Caching problem

[Anon]

PHP4's default seems to be to prohibit browser caching. For some basically static pages, though, I want to allow browsers to cache the pages for a short amount of time.

I've tried the following code, which inserts an Expires header, but it doesn't seem to have any effect. Can anyone see what I'm doing wrong? Or does anyone have a better idea to control the browser caching?

<?php
$later = time() + 60603; // 3 hours from now
$header_str = 'Expires: '.gmstrftime('%A, %d-%b-%y %H:%M:00 GMT',$later);
header($header_str);
?>

Also, does anyone know how I can view what headers were sent in a browser? I just want to make sure the header is actually being sent and retrieved by the browser.

Thanks everyone. This group is such a great resource.

-Keegan

[Anon]

Your Expires-header is wrong. The format to use with gmstrftime is '%a, %d %b %Y %R GMT'.

You should probably also add a header which explicitly allows caching. Perhaps this will do it:
header('Cache-Control: private');
or
header('Cache-Control: public');

If you use PHP 4's session facilities, then PHP will make your pages totally un-cacheable.

Note it it's very hard (impossible?) to make Netscape cache pages properly.

About HTTP header-analysis: At http://www.mdb.ku.dk/tarvin/http-tool/ I have an old online-tool for looking at HTTP response headers. (It's at a server which I no longer control; that's why the syntax-highlighted source doesn't work.)

[Anon]

Interesting utility... Before, I used to do it by hand with the good old telnet :

telnet onesite 80

HEAD /page HTTP/1.0

Or, if the server is multi-hosted :

HEAD /page HTTP/1.1
Host: onesite

But from now on, I think I'll use a more modern tool ;-)