How to serve compressed HTML, JavaScript and CSS

Orange Crushed by Susan Murtaugh
used under a Creative Commons licence

Compressing web pages saves storage and bandwidth, and speeds up websites. Here is a way to compress HTML, CSS and JavaScript pages.

Why gzip static pages?

Compressing static web pages (web pages which do not change each time they are loaded) with gzip (see The gzip home page) reduces the total amount of bandwidth used serving web pages, and reduces the time it takes a page to travel across the internet, because the file is smaller.

This is effective for HTML, JavaScript, CSS or text files, but image formats such as JPEG or PNG files are already compressed, so there is no point in gzipping them, since the file size will not reduce by very much.

How to compress files

The gzip utility compresses files. It's standard on Unix, Linux, and BSD computers, and also available for Windows: Gzip for Windows.

On the command line, gzip --keep file.html creates a file called file.html.gz. (The --keep option stops gzip from deleting the original file.)

Make Apache use gzipped files

With Apache, make a site serve a gzipped version of a file by adding the following to .htaccess in the top directory of your public directory: 

RewriteEngine on 
RewriteCond %{HTTP:Accept-Encoding} gzip 
RewriteCond %{REQUEST_FILENAME}.gz -f 
RewriteRule ^(.*)$ $1.gz [L]

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This tells Apache to serve the file ending in .gz if it is available as if it was the original file, if the requester accepts the gzip encoding. So this assumes you have files like index.html and index.html.gz or program.js as well as program.js.gz.

For more about .htaccess, see Apache Tutorial: .htaccess files.

How to test whether it's working

The website HTTP Compression Test (whatsmyip.org) lets you test whether the gzipping is working OK or not. Type the URL of the static page which should be compressed into the box, and it will give you a green tick if compressed content is being sent OK.

For a more sophisticated check, Rex Swain's HTTP Viewer provides a facility to view the exact header and content. To get the content with "gzip", enter the word "gzip" in the Accept-Encoding box.

To crush a lot of files

For someone with a lot of files, this script automates the process: 

#!/usr/local/bin/perl
use warnings;
use strict;
# Set $verbose to a true value if you need to debug this script.
my $verbose;
use File::Find;
find (\&wanted, ("."));
sub wanted
{
    if (/(.*\.(?:html|css|js)$)/) {
        my $gz = "$_.gz";
        if (-f $gz) {
            if (age ($_) <= age ($gz)) {
                if ($verbose) {
                    print "Don't need to compress $_\n";
                }
                return;
            }
        }
        if ($verbose) {
            print "Compressing $_\n";
        }
        # The following substitution is for the case that the file
        # name contains double quotation marks ".
        $_ =~ s/"/\\"/g;
        # Now compress the file.
        system ("gzip --keep --best --force \"$_\"");
    }
    else {
        if ($verbose) {
            print "Rejecting $_\n";
        }
    }
}

# This returns the age of the file.

sub age
{
    my ($file) = @_;
    my @stat = stat $file;
    return $stat[9];
}

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Run this from the top public directory. It will find and compress any file ending in .html, .css, or .js, regardless of upper or lower case.

This article was originally written for the internal Wiki of web hosts NearlyFreeSpeech.net. I'm also publishing it here publicly for the benefit of non-members. If you are a member of NearlyFreeSpeech.net web hosts, you can view this page at https://members.nearlyfreespeech.net/wiki/HowTo/GzipStatic.

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