Do not attempt to send an offer if the PCTransport was closed (#562)

engine.go

@@ -368,13 +368,23 @@ func (e *RTCEngine) configure(
 
 	// configure client
 	e.client.OnAnswer = func(sd webrtc.SessionDescription) {
+		if e.closed.Load() {
+			e.log.Debugw("ignoring SDP answer after closed")
+			return
+		}
+
 		if err := e.publisher.SetRemoteDescription(sd); err != nil {
 			e.log.Errorw("could not set remote description", err)
 		} else {
 			e.log.Debugw("successfully set publisher answer")
 		}
 	}
 	e.client.OnTrickle = func(init webrtc.ICECandidateInit, target livekit.SignalTarget) {
+		if e.closed.Load() {
+			e.log.Debugw("ignoring trickle after closed")
+			return
+		}
+
 		var err error
 		e.log.Debugw("remote ICE candidate",
 			"target", target,
@@ -390,6 +400,11 @@ func (e *RTCEngine) configure(
 		}
 	}
 	e.client.OnOffer = func(sd webrtc.SessionDescription) {
+		if e.closed.Load() {
+			e.log.Debugw("ignoring SDP offer after closed")
+			return
+		}
+
 		e.log.Debugw("received offer for subscriber")
 		if err := e.subscriber.SetRemoteDescription(sd); err != nil {
 			e.log.Errorw("could not set remote description", err)

errors.go

@@ -29,4 +29,5 @@ var (
 	ErrCannotConnectSignal      = errors.New("could not establish signal connection")
 	ErrCannotDialSignal         = errors.New("could not dial signal connection")
 	ErrNoPeerConnection         = errors.New("peer connection not established")
+	ErrAborted                  = errors.New("operation was aborted")
 )

transport.go

@@ -59,6 +59,7 @@ type PCTransport struct {
 	pendingRestartIceOffer    *webrtc.SessionDescription
 	restartAfterGathering     bool
 	nackGenerator             *sdkinterceptor.NackGeneratorInterceptorFactory
+	closed                    bool
 	rttFromXR                 atomic.Bool
 
 	onRemoteDescriptionSettled func() error
@@ -257,6 +258,11 @@ func (t *PCTransport) IsConnected() bool {
 }
 
 func (t *PCTransport) Close() error {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	t.closed = true
+
 	return t.pc.Close()
 }
 
@@ -381,6 +387,11 @@ func (t *PCTransport) createAndSendOffer(options *webrtc.OfferOptions) error {
 	t.lock.Lock()
 	defer t.lock.Unlock()
 
+	if t.closed {
+		t.log.Debugw("aborting Offer since transport is closed")
+		return ErrAborted
+	}
+
 	iceRestart := options != nil && options.ICERestart
 	if iceRestart {
 		if t.pc.ICEGatheringState() == webrtc.ICEGatheringStateGathering {