Add announce_port support

include/libtorrent/settings_pack.hpp

@@ -2068,6 +2068,16 @@ namespace aux {
 			i2p_inbound_length,
 			i2p_outbound_length,
 
+			// ``announce_port`` is the port passed along to trackers as the
+			// ``&port=`` parameter. If left as the default, the listening port
+			// is used.
+			//
+			// .. note::
+			//    This setting is only meant for very special cases
+			//    where a seed's listening port differs from the exposed
+			//    port (e.g., through external NAT-PMP).
+			announce_port,
+
 			max_int_setting_internal
 		};
 

src/http_tracker_connection.cpp

@@ -126,6 +126,7 @@ namespace libtorrent {
 		if (!(tracker_req().kind & tracker_request::scrape_request))
 		{
 			static aux::array<const char*, 4> const event_string{{{"completed", "started", "stopped", "paused"}}};
+			const auto announce_port = std::uint16_t(settings.get_int(settings_pack::announce_port));
 
 			char str[1024];
 			std::snprintf(str, sizeof(str)
@@ -143,7 +144,7 @@ namespace libtorrent {
 				, escape_string({tracker_req().pid.data(), 20}).c_str()
 				// the i2p tracker seems to verify that the port is not 0,
 				// even though it ignores it otherwise
-				, tracker_req().listen_port
+				, announce_port ? announce_port : tracker_req().listen_port
 				, tracker_req().uploaded
 				, tracker_req().downloaded
 				, tracker_req().left

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/tracker_manager.cpp

@@ -278,8 +278,15 @@ constexpr tracker_request_flags_t tracker_request::i2p;
 
 #ifndef TORRENT_DISABLE_LOGGING
 		std::shared_ptr<request_callback> cb = c.lock();
-		if (cb) cb->debug_log("*** QUEUE_TRACKER_REQUEST [ listen_port: %d ]"
-			, req.listen_port);
+		if (cb) {
+			if (const auto announce_port = std::uint16_t(sett.get_int(settings_pack::announce_port))) {
+				cb->debug_log("*** QUEUE_TRACKER_REQUEST [ listen_port: %d, announce_port: %d ]"
+				, req.listen_port, announce_port);
+			} else {
+				cb->debug_log("*** QUEUE_TRACKER_REQUEST [ listen_port: %d ]"
+				, req.listen_port);
+			}
+		}
 #endif
 
 		std::string const protocol = req.url.substr(0, req.url.find(':'));

src/udp_tracker_connection.cpp

@@ -729,7 +729,9 @@ namespace libtorrent {
 		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
+
+		const auto announce_port = std::uint16_t(settings.get_int(settings_pack::announce_port));
+		aux::write_uint16(announce_port ? announce_port : req.listen_port, out); // port
 
 		std::string request_string;
 		error_code ec;