don't use default source address for onboard udp link, wait on remote

src/modules/mavlink/mavlink_main.cpp

@@ -930,7 +930,9 @@ Mavlink::send_message(const uint8_t msgid, const void *msg, uint8_t component_ID
 	}
 #else
 	if (get_protocol() == UDP) {
-		ret = sendto(_socket_fd, buf, packet_len, 0, (struct sockaddr *)&_src_addr, sizeof(_src_addr));
+		if (get_client_source_initialized()) {
+			ret = sendto(_socket_fd, buf, packet_len, 0, (struct sockaddr *)&_src_addr, sizeof(_src_addr));
+		}
 
 		struct telemetry_status_s &tstatus = get_rx_status();
 
@@ -1045,11 +1047,14 @@ Mavlink::init_udp()
 		return;
 	}
 
-	/* set default target address */
+	/* set default target address, but not for onboard mode (will be set on first recieved packet) */
 	memset((char *)&_src_addr, 0, sizeof(_src_addr));
-	_src_addr.sin_family = AF_INET;
-	inet_aton("127.0.0.1", &_src_addr.sin_addr);
-	_src_addr.sin_port = htons(DEFAULT_REMOTE_PORT_UDP);
+	if (_mode != MAVLINK_MODE_ONBOARD) {
+		set_client_source_initialized();
+		_src_addr.sin_family = AF_INET;
+		inet_aton("127.0.0.1", &_src_addr.sin_addr);
+		_src_addr.sin_port = htons(DEFAULT_REMOTE_PORT_UDP);
+	}
 
 	/* default broadcast address */
 	memset((char *)&_bcast_addr, 0, sizeof(_bcast_addr));

src/modules/mavlink/mavlink_main.h

@@ -339,6 +339,10 @@ public:
 	int 			get_socket_fd () { return _socket_fd; };
 #ifdef __PX4_POSIX
 	struct sockaddr_in * get_client_source_address() {return &_src_addr;};
+
+	void			set_client_source_initialized() { _src_addr_initialized = true; };
+
+	bool			get_client_source_initialized() { return _src_addr_initialized; };
 #endif
 	static bool		boot_complete() { return _boot_complete; }
 
@@ -423,6 +427,7 @@ private:
 	struct sockaddr_in _myaddr;
 	struct sockaddr_in _src_addr;
 	struct sockaddr_in _bcast_addr;
+	bool _src_addr_initialized;
 
 #endif
 	int _socket_fd;

src/modules/mavlink/mavlink_receiver.cpp

@@ -1814,10 +1814,12 @@ MavlinkReceiver::receive_thread(void *arg)
 
 			struct sockaddr_in * srcaddr_last = _mavlink->get_client_source_address();
 			int localhost = (127 << 24) + 1;
-			if (srcaddr_last->sin_addr.s_addr == htonl(localhost) && srcaddr.sin_addr.s_addr != htonl(localhost)) {
+			if ((srcaddr_last->sin_addr.s_addr == htonl(localhost) && srcaddr.sin_addr.s_addr != htonl(localhost))
+					|| (_mavlink->get_mode() == Mavlink::MAVLINK_MODE_ONBOARD && !_mavlink->get_client_source_initialized())) {
 				// if we were sending to localhost before but have a new host then accept him
 				memcpy(srcaddr_last, &srcaddr, sizeof(srcaddr));
 				PX4_WARN("UDP source addr changed: %s", inet_ntoa(srcaddr.sin_addr));
+				_mavlink->set_client_source_initialized();
 			}
 #endif
 			/* if read failed, this loop won't execute */