source: trunk/www.guidonia.net/wp/wp-content/plugins/wp-super-cache/wp-cache-phase1.php@ 44

<?php
// Pre-2.6 compatibility
if( !defined('WP_CONTENT_DIR') )
        define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' );

if( !include( WP_CONTENT_DIR . '/wp-cache-config.php' ) )
        return true;
if( !defined( 'WPCACHEHOME' ) )
        define('WPCACHEHOME', dirname(__FILE__).'/');

include( WPCACHEHOME . 'wp-cache-base.php');

if( $blogcacheid != '' ) {
        $blog_cache_dir = str_replace( '//', '/', $cache_path . "blogs/" . $blogcacheid . '/' );
} else {
        $blog_cache_dir = $cache_path;
}

if(defined('DOING_CRON')) {
        require_once( WPCACHEHOME . 'wp-cache-phase2.php');
        return true;
}

$mutex_filename = 'wp_cache_mutex.lock';
$new_cache = false;

// Don't change variables behind this point

if( !isset( $wp_cache_plugins_dir ) )
        $wp_cache_plugins_dir = WPCACHEHOME . 'plugins';
$plugins = glob( $wp_cache_plugins_dir . '/*.php' );
if( is_array( $plugins ) ) {
        foreach ( $plugins as $plugin ) {
        if( is_file( $plugin ) )
                require_once( $plugin );
        }
}

if (!$cache_enabled || $_SERVER["REQUEST_METHOD"] == 'POST') 
        return true;

$file_expired = false;
$cache_filename = '';
$meta_file = '';
$wp_cache_gzip_encoding = '';

$gzipped = 0;
$gzsize = 0;

function gzip_accepted(){
        if( ini_get( 'zlib.output_compression' ) ) // don't compress WP-Cache data files when PHP is already doing it
                return false;

        if (strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') === false) return false;
        return 'gzip';
}

if ($cache_compression) {
        $wp_cache_gzip_encoding = gzip_accepted();
}

add_cacheaction( 'wp_cache_get_cookies_values', 'wp_cache_check_mobile' );

$wp_cache_request_uri = $_SERVER[ 'REQUEST_URI' ]; // Cache this in case any plugin modifies it.

$key = $blogcacheid . md5( do_cacheaction( 'wp_cache_key', $_SERVER['HTTP_HOST'].preg_replace('/#.*$/', '', str_replace( '/index.php', '/', $wp_cache_request_uri ) ).$wp_cache_gzip_encoding.wp_cache_get_cookies_values() ) );

if( false == @is_dir( $blog_cache_dir ) ) {
        @mkdir( $cache_path . "blogs" );
        @mkdir( $blog_cache_dir );
}

if( false == @is_dir( $blog_cache_dir . 'meta' ) )
        @mkdir( $blog_cache_dir . 'meta' );


$cache_filename = $file_prefix . $key . '.html';
$meta_file = $file_prefix . $key . '.meta';
$cache_file = realpath( $blog_cache_dir . $cache_filename );
$meta_pathname = realpath( $blog_cache_dir . 'meta/' . $meta_file );

$wp_start_time = microtime();
if( file_exists( $cache_file ) && !wp_cache_user_agent_is_rejected() ) {
                if (! ($meta = unserialize(@file_get_contents($meta_pathname))) ) 
                        return true;
                if( is_array( $meta ) == false ) {
                        @unlink( $meta_pathname );
                        @unlink( $cache_file );
                        return true;
                }
                $cache_file = do_cacheaction( 'wp_cache_served_cache_file', $cache_file );
                // Sometimes the gzip headers are lost. If this is a gzip capable client, send those headers.
                if( $wp_cache_gzip_encoding && !in_array( 'Content-Encoding: ' . $wp_cache_gzip_encoding, $meta[ 'headers' ] ) ) {
                        $meta[ 'headers' ][ 'Content-Encoding' ] =  'Content-Encoding: ' . $wp_cache_gzip_encoding;
                        $meta[ 'headers' ][ 'Vary' ] = 'Vary: Accept-Encoding, Cookie';
                        wp_cache_debug( "Had to add gzip headers to the page {$_SERVER[ 'REQUEST_URI' ]}." );
                }
                foreach ($meta[ 'headers' ] as $t => $header) {
                        // godaddy fix, via http://blog.gneu.org/2008/05/wp-supercache-on-godaddy/ and http://www.littleredrails.com/blog/2007/09/08/using-wp-cache-on-godaddy-500-error/
                        if( strpos( $header, 'Last-Modified:' ) === false ) 
                                header($header);
                }
                header( 'WP-Super-Cache: WP-Cache' );
                if ( $meta[ 'dynamic' ] ) {
                        include($cache_file);
                } else {
                        readfile( $cache_file );
                }
                die();
}

