fix: use UDP connect to probe local address (#121)

src/Connection.c

@@ -377,6 +377,19 @@ int LiStartConnection(PSERVER_INFORMATION serverInfo, PSTREAM_CONFIGURATION stre
         ListenerCallbacks.stageFailed(STAGE_NAME_RESOLUTION, err);
         goto Cleanup;
     }
+
+    // Resolve LocalAddr by RemoteAddr.
+    {
+        SOCKADDR_LEN localAddrLen;
+        err = getLocalAddressByUdpConnect(&RemoteAddr, AddrLen, &LocalAddr, &localAddrLen);
+        if (err != 0) {
+            Limelog("failed to resolve local addr: %d\n", err);
+            ListenerCallbacks.stageFailed(STAGE_NAME_RESOLUTION, err);
+            goto Cleanup;
+        }
+        LC_ASSERT(localAddrLen == AddrLen);
+    }
+
     stage++;
     LC_ASSERT(stage == STAGE_NAME_RESOLUTION);
     ListenerCallbacks.stageComplete(STAGE_NAME_RESOLUTION);

src/PlatformSockets.c

@@ -568,6 +568,34 @@ Exit:
     return s;
 }
 
+int getLocalAddressByUdpConnect(const struct sockaddr_storage* targetAddr, SOCKADDR_LEN targetAddrLen,
+    struct sockaddr_storage* localAddr, SOCKADDR_LEN* localAddrLen) {
+    SOCKET udpSocket;
+
+    udpSocket = createSocket(targetAddr->ss_family, SOCK_DGRAM, IPPROTO_UDP, false);
+    if (udpSocket == INVALID_SOCKET) {
+        return LastSocketError();
+    }
+
+    if (connect(udpSocket, (struct sockaddr*)targetAddr, targetAddrLen) < 0) {
+        int err = LastSocketError();
+        Limelog("UDP connect() failed: %d\n", err);
+        closeSocket(udpSocket);
+        return err;
+    }
+
+    *localAddrLen = sizeof(*localAddr);
+    if (getsockname(udpSocket, (struct sockaddr*)localAddr, localAddrLen) < 0) {
+        int err = LastSocketError();
+        Limelog("getsockname() failed: %d\n", err);
+        closeSocket(udpSocket);
+        return err;
+    }
+
+    closeSocket(udpSocket);
+    return 0;
+}
+
 // See TCP_MAXSEG note in connectTcpSocket() above for more information.
 // TCP_NODELAY must be enabled on the socket for this function to work!
 int sendMtuSafe(SOCKET s, char* buffer, int size) {

src/PlatformSockets.h

@@ -107,6 +107,8 @@ void addrToUrlSafeString(struct sockaddr_storage* addr, char* string, size_t str
 
 SOCKET createSocket(int addressFamily, int socketType, int protocol, bool nonBlocking);
 SOCKET connectTcpSocket(struct sockaddr_storage* dstaddr, SOCKADDR_LEN addrlen, unsigned short port, int timeoutSec);
+int getLocalAddressByUdpConnect(const struct sockaddr_storage* targetAddr, SOCKADDR_LEN targetAddrLen,
+    struct sockaddr_storage* localAddr, SOCKADDR_LEN* localAddrLen);
 int sendMtuSafe(SOCKET s, char* buffer, int size);
 SOCKET bindUdpSocket(int addressFamily, struct sockaddr_storage* localAddr, SOCKADDR_LEN addrLen, int bufferSize, int socketQosType);
 int enableNoDelay(SOCKET s);

src/RtspConnection.c

@@ -477,18 +477,6 @@ static bool transactRtspMessageTcp(PRTSP_MESSAGE request, PRTSP_MESSAGE response
     // Decrypt (if necessary) and deserialize the RTSP response
     ret = unsealRtspMessage(responseBuffer, offset, response);
 
-    // Fetch the local address for this socket if it's not populated yet
-    if (LocalAddr.ss_family == 0) {
-        SOCKADDR_LEN addrLen = (SOCKADDR_LEN)sizeof(LocalAddr);
-        if (getsockname(sock, (struct sockaddr*)&LocalAddr, &addrLen) < 0) {
-            Limelog("Failed to get local address: %d\n", LastSocketError());
-            memset(&LocalAddr, 0, sizeof(LocalAddr));
-        }
-        else {
-            LC_ASSERT(addrLen == AddrLen);
-        }
-    }
-
 Exit:
     if (serializedMessage != NULL) {
         free(serializedMessage);