Code Samples: Image Caching in Browser

Sunday, October 8, 2023
PHP image output and browser caching

This post is for return image from server by PHP script and cache in browser to save on our bandwidth.




Below code will return image using PHP script

<?php

function image_function_cache($file_name) {
    $file = "WWW_ROOT/public/img/$file_name";
    if (!file_exists($file) || !is_file($file)) {
        echo "";
        exit;
    }

    $fileTime = filemtime($file);
    $headerTime = IfModifiedSince();

    // Will return 304 when image source not changed
    if (!is_null($headerTime) && (strtotime($headerTime) == $fileTime)) {
        header('Last-Modified: '.gmdate('D, d M Y H:i:s', $fileTime).' GMT', true, 304);
        exit;
    }
    session_cache_limiter('none');

    $type = 'image/png';
    header('Content-Type:'.$type);
    header('Content-Length: ' . filesize($file));
    header('Cache-control: max-age='.(60*60*24*365));
    header('Expires: '.gmdate(DATE_RFC1123,time()+60*60*24*365));
    header('Last-Modified: '.gmdate('D, d M Y H:i:s', $fileTime).' GMT', true, 200);
    readfile($file);
    exit;
}

function IfModifiedSince() {
    if (function_exists("apache_request_headers")) {
        if ($headers = apache_request_headers()) {
            if (isset($headers['If-Modified-Since'])) {
                return $headers['If-Modified-Since'];
            }
        }
    }
    if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
        return $_SERVER['HTTP_IF_MODIFIED_SINCE'];
    }
    return null;
}



Check below image, there are two request for an image, first request status is 200 and image returned, but 2nd call if you see Size column image returned from cache. All happened for above functionality:
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Sunday, October 8, 2023

PHP image output and browser caching
