This PR was merged into the master branch.
Discussion
----------
[2.3] [WIP] Synchronized services...
| Q | A
| ------------- | ---
| Bug fix? | no
| New feature? | no
| BC breaks? | no
| Deprecations? | no
| Tests pass? | yes
| Fixed tickets | #5300, #6756
| License | MIT
| Doc PR | symfony/symfony-docs#2343
Todo:
- [x] update documentation
- [x] find a better name than contagious (synchronized)?
refs #6932, refs #5012
This PR is a proof of concept that tries to find a solution for some problems we have with scopes and services depending on scoped services (mostly the request service in Symfony).
Basically, whenever you want to inject the Request into a service, you have two possibilities:
* put your own service into the request scope (a new service will be created whenever a sub-request is run, and the service is not available outside the request scope);
* set the request service reference as non-strict (your service is always available but the request you have depends on when the service is created the first time).
This PR addresses this issue by allowing to use the second option but you service still always has the right Request service (see below for a longer explanation on how it works).
There is another issue that this PR fixes: edge cases and weird behaviors. There are several bug reports about some weird behaviors, and most of the time, this is related to the sub-requests. That's because the Request is injected into several Symfony objects without being updated correctly when leaving the request scope. Let me explain that: when a listener for instance needs the Request object, it can listen to the `kernel.request` event and store the request somewhere. So, whenever you enter a sub-request, the listener will get the new one. But when the sub-request ends, the listener has no way to know that it needs to reset the request to the master one. In practice, that's not really an issue, but let me show you an example of this issue in practice:
* You have a controller that is called with the English locale;
* The controller (probably via a template) renders a sub-request that uses the French locale;
* After the rendering, and from the controller, you try to generate a URL. Which locale the router will use? Yes, the French locale, which is wrong.
To fix these issues, this PR introduces a new notion in the DIC: synchronized services. When a service is marked as synchronized, all method calls involving this service will be called each time this service is set. When in a scope, methods are also called to restore the previous version of the service when the scope leaves.
If you have a look at the router or the locale listener, you will see that there is now a `setRequest` method that will called whenever the request service changes (because the `Container::set()` method is called or because the service is changed by a scope change).
Commits
-------
17269e1 [DependencyInjection] fixed management of scoped services with an invalid behavior set to null
bb83b3e [HttpKernel] added a safeguard for when a fragment is rendered outside the context of a master request
5d7b835 [FrameworkBundle] added some functional tests
ff9d688 fixed Request management for FragmentHandler
1b98ad3 fixed Request management for LocaleListener
a7b2b7e fixed Request management for RequestListener
0892135 [HttpKernel] ensured that the Request is null when outside of the Request scope
2ffcfb9 [FrameworkBundle] made the Request service synchronized
ec1e7ca [DependencyInjection] added a way to automatically update scoped services
This change allows any service to depend on the Request (via a method
call) and always have the right Request instance without the need for
the service to be in the request scope (you still need to set the
Request reference as non-strict).
This feature added complexity to the framework but wasn't used in the core anyway.
You can still use the Map class loader in your application though. But most of the time, using the APC
autoloader is just better.
The only missing part is ContainerAwareEventManager::addEventSubscriberService(),
because I'm not sure how to find out the class name of a service in the DIC.
Also, inline documentation of this code needs to be finished once it is accepted.
Doctrine's EventManager implementation has several advantages over the
EventDispatcher implementation of Symfony2. Therefore I suggest that we
use their implementation.
Advantages:
* Event Listeners are objects, not callbacks. These objects have handler
methods that have the same name as the event. This helps a lot when
reading the code and makes the code for adding an event listener shorter.
* You can create Event Subscribers, which are event listeners with an
additional getSubscribedEvents() method. The benefit here is that the
code that registers the subscriber doesn't need to know about its
implementation.
* All events are defined in static Events classes, so users of IDEs benefit
of code completion
* The communication between the dispatching class of an event and all
listeners is done through a subclass of EventArgs. This subclass can be
tailored to the type of event. A constructor, setters and getters can be
implemented that verify the validity of the data set into the object.
See examples below.
