Fix for proxy deadlock bug

This is a fix for the proxy-go deadlock bug (ticket #25688). The
assumption that OnIceComplete is always followed by a successful
connection where OnDataChannel has been called turns out not to occur in
practice. OnICEComplete looks like it is being deprecated in other
libraries anyway, so it's safer to just remove it.

proxy-go/snowflake.go

@@ -259,8 +259,6 @@ func datachannelHandler(conn *webRTCConn, remoteAddr net.Addr) {
 // Installs an OnDataChannel callback that creates a webRTCConn and passes it to
 // datachannelHandler.
 func makePeerConnectionFromOffer(sdp *webrtc.SessionDescription, config *webrtc.Configuration) (*webrtc.PeerConnection, error) {
-	errChan := make(chan error)
-	answerChan := make(chan struct{})
 
 	pc, err := webrtc.NewPeerConnection(config)
 	if err != nil {
@@ -269,9 +267,6 @@ func makePeerConnectionFromOffer(sdp *webrtc.SessionDescription, config *webrtc.
 	pc.OnNegotiationNeeded = func() {
 		panic("OnNegotiationNeeded")
 	}
-	pc.OnIceComplete = func() {
-		answerChan <- struct{}{}
-	}
 	pc.OnDataChannel = func(dc *webrtc.DataChannel) {
 		log.Println("OnDataChannel")
 
@@ -310,30 +305,25 @@ func makePeerConnectionFromOffer(sdp *webrtc.SessionDescription, config *webrtc.
 	}
 	log.Println("sdp offer successfully received.")
 
-	go func() {
-		log.Println("Generating answer...")
-		answer, err := pc.CreateAnswer() // blocking
-		if err != nil {
-			errChan <- err
-			return
-		}
-		err = pc.SetLocalDescription(answer)
-		if err != nil {
-			errChan <- err
-			return
-		}
-	}()
+	log.Println("Generating answer...")
+	answer, err := pc.CreateAnswer()
+        // blocks on ICE gathering. we need to add a timeout if needed
+        // not putting this in a separate go routine, because we need
+        // SetLocalDescription(answer) to be called before sendAnswer
+	if err != nil {
+		pc.Destroy()
+		return nil, err
+	}
 
-	// Wait until answer is ready.
-	select {
-	case err = <-errChan:
+	if answer == nil {
+		pc.Destroy()
+		return nil, fmt.Errorf("Failed gathering ICE candidates.")
+	}
+
+	err = pc.SetLocalDescription(answer)
+	if err != nil {
 		pc.Destroy()
 		return nil, err
-	case _, ok := <-answerChan:
-		if !ok {
-			pc.Destroy()
-			return nil, fmt.Errorf("Failed gathering ICE candidates.")
-		}
 	}
 	return pc, nil
 }