[nycphp-talk] Overwriting Cache Headers
Darryle Steplight
dsteplight at gmail.com
Sun Sep 14 20:02:31 EDT 2008
Michael,
Firebug doesn't show you header information but the Web Developer
Toolkit for FireFox does. Once installed, just go to Information >
View Response Headers. Also, if you want to see what files are being
used during your ajax scripts or any header redirects,etc then
download FF's Live HTTP Headers plugin. Chrome's Inspect Element does
a pretty good job at this too, IMHO.
On Sun, Sep 14, 2008 at 12:25 PM, Michael B Allen <ioplex at gmail.com> wrote:
> On Sun, Sep 14, 2008 at 11:15 AM, Tom Melendez <tom at supertom.com> wrote:
>> Have you tried overwriting the header with the header() function,
>> either by making it blank ("Pragma:") or with the desired value?
>
> Hi Tom,
>
> That sort of works. What it does is actually send blank headers to the
> client like:
>
> Cache-Control: \r\n
> Pragma: \r\n
>
> But Firefox at least seems to handle this correctly.
>
> [Note: Firebug does not show you what was received on the network. It
> shows you what FF knows from the communication. This is actually good
> IMO but if you want to know what was really sent out on the network
> you'll want to double check with WireShark.]
>
> Also, in the process of Googling this issue I read some forum posts
> that claimed a blank header generated an error. But with at least PHP
> 5.2.6, calling header('Pragma:') doesn't seem to generate any errors
> that I can see so far. Or perhaps the posts were just wrong (e.g.
> actually a headers-already-sent problem).
>
> Anyway, from playing around with this, I have finally settled on the
> following to enable caching of PHP output on the client:
>
> header('Expires: ' . gmdate('D, d M Y H:i:s ', time() + (60 * 60)) . 'GMT');
> header('Cache-Control:');
> header('Pragma:');
>
> At least with Firefox it seems caching is largely controlled by the
> Expires header. Note that I set the expiration for one hour. And I've
> only tried this will application/x-javascript and text/css output with
> Content-Disposition: filename=<filename>.
>
> Mike
>
>> On Sun, Sep 14, 2008 at 12:21 AM, justin <justin at justinhileman.info> wrote:
>>> On Sat, Sep 13, 2008 at 11:41 PM, Michael B Allen <ioplex at gmail.com> wrote:
>>>> I want to send css and js files from a PHP script so I want to allow caching.
>>>>
>>>> But PHP always sends the following headers:
>>>>
>>>> Array
>>>> (
>>>> [0] => X-Powered-By: PHP/5.2.6
>>>> [1] => Expires: Thu, 19 Nov 1981 08:52:00 GMT
>>>> [2] => Cache-Control: no-store, no-cache, must-revalidate,
>>>> post-check=0, pre-check=0
>>>> [3] => Pragma: no-cache
>>>> )
>>>>
>>>> AFAIK it's not possible to remove or suppress headers but I can of
>>>> course overwrite them.
>>>>
>>>> The question is: with what?
>>>>
>>>> For the Expires header I suppose it could just be the RFC822 time for
>>>> now + 1 hour.
>>>>
>>>> For the Cache-Control header it's less clear. Here's the spec but I'm
>>>> still trying to decipher the meaning of each directive:
>>>>
>>>> http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9
>>>>
>>>> For the Pragma header I'm largely clueless.
>>>>
>>>> Does anyone know what values for these headers would be equivalent to
>>>> not specifying them at all?
>>>>
>>>
>>> Is there any particular reason you need PHP to send the files? You do
>>> have a couple more options. I usually use PHP to write a static file,
>>> then let Apache serve it up as an actual css/js file. You can even use
>>> sweet mod_rewrite rules to hit the php file if the requested css/js
>>> file isn't present. If you're just reading a file from disk and
>>> spitting it out with PHP, you might want to have PHP send your
>>> favorite flavor of redirect header instead.
>>>
>>> As far as which headers to send, I poked around a bit. You'd be
>>> surprised how many of the big guys just dump the css on every single
>>> page... But a few that served actual files had headers like the
>>> following. Note that all these css files are coming from a CDN. For
>>> what that's worth.
>>>
>>>
>>> Headers for an Amazon.com css file:
>>>
>>> Cache-Control: max-age=630720000
>>> Date: Sun, 14 Sep 2008 04:03:45 GMT
>>> Content-Type: text/css
>>> Last-Modified: Thu, 28 Aug 2008 00:32:03 GMT
>>> Server: Server
>>> X-Cache-Lookup: MISS from cdn-images.amazon.com:8080
>>> X-Cache: MISS from cdn-images.amazon.com
>>> Content-Encoding: deflate
>>> Expires: Wed, 23 Aug 2028 00:39:01 GMT
>>> Content-Length: 2018
>>> X-WR-MODIFICATION: Content-Length
>>>
>>>
>>> And one from Yahoo.com:
>>>
>>> Date: Thu, 11 Sep 2008 21:50:36 GMT
>>> Cache-Control: max-age=315360000
>>> Expires: Sun, 09 Sep 2018 21:50:36 GMT
>>> Last-Modified: Mon, 17 Mar 2008 17:19:43 GMT
>>> Accept-Ranges: bytes
>>> Vary: Accept-Encoding
>>> Content-Type: text/css
>>> Content-Encoding: gzip
>>> Age: 195294
>>> Content-Length: 1921
>>> Server: YTS/1.17.8
>>>
>>>
>>> Twitter seems to use a more reasonable cache length, you might try
>>> something like this:
>>>
>>> Date: Sun, 14 Sep 2008 04:07:46 GMT
>>> Server: Apache
>>> Last-Modified: Fri, 12 Sep 2008 00:23:22 GMT
>>> Accept-Ranges: bytes
>>> Cache-Control: max-age=86400
>>> Expires: Mon, 15 Sep 2008 04:07:46 GMT
>>> Vary: Accept-Encoding
>>> Content-Encoding: gzip
>>> Content-Length: 6509
>>> Content-Type: text/css
>>>
>>>
>>> I wasn't able to find a css file that returned a Pragma header.
>>> Perhaps you could try "Pragma: " ?
>>>
>>> justin
>>> --
>>> http://justinhileman.com
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>
>
>
> --
> Michael B Allen
> PHP Active Directory SPNEGO SSO
> http://www.ioplex.com/
> _______________________________________________
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