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:
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.
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”.
Be prepared to marvel at the results. The instacalc homepage shrunk from 36k to 10k, a 75% reduction in size.
Try Some Examples
I’ve set up some pages and a downloadable example:
- index.html – No explicit compression (on this server, I am using compression by default ).
- index.htm – Explicitly compressed with Apache .htaccess using *.htm as a rule
- index.php – Explicitly compressed using the PHP header
Feel free to download the files, put them on your server and tweak the settings.