WebRTC: RTCDataChannel is not 'open'

Question

I followed an entire tutorial about WebRTC and implementing a simple p2p chat. My signaling server is working aside on localhost:9090. When I try to send a message, I am receiving:

RTCDataChannel.readyState is not 'open'

However, the connection seems to have been established properly:

Connected
Got message {"type":"login","success":true}
RTCPeerConnection object was created
RTCPeerConnection {localDescription: RTCSessionDescription, remoteDescription: RTCSessionDescription, signalingState: "stable", iceGatheringState: "new", iceConnectionState: "new"…}
Channel created
Got message {"type":"answer","answer":{"type":"answer","sdp":"v=0\r\no=- 5123156273253761787 2 IN IP4 127.0.0.1\r\ns=-\r\nt=0 0\r\na=group:BUNDLE data\r\na=msid-semantic: WMS\r\nm=application 9 UDP/TLS/RTP/SAVPF 127\r\nc=IN IP4 0.0.0.0\r\nb=AS:30\r\na=rtcp:9 IN IP4 0.0.0.0\r\na=ice-ufrag:aWnc+x1ot0kpmCj6\r\na=ice-pwd:o8BH8EIsb/FVLBDkUt5Mw6V4\r\na=fingerprint:sha-256 D6:18:83:20:FC:3F:0B:87:8F:FB:D8:5D:D6:33:13:FE:C6:EE:53:3D:18:69:DD:C0:BF:23:35:95:F7:26:4D:F2\r\na=setup:active\r\na=mid:data\r\na=sendrecv\r\na=rtcp-mux\r\na=rtpmap:127 google-data/90000\r\na=ssrc:2024832766 cname:y/zAQto2dzSH04r0\r\na=ssrc:2024832766 msid:myDataChannel myDataChannel\r\na=ssrc:2024832766 mslabel:myDataChannel\r\na=ssrc:2024832766 label:myDataChannel\r\n"}}
Got message {"type":"candidate","candidate":{"candidate":"candidate:2633341356 1 udp 2113937151 172.20.10.6 54721 typ host generation 0 ufrag aWnc+x1ot0kpmCj6","sdpMid":"data","sdpMLineIndex":0}}
candidate added

Here is the code of client.js:

How can I make sure that each client is really connected to the other and that the answer / SDP was correct? Any tips for this: maybe the channel creation as done too early and should only be done after the whole "handshake"? Thanks a lot

__ EDIT After Jib's 1st answer __

var connectedUser, myConnection, dataChannel;

//when a user clicks the login button
loginBtn.addEventListener("click", function(event) {
    name = loginInput.value;
        send({
            type: "login",
            name: name
            });
    });

//handle messages from the server
connection.onmessage = function (message) {
    console.log("Got message", message.data);
    var data = JSON.parse(message.data);

    switch(data.type) {
    case "login":
    onLogin(data.success);
    break;
    case "offer":
    onOffer(data.offer, data.name);
    break;
    case "answer":
    onAnswer(data.answer);
    break;
    case "candidate":
    onCandidate(data.candidate);
    break;
    default:
    break;
    }
};

//when a user logs in
function onLogin(success) {

    if (success === false) {
    alert("oops...try a different username");
    } else {
    //creating our RTCPeerConnection object
    var configuration = {
        "iceServers": [{ "urls": "stun:stun.1.google.com:19302" }]
    };

    myConnection = new webkitRTCPeerConnection(configuration, {
        optional: [{RtpDataChannels: true}]
        });
    //ondatachannel is defined a bit later, commented out this line.
    //myConnection.ondatachannel = event => dataChannel = event.channel;
    console.log("RTCPeerConnection object was created");
    console.log(myConnection);

    //setup ice handling
    //when the browser finds an ice candidate we send it to another peer
    myConnection.onicecandidate = function (event) {

        if (event.candidate) {
        send({
            type: "candidate",
            candidate: event.candidate
            });
        }
    };
    myConnection.oniceconnectionstatechange = e => console.log(myConnection.iceConnectionState);
    myConnection.ondatachannel = function(ev) {
        console.log('Data channel is created!');
        ev.channel.onopen = function() {
          console.log('Data channel is open and ready to be used.');
        };
    }
    }
};

connection.onopen = function () {
    console.log("Connected");
};

connection.onerror = function (err) {
    console.log("Got error", err);
};

// Alias for sending messages in JSON format
function send(message) {
    if (connectedUser) {
    message.name = connectedUser;
    }

    connection.send(JSON.stringify(message));
};

//setup a peer connection with another user
connectToOtherUsernameBtn.addEventListener("click", function () {

    var otherUsername = otherUsernameInput.value;
    connectedUser = otherUsername;

    if (otherUsername.length > 0) {
        //Create channel before sending the offer
        openDataChannel();
        //make an offer
        myConnection.createOffer(function (offer) {
            send({
                type: "offer",
                offer: offer
                });

            myConnection.setLocalDescription(offer);
        }, function (error) {
            alert("An error has occurred.:", error);
        });
    }
    });

//when somebody wants to call us
function onOffer(offer, name) {
    connectedUser = name;
    myConnection.setRemoteDescription(new RTCSessionDescription(offer));

    myConnection.createAnswer(function (answer) {
        myConnection.setLocalDescription(answer);
        send({
            type: "answer",
            answer: answer
            });

    }, function (error) {
        alert("oops...error: ", error);
    });
}

//when another user answers to our offer
function onAnswer(answer) {
    myConnection.setRemoteDescription(new RTCSessionDescription(answer));
}

//when we got ice candidate from another user
function onCandidate(candidate) {
    myConnection.addIceCandidate(new RTCIceCandidate(candidate));
    console.log("candidate added");
}

//creating data channel
function openDataChannel() {

    var dataChannelOptions = {
    reliable:true
    };
    dataChannel = myConnection.createDataChannel("myDataChannel", dataChannelOptions);
    console.log("Channel created");

    dataChannel.onerror = function (error) {
        console.log("Error:", error);
    };

    dataChannel.onmessage = function (event) {
        console.log("new message received");
        console.log("Got message:", event.data);
    };
    dataChannel.onopen = function() {
        console.log("channel opened");
    };
}


//when a user clicks the send message button
sendMsgBtn.addEventListener("click", function (event) {
    console.log("send message");
    var val = msgInput.value;
    dataChannel.send(val);
    });

Answer 1

Data channel creation is asymmetric, just like the offer/answer exchange. Only the offerer calls pc.createDataChannel(), while the answerer listens to pc.ondatachannel.

Move your createDataChannel call to right before you call createOffer, and add somewhere:

myConnection.ondatachannel = event => dataChannel = event.channel;

In addition, use dataChannel.onopen to learn when the channel is opened (works on both ends).

How can I make sure that each client is really connected to the other and that the answer / SDP was correct?

You can do two things:

1. Check the ICE connection state ("checking", "connected"):

   pc.oniceconnectionstatechange = e => console.log(pc.iceConnectionState);

2. Add error callbacks. Calls like setLocalDescription can fail, and tell you why, but you're not checking for failure.

Answer 2

Add ondatachannel handling after removing {optional: [{RtpDataChannels: true}]}:

myConnection.onicecandidate = function (event) { 

 if (event.candidate) { 
    send({ 
       type: "candidate", 
       candidate: event.candidate 
    });
 } };   

myConnection.ondatachannel = function(event) {
 var receiveChannel = event.channel;
 receiveChannel.onmessage = function(event) {
    console.log("ondatachannel message:", event.data);
 };     };  openDataChannel();