>

How to use RTCDataChannel?

HOME © Muaz Khan . @WebRTCWeb . Github . Latest issues . What's New?

This tutorial is out-dated (written in 2013). Please check this tutorial instead: https://codelabs.developers.google.com/codelabs/webrtc-web/#0

This document guides you through:

  1. How to setup SCTP data connection (for chrome)?
  2. How to setup SCTP data connection (for firefox)?
  3. How to setup RTP data connection (for older chrome releases)?

A few terminologies:

  1. There is always an "offerer".
  2. There is always an "answerer".
  3. "Offerer" creates offer; it must be shared with "answerer".
  4. "answerer" sets his remote session-descriptions based on "offer-sdp" provided by offerer.
  5. "answerer" creates answer; it must be shared with "Offerer".
  6. "Offerer" sets his remote session-descriptions based on "answerer-sdp" provided by answerer.

SCTP data-connection and Chrome!

Setting global variables used by both offerer and answerer.

Global variables:

var iceServers = {
    iceServers: [{
        url: 'stun:stun.l.google.com:19302'
    }]
};
var offererDataChannel, answererDataChannel;

Creating two objects; one for offerer; and other for answerer.

Object for offerer:

var Offerer = {
    createOffer: function () {
        var peer = new webkitRTCPeerConnection(iceServers);

        offererDataChannel = peer.createDataChannel('channel', {});
        setChannelEvents(offererDataChannel);

        peer.onicecandidate = function (event) {
            if (event.candidate)
                Send_to_Other_Peer(event.candidate);
        };

        peer.createOffer(function (sdp) {
            peer.setLocalDescription(sdp);
            Send_to_Other_Peer(sdp);
        });

        this.peer = peer;

        return this;
    },
    setRemoteDescription: function (sdp) {
        this.peer.setRemoteDescription(new RTCSessionDescription(sdp));
    },
    addIceCandidate: function (candidate) {
        this.peer.addIceCandidate(new RTCIceCandidate({
            sdpMLineIndex: candidate.sdpMLineIndex,
            candidate: candidate.candidate
        }));
    }
};

Object for answerer:

var Answerer = {
    createAnswer: function (offerSDP) {
        var peer = new RTCPeerConnection(iceServers);
        peer.ondatachannel = function (event) {
            answererDataChannel = event.channel;
            setChannelEvents(answererDataChannel);
        };

        peer.onicecandidate = function (event) {
            if (event.candidate)
                Send_to_Other_Peer(event.candidate);
        };

        peer.setRemoteDescription(new RTCSessionDescription(offerSDP));
        peer.createAnswer(function (sdp) {
            peer.setLocalDescription(sdp);
            Send_to_Other_Peer(sdp);
        });

        this.peer = peer;

        return this;
    },
    addIceCandidate: function (candidate) {
        this.peer.addIceCandidate(new RTCIceCandidate({
            sdpMLineIndex: candidate.sdpMLineIndex,
            candidate: candidate.candidate
        }));
    }
};

setChannelEvents function:

function setChannelEvents(channel) {
    channel.onmessage = function (event) {
        var data = JSON.parse(event.data);
        console.log(data);
    };
    channel.onopen = function () {
        channel.push = channel.send;
        channel.send = function (data) {
            channel.push(JSON.stringify(data));
        };
    };

    channel.onerror = function (e) {
        console.error('channel.onerror', JSON.stringify(e, null, '\t'));
    };

    channel.onclose = function (e) {
        console.warn('channel.onclose', JSON.stringify(e, null, '\t'));
    };
}

Now, you've two objects; one for offerer; and last one for answerer. You can execute/call them according to the situation of the user.

