HTTP Cache- Control

Question

I am struggling with this - In PHP, I do this for a GET AJAX call

header('Cache-Control: max-age = 10000, private');

The browser still manages to place a request thereafter? Why?

header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 10000) . ' GMT');

works fine, though!

Thanks

EDIT

header("Cache-Control: private, max-age=10000");

seems to work!!

MORE

The specification is explicit about this.

cache-directive = cache-request-directive | cache-response-directive

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.1

score 3 · Accepted Answer · answered Dec 05 '10 at 18:06

3

Do you use Firebug? If yes, then go to the NET tab when your page loads & inspect what headers the browser is seeing. This will give you an idea as to what might be wrong...

I use this -

Cache-Control   public, max-age=60
Content-Type    text/html; charset=utf-8

answered Dec 05 '10 at 18:06

Srikar Appalaraju

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Using firebug already. Your stuff works, not mine. Must explore. – Mr Hyde Dec 05 '10 at 18:16
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maybe it's the order of the terms? try to put `private` before `max-age`... These things are finicky! – Srikar Appalaraju Dec 05 '10 at 18:18
Thanks! The order of the terms was the key, but I do would like see some (easy) documentation – Mr Hyde Dec 05 '10 at 18:33

Daniel Trebbien · Answer 2 · 2010-12-05T20:58:32.173

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Am I correct that you want the browser to cache the page? If so, Cache-Control "private" is likely the culprit that is preventing the browser from caching the page. According to RFC-2616 Section 14.9.1 What is Cacheable, "private" means:

Indicates that all or part of the response message is intended for a single user and MUST NOT be cached by a shared cache. This allows an origin server to state that the specified parts of the response are intended for only one user and are not a valid response for requests by other users. A private (non-shared) cache MAY cache the response.

Translated to plain English, this means that caching HTTP proxies may not cache the page, but the web browser can. Note, however, that web browsers often do not cache a page if Cache-Control includes "private".

edited Dec 05 '10 at 20:58

answered Dec 05 '10 at 18:21

Daniel Trebbien

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This is intriguing. I wouldn't want a public cache in certain cases. – Mr Hyde Dec 05 '10 at 18:43
@RisingSun Neither the user nor the web server can control whether a public cache exists between the two. – Daniel Trebbien Dec 05 '10 at 21:03
Yes, I agree. What I meant was: I dont want a proxy cache to *cache* the message. After all the specification says 'MUST NOT cache IF private'. – Mr Hyde Dec 06 '10 at 05:26

HTTP Cache- Control

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