app.js

var express = require('express');
var EventEmitter = require('events').EventEmitter;
var emitter = new EventEmitter();
var app = express.createServer();
var fs = require('fs');

var eventQueue = [];
var queueStart = 0;

app.configure(function(){
  emitter.setMaxListeners(0);
  app.use(express.logger());
  app.set('port', process.env.PORT || 3000);
  app.use(express.bodyParser());
  app.use(express.static(__dirname + '/public', { maxAge: 86400}));
});

// Run on port 80 when in production mode
app.configure('production', function(){
  app.use(express.errorHandler()); 
  app.set('port', process.env.PORT || 80);
});

// receives connect events
app.post('/connect', function(req, res){
    eventQueue.push({ua: req.body.ua});
    emitter.emit("connect", req.body.ua);
    res.end();
});


// receives draw events
app.post('/draw', function(req, res){
    eventQueue.push({from: req.body.from, to: req.body.to});
    emitter.emit("path", req.body.from, req.body.to, eventQueue.length);
    res.end();
});

// receives clear signal
app.post('/clear', function(req, res){
    queueStart = eventQueue.length;
    emitter.emit("clear");
    res.end();
});

app.get('/', function(req, res) {
    fs.readFile(__dirname + '/public/index.html', 'utf8', function(err, text){
        response.send(text);
    });
});

// broadcast received draw/clear events
app.get('/stream', function(req, res) {
    res.setHeader("Content-Type", 'text/event-stream');
    res.setHeader("Cache-Control", "no-cache");
    res.setHeader("Connection", "keep-alive");
    res.writeHead(200);
    if (req.headers["last-event-id"]) {
	console.log("Last-Event-ID: " + req.headers["last-event-id"]);
	for(var i=Math.max(queueStart,req.headers["last-event-id"]) ; i<eventQueue.length;i++) {
	    res.write("data: " + JSON.stringify({'from': eventQueue[i].from, 'to': eventQueue[i].to}) + "\n");
	    res.write("id:" + i + "\n\n");
	}
    }
    // Heroku requires activity to avoid request timeout
    setInterval(function() { res.write(":\n"); }, 30);

    emitter.on("path", function(from, to, id) {
	res.write("data: " + JSON.stringify({'from': from, 'to': to})+ "\n");
	res.write("id: " + id + "\n\n");
    });
    emitter.on("clear", function() {
	res.write("event: clear\n");
	res.write("id: \n");
	res.write("data: \n\n");
    });
    emitter.on("connect", function(ua) {
	res.write("event: connect\n");
	res.write("data: " + JSON.stringify({'ua': ua})+ "\n\n");
    });

});

app.listen(app.set('port'));
console.log("Express server listening on port %d in %s mode", app.address().port, app.settings.env);