Queue negotiation if not in stable state.

If we send two offers back to back, the second answer will arive in
stable state, which will confuse us.  Instead, queue the second offer.

rtpconn/rtpconn.go

@@ -129,13 +129,20 @@ func (down *rtpDownTrack) SetCname(cname string) {
 	down.cname.Store(cname)
 }
 
+const (
+	negotiationUnneeded = iota
+	negotiationNeeded
+	negotiationRestartIce
+)
+
 type rtpDownConnection struct {
-	id             string
-	pc             *webrtc.PeerConnection
-	remote         conn.Up
-	tracks         []*rtpDownTrack
-	maxREMBBitrate *bitrate
-	iceCandidates  []*webrtc.ICECandidateInit
+	id                string
+	pc                *webrtc.PeerConnection
+	remote            conn.Up
+	tracks            []*rtpDownTrack
+	maxREMBBitrate    *bitrate
+	iceCandidates     []*webrtc.ICECandidateInit
+	negotiationNeeded int
 }
 
 func newDownConn(c group.Client, id string, remote conn.Up) (*rtpDownConnection, error) {

rtpconn/webclient.go

@@ -423,6 +423,18 @@ func addDownTrack(c *webClient, conn *rtpDownConnection, remoteTrack conn.UpTrac
 }
 
 func negotiate(c *webClient, down *rtpDownConnection, renegotiate, restartIce bool) error {
+	if down.pc.SignalingState() == webrtc.SignalingStateHaveLocalOffer {
+		// avoid sending multiple offers back-to-back
+		if restartIce {
+			down.negotiationNeeded = negotiationRestartIce
+		} else if down.negotiationNeeded == negotiationUnneeded {
+			down.negotiationNeeded = negotiationNeeded
+		}
+		return nil
+	}
+
+	down.negotiationNeeded = negotiationUnneeded
+
 	options := webrtc.OfferOptions{ICERestart: restartIce}
 	offer, err := down.pc.CreateOffer(&options)
 	if err != nil {
@@ -808,6 +820,9 @@ func clientLoop(c *webClient, ws *websocket.Conn) error {
 				if down != nil {
 					err = negotiate(c, down, false, false)
 					if err != nil {
+						log.Printf(
+							"Negotiation failed: %v",
+							err)
 						delDownConn(c, down.id)
 						c.error(group.UserError(
 							"Negotiation failed",
@@ -1154,13 +1169,26 @@ func handleClientMessage(c *webClient, m clientMessage) error {
 			}
 			return failDownConnection(c, m.Id, message)
 		}
+		down := getDownConn(c, m.Id)
+		if down.negotiationNeeded > negotiationUnneeded {
+			err := negotiate(
+				c, down, true,
+				down.negotiationNeeded == negotiationRestartIce,
+			)
+			if err != nil {
+				return failDownConnection(
+					c, m.Id, "negotiation failed",
+				)
+			}
+		}
 	case "renegotiate":
 		down := getDownConn(c, m.Id)
 		if down != nil {
 			err := negotiate(c, down, true, true)
 			if err != nil {
-				return failDownConnection(c, m.Id,
-					"renegotiation failed")
+				return failDownConnection(
+					c, m.Id, "renegotiation failed",
+				)
 			}
 		} else {
 			log.Printf("Trying to renegotiate unknown connection")