Fixes issue 1822

Previously we could have situations where during
first condition like `transceiver.Sender() != nil`
there would be another condition like
`transceiver.Sender().isNegotiated()` where
`.Sender()` could become nil if changed in
a different goroutine.

peerconnection.go

@@ -1220,7 +1220,7 @@ func (pc *PeerConnection) startRTPReceivers(incomingTracks []trackDetails, curre
 		incomingTrack := incomingTracks[i]
 
 		for _, t := range localTransceivers {
-			if (t.Receiver()) == nil || t.Receiver().Track() == nil || t.Receiver().Track().ssrc != incomingTrack.ssrc {
+			if receiver := t.Receiver(); receiver == nil || receiver.Track() == nil || receiver.Track().ssrc != incomingTrack.ssrc {
 				continue
 			}
 
@@ -1239,14 +1239,15 @@ func (pc *PeerConnection) startRTPReceivers(incomingTracks []trackDetails, curre
 				continue
 			}
 
+			receiver := t.Receiver()
 			if (incomingTrack.kind != t.kind) ||
 				(t.Direction() != RTPTransceiverDirectionRecvonly && t.Direction() != RTPTransceiverDirectionSendrecv) ||
-				(t.Receiver()) == nil ||
-				(t.Receiver().haveReceived()) {
+				receiver == nil ||
+				(receiver.haveReceived()) {
 				continue
 			}
 
-			pc.startReceiver(incomingTrack, t.Receiver())
+			pc.startReceiver(incomingTrack, receiver)
 			trackHandled = true
 			break
 		}
@@ -1273,8 +1274,8 @@ func (pc *PeerConnection) startRTPReceivers(incomingTracks []trackDetails, curre
 // startRTPSenders starts all outbound RTP streams
 func (pc *PeerConnection) startRTPSenders(currentTransceivers []*RTPTransceiver) error {
 	for _, transceiver := range currentTransceivers {
-		if transceiver.Sender() != nil && transceiver.Sender().isNegotiated() && !transceiver.Sender().hasSent() {
-			err := transceiver.Sender().Send(transceiver.Sender().GetParameters())
+		if sender := transceiver.Sender(); sender != nil && sender.isNegotiated() && !sender.hasSent() {
+			err := sender.Send(sender.GetParameters())
 			if err != nil {
 				return err
 			}
@@ -1394,15 +1395,16 @@ func (pc *PeerConnection) handleUndeclaredSSRC(rtpStream io.Reader, ssrc SSRC) e
 		}
 
 		for _, t := range pc.GetTransceivers() {
-			if t.Mid() != mid || t.Receiver() == nil {
+			receiver := t.Receiver()
+			if t.Mid() != mid || receiver == nil {
 				continue
 			}
 
-			track, err := t.Receiver().receiveForRid(rid, params, ssrc)
+			track, err := receiver.receiveForRid(rid, params, ssrc)
 			if err != nil {
 				return err
 			}
-			pc.onTrack(track, t.Receiver())
+			pc.onTrack(track, receiver)
 			return nil
 		}
 	}
@@ -1521,8 +1523,8 @@ func (pc *PeerConnection) GetSenders() (result []*RTPSender) {
 	defer pc.mu.Unlock()
 
 	for _, transceiver := range pc.rtpTransceivers {
-		if transceiver.Sender() != nil {
-			result = append(result, transceiver.Sender())
+		if sender := transceiver.Sender(); sender != nil {
+			result = append(result, sender)
 		}
 	}
 	return result
@@ -1534,8 +1536,8 @@ func (pc *PeerConnection) GetReceivers() (receivers []*RTPReceiver) {
 	defer pc.mu.Unlock()
 
 	for _, transceiver := range pc.rtpTransceivers {
-		if transceiver.Receiver() != nil {
-			receivers = append(receivers, transceiver.Receiver())
+		if receiver := transceiver.Receiver(); receiver != nil {
+			receivers = append(receivers, receiver)
 		}
 	}
 	return
@@ -2031,28 +2033,29 @@ func (pc *PeerConnection) startRTP(isRenegotiation bool, remoteDesc *SessionDesc
 	trackDetails := trackDetailsFromSDP(pc.log, remoteDesc.parsed)
 	if isRenegotiation {
 		for _, t := range currentTransceivers {
-			if t.Receiver() == nil || t.Receiver().Track() == nil {
+			receiver := t.Receiver()
+			if receiver == nil || t.Receiver().Track() == nil {
 				continue
 			}
 
-			t.Receiver().Track().mu.Lock()
-			ssrc := t.Receiver().Track().ssrc
+			receiver.Track().mu.Lock()
+			ssrc := receiver.Track().ssrc
 
 			if details := trackDetailsForSSRC(trackDetails, ssrc); details != nil {
-				t.Receiver().Track().id = details.id
-				t.Receiver().Track().streamID = details.streamID
-				t.Receiver().Track().mu.Unlock()
+				receiver.Track().id = details.id
+				receiver.Track().streamID = details.streamID
+				receiver.Track().mu.Unlock()
 				continue
 			}
 
