long_pull_client.js

var LongPuller = function() {
	var internals = {};
	internals.subscribers = {};
	internals.xhrs = {};
	
	internals.doXHR = function(key, url, errorTimeout, reconnectTimeout) {
		var xhr = new XMLHttpRequest();
		xhr.myCustomData = { key: key, url: url, errorTimeout: errorTimeout || 5000, reconnectTimeout: reconnectTimeout || 100 };
		xhr.onreadystatechange = internals.handleResponse;
		xhr.open("GET", url);
		xhr.send();
		internals.xhrs[key] = xhr;
	};
	
	internals.handleResponse = function() {
		if(this.readyState != 4) { return; }
		if(this.status == 200) {
			internals.fire(this.myCustomData.key, { url: this.myCustomData.url, response: this.responseText });
			sleep(this.myCustomData.reconnectTimeout);
		} else {
			sleep(this.myCustomData.errorTimeout);
		}
		internals.doXHR(this.myCustomData.key, this.myCustomData.url);
	};
	
	internals.stop = function(key) {
		if(internals.xhrs[key]) {
			internals.xhrs[key].abort();
		}
	};
	
	internals.fire = function(key, value) {
		if(!internals.subscribers[key]) {
			log("No subscribers for '", key, "'!");
			log(value.toSource());
			return;
		}
		for (var index in internals.subscribers[key]) {
			if(internals.subscribers[key][index] instanceof Function) {
				internals.subscribers[key][index](value);
			}
		}
	};
	
	return {
		start: internals.doXHR,
		stop: internals.stop,
		_subscribers: internals.subscribers
	};
}();

long_pull_server.js

// do our includes
var http = require('http'),
	events = require('events');
	
// setup some local variables we need
var port = process.env.PORT || 8001,
	dataStore = new events.EventEmitter(),
	mostRecentStored;

// create our HTTP server which will listen for requests
http.createServer(function (req, res) {
	
	// check to see if this is a store request, if it is, handle as such
	if(req.url.indexOf("/store?") == 0) {
		
		var query = require('url').parse(req.url).query;
		mostRecentStored = query;
		res.writeHead(200, {'Content-Type': 'text/plain'})
		res.end('OK - ' + query);
		dataStore.emit("store", query);
		
  	} else {
	
		// see if we have a saved value which was never sent to a receiving client
		if(mostRecentStored) {
			// we have a saved value, so send it closing the connection
			// then clear the variable so another request doesn't get it
			res.writeHead(200, {'Content-Type': 'text/plain'})
			res.end(mostRecentStored);
			mostRecentStored = null;
		} else {
			// we don't have a saved value waiting, so we must wait for someone to store one
			dataStore.addListener('store', function(value) {
				// we got one! now send it to the client
				res.writeHead(200, {'Content-Type': 'text/plain'})
				res.end(value);
				// we don't want to send the same value twice, so clear out the saved value
				mostRecentStored = null;
			});
			
		}
		
  	}

// listen on the PORT defined in the environment or 8001 if not provided
}).listen(parseInt(port))