avoid port mapping of local addresses (#2296)

src/broadcast_socket.cpp

@@ -69,10 +69,17 @@ namespace libtorrent {
 #if TORRENT_USE_IPV6
 			if (a.is_v6())
 			{
+				// NOTE: site local is deprecated but by
+				// https://www.ietf.org/rfc/rfc3879.txt:
+				// routers SHOULD be configured to prevent
+				// routing of this prefix by default.
+
 				address_v6 const a6 = a.to_v6();
 				return a6.is_loopback()
 					|| a6.is_link_local()
+					|| a6.is_site_local()
 					|| a6.is_multicast_link_local()
+					|| a6.is_multicast_site_local()
 					//  fc00::/7, unique local address
 					|| (a6.to_bytes()[0] & 0xfe) == 0xfc;
 			}

src/session_impl.cpp

@@ -2172,12 +2172,20 @@ namespace {
 			if (map_handle != -1) m.delete_mapping(map_handle);
 			map_handle = -1;
 
+#if TORRENT_USE_IPV6
+			address const addr = ep.address();
+			// with IPv4 the interface might be behind NAT so we can't skip them
+			// based on the scope of the local address
+			if (addr.is_v6() && is_local(addr))
+				return;
+#endif
+
 			// only update this mapping if we actually have a socket listening
 			if (ep != EndpointType())
 				map_handle = m.add_mapping(protocol, ep.port(), ep);
 		}
 
-		tcp::endpoint to_tcp(udp::endpoint const ep)
+		tcp::endpoint to_tcp(udp::endpoint const& ep)
 		{
 			return tcp::endpoint(ep.address(), ep.port());
 		}