function wp_cache_postload() {
        global $cache_enabled;

        if ( !$cache_enabled || isset( $_GET[ 'preview' ] ) )
                return true;
        require_once( WPCACHEHOME . 'wp-cache-phase2.php');
        wp_cache_phase2();
}

function wp_cache_get_cookies_values() {
        $string = '';
        while ($key = key($_COOKIE)) {
                if ( preg_match( "/^wp-postpass|^wordpress|^comment_author_/", $key ) && $_COOKIE[ $key ] != 'WP Cookie check' ) {
                        $string .= $_COOKIE[$key] . ",";
                }
                next($_COOKIE);
        }
        reset($_COOKIE);

        // If you use this hook, make sure you update your .htaccess rules with the same conditions
        $string = do_cacheaction( 'wp_cache_get_cookies_values', $string );
        return $string;
}

function add_cacheaction( $action, $func ) {
        global $wp_supercache_actions;
        $wp_supercache_actions[ $action ][] = $func;
}

function do_cacheaction( $action, $value = '' ) {
        global $wp_supercache_actions;
        if( is_array( $wp_supercache_actions[ $action ] ) ) {
                $actions = $wp_supercache_actions[ $action ];
                foreach( $actions as $func ) {
                        $value = $func( $value );
                }
        }

        return $value;
}

// From http://wordpress.org/extend/plugins/wordpress-mobile-edition/ by Alex King
function wp_cache_check_mobile( $cache_key ) {
        global $wp_cache_mobile_enabled, $wp_cache_mobile_browsers, $wp_cache_mobile_whitelist;
        if( !isset( $wp_cache_mobile_enabled ) || false == $wp_cache_mobile_enabled )
                return $cache_key;

        if (!isset($_SERVER["HTTP_USER_AGENT"])) {
                return $cache_key;
        }
        $whitelist = explode( ',', $wp_cache_mobile_whitelist );
        foreach ($whitelist as $browser) {
                if (strstr($_SERVER["HTTP_USER_AGENT"], trim($browser))) {
                        return $cache_key;
                }
        }

        $browsers = explode( ',', $wp_cache_mobile_browsers );
        foreach ($browsers as $browser) {
                if (strstr($_SERVER["HTTP_USER_AGENT"], trim( $browser ))) {
                        return $cache_key . $browser;
                }
        }
        return $cache_key;
}

function wp_cache_debug( $message ) {
        global $wp_cache_debug;
        if( !isset( $wp_cache_debug ) )
                return;
        $message .= "\n\nDisable these emails by commenting out or deleting the line containing\n\$wp_cache_debug in wp-content/wp-cache-config.php on your server.\n";
        mail( $wp_cache_debug, '[' . addslashes( $_SERVER[ 'HTTP_HOST' ] ) . "] WP Super Cache Debug", $message );
}

function wp_cache_user_agent_is_rejected() {
        global $cache_rejected_user_agent;

        if (!function_exists('apache_request_headers')) return false;
        $headers = apache_request_headers();
        if (!isset($headers["User-Agent"])) return false;
        foreach ($cache_rejected_user_agent as $expr) {
                if (strlen($expr) > 0 && stristr($headers["User-Agent"], $expr))
                        return true;
        }
        return false;
}

?>