Node.js and Phantom Screen Capture Server

gistfile1.js

/**
 * Server will save rendered file to same directory and stream png
 * to the response.
 * 
 * npm install phantom
 * npm install path
 * npm install mu2
 * npm install fs
 * npm install url
 * 
 **/

var http = require("http");
var path = require('path');
var fs = require('fs');
var url = require('url');
var mu = require('mu2');

var mimeTypes = {
    "html": "text/html",
    "jpeg": "image/jpeg",
    "jpg": "image/jpeg",
    "png": "image/png",
    "js": "text/javascript",
    "css": "text/css"};

function onRequest(request, response) {
    
  	var url_parts = url.parse(request.url, true);
	var query = url_parts.query;
  
	var phantom = require('phantom');
	
	phantom.create(function(ph) {
	  return ph.createPage(function(page) {
		return page.open(query['url'], function(status) {
					
		  	console.log(
		  		mu.renderText(
		  		'url to render: {{ url }} {{ foo }}', 
		  		{url:query['url'], foo:'boo'}));
		  				  
		  	var fname = genS4()+'.png'
		  	page.render(fname, function(){
		  		var filename = path.join(process.cwd(), fname);
				
				fs.exists(filename, function(exists) {
					if(!exists) {
						console.log("not exists: " + filename);
						response.writeHead(200, {'Content-Type': 'text/plain'});
						response.write('404 Not Found\n');
						response.end();
					}
					var mimeType = mimeTypes[path.extname(filename).split(".")[1]];
					response.writeHead(200, mimeType);
					
					var fileStream = fs.createReadStream(filename);
					fileStream.pipe(response);
				
				}); //end path.exists
		  	
		  	});
		  	
		});
	  });
	}); 
}

http.createServer(onRequest).listen(8888);

//----------- functions -----------//

function genS4() {
   return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
}


console.log("Server has started.");