webrtc: set buffer amount to 0 when closing stream

p2p/transport/webrtc/stream.go

@@ -192,6 +192,13 @@ func (s *stream) maybeDeclareStreamDone() {
 		(s.receiveState == receiveStateReset || s.receiveState == receiveStateDataRead) &&
 		len(s.controlMsgQueue) == 0 {
 		_ = s.SetReadDeadline(time.Now().Add(-1 * time.Hour)) // pion ignores zero times
+		// TODO: it's not clear if this is actually a fix or just a workaround.
+		// What happens if this message is lost?
+		// See https://github.com/libp2p/go-libp2p/pull/2337#issuecomment-1696619731.
+		s.dataChannel.SetBufferedAmountLowThreshold(0)
+		ch := make(chan struct{})
+		s.dataChannel.OnBufferedAmountLow(func() { ch <- struct{}{} })
+		<-ch
 		_ = s.dataChannel.Close()
 		// TODO: write for the spawned reader to return
 		s.onDone()