* Because each event type corresponds to an EventArgs implementation,
developers of event listeners can look up the available EventArgs methods
and benefit of code completion.
* EventArgs::stopPropagation() is more flexible and (IMO) clearer to use
than notifyUntil(). Also, it is a concept that is also used in other
event implementations
Before:
class EventListener
{
public function handle(EventInterface $event, $data) { ... }
}
$dispatcher->connect('core.request', array($listener, 'handle'));
$dispatcher->notify('core.request', new Event(...));
After (with listeners):
final class Events
{
const onCoreRequest = 'onCoreRequest';
}
class EventListener
{
public function onCoreRequest(RequestEventArgs $eventArgs) { ... }
}
$evm->addEventListener(Events::onCoreRequest, $listener);
$evm->dispatchEvent(Events::onCoreRequest, new RequestEventArgs(...));
After (with subscribers):
class EventSubscriber
{
public function onCoreRequest(RequestEventArgs $eventArgs) { ... }
public function getSubscribedEvents()
{
return Events::onCoreRequest;
}
}
$evm->addEventSubscriber($subscriber);
$evm->dispatchEvent(Events::onCoreRequest, new RequestEventArgs(...));
The Response is not available in the DIC anymore.
When you need to create a response, create an instance of
Symfony\Component\HttpFoundation\Response instead.
As a side effect, the Controller::createResponse() and Controller::redirect()
methods have been removed and can easily be replaced as follows:
return $this->createResponse('content', 200, array('foo' => 'bar'));
return new Response('content', 200, array('foo' => 'bar'));
return $this->redirect($url);
return Response::createRedirect($url);
A class in Symfony2 can be loaded by four different mechanisms:
* bootstrap.php: This file contains classes that are always required and
needed very early in the request handling;
* classes.php: This file contains classes that are always required and
managed by extensions via addClassesToCompile();
* MapFileClassLoader: This autoloader uses a map of class/file to load
classes (classes are managed by extensions via addClassesToAutoloadMap(),
and should contain often used classes);
* UniversalAutolaoder: This autoloader loads all other classes (it's the
slowest one).
Cache warmer will come in the next commits.
To warm up the cache on a production server, you can use
the cache:warmup command:
./app/console_prod cache:warmup
* The register() method on all listeners has been removed
* Instead, the information is now put directly in the DIC tag
For instance, a listener on core.request had this method:
public function register(EventDispatcher $dispatcher, $priority = 0)
{
$dispatcher->connect('core.response', array($this, 'filter'), $priority);
}
And this tag in the DIC configuration:
<tag name="kernel.listener" />
Now, it only has the following configuration:
<tag name="kernel.listener" event="core.response" method="filter" priority="0" />
The event and method attributes are now mandatory.
Previously, HttpKernel performed request-stashing. By moving this to the Kernel class, the request is now available immediately after the kernel becomes aware of it. If the kernel is allowed to boot lazily (during the first call to handle()), this also allows an actual master Request to be available during booting.
The old "request" service definition (with a bogus class name) can be replaced with a factory-aware definition that retrieves the request directly from the kernel.
Some explanations on how it works now:
* The Session is an optional dependency of the Request. If you create the
Request yourself (which is mandatory now in the front controller) and if
you don't inject a Session yourself (which is recommended if you want the
session to be configured via dependency injection), the Symfony2 Kernel
will associate the Session configured in the Container with the Request
automatically.
* When duplicating a request, the session is shared between the parent and
the child (that's because duplicated requests are sub-requests of the main
one most of the time.) Notice that when you use ::create(), the behavior is
the same as for the constructor; no session is attached to the Request.
* Symfony2 tries hard to not create a session cookie when it is not needed
but a Session object is always available (the cookie is only created when
"something" is stored in the session.)
* Symfony2 only starts a session when:
* A session already exists in the request ($_COOKIE[session_name()] is
defined -- this is done by RequestListener);
* There is something written in the session object (the cookie will be sent
to the Client).
* Notice that reading from the session does not start the session anymore (as
we don't need to start a new session to get the default values, and because
if a session exists, it has already been started by RequestListener.)
