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

Answer 1

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:

1. changing the PHP configuration (session.cache_limiter) to e.g. none - but this could introduce problems to other PHP applications
2. set the session.cache_limiter on each request using session_cache_limiter()
3. 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

Answer 2

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.