缓存1个多域的文件

Question

First of all, I'm sorry about the title. I couldn't find a better one.

I've a image file, generated by a PHP script. this script (image) is connected to a database and saves its referrer url in a table. Because the output image doesn't change, I think it's better to cache it.

But as I know, if I cache 1 file (for example http://www.example.com/img.png.php), on every pages, the browsers reads it from cache. and it's not good for my script. because on the first call, it save the referrer url and cached by browser. And on the next calls, on different websites (referrers), cached version will be used and browser don't send any request to the server, and finally referrer url won't save in the database.

Can I say to browser, please cache 1 copy of the image for each domain? I mean:

http://wwww.abc.com/index.html sends a request to get my image (script)

browser checks its cache, and doesn't find it. so get it from the server. and PHP script saves the referrer url.

the user goes to another page of ABC.COM. (for example: http://wwww.abc.com/about.html) browser check the cache, it finds it. so doesn't send a request to the server to get the file content. and PHP script won't run.

another site (http://wwww.efg.com/index.html) sends a request to get my image (script) browser checks cache, and WILL NOT find it. so send a request for file content. and PHP script runs...............................

Is it possible? (sorry for long text, with a lots of grammatical problems)

Answer 1

You could use a redirect page (that is not cached) that saves the referrer to your database and then redirects to the cached image.

That way you always get a hit but the actual image is cached.

---

In your HTML you could use:

<img src="/image.php">

And in image.php:

<?php
    // save the referrer in here

    header('Location: /image.jpg');
?>

and /image.jpg is your actual image (which can be cached)