Preventing error pages caching when using Zend_Cache_Backend_Static - php

Question

We're currently running an app that caches pages to static html files using Zend_Cache_Backend_Static. This works really well, except that our cache is getting filled with hundreds of empty files and folders when incorrect urls are requested. Is there any way to prevent a page being cached if an Exception is being thrown? I was surprised to discover that this wasn't standard behaviour.
I've done a little digging and the ZF code that actually deals with saving out the static html pages is as follows in Zend_Cache_Frontend_Capture:
public function _flush($data) {
$id = array_pop($this->_idStack);
if ($id === null) {
Zend_Cache::throwException('use of _flush() without a start()');
}
if ($this->_extension) {
$this->save(serialize(array($data, $this->_extension)), $id, $this->_tags);
} else {
$this->save($data, $id, $this->_tags);
}
return $data;
}
This function is the output_callback for ob_start. I've tried getting hold of the response object to test for status but it doesn't seem to work inside _flush.
$response = Zend_Controller_Front::getInstance()->getResponse();
if($response->getStatus() == '200') {
// do the save as normal
}
else {
// do nothing
return false;
}
My only other thought was to test the length of $data, only caching if strlen($data) > 0 seems to work but it doesn't feel robust enough.
Update:
Unfortunately by the time we hit the ErrorController the static page has already been written to the cache, so disabling the cache at that point won't work. However it is possible to remove the page based on $_SERVER['REQUEST_URI'], which is what is used as an id when the page is first written. This line can be added to the start of errorAction in the ErrorController:
$this->_helper->cache->removePage($_SERVER['REQUEST_URI'], true);
It works nicely, but I'd prefer not to write the page in the first place!

Answer 1

From further experimentation the problem is not down to standard Zend Framework exceptions that cause 404s (ie. Zend_Controller_Plugin_ErrorHandler::EXCEPTION_NO_ROUTE, Zend_Controller_Plugin_ErrorHandler::EXCEPTION_NO_CONTROLLER, Zend_Controller_Plugin_ErrorHandler::EXCEPTION_NO_ACTION) but to my custom exceptions. This is now really obvious now that I think about it, as Zend_Cache_Backend_Static needs to be initialised in the init method of an action controller. Any situation where there is no route, controller or action it won't ever be initialised anyway.
I'm throwing exceptions in existing actions where a user may be querying for a non-existent article. Therefore caching has been enabled in init and the page has been written by the time we hit postDispatch in a Front Controller Plugin (still not sure why this is the case it just is) so I can't cancel at that point. One solution then is to cancel the cache at the point of throwing the exception. The standard method of managing static page caching is using the Zend_Controller_Action_Helper_Cache action helper. I've extended this to add a cancel method like so:
<?php
class Zend_Controller_Action_Helper_PageCache extends Zend_Controller_Action_Helper_Cache {
public function cancel() {
$cache = $this->getCache(Zend_Cache_Manager::PAGECACHE);
$cache->setOption('caching', false);
$cache->getBackend('disable_caching', true);
}
}
My action controller now looks like this:
<?php
class IndexController extends Zend_Controller_Action {
private $_model;
public function init() {
$this->_model = new Model();
// using extended pageCache rather than $this->_helper->cache:
$this->_helper->pageCache(array('index'), array('indexaction'));
}
public function indexAction() {
$alias = $this->_request->getParam('article');
$article = $this->_model->getArticleByAlias($alias);
if(!$article) {
// new cancel method will disable caching
$this->_helper->pageCache->cancel();
throw new Zend_Controller_Action_Exception('Invalid article alias', 404);
}
$this->view->article = $article;
}
}

Answer 2

You should alter your .htaccess file RewriteRules to check for filesizes with option -s
This way if an error should occur when a page is being cached (thus producing a 0 byte file) it won't permanently be stored in the cache.

Answer 3

If you are using the standard ErrorController to handle 404, 500, and unhandled exceptions, and you can get a reference to your cache object from there, you could disable caching from the error handler.
In your error controller (or wherever you would like to cancel caching from), try:
$cache->setOption('caching', false);
When the save() metod of Zend_Cache_Core is called by Zend_Cache_Frontend_Capture::_flush(), it will see the caching option is set to false and it will not actually save the data to the cache and return true.