Speed up a web site by enabling Apache file gzip compression

Setting up the server

The "good news" is that we can't control the browser. It either sends the Accept-encoding: gzip, deflate header or it doesn't.

Our job is to configure the server so it returns zipped content if the browser can handle it, saving bandwidth for everyone (and giving us a happy user).

For IIS, enable compression in the settings.

In Apache, enabling output compression is fairly straightforward. Add the following to your .htaccess file:

# compress text, html, javascript, css, xml:
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript

# Or, compress certain file types by extension:
<files *.html>
SetOutputFilter DEFLATE
</files>

Apache actually has two compression options:

• mod_deflate is easier to set up and is standard.
• mod_gzip seems more powerful: you can pre-compress content.

Deflate is quick and works, so I use it; use mod_gzip if that floats your boat. In either case, Apache checks if the browser sent the "Accept-encoding" header and returns the compressed or regular version of the file. However, some older browsers may have trouble (more below) and there are special directives you can add to correct this.

If you can't change your .htaccess file, you can use PHP to return compressed content. Give your HTML file a .php extension and add this code to the top:

In PHP:

<?php if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip')) ob_start("ob_gzhandler"); else ob_start(); ?>

We check the "Accept-encoding" header and return a gzipped version of the file (otherwise the regular version). This is almost like building your own webserver (what fun!). But really, try to use Apache to compress your output if you can help it. You don't want to monkey with your files.

How to enable file compression

Apache 1.x and 2.x can automatically compress files, but neither one comes with a compressor enabled by default. Enabling compression reduces CSS, HTML, and JavaScript file sizes by 55-65% and speeds up overall page load times by 35-40%.

Apache uses plug-in modules to add functionality. For Apache 1.x, use the free mod_gzip module to compress files. For Apache 2.x, use mod_gzip or the built-in mod_deflatemodule.

Enable file compression using mod_gzip

The mod_gzip module can be used with Apache 1.x or 2.x, but it doesn’t come with either Apache distribution. You’ll need to download and install it separately.

1. Windows:
   1. Log in to your PC using an account with administrator privileges.
   2. Download the zip file containing ApacheModuleGzip.dll from SourceForge.
   3. Unzip the file.
   4. Move ApacheModuleGzip.dll to your Apache modules folder (typically “c:\Program Files\Apache Group\Apache\modules”).
   5. Edit your server configuration file using a text editor like NotePad (typically “c:\Program Files\Apache Group\Apache\conf\httpd.conf”). Add the following line to your server configuration file as the last loaded module:

      LoadModule gzip_module modules/ApacheModuleGzip.dll

      Add the following lines to your server configuration file or to a site’s “.htaccess” file:

      <IfModule mod_gzip.c>
          mod_gzip_on       Yes
          mod_gzip_dechunk  Yes
          mod_gzip_item_include file      \.(html?|txt|css|js|php|pl)$
          mod_gzip_item_include handler   ^cgi-script$
          mod_gzip_item_include mime      ^text/.*
          mod_gzip_item_include mime      ^application/x-javascript.*
          mod_gzip_item_exclude mime      ^image/.*
          mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
      </IfModule>

2. Mac:
   1. Log in to your Mac using an account with administrator privileges.
   2. Download the zip file containing the module’s C source code from SourceForge.
   3. Unzip the file.
   4. Compile the module using the included instructions.
   5. Move mod_gzip.so to your Apache modules folder (typically “/usr/libexec/httpd”).
   6. Edit your server configuration file using a text editor like TextEdit or vim (typically “/etc/httpd/httpd.conf”). Add the following line to your server configuration file as the last loaded module:

      LoadModule gzip_module libexec/mod_gzip.so

      Add the following lines to your server configuration file or to a site’s “.htaccess” file:

      <IfModule mod_gzip.c>
          mod_gzip_on       Yes
          mod_gzip_dechunk  Yes
          mod_gzip_item_include file      \.(html?|txt|css|js|php|pl)$
          mod_gzip_item_include handler   ^cgi-script$
          mod_gzip_item_include mime      ^text/.*
          mod_gzip_item_include mime      ^application/x-javascript.*
          mod_gzip_item_exclude mime      ^image/.*
          mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
      </IfModule>
                          

3. Restart Apache.

The “LoadModule” line in the configuration file makes the module ready, while the other lines configure and enable it. Put these other lines in the server’s configuration file to affect all sites served by the web server. Or put them within a site’s “VirtualHost” block or in its own “.htaccess” file to affect only that site.

The remaining lines tell the module to compress files with .htm, .html, .txt, .css, .js, .php, and .pl file name extensions, the output of CGI scripts, and any output that is text or JavaScript, but not images. The last line tells the module to skip compressing content that is already compressed.

Enable file compression using mod_deflate

The mod_deflate module comes with Apache 2.x. All you need to do is enable it.