If a user is offerer:

var offerer = Offerer.createOffer();

If a user is answerer:

var answerer = Answerer.createAnswer(offerSDP);

A simple example:

var websocket = new WebSocket('ws://localhost:8888/');

websocket.onmessage = function (e) {
    e = JSON.parse(e.data);

    // Don't get self sent messages
    if (e.senderid == userid) return;

    var data = e.data;

    // if other user created offer; and sent you offer-sdp
    if (data.offerSDP) {
        window.answerer = Answerer.createAnswer(data.offerSDP);
    }

    // if other user created answer; and sent you answer-sdp
    if (data.answerSDP) {
        window.offerer.setRemoteDescription(data.answerSDP);
    }

    // if other user sent you ice candidates
    if (data.ice) {
        // it will be fired both for offerer and answerer
        (window.answerer || window.offerer).addIceCandidate(data.ice);
    }
};

var userid = Math.random() * 1000;

websocket.push = websocket.send;
websocket.send = function (data) {
    // wait/loop until socket connection gets open
    if (websocket.readState != 1) {
        // websocket connection is not opened yet.
        return setTimeout(function () {
            websocket.send(data);
        }, 500);
    }

    // data is stringified because websocket protocol accepts only string data
    var json_stringified_data = JSON.stringify({
        senderid: userid,
        data: data
    });

    websocket.push(json_stringified_data);
}

SCTP data-connection and Firefox!

Setting global variables used by both offerer and answerer.

Global variables:

var iceServers = {
    iceServers: [{
        url: 'stun:23.21.150.121'
    }]
};

var offerAnswerConstraints = {
    optional: [],
    mandatory: {
        OfferToReceiveAudio: true,
        OfferToReceiveVideo: true
    }
};

var offererDataChannel, answererDataChannel;

Creating two objects; one for offerer; and other for answerer.

Object for offerer:

var Offerer = {
    createOffer: function () {
        var peer = new mozRTCPeerConnection(iceServers);

        peer.onicecandidate = function (event) {
            if (event.candidate)
                Send_to_Other_Peer(event.candidate);
        };

        peer.ondatachannel = function (event) {
            offererDataChannel = event.channel;
            setChannelEvents(offererDataChannel);
        };

        peer.onconnection = function () {
            websocket.send({askToCreateDataChannel:true});
        };

        navigator.mozGetUserMedia({
            audio: true,
            fake: true
        }, function (stream) {
            peer.addStream(stream);

            offererDataChannel = peer.createDataChannel('channel', {});
            setChannelEvents(offererDataChannel);

            // create offer after attaching fake media stream
            peer.createOffer(function (sdp) {
                peer.setLocalDescription(sdp);
                Send_to_Other_Peer(sdp);
            });
        }, function(error) {} );

        this.peer = peer;

        return this;
    },
    setRemoteDescription: function (sdp) {
        this.peer.setRemoteDescription(new mozRTCSessionDescription(sdp));
    },
    addIceCandidate: function (candidate) {
        this.peer.addIceCandidate(new mozRTCIceCandidate({
            sdpMLineIndex: candidate.sdpMLineIndex,
            candidate: candidate.candidate
        }));
    }
};

Object for answerer:

var Answerer = {
    createAnswer: function (offerSDP) {
        var peer = new mozRTCPeerConnection(iceServers);
        peer.ondatachannel = function (event) {
            answererDataChannel = event.channel;
            setChannelEvents(answererDataChannel);
        };

        peer.onicecandidate = function (event) {
            if (event.candidate)
                Send_to_Other_Peer(event.candidate);
        };

        navigator.mozGetUserMedia({
            audio: true,
            fake: true
        }, function (stream) {
            peer.addStream(stream);

            // create answer after attaching fake media stream
            peer.setRemoteDescription(new mozRTCSessionDescription(offerSDP));
            peer.createAnswer(function (sdp) {
                peer.setLocalDescription(sdp);
                Send_to_Other_Peer(sdp);
            });

        }, function(error) {});

        this.peer = peer;

        return this;
    },
    addIceCandidate: function (candidate) {
        this.peer.addIceCandidate(new mozRTCIceCandidate({
            sdpMLineIndex: candidate.sdpMLineIndex,
            candidate: candidate.candidate
        }));
    }
};

setChannelEvents function:

function setChannelEvents(channel) {
    channel.onmessage = function (event) {
        var data = JSON.parse(event.data);
        console.log(data);
    };
    channel.onopen = function () {
        channel.push = channel.send;
        channel.send = function (data) {
            channel.push(JSON.stringify(data));
        };
    };

    channel.onerror = function (e) {
        console.error('channel.onerror', JSON.stringify(e, null, '\t'));
    };

    channel.onclose = function (e) {
        console.warn('channel.onclose', JSON.stringify(e, null, '\t'));
    };
}

Now, you've two objects; one for offerer; and last one for answerer. You can execute/call them according to the situation of the user.

