Solve data race in ReadSimulcast

TrackEndcodings could change when reading

Author: cnderrauber

peerconnection_renegotiation_test.go

@@ -34,7 +34,7 @@ func sendVideoUntilDone(t *testing.T, done <-chan struct{}, tracks []*TrackLocal
 		select {
 		case <-time.After(20 * time.Millisecond):
 			for _, track := range tracks {
-				assert.NoError(t, track.WriteSample(media.Sample{Data: []byte{0x00}, Duration: time.Second}))
+				assert.NoError(t, track.WriteSample(media.Sample{Data: []byte{0x00}, Duration: 20 * time.Millisecond}))
 			}
 		case <-done:
 			return

rtpsender.go

@@ -437,11 +437,16 @@ func (r *RTPSender) ReadRTCP() ([]rtcp.Packet, interceptor.Attributes, error) {
 func (r *RTPSender) ReadSimulcast(b []byte, rid string) (n int, a interceptor.Attributes, err error) {
 	select {
 	case <-r.sendCalled:
+		r.mu.Lock()
 		for _, t := range r.trackEncodings {
 			if t.track != nil && t.track.RID() == rid {
-				return t.rtcpInterceptor.Read(b, a)
+				reader := t.rtcpInterceptor
+				r.mu.Unlock()
+
+				return reader.Read(b, a)
 			}
 		}
+		r.mu.Unlock()
 
 		return 0, nil, fmt.Errorf("%w: %s", errRTPSenderNoTrackForRID, rid)
 	case <-r.stopCalled: