index.js

let http        = require('http');
let express		= require('express');
let cors 		= require('cors')
let fs			= require('fs');
let io			= require('socket.io');
let crypto		= require('crypto');

let app       	= express();
let staticDir 	= express.static;

app.use(cors()); // enable cors for all origins

let server    	= http.createServer(app);

let socketsIO = io(server, {
	cors: {
	  origin: "*",
	  methods: ["GET", "POST", "PUT", "DELETE", "OPTIONS" ]
	}
  });

let opts = {
	port: process.env.PORT || 1948,
	baseDir : process.cwd()
};

socketsIO.on( 'connection', socket => {
	console.debug('Connection opened');
	socket.on('multiplex-statechanged', data => {
		if (typeof data.secret == 'undefined' || data.secret == null || data.secret === '') return;
		if (createHash(data.secret) === data.socketId) {
			console.debug('Broadcasting state change');
			data.secret = null;
			socket.broadcast.emit(data.socketId, data);
		} else {
			console.warn('Secret and socketId do not match');
		}
	});
});

app.use( express.static( opts.baseDir ) );

app.get("/", ( req, res ) => {
	res.writeHead(200, {'Content-Type': 'text/html'});

	let stream = fs.createReadStream( opts.baseDir + '/index.html' );
	stream.on('error', error => {
		res.write('<style>body{font-family: sans-serif;}</style><h2>reveal.js multiplex server.</h2><a href="/token">Generate token</a>');
		res.end();
	});
	stream.on('open', () => {
		stream.pipe( res );
	});
});

app.get("/token", ( req, res ) => {
	let secret = crypto.randomBytes(16).toString('hex');
	res.send({secret: secret, socketId: createHash(secret)});
});

let createHash = (secret) => {
	let hash = crypto.createHash('sha256').update(secret);
	return hash.digest('hex');
};

// Open the listening port
server.listen( opts.port || null );

console.log(`reveal.js: Multiplex running on port: ${opts.port}`);