Optimizing External CSS & JavaScript Files With PHP & mod_rewrite

The landscape of the internet has changed a great deal over the years. Websites are no longer static and lifeless, they have become dynamic and interactive. A consequence of this is that the size of modern websites has increased significantly. This poses a couple of important issues:

  1. It takes more time for webpages to be downloaded by client browsers.
  2. Average website bandwidth usage has increased.

Most internet surfers won’t wait 30 seconds for a page to load in its entirety, they’ll simply move on to something else. Also, if you own or manage an even moderately busy website you will know just how much bandwidth is worth. It is a precious commodity that can increase the figures on your monthly hosting bill. As a result of this, a lot of emphasis is now being placed on website optimization.

Yahoo has published a set of rules which outlines some of the methods that can be employed to make your website as lean and fast as possible. One of the methods suggested is to compress and minify external CSS and JavaScript files. Some PHP frameworks employ some form of optimization of these files and if you have control over your server you can always install mod_gzip which would handle compression of these files. If you are not using a PHP framework or you use a shared hosting plan (most of which won’t allow you to use mod_gzip because it can be a CPU hog) then read on.

First off, we will create a .htaccess file in which we will put our rewrite rules:

IndexIgnore *
<IfModule mod_rewrite.c>
	RewriteEngine on
	RewriteRule ^(.*.((js)|(css)))$ optimizer.php?file=$1
</IfModule>

Place a copy of this file in your /js and your /css folders. The first line really has nothing to with our optimization, all it does is it prevents listing of the contents of the directory when someone navigates to /web/20100225153251/http://www.yourdomain.com/js or /web/20100225153251/http://www.yourdomain.com/css. Not necessary but good practice. The next few lines redirects incoming requests to the file optimizer.php if the file extension is .js or .css and passes the filename to it as a query string. Next, we’ll create a file called optimizer.php:

<?php
if(!isset($_GET['file'])) die('Invalid parameter!');
$allowed = array('js','css'); // Defines array of allowed file extensions
$ext = end(explode('.',$_GET['file'])); // Retrieves the file extension
if(!in_array($ext,$allowed)) die('Invalid file!'); //Checks to ensure the file extension is either .js or .css
$file = file_get_contents($_GET['file']);
$file = preg_replace("/((?:/*(?:[^*]|(?:*+[^*/]))**+/)|(?://.*))/", "", $file);
header("Expires: Fri, 21 Dec 2012 00:00:00 GMT");
header("Content-type: application/x-javascript");
ob_start("ob_gzhandler");
echo $file;
ob_flush();
flush();
?>

This file should also be placed in both the /css and /js folders. What this script does is it grabs the filename from the $_GET array, reads the contents of the file into a variable, strips the file of all comments, sends content type and expires headers to the browser, compresses the contents of the variable (via output buffering) and sends the optimized CSS or JavaScript back to the browser. Simple and straightforward.

This method is a simple way to optimize your external .js and .css files when you don’t have access to better(?) methods. The only issue I have noted so far with this method is that it will mess up the minified version of the jQuery library which really isn’t an issue since its already minified. If you are using the minified version of jQuery on your website simply use this code in your optimize.php file instead:

<?php
if(!isset($_GET['file'])) die('Invalid parameter!');
$allowed = array('js','css'); // Defines array of allowed file extensions
$ext = end(explode('.',$_GET['file'])); // Retrieves the file extension
if(!in_array($ext,$allowed)) die('Invalid file!'); //Checks to ensure the file extension is either .js or .css
$file = file_get_contents($_GET['file']);
$jqueryFile = 'name_of_your-jquery_file';
if($file!=$jqueryFile) $file = preg_replace("/((?:/*(?:[^*]|(?:*+[^*/]))**+/)|(?://.*))/", "", $file);
header("Expires: Fri, 21 Dec 2012 00:00:00 GMT");
header("Content-type: application/x-javascript");
ob_start("ob_gzhandler");
echo $file;
ob_flush();
flush();
?>

Now go optimize your stylesheets and JavaScripts and make your users happier!

Footnote #1: This implementation will obviously only work on an apache server as a .htaccess file is used.

Footnote #2: The code used in this post is simply a proof of concept. Little or no attention was paid to security. In an actual implementation of this technique you would need to ensure that this script is as secure as possible.






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