1. Windows:
   1. Log in to your PC using an account with administrator privileges.
   2. Edit your server configuration file using a text editor like NotePad (typically “c:\Program Files\Apache Group\Apache\conf\httpd.conf”). Add the following lines to your server configuration file or to a site’s “.htaccess” file:

      <Location />
          SetOutputFilter DEFLATE
            SetEnvIfNoCase Request_URI  \
              \.(?:gif|jpe?g|png)$ no-gzip dont-vary
          SetEnvIfNoCase Request_URI  \
              \.(?:exe|t?gz|zip|gz2|sit|rar)$ no-gzip dont-vary
      </Location> 

2. Mac:
   1. Log in to your Mac using an account with administrator privileges.
   2. Edit your server configuration file using a text editor like TextEdit or vim (typically “/etc/httpd/httpd.conf”). Add the following lines to your server configuration file or to a site’s “.htaccess” file:

      <Location />
          SetOutputFilter DEFLATE
          SetEnvIfNoCase Request_URI  \
              \.(?:gif|jpe?g|png)$ no-gzip dont-vary
          SetEnvIfNoCase Request_URI  \
              \.(?:exe|t?gz|zip|gz2|sit|rar)$ no-gzip dont-vary
      </Location> 

3. Restart Apache.

Put the configuration lines in the server’s configuration file to affect all sites served by the web server. Or put them within a site’s “VirtualHost” block or in its “.htaccess” file to affect only that site.

The “SetOutputFilter” line enables the module.

The next two lines instruct the module to skip compressing image files (.gif, .jpg, .jpeg, .png), executables (.exe), and compressed files (.gz, .tgz, .zip, .gz2, .sit, .rar). Everything else gets compressed.

Example copy

Verify Your Compression

Once you've configured your server, check to make sure you're actually serving up compressed content.

• Online: Use the online gzip test to check whether your page is compressed.
• In your browser: Use Web Developer Toolbar > Information > View Document Size (like I did for Yahoo, above) to see whether the page is compressed.
• View the headers: Use Live HTTP Headers to examine the response. Look for a line that says "Content-encoding: gzip".

Compressed CSS Compression using PHP

Method One

Overview: This method involves adding a small PHP script to your CSS document and replacing its.css extension with a .php extension.

Place the following PHP script into the top of the CSS document that you wish to compress. Then change the .css extension to .php, to arrive at something similar to: compressed-css.php. Remember to use the new name when referencing the file.

<?php 
   ob_start ("ob_gzhandler");
   header ("content-type: text/css; charset: UTF-8");
   header ("cache-control: must-revalidate");
   $offset = 60 * 60;
   $expire = "expires: " . gmdate ("D, d M Y H:i:s", time() + $offset) . " GMT";
   header ($expire);
?>

Here is the same PHP script commented with functional explanations:

<?php

   // initialize ob_gzhandler function to send and compress data
   ob_start ("ob_gzhandler");

   // send the requisite header information and character set
   header ("content-type: text/css; charset: UTF-8");

   // check cached credentials and reprocess accordingly
   header ("cache-control: must-revalidate");

   // set variable for duration of cached content
   $offset = 60 * 60;

   // set variable specifying format of expiration header
   $expire = "expires: " . gmdate ("D, d M Y H:i:s", time() + $offset) . " GMT";

   // send cache expiration header to the client broswer
   header ($expire); 

   // output css contents

   readfile("some_location/some_name.css"); 

?>

Functional Summary: The previous PHP function will first check to see if the browser requesting the file will accept "gzip-deflate" encoding. If no such support is detected, the requested file is sent without compression. Next, the function sends a header for the content type and character set (in this case, "text/css" and "UTF-8"). Then, a "must-revalidate" "cache-control" header requires revalidation against currently specified variables. Finally, an "expires" header specifies the time duration for which the cached content should persist (one hour in this case).

Method Two

Overview: This method involves placing the PHP script in a separate .php file and adding a set of rules to an .htaccess file.

A more discrete, unobtrusive method for compressing CSS involves two steps. First, save the script provided in the first method (above) as a seperate gzip-css.php file and place it in a CSS-exclusive directory. Then, add the following ruleset to an .htaccess file located in the same CSS-exclusive directory (i.e., the CSS directory should contain only CSS files):

# css compression htaccess ruleset
AddHandler application/x-httpd-php .css
php_value auto_prepend_file gzip-css.php
php_flag zlib.output_compression On

Here is the same htaccess ruleset commented with functional explanations:

# css compression htaccess ruleset

# process all CSS files in current directory as PHP
AddHandler application/x-httpd-php .css

# prepend the PHP script to all PHP files in the current directory
php_value auto_prepend_file gzip-css.php

# compress all parsed PHP pages from current directory
# this rule is redundantly present as the first line of the PHP script
php_flag zlib.output_compression On

Functional Summary: The .htaccess rules above first instruct Apache to parse all CSS files in the current directory as PHP. After this, Apache is instructed to insert the contents of the "gzip-css.php" file into the beginning of each PHP (i.e., CSS) file parsed from the current directory. And finally, Apache is instructed to compress automatically every parsed document in the current directory.

Confirmed Browsers

• Internet Explorer 5 and up: works great
• Netscape Navigator 6 and up: works fine
• Mozilla/Firefox: all versions seem to work
• Opera: does not cache compressed CSS

References

• PHP ob_gzhandler
• zlib compression
• mod_gzip module
• fiftyfoureleven.com