fix: return 461 if client requested an invalid transport method

pkg/rtsp/server.go

@@ -150,28 +150,35 @@ func (c *Conn) Accept() error {
 
 			const transport = "RTP/AVP/TCP;unicast"
 
-			c.session = core.RandString(8, 10)
-			c.state = StateSetup
-
-			if c.mode == core.ModePassiveConsumer {
-				if i := reqTrackID(req); i >= 0 && i < len(c.Senders) {
-					// mark sender as SETUP
-					c.Senders[i].Media.ID = MethodSetup
-					interleaved := fmt.Sprintf("%d-%d", i*2, i*2+1)
+			// Test if client requests unicast with TCP transport, otherwise return 461 Transport not supported
+			// This allows smart clients who initially requested UDP to fall back on TCP transport.
+			if strings.HasPrefix(tr, transport) {
+
+				c.session = core.RandString(8, 10)
+				c.state = StateSetup
 
-					// Check if transport already contains the 'interleaved' parameter
-					if strings.Contains(transport, "interleaved=") {
-						// If so, just update the interleaved value
-						res.Header.Set("Transport", strings.Replace(transport, "interleaved=[^;]*", "interleaved="+interleaved, 1))
+				if c.mode == core.ModePassiveConsumer {
+					if i := reqTrackID(req); i >= 0 && i < len(c.Senders) {
+						// mark sender as SETUP
+						c.Senders[i].Media.ID = MethodSetup
+						interleaved := fmt.Sprintf("%d-%d", i*2, i*2+1)
+
+						// Check if transport already contains the 'interleaved' parameter
+						if strings.Contains(transport, "interleaved=") {
+							// If so, just update the interleaved value
+							res.Header.Set("Transport", strings.Replace(transport, "interleaved=[^;]*", "interleaved="+interleaved, 1))
+						} else {
+							// Otherwise, append the interleaved parameter
+							res.Header.Set("Transport", transport+";interleaved="+interleaved)
+						}
 					} else {
-						// Otherwise, append the interleaved parameter
-						res.Header.Set("Transport", transport+";interleaved="+interleaved)
+						res.Status = "400 Bad Request"
 					}
 				} else {
-					res.Status = "400 Bad Request"
+					res.Header.Set("Transport", tr)
 				}
-			} else {
-				res.Header.Set("Transport", tr)
+			else {
+				res.Status = "461 Unsupported transport"
 			}
 
 			if err = c.WriteResponse(res); err != nil {