7.4. Thumbnail Caching

Dynamically generating thumbnails on the fly is certainly convenient, but you may find the album's performance somewhat lacking depending on the original size of an image, how many images are in an album and the load on the server. You may therefore want to put some form of caching in place. To keep everything simple and easy to update, I recommend making the modifications thumbnail.php.

Since all cached thumbnail images will be stored in one central cache directory, the inherent protection that comes from the album and image names being a unique combination is lost. The received file parameter may be run through sha1() to make sure valid thumbnail caches aren't overwritten.

The script should check to see if the thumbnail already exists within the cache directory and then its timestamp can be compared with that of the original image. If the thumbnail is newer than the original image then the thumbnail is still fresh and can be sent to the viewer instead of having to generate a new one for each request. However, if the thumbnail is older than the original image then it means someone updated the album and the thumbnail must be regenerated.

<?php
// include shared code
include '../lib/config.php';

// assumes CACHEDIR is defined alongside BASEDIR in config.php

// make sure users only access files in the albums
$file = (isset($_GET['file'])) ? (BASEDIR . '/' . $_GET['file']) : '';
if ($file && strpos(realpath($file), BASEDIR) === 0 && file_exists($file))
{
    // file name hashed to ensure unique names for cache files
    $cache_file = sha1(realpath($file));

    // retrieve timestamps to determine cached file's "freshness"
    $f_time = filemtime($file);
    $c_time = (file_exists(CACHEDIR . '/' . $cache_file)) ?
        filemtime(CACHEDIR . '/' . $cache_file) : 0;
    // output thumbnail
    switch (substr($file, strrpos($file, '.') + 1))

{
        // thumbnail is for jpeg image
        case 'jpg':
        case 'jpeg':
            header('Content-Type: image/jpeg'),

            // cache still valid
            if ($f_time <= $c_time)
            {
                readfile(CACHEDIR . '/' . $cache_file);
            }
            // regenerate cache file
            else
            {
                include '../lib/JpegThumbnail.php';
                $thumbnail = new JpegThumbnail(100, 100);
                imagejpeg($thumb = $thumbnail->generate($file), '', 100);
                imagejpeg($thumb, CACHEDIR . '/' . $cache_file, 100);
                imagedestroy($thumb);
            break;

        // thumbnail is for quicktime video
        case 'mov':
            header('Content-Type: movie/quicktime'),
            if ($f_time <= $c_time)
            {
                readfile(CACHEDIR . '/' . $cache_file);
            }
            else
            {
                include '../lib/MovThumbnail.php';
                $thumbnail = new MovThumbnail();
                imagejpeg($thumb = $thumbnail->generate($file), '', 100);
                imagejpeg($thumb, CACHEDIR . '/' . $cache_file, 100);
                imagedestroy($thumb);
            }
            break;
    }
}
?>