The PHP native cache limiter feature has been disabled as this is now managed
by the HeaderBag class directly instead (see below.)
The HeaderBag class uses the following rules to define a sensible and
convervative default value for the Response 'Cache-Control' header:
* If no cache header is defined ('Cache-Control', 'ETag', 'Last-Modified',
and 'Expires'), 'Cache-Control' is set to 'no-cache';
* If 'Cache-Control' is empty, its value is set to "private, max-age=0,
must-revalidate";
* But if at least one 'Cache-Control' directive is set, and no 'public' or
'private' directives have been explicitely added, Symfony2 adds the
'private' directive automatically (except when 's-maxage' is set.)
So, remember to explicitly add the 'public' directive to 'Cache-Control' when
you want shared caches to store your application resources:
// The Response is private by default
$response->setEtag($etag);
$response->setLastModified($date);
$response->setMaxAge(10);
// Change the Response to be public
$response->setPublic();
// Set cache settings in one call
$response->setCache(array(
'etag' => $etag,
'last_modified' => $date,
'max_age' => 10,
'public' => true,
));
Some explanations on how it works now:
* The Session is an optional dependency of the Request. If you create the
Request yourself (which is mandatory now in the front controller) and if
you don't inject a Session yourself (which is recommended if you want the
session to be configured via dependency injection), the Symfony2 Kernel
will associate the Session configured in the Container with the Request
automatically.
* When duplicating a request, the session is shared between the parent and
the child (that's because duplicated requests are sub-requests of the main
one most of the time.) Notice that when you use ::create(), the behavior is
the same as for the constructor; no session is attached to the Request.
* Symfony2 tries hard to not create a session cookie when it is not needed
but a Session object is always available (the cookie is only created when
"something" is stored in the session.)
* Symfony2 only starts a session when:
* A session already exists in the request ($_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.)
