_ctx;
 #endif
-
-		auto ls = req.outgoing_socket.get();
-		if (ls)
+		if (const auto announce_port = std::uint16_t(m_settings.get_int(settings_pack::announce_port)))
+		{
+			req.listen_port = announce_port;
+		}
+		else if (auto ls = req.outgoing_socket.get())
 		{
 			req.listen_port =
 #ifdef TORRENT_SSL_PEERS

src/settings_pack.cpp

@@ -401,7 +401,8 @@ constexpr int DISK_WRITE_MODE = settings_pack::enable_os_cache;
 		SET(i2p_inbound_quantity, 3, nullptr),
 		SET(i2p_outbound_quantity, 3, nullptr),
 		SET(i2p_inbound_length, 3, nullptr),
-		SET(i2p_outbound_length, 3, nullptr)
+		SET(i2p_outbound_length, 3, nullptr),
+		SET(announce_port, 0, nullptr)
 	}});
 
 #undef SET

src/torrent.cpp

@@ -2807,23 +2807,25 @@ bool is_downloading_state(int const st)
 		// If this is an SSL torrent the announce needs to specify an SSL
 		// listen port. DHT nodes only operate on non-SSL ports so SSL
 		// torrents cannot use implied_port.
-		// if we allow incoming uTP connections, set the implied_port
-		// argument in the announce, this will make the DHT node use
+		// if we allow incoming uTP connections and don't overwrite
+		// the announced port, set the implied_port argument
+		// in the announce, this will make the DHT node use
 		// our source port in the packet as our listen port, which is
 		// likely more accurate when behind a NAT
+		const auto announce_port = std::uint16_t(settings().get_int(settings_pack::announce_port));
 		if (is_ssl_torrent())
 		{
 			flags |= dht::announce::ssl_torrent;
 		}
-		else if (settings().get_bool(settings_pack::enable_incoming_utp))
+		else if (!announce_port && settings().get_bool(settings_pack::enable_incoming_utp))
 		{
 			flags |= dht::announce::implied_port;
 		}
 
 		std::weak_ptr<torrent> self(shared_from_this());
 		m_torrent_file->info_hashes().for_each([&](sha1_hash const& ih, protocol_version v)
 		{
-			m_ses.dht()->announce(ih, 0, flags
+			m_ses.dht()->announce(ih, announce_port, flags
 				, std::bind(&torrent::on_dht_announce_response_disp, self, v, _1));
 		});
 	}