Caching image by setting non expire image headers using php

Sanjay_123

Is it possible to call a php script from img src tag and deliver an
image in such a way that if any other page of the site seeks the same image, then the query should not be forwarded right up to the web server, rather the browser cache or the public isp cache should process that request for that image file and deliver the cached copy of the same image, reducing load on servers and ample bandwidth everywhere... I checked out hundreds of tutorials on php that discuss something similar, but non of them clearly suggests and provides code-set on what image-eaders
should be set while delivering the image and what headers should be set for the url seeking those images to be cached so that no such queries are forwarded everytime a page is sought from the server... I'm trying to stop such queries that seek more than 30 template images that are true common on all pages of our web site.

My true thanks in advance.
Sanjay.

bradgrafelman

Link to the script via this manner:

<img src="myscript.php?src=myimage.jpg">

then use the following code in myscript.php:

<?PHP

$filename = ((@$_GET['src']) ? $_GET['src'] : "");

if($filename == "") die('no src= tag');

header("Cache-Control: must-revalidate");

$offset = 60 * 60 * 24 * 3;
$ExpStr = "Expires: " . gmdate("D, d M Y H:i:s", time() + $offset) . " GMT";
header($ExpStr);

$fp = fopen("/path/to/images/$filename", "rb");
fpassthru($fp);
?>

NOTE: This script loads files based on user-input. You should implement checking methods to make sure they didn't manually type in ".." (goes to parent directory) to include scripts you don't want them to. [man]dirname[/man] and [man]realpath[/man] provide ways to take a string and make sure it is in the directory you want it to be in.

Sanjay_123

Hello bradgrafelman,

Thanks for the reply. Now tell me what should be send inside the headers of the calling url ? I've experimented with almost all options and I'm not sure if no-cache or no-store or revalidate will bar all files declared in the calling url from being cached in browser and at isp level....

Thanks.

bradgrafelman

In the above example, I used the "Cache-control" header in conjunction with the "Expires" header to tell the browser when to expire the content. Presumably, it would apply this to the image only, as that is when the header was outputted; on the image script.

You could instead load the image normally ("<img src='myimage.jpg'") and instead output the headers on the HTML page itself; simply copy the headers I used and paste them into your script.

I'm not an expert on cache controlling, but I found this solution elsewhere, and presumed it would work.