server.js

const  PORT = process.env.PORT || 3000;

const  express = require('express');
const  http = require('http');
const  app = express()
const  server = http.createServer(app);
const  io  = require('socket.io').listen(server);
//io.set('log level', 2);

app.use(express.static(__dirname));
server.listen(PORT, null, function() {
    console.log("Listening on port " + PORT);
});

app.get(['/', '/:room'], (req, res) => res.sendFile(__dirname + '/index.html'));

/**
 * Users will connect to the signaling server, after which they'll issue a "join"
 * to join a particular channel. The signaling server keeps track of all sockets
 * who are in a channel, and on join will send out 'addPeer' events to each pair
 * of users in a channel. When clients receive the 'addPeer' even they'll begin
 * setting up an RTCPeerConnection with one another. During this process they'll
 * need to relay ICECandidate information to one another, as well as SessionDescription
 * information. After all of that happens, they'll finally be able to complete
 * the peer connection and will be streaming audio/video between eachother.
 */
const channels = {};
const sockets = {};

io.sockets.on('connection', (socket) => {
    socket.channels = {};
    sockets[socket.id] = socket;

    //console.log("["+ socket.id + "] connection accepted");
    socket.on('disconnect', () => {
        for (const channel in socket.channels) {
            part(channel);
        }
        //console.log("["+ socket.id + "] disconnected");
        delete sockets[socket.id];
    });

    socket.on('join', (config) => {
        //console.log("["+ socket.id + "] join ", config);
        const channel = config.channel;
        const userdata = config.userdata;

        if (channel in socket.channels) {
            //console.log("["+ socket.id + "] ERROR: already joined ", channel);
            return;
        }

        if (!(channel in channels)) {
            channels[channel] = {};
        }

        for (id in channels[channel]) {
            channels[channel][id].emit('addPeer', {'peer_id': socket.id, 'should_create_offer': false});
            socket.emit('addPeer', {'peer_id': id, 'should_create_offer': true});
        }

        channels[channel][socket.id] = socket;
        socket.channels[channel] = channel;
    });

    const part = (channel) => {
        //console.log("["+ socket.id + "] part ");

        if (!(channel in socket.channels)) {
            //console.log("["+ socket.id + "] ERROR: not in ", channel);
            return;
        }

        delete socket.channels[channel];
        delete channels[channel][socket.id];

        for (id in channels[channel]) {
            channels[channel][id].emit('removePeer', {'peer_id': socket.id});
            socket.emit('removePeer', {'peer_id': id});
        }
    }
    socket.on('part', part);

    socket.on('relayICECandidate', (config) => {
        let peer_id = config.peer_id;
        let ice_candidate = config.ice_candidate;
        //console.log("["+ socket.id + "] relaying ICE candidate to [" + peer_id + "] ", ice_candidate);

        if (peer_id in sockets) {
            sockets[peer_id].emit('iceCandidate', {'peer_id': socket.id, 'ice_candidate': ice_candidate});
        }
    });

    socket.on('relaySessionDescription', (config) => {
        let peer_id = config.peer_id;
        let session_description = config.session_description;
        //console.log("["+ socket.id + "] relaying session description to [" + peer_id + "] ", session_description);

        if (peer_id in sockets) {
            sockets[peer_id].emit('sessionDescription', {'peer_id': socket.id, 'session_description': session_description});
        }
    });
});