Use GatheringCompletePromise in examples/webrtc

pion/webrtc@v3 enables trickle ICE by default now. Use provided helper
to block until ICE is finished gathering. For a production application
setting OnICECandidate is recommended.

examples/webrtc/main.go

@@ -111,13 +111,23 @@ func main() {
 		panic(err)
 	}
 
+	// Create channel that is blocked until ICE Gathering is complete
+	gatherComplete := webrtc.GatheringCompletePromise(peerConnection)
+
 	// Sets the LocalDescription, and starts our UDP listeners
 	err = peerConnection.SetLocalDescription(answer)
 	if err != nil {
 		panic(err)
 	}
 
+	// Block until ICE Gathering is complete, disabling trickle ICE
+	// we do this because we only can exchange one signaling message
+	// in a production application you should exchange ICE Candidates via OnICECandidate
+	<-gatherComplete
+
 	// Output the answer in base64 so we can paste it in browser
-	fmt.Println(signal.Encode(answer))
+	fmt.Println(signal.Encode(*peerConnection.LocalDescription()))
+
+	// Block forever
 	select {}
 }