prevent caching of gd image

[dave Cheseldine]

Hi
I want to stop a gd generated image from being cached.

It is called into index.php file as follows:

<image src =
"http://www.daveches.co.uk/importimage/importimage.php?x=$randomNumber"
alt = "battle area" usemap="#battlegrid" border="0">

(importimage4real.php contains the gd functionality that load and modify
the image).

The random number querystring in the code above is an attempt to trick
the browser into thinking the image is different from what it has in
its cache. But still it displays its cached version of the image.

I have tried every "stop caching" header I can think of in both
index.php and importimage.php, set expires to a time in the past and all
the rest. Still, refresh the browser: you get the cached, not the
latest, image (same in ie6 and Firefox). After a few minutes something
expires and you do get the latest version by Refreshing, but this is no
good for my application.

Is it possible that some settings on my hosting company's server are
overwriting any changes I can make?

dave Cheseldine

[WhatsPHP]

It might not be just the PHP caching.. Did u check the IE and firefox
browser setting? in IE: Tools > Internet Options > Settings check if
the setting shows you how the caching is done.. this might help.

[AD7six]

Try this in your import image script.

//**** Lots of headers to ensure the image is not cached.
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
// always modified
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
// HTTP/1.1
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
// HTTP/1.0
header("Pragma: no-cache");
//**** End of crappy headers.

It's not my own work, and I don't remember where I got it from but it
worked for me for a similar application.

Regards,

AD7six

[dave ches]

Hi
Thanks: yes I've tried those headers. It still delivers a cached
version of the gd image unless the browser is idle for a minute or 2.

I'm going to contact my hosting provider and see if it's anything in the
server config.

What I don't understand is how it can go to the cached version of the
php script that generates the gd image even when the php script is
called via a URL with a unique querystring. (and it is: each time you
refresh and look at the source it is a different querystring.

regards
dave

AD7six wrote:

Try this in your import image script.

//**** Lots of headers to ensure the image is not cached.
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
// always modified
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
// HTTP/1.1
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
// HTTP/1.0
header("Pragma: no-cache");
//**** End of crappy headers.

It's not my own work, and I don't remember where I got it from but it
worked for me for a similar application.

Regards,

AD7six

[Philip Ronan]

"dave ches" wrote:

Thanks: yes I've tried those headers. It still delivers a cached
version of the gd image unless the browser is idle for a minute or 2.

I'm going to contact my hosting provider and see if it's anything in the
server config.

What I don't understand is how it can go to the cached version of the
php script that generates the gd image even when the php script is
called via a URL with a unique querystring. (and it is: each time you
refresh and look at the source it is a different querystring.

This sounds more like a browser problem than anything else. Can we have some
URLs please (i.e., the image script and the page that references it)? The
URL you posted earlier just points to a 404 error page.

--
phil [dot] ronan @ virgin [dot] net
http://vzone.virgin.net/phil.ronan/

[AD7six]

dave ches,

URL would help investigations. I'm interested to here what the problem
is, when it is found.

What does a site like this http://www.delorie.com/web/headers.html have
to say about your headers?

Regards,

AD7six

[dave ches]

Hi
Thanks for the interest.

delorie reports as follows:
for the file that references the image:

HTTP/1.1 200 OK
Date: Wed, 23 Nov 2005 14:59:42 GMT
Server: Apache/2.0.54 (Unix) mod_perl/1.99_17 Perl/v5.8.7
FrontPage/5.0.2.2635 PHP/4.3.11 mod_webapp/1.2.0-dev mod_python/3.1.4
Python/2.2.2 mod_ssl/2.0.54 OpenSSL/0.9.7d
X-Powered-By: PHP/4.4.1
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0,
pre-check=0
Pragma: no-cache
Last-Modified: Wed, 23 Nov 2005 14:59:42 GMT
Vary: Accept-Encoding
Connection: close
Content-Type: text/html; charset=iso-8859-1
for the file containing the image script:

HTTP/1.1 200 OK
Date: Wed, 23 Nov 2005 15:01:24 GMT
Server: Apache/2.0.54 (Unix) mod_perl/1.99_17 Perl/v5.8.7
FrontPage/5.0.2.2635 PHP/4.3.11 mod_webapp/1.2.0-dev mod_python/3.1.4
Python/2.2.2 mod_ssl/2.0.54 OpenSSL/0.9.7d
X-Powered-By: PHP/4.4.1
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0,
pre-check=0
Pragma: no-cache
Last-Modified: Wed, 23 Nov 2005 15:01:24 GMT
Connection: close
Content-Type: image/gif

AD7six wrote:

dave ches,

URL would help investigations. I'm interested to here what the problem
is, when it is found.

What does a site like this http://www.delorie.com/web/headers.html have
to say about your headers?

Regards,

AD7six

[AD7six]

test URL please.

It's only the headers for the image file that are relavent, all _seems_
present and correct. Have you deleted your cache before testing?

Regards,

AD7six

[dave ches]

Hi
The URL is www.companybattleships.com/index.php

The best way to show the unwanted caching is as follows.

1. open 2 new browsers.

2. in browser 1, go to www.companybattleships.com/index.php

3. in browser 2, go to www.companybattleships.com/callingpage.php

4. follow the link in browser 2. Observe that the image has changed.

5. refresh browser 1. The image has also changed. Great.

6. in browser 2, go back to www.companybattleships.com/callingpage.php

7. follow the link in browser 2 once again. Observe that the image has
changed again.

8. refresh browser 1. The image does not change. Problem.

cheers
dave

AD7six wrote:

test URL please.

It's only the headers for the image file that are relavent, all _seems_
present and correct. Have you deleted your cache before testing?

Regards,

AD7six

[AD7six]

Well that's not an easy one, I can't tell if it's updating or not (on
any step) ;o).

Are you sure the image is being updated on every request? Compare the
behaviour of the below link when visiting multiple times & refreshing.
I think your headers are probably fine and the image is not being
updated.

http://www.noswad.me.uk/cachetest.html

Regards,

AD7six

[dave ches]

Yes, the image is being updated every time you follow the link on

www.companybattleships.com/callingpage.php

you can see that because 6 additional black squares appear on the image
each time you follow that link.

But in your other browser (the one where you arrive at index.php with
not referer) you don't see the latest image: compare the 2 and the
black squares aren't there.

So why is the latest image not being displayed if the headers are in order?

In the example you send, the 2 images:
This image does not set any extra HTTP Headers
and
This image has headers set to prevent caching

are identical, so doesn't that just confirm that the headers don't do as
they are supposed to when drawing in gd images?

regards
dave

AD7six wrote:

Well that's not an easy one, I can't tell if it's updating or not (on
any step) ;o).

Are you sure the image is being updated on every request? Compare the
behaviour of the below link when visiting multiple times & refreshing.
I think your headers are probably fine and the image is not being
updated.

http://www.noswad.me.uk/cachetest.html

Regards,

AD7six