Symfony HttpCache¶
Symfony comes with a built-in reverse proxy written in PHP, known as
HttpCache
. While it is certainly less efficient
than using Varnish or Nginx, it can still provide considerable performance
gains over an installation that is not cached at all. It can be useful for
running an application on shared hosting for instance
(see the Symfony HttpCache documentation).
You can use features of this library with the Symfony HttpCache
. The basic
concept is to use event subscribers on the HttpCache class.
Warning
Symfony HttpCache support is currently limited to following features:
- Purge
- Refresh
- User context
Extending the correct HttpCache¶
Instead of extending Symfony\Bundle\FrameworkBundle\HttpCache\HttpCache
, your
AppCache
should extend FOS\HttpCacheBundle\SymfonyCache\EventDispatchingHttpCache
:
require_once __DIR__.'/AppKernel.php';
use FOS\HttpCacheBundle\SymfonyCache\EventDispatchingHttpCache;
class AppCache extends EventDispatchingHttpCache
{
}
Tip
If your class already needs to extend a different class, simply copy the event
handling code from the EventDispatchingHttpCache
into your AppCache
class.
The drawback is that you need to manually check whether you need to adjust your
AppCache
each time you update the FOSHttpCache library.
By default, the event dispatching cache kernel registers all subscribers it knows about. You can disable subscribers, or customize how they are instantiated.
If you do not need all subscribers, or need to register some yourself to
customize their behavior, overwrite getOptions
and return the right bitmap
in fos_default_subscribers
. Use the constants provided by the
EventDispatchingHttpCache
:
public function getOptions()
{
return array(
'fos_default_subscribers' => self::SUBSCRIBER_NONE,
);
}
To register subscribers that you need to instantiate yourself, overwrite
getDefaultSubscribers
:
use FOS\HttpCache\SymfonyCache\UserContextSubscriber;
// ...
public function getDefaultSubscribers()
{
// get enabled subscribers with default settings
$subscribers = parent::getDefaultSubscribers();
$subscribers[] = new UserContextSubscriber(array(
'session_name_prefix' => 'eZSESSID',
));
$subscribers[] = new CustomSubscriber();
return $subscribers;
}
Warning
Since Symfony 2.8, the class cache (classes.php
) is compiled even in
console mode by an optional warmer (ClassCacheCacheWarmer
). This can
produce conflicting results with the regular web entry points, because the
class cache may contain definitions (such as the subscribers above) that
are loaded before the class cache itself; leading to redeclaration fatal
errors.
There are two workarounds:
Disable class cache warming in console mode with e.g. a compiler pass:
$container->getDefinition('kernel.class_cache.cache_warmer')->clearTag('kernel.cache_warmer');
Force loading of all classes and interfaced used by the
HttpCache
inapp/console
to make the class cache omit those classes. The simplest way to achieve this is to callclass_exists
resp.interface_exists
with each of them.
Subscribers¶
Each feature has its subscriber. Subscribers are provided by the FOSHttpCache library. You can find the documentation for the subscribers in the FOSHttpCache Symfony Cache documentation section.