If a user is offerer:

var offerer = Offerer.createOffer();

If a user is answerer:

var answerer = Answerer.createAnswer(offerSDP);

A simple example:

var websocket = new WebSocket('ws://localhost:8888/');

websocket.onmessage = function (e) {
    e = JSON.parse(e.data);

    // Don't get self sent messages
    if (e.senderid == userid) return;

    var data = e.data;

    // if other user created offer; and sent you offer-sdp
    if (data.offerSDP) {
        window.answerer = Answerer.createAnswer(data.offerSDP);
    }

    // if other user created answer; and sent you answer-sdp
    if (data.answerSDP) {
        window.offerer.setRemoteDescription(data.answerSDP);
    }

    // if other user sent you ice candidates
    if (data.ice) {
        // it will be fired both for offerer and answerer
        (window.answerer || window.offerer).addIceCandidate(data.ice);
    }
	
    // we need to create data channel for both ends! (on Firefox only)
    if(data.askToCreateDataChannel) {
        answererDataChannel = peer.createDataChannel('channel', {});
        setChannelEvents(answererDataChannel);
    }
};

var userid = Math.random() * 1000;

websocket.push = websocket.send;
websocket.send = function (data) {
    // wait/loop until socket connection gets open
    if (websocket.readState != 1) {
        // websocket connection is not opened yet.
        return setTimeout(function () {
            websocket.send(data);
        }, 500);
    }

    // data is stringified because websocket protocol accepts only string data
    var json_stringified_data = JSON.stringify({
        senderid: userid,
        data: data
    });

    websocket.push(json_stringified_data);
}

RTP data-connection and Chrome!

var iceServers = {
    iceServers: [{
        url: 'stun:stun.l.google.com:19302'
    }]
};

var optionalRtpDataChannels = {
    optional: [{
        RtpDataChannels: true
    }]
};

var offerer = new webkitRTCPeerConnection(iceServers, optionalRtpDataChannels),
    answerer, answererDataChannel;

var offererDataChannel = offerer.createDataChannel('RTCDataChannel', {
    reliable: false
});
setChannelEvents(offererDataChannel, 'offerer');

offerer.onicecandidate = function (event) {
    if (!event || !event.candidate) return;
    answerer && answerer.addIceCandidate(event.candidate);
};

var mediaConstraints = {
    optional: [],
    mandatory: {
        OfferToReceiveAudio: false, // Hmm!!
        OfferToReceiveVideo: false // Hmm!!
    }
};

offerer.createOffer(function (sessionDescription) {
    offerer.setLocalDescription(sessionDescription);
    createAnswer(sessionDescription);
}, null, mediaConstraints);


function createAnswer(offerSDP) {
    answerer = new webkitRTCPeerConnection(iceServers, optionalRtpDataChannels);
    answererDataChannel = answerer.createDataChannel('RTCDataChannel', {
        reliable: false
    });

    setChannelEvents(answererDataChannel, 'answerer');

    answerer.onicecandidate = function (event) {
        if (!event || !event.candidate) return;
        offerer && offerer.addIceCandidate(event.candidate);
    };

    answerer.setRemoteDescription(offerSDP);
    answerer.createAnswer(function (sessionDescription) {
        answerer.setLocalDescription(sessionDescription);
        offerer.setRemoteDescription(sessionDescription);
    }, null, mediaConstraints);
}

function setChannelEvents(channel, channelNameForConsoleOutput) {
    channel.onmessage = function (event) {
        console.debug(channelNameForConsoleOutput, 'received a message:', event.data);
    };

    channel.onopen = function () {
        channel.send('first text message over RTP data ports');
    };
    channel.onclose = function (e) {
        console.error(e);
    };
    channel.onerror = function (e) {
        console.error(e);
    };
}

After executing above code in the console; try to send messages over RTP data ports like this: 

offererDataChannel.send('message from offerer');
answererDataChannel.send('message from answerer');

Latest Updates

Feedback

Enter your email too; if you want "direct" reply!