-			t.Receiver().Track().mu.Unlock()
+			receiver.Track().mu.Unlock()
 
-			if err := t.Receiver().Stop(); err != nil {
+			if err := receiver.Stop(); err != nil {
 				pc.log.Warnf("Failed to stop RtpReceiver: %s", err)
 				continue
 			}
 
-			receiver, err := pc.api.NewRTPReceiver(t.Receiver().kind, pc.dtlsTransport)
+			receiver, err := pc.api.NewRTPReceiver(receiver.kind, pc.dtlsTransport)
 			if err != nil {
 				pc.log.Warnf("Failed to create new RtpReceiver: %s", err)
 				continue
@@ -2106,8 +2109,8 @@ func (pc *PeerConnection) generateUnmatchedSDP(transceivers []*RTPTransceiver, u
 			} else if t.kind == RTPCodecTypeAudio {
 				audio = append(audio, t)
 			}
-			if t.Sender() != nil {
-				t.Sender().setNegotiated()
+			if sender := t.Sender(); sender != nil {
+				sender.setNegotiated()
 			}
 		}
 
@@ -2123,8 +2126,8 @@ func (pc *PeerConnection) generateUnmatchedSDP(transceivers []*RTPTransceiver, u
 		}
 	} else {
 		for _, t := range transceivers {
-			if t.Sender() != nil {
-				t.Sender().setNegotiated()
+			if sender := t.Sender(); sender != nil {
+				sender.setNegotiated()
 			}
 			mediaSections = append(mediaSections, mediaSection{id: t.Mid(), transceivers: []*RTPTransceiver{t}})
 		}
@@ -2209,8 +2212,8 @@ func (pc *PeerConnection) generateMatchedSDP(transceivers []*RTPTransceiver, use
 					}
 					break
 				}
-				if t.Sender() != nil {
-					t.Sender().setNegotiated()
+				if sender := t.Sender(); sender != nil {
+					sender.setNegotiated()
 				}
 				mediaTransceivers = append(mediaTransceivers, t)
 			}
@@ -2223,8 +2226,8 @@ func (pc *PeerConnection) generateMatchedSDP(transceivers []*RTPTransceiver, use
 			if t == nil {
 				return nil, fmt.Errorf("%w: %q", errPeerConnTranscieverMidNil, midValue)
 			}
-			if t.Sender() != nil {
-				t.Sender().setNegotiated()
+			if sender := t.Sender(); sender != nil {
+				sender.setNegotiated()
 			}
 			mediaTransceivers := []*RTPTransceiver{t}
 			mediaSections = append(mediaSections, mediaSection{id: midValue, transceivers: mediaTransceivers, ridMap: getRids(media)})
@@ -2235,8 +2238,8 @@ func (pc *PeerConnection) generateMatchedSDP(transceivers []*RTPTransceiver, use
 	if includeUnmatched {
 		if !detectedPlanB {
 			for _, t := range localTransceivers {
-				if t.Sender() != nil {
-					t.Sender().setNegotiated()
+				if sender := t.Sender(); sender != nil {
+					sender.setNegotiated()
 				}
 				mediaSections = append(mediaSections, mediaSection{id: t.Mid(), transceivers: []*RTPTransceiver{t}})
 			}

rtptransceiver.go

@@ -141,13 +141,13 @@ func (t *RTPTransceiver) Direction() RTPTransceiverDirection {
 
 // Stop irreversibly stops the RTPTransceiver
 func (t *RTPTransceiver) Stop() error {
-	if t.Sender() != nil {
-		if err := t.Sender().Stop(); err != nil {
+	if sender := t.Sender(); sender != nil {
+		if err := sender.Stop(); err != nil {
 			return err
 		}
 	}
-	if t.Receiver() != nil {
-		if err := t.Receiver().Stop(); err != nil {
+	if receiver := t.Receiver(); receiver != nil {
+		if err := receiver.Stop(); err != nil {
 			return err
 		}
 	}

sdp.go

@@ -344,9 +344,9 @@ func addTransceiverSDP(d *sdp.SessionDescription, isPlanB, shouldAddCandidates b
 	}
 
 	for _, mt := range transceivers {
-		if mt.Sender() != nil && mt.Sender().Track() != nil {
-			track := mt.Sender().Track()
-			media = media.WithMediaSource(uint32(mt.Sender().ssrc), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
+		if sender := mt.Sender(); sender != nil && sender.Track() != nil {
+			track := sender.Track()
+			media = media.WithMediaSource(uint32(sender.ssrc), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
 			if !isPlanB {
 				media = media.WithPropertyAttribute("msid:" + track.StreamID() + " " + track.ID())
 				break