client: avoid sending/receiving invalid packet when reading with multicast

client.go

@@ -1664,9 +1664,11 @@ func (c *Client) doPlay(ra *headers.Range, isSwitchingProtocol bool) (*base.Resp
 		return nil, err
 	}
 
-	// open the firewall by sending packets to the counterpart.
+	// open the firewall by sending test packets to the counterpart.
 	// do this before sending the request.
-	if *c.effectiveTransport == TransportUDP || *c.effectiveTransport == TransportUDPMulticast {
+	// don't do this with multicast, otherwise the RTP packet is going to be broadcasted
+	// to all listeners, including us, messing up the stream.
+	if *c.effectiveTransport == TransportUDP {
 		for _, ct := range c.tracks {
 			byts, _ := (&rtp.Packet{Header: rtp.Header{Version: 2}}).Marshal()
 			ct.udpRTPListener.write(byts)

client_read_test.go

@@ -368,11 +368,13 @@ func TestClientRead(t *testing.T) {
 				switch transport {
 				case "udp", "multicast":
 					// skip firewall opening
+					if transport == "udp" {
 						buf := make([]byte, 2048)
 						_, _, err := l2.ReadFrom(buf)
 						require.NoError(t, err)
+					}
 
-					buf = make([]byte, 2048)
+					buf := make([]byte, 2048)
 					n, _, err := l2.ReadFrom(buf)
 					require.NoError(t, err)
 					packets, err := rtcp.Unmarshal(buf[:n])
@@ -403,8 +405,6 @@ func TestClientRead(t *testing.T) {
 				require.NoError(t, err)
 			}()
 
-			counter := 0
-
 			c := &Client{
 				TLSConfig: &tls.Config{
 					InsecureSkipVerify: true,
@@ -427,14 +427,6 @@ func TestClientRead(t *testing.T) {
 			}
 
 			c.OnPacketRTP = func(ctx *ClientOnPacketRTPCtx) {
-				// ignore multicast loopback
-				if transport == "multicast" {
-					counter++
-					if counter <= 1 || counter >= 3 {
-						return
-					}
-				}
-
 				require.Equal(t, 0, ctx.TrackID)
 				require.Equal(t, &testRTPPacket, ctx.Packet)
 

server_read_test.go

@@ -347,7 +347,7 @@ func TestServerRead(t *testing.T) {
 						}, nil
 					},
 					onPacketRTCP: func(ctx *ServerHandlerOnPacketRTCPCtx) {
-						// skip multicast loopback
+						// ignore multicast loopback
 						if transport == "multicast" && atomic.AddUint64(&counter, 1) <= 1 {
 							return
 						}

serversession.go

@@ -987,7 +987,7 @@ func (ss *ServerSession) handleRequest(sc *ServerConn, req *base.Request) (*base
 			go ss.runWriter()
 
 			for trackID, st := range ss.setuppedTracks {
-				// open the firewall by sending packets to the counterpart
+				// open the firewall by sending test packets to the counterpart.
 				ss.WritePacketRTP(trackID, &rtp.Packet{Header: rtp.Header{Version: 2}})
 				ss.WritePacketRTCP(trackID, &rtcp.ReceiverReport{})