support for ip address in announce

include/libtorrent/session_settings.hpp

@@ -238,6 +238,10 @@ namespace libtorrent
 		// the number of seconds between chokes/unchokes
 		int unchoke_interval;
 
+		// if this is set, this IP will be reported do the
+		// tracker in the ip= parameter.
+		address announce_ip;
+
 #ifndef TORRENT_DISABLE_DHT
 		// while this is true, the dht will note be used unless the
 		// tracker is online

src/http_tracker_connection.cpp

@@ -411,6 +411,12 @@ namespace libtorrent
 					std::min(req.num_want, 999));
 				m_send_buffer += '&';
 			}
+			if (m_settings.announce_ip != address() && !url_has_argument(request, "ip"))
+			{
+				m_send_buffer += "ip=";
+				m_send_buffer += m_settings.announce_ip.to_string();
+				m_send_buffer += '&';
+			}
 
 #ifndef TORRENT_DISABLE_ENCRYPTION
 			m_send_buffer += "supportcrypto=1&";

src/udp_tracker_connection.cpp

@@ -307,7 +307,10 @@ namespace libtorrent
 		// event
 		detail::write_int32(req.event, out);
 		// ip address
-		detail::write_int32(0, out);
+		if (m_settings.announce_ip != address() && m_settings.announce_ip.is_v4())
+			detail::write_uint32(m_settings.announce_ip.to_v4().to_ulong(), out);
+		else
+			detail::write_int32(0, out);
 		// key
 		detail::write_int32(req.key, out);
 		// num_want