cache-busting

buster.php

<?php
// assumes SITE_VERSION, BASEPATH constants are set; assumes CodeIgniter configuration

function buster($url) {
    if (!($url && is_scalar($url))) {
        return '';
    }
    
    // trim off any leading '/' in the URL; we'll re-add it later
    $url   = ltrim($url, '/');
    $parts = explode('.', $url);
    $ext   = array_pop($parts);
    
    // should we bust cache at all?
    if (get_instance()->config->item('bust-cache')) {
        // last-modified time on dev sites
        if (SITE_VERSION == 'vDEV') {
            $file = realpath(BASEPATH . '../../public/' . $url);
            if (is_readable($file)) {
                $parts[] = 'v0.0.' . filemtime($file);
            }
        }
        
        // deployed version on the live site
        else {
            $parts[] = SITE_VERSION;
        }
    }
    
    // rebuild a valid URL
    $parts[] = $ext;
    return '/' . join('.', array_filter($parts));
}
?>

output.html

<!-- with cache-busting completely disabled -->
<script src="/javascripts/somefile.js"></script>

<!-- with cache-busting enabled, in dev mode - always refresh -->
<script src="/javascripts/somefile.v0.0.1374498234.js"></script>

<!-- with cache-busting enabled, in production mode; use deployed version tag -->
<script src="/javascripts/somefile.v1.2.3.js"></script>

<!-- with cache-busting enabled, in production mode; rewrite rule also supports git SHA1 version strings -->
<script src="/javascripts/somefile.SHA1-52145c.js"></script>

rewrite.conf

# Handle requests for CSS/JS/images that specify a version
RewriteRule ^(images|css|javascripts)/(.*)\.(?:(?:v[0-9]+\.[0-9]+\.[0-9]+[a-z]?[0-9]*)|(?:SHA1\-[a-zA-Z0-9]+))\.(js|css|png|jpg|gif|ico)$ /$1/$2.$3 [L,NC]

source.html

<script src="<?=buster('javascripts/somefile.js')?>"></script>