Cache-Control Header Modified By PHP Session?

Question

I'm outputting an image to the browser using a Zend_Controller_Response object. It is my intention to apply caching to the image, however something is causing the Cache-Control header to be overwritten.

My code is as follows:

$this->getResponse()
    ->setHeader('Last-Modified', $modifiedTime, true)
    ->setHeader('ETag', md5($modifiedTime), true)
    ->setHeader('Expires', $expires, true)
    ->setHeader('Pragma', '', true)
    ->setHeader('Cache-Control', 'max-age=3600')
    ->setHeader('Content-Type', $mimeType, true)
    ->setHeader('Content-Length', $size, true)
    ->setBody($data);

The output (as viewed in Firebug) is:

Response Headers

Date
Wed, 25 Mar 2009 10:34:40 GMT

Server
Apache/2.2.3 (Ubuntu) mod_ssl/2.2.3 OpenSSL/0.9.8c

Expires
Thu, 26 Mar 2009 10:34:41 GMT

Cache-Control
no-store, no-cache, must-revalidate, post-check=0, pre-check=0, max-age=3600

Last-Modified
1234872514

Etag
d3ef646c640b689b0101f3e03e08a524

Content-Length
1452

X-UA-Compatible
IE=EmulateIE7

X-Robots-Tag
noindex

Keep-Alive
timeout=15, max=100

Connection
Keep-Alive

Content-Type
image/jpeg

Request Headers

Host
khall.####.###.######.com

User-Agent
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.7) Gecko/2009030422 Ubuntu/8.04 (hardy) Firefox/3.0 .7

Accept
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Language
en-gb,en;q=0.5

Accept-Encoding
gzip,deflate

Accept-Charset
ISO-8859-1,utf-8;q=0.7,*;q=0.7

Keep-Alive
300

Connection
keep-alive

Referer
http://khall.####.###.######.com/

Cookie
PHPSESSID=abf5056e1289d3010448107632a1c1bd

As you can see, the cache control is modified to include:

no-store, no-cache, must-revalidate, post-check=0, pre-check=0

My suspicion is towards the session cookie being sent in the request. Does anybody know a way to send the header that I require, yet still keep the session in the request? My application is run through a bootstrap, and sessions are handled using Zend_Session.

Any help would be appreciated.

Stefan Gehrig · Accepted Answer · 2009-03-25 13:25:44Z

29

You're right by assuming that this behaviour is connected to the session mechanism in PHP. There is a configuration setting session.cache_limiter that controls the caching HTTP headers that will be sent with the response. The default setting here is nocache which sends

Expires: Thu, 19 Nov 1981 08:52:00 GMT 
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 
Pragma: no-cache

You overwrite all of these headers within your controller besides the Cache-Control-header (you only append your max-age=3600 setting here).

Possible solutions are:

changing the PHP configuration (session.cache_limiter) to e.g. none - but this could introduce problems to other PHP applications
set the session.cache_limiter on each request using session_cache_limiter()
overwrite the full Cache-Control-header in your controller with the designated string

The possible values for session.cache_limiter and session_cache_limiter() are:

none: no header will be sent

nocache:

Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache

private:

Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: private, max-age=10800, pre-check=10800

private_no_expire:

Cache-Control: private, max-age=10800, pre-check=10800

public:

Expires: pageload + 3 hours
Cache-Control: public, max-age=10800

answered Mar 25, 2009 at 13:25

Stefan Gehrig

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2 Comments

Kieran Hall Over a year ago

Thanks for your reply. The problem was my hasty coding, as karim79 pointed out: the problem is more Zend Framework based. Thanks for the insight, though.

Bart van Heukelom Over a year ago

Nice, this solved my question: stackoverflow.com/questions/1937581/php-remove-http-header

karim79 · Accepted Answer · 2009-03-25 11:32:55Z

13

From the Zend_Controller documentation, section 10.9. The Response Object

setHeader($name, $value, $replace = false) is used to set an individual header. By default, it does not replace existing headers of the same name in the object; however, setting $replace to true will force it to do so.

The problem you are having is your max-age=3600 is being appended to the cache-control header, as opposed to replacing it. Try setting the $replace parameter to true.

answered Mar 25, 2009 at 11:32

karim79

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2 Comments

Kieran Hall Over a year ago

GAH! I should smack myself in the face. I thought I was passing that parameter! You are quite right though, that is the answer.

karim79 Over a year ago

Hehe, I do it all the time! Proof? see stackoverflow.com/questions/657600/…

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