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javascriptgoogle-app-enginewebrtcchannel-apirtcdatachannel

RTCDataChannel with Google Channel API

I'm trying to follow this example by Dan Ristic for RTCDataChannel browser p2p communication with Google's Channel API for signaling. It seems to be failing silently - I can't get the RTCDataChannel.onopen, RTCPeerConnection.onicecandidate, or RTCPeerConnection.ondatachannel events to fire.

Client JS/HTML:

<html>
<head>
<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<script type="text/javascript" src="/_ah/channel/jsapi"></script>
<script>
    $(document).ready(function(){

        var IS_CHROME = !!window.webkitRTCPeerConnection,
            RTCPeerConnection = window.webkitRTCPeerConnection || mozRTCPeerConnection,
            RTCIceCandidate = window.RTCIceCandidate || RTCSessionDescription,
            RTCSessionDescription = window.RTCSessionDescription || mozRTCSessionDescription,
            SESSION_ID = "12345",
            weAreHost,
            optionalRtpDataChannels = {
                optional: [{RtpDataChannels: true}]
            },
            mediaConstraints = {
                    optional: [],
                    mandatory: {
                        OfferToReceiveAudio: false, // Hmm!!
                        OfferToReceiveVideo: false // Hmm!!
                    }
                };

        // Signaling Channel Object
        function SignalingChannel(peerConnection) {
          // Setup the signaling channel here
          this.peerConnection = peerConnection;
        }

        function setChannelEvents(dataChannel) {
            dataChannel.onmessage = function (event) {   
                console.log("I got data channel message: ", event.data);
            }

            dataChannel.onopen = function (event) {
                dataChannel.send("RTCDataChannel Open!");
            }

            dataChannel.error = function(event) {
                console.log("data channel error:", event)
            }
        }

        SignalingChannel.prototype.send = function(message) {
            console.log("signal send:", message);           
            var url = "/api/signal/send/";
            url += weAreHost ? "client"+SESSION_ID : "host"+SESSION_ID;
            $.ajax({
                type: "PUT",
                url: url,
                contentType: "application/json",
                data: JSON.stringify(message)
            });
        };

        SignalingChannel.prototype.onmessage = function(message) {
          console.log("signal receive:", message);
          // If we get a sdp we have to sign and return it
          if (message.sdp != null) {
            var that = this;
            this.peerConnection.setRemoteDescription(new RTCSessionDescription(message), function () {
              that.peerConnection.createAnswer(function (description) {
                that.send(description);
              }, null, mediaConstraints);
            });
          } else {
            this.peerConnection.addIceCandidate(new RTCIceCandidate(message.candidate));
          }
        };

        function initiateConnection(input) {
            weAreHost = input;

            // setup signaling mechanism with Google Channel API
            var url = "/api/signal/init/";
            url += weAreHost ? "host"+SESSION_ID : "client"+SESSION_ID;
            $.post(url, "", function(response){     

                var channel = new goog.appengine.Channel(response.token);
                var socket = channel.open();
                socket.onerror = function(){console.log(arguments);};
                socket.onclose = function(){console.log(arguments);};

                var closeSocket = function() {
                    if(socket) return socket.close();
                    else return "google socket does not exist"
                }
                $(window).unload(closeSocket);
                window.onbeforeunload = closeSocket;

                socket.onopen = function() {
                    console.log("google socket opened");

                    // Create a peer connection object
                    var connection = new RTCPeerConnection({
                      iceServers: [
                        { 'url': (IS_CHROME ? 'stun:stun.l.google.com:19302' : 'stun:23.21.150.121') }
                      ]
                    }, optionalRtpDataChannels);

                    // Initiate a signaling channel between two users
                    var signalingChannel = new SignalingChannel(connection);

                    connection.onicecandidate = function (event) {
                        console.log("onicecandidate:", event);
                        if (!event || !event.candidate) return;
                        signalingChannel.send({candidate:event.candidate});
                    };

                    // Effectively set SignalingChannel as google channel socket inbound event handler
                    socket.onmessage = function(input) {
                        console.log("received from google:", input);                        
                        var message = $.parseJSON(input.data);
                        signalingChannel.onmessage(message);
                    };

                    // Only one client should initiate the connection, the other client should wait.
                    if(weAreHost) {
                        connection.ondatachannel = function(event) {
                            setChannelEvents(event.channel);
                        }
                    } else {                        
                        // Create client RTCDataChannel
                        var clientChannel = connection.createDataChannel("my_label", {reliable: false});
                        setChannelEvents(clientChannel);

                        connection.createOffer(function (description) {
                            signalingChannel.send(description);
                        }, function(error){
                            console.log(error);
                        }, mediaConstraints);
                    }           
                };
            }, "json");
        };

        // Create a button on the page so only one client initiates the connection.         
        $("#i-am-host").click(function() {
            initiateConnection(true);
        });
        $("#i-am-client").click(function() {
            initiateConnection(false);
        });
    });
</script>
</head>
<body>
    <p id="i-am-host" style="background-color: green;">I AM HOST</p>
    <p id="i-am-client" style="background-color: blue;">I AM CLIENT</p>
</body>
</html>

App Engine Python:

from google.appengine.api import channel

from django.shortcuts import render
from django.http import HttpResponse

import json

def init(request, browser_id):

    token = channel.create_channel(browser_id);

    return HttpResponse(json.dumps({'token':token}))

def send(request, browser_id):

    channel.send_message(browser_id, request.body)

    return HttpResponse()

Browser Consoles:

[HOST]
received from google: 
Object {data: "{"sdp":"v=0\r\no=- 6804947085651458452 2 IN IP4 12…5000 webrtc-datachannel 1024\r\n","type":"offer"}"}
test.html:34
signal receive: 
Object {sdp: "v=0
↵o=- 6804947085651458452 2 IN IP4 127.0.0.1
↵s…id:data
↵a=sctpmap:5000 webrtc-datachannel 1024
↵", type: "offer"}
test.html:22
signal send: 
RTCSessionDescription {sdp: "v=0
↵o=- 600524556593905006 2 IN IP4 127.0.0.1
↵s=…id:data
↵a=sctpmap:5000 webrtc-datachannel 1024
↵", type: "answer"}

[CLIENT]
 signal send: 
RTCSessionDescription {sdp: "v=0
↵o=- 6804947085651458452 2 IN IP4 127.0.0.1
↵s…id:data
↵a=sctpmap:5000 webrtc-datachannel 1024
↵", type: "offer"}
test.html:82
received from google: 
Object {data: "{"sdp":"v=0\r\no=- 600524556593905006 2 IN IP4 127…000 webrtc-datachannel 1024\r\n","type":"answer"}"}
test.html:34
signal receive: Object {sdp: "v=0
↵o=- 600524556593905006 2 IN IP4 127.0.0.1
↵s=…id:data
↵a=sctpmap:5000 webrtc-datachannel 1024
↵", type: "answer"}
Solution

  • Firefox does not (and never will) support RtpDataChannels. It only supports the spec-compliant (and more advanced) SCTP datachannels. Removing the optional constraint should switch you over to them without requiring other changes.

    It is somewhat odd that your SDP appears to have sctp lines in it. The google sample at http://googlechrome.github.io/webrtc/samples/web/content/datachannel/ does not when using rtp data channels.