bug #25583 [HttpKernel] Call Response->setPrivate() instead of sending raw header() when session is started (Toflar)

This PR was merged into the 3.4 branch.

Discussion
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[HttpKernel] Call Response->setPrivate() instead of sending raw header() when session is started

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony/issues/24988
| License       | MIT
| Doc PR        | -

As described in #24988 I think the current handling of the `Cache-Control` header set by the `NativeSessionStorage` causes inconsistent behaviour.

In #24988 @nicolas-grekas states that if you start a session a response should be considered to be private. I do agree with this but up until now, nobody takes care of this on `kernel.response`.

I think we must always suppress the `NativeSessionStorage` from generating any headers by default. Otherwise the `Cache-Control` header never makes it to the `Response` instance and is thus missed by `kernel.response` listeners and for example the Symfony HttpCache. So depending on whether you use Symfony's HttpCache  or Varnish as a reverse proxy, caching would be handled differently.  Varnish would consider the response to be private if you set the php.ini setting `session.cache_limiter` to `nocache` (which is default) because it will receive the header. HttpCache would not because the `Cache-Control` header is not present on the `Response`.  That's inconsistent and may cause confusion or problems when switching proxies.

Commits
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dbc1c1c4b6 [HttpKernel] Call Response->setPrivate() instead of sending raw header() when session is started

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -825,7 +825,7 @@ class FrameworkExtension extends Extension
 
         // session storage
         $container->setAlias('session.storage', $config['storage_id'])->setPrivate(true);
-        $options = array();
+        $options = array('cache_limiter' => '0');
         foreach (array('name', 'cookie_lifetime', 'cookie_path', 'cookie_domain', 'cookie_secure', 'cookie_httponly', 'use_cookies', 'gc_maxlifetime', 'gc_probability', 'gc_divisor', 'use_strict_mode') as $key) {
             if (isset($config[$key])) {
                 $options[$key] = $config[$key];

src/Symfony/Component/HttpKernel/EventListener/SaveSessionListener.php

@@ -53,6 +53,10 @@ class SaveSessionListener implements EventSubscriberInterface
         $session = $event->getRequest()->getSession();
         if ($session && $session->isStarted()) {
             $session->save();
+            $event->getResponse()
+                ->setPrivate()
+                ->setMaxAge(0)
+                ->headers->addCacheControlDirective('must-revalidate');
         }
     }
 

src/Symfony/Component/HttpKernel/Tests/EventListener/SaveSessionListenerTest.php

@@ -0,0 +1,53 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpKernel\Tests\EventListener;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpFoundation\Session\SessionInterface;
+use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
+use Symfony\Component\HttpKernel\EventListener\SaveSessionListener;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+
+class SaveSessionListenerTest extends TestCase
+{
+    public function testOnlyTriggeredOnMasterRequest()
+    {
+        $listener = new SaveSessionListener();
+        $event = $this->getMockBuilder(FilterResponseEvent::class)->disableOriginalConstructor()->getMock();
+        $event->expects($this->once())->method('isMasterRequest')->willReturn(false);
+        $event->expects($this->never())->method('getRequest');
+
+        // sub request
+        $listener->onKernelResponse($event);
+    }
+
+    public function testSessionSavedAndResponsePrivate()
+    {
+        $listener = new SaveSessionListener();
+        $kernel = $this->getMockBuilder(HttpKernelInterface::class)->disableOriginalConstructor()->getMock();
+
+        $session = $this->getMockBuilder(SessionInterface::class)->disableOriginalConstructor()->getMock();
+        $session->expects($this->once())->method('isStarted')->willReturn(true);
+        $session->expects($this->once())->method('save');
+
+        $request = new Request();
+        $request->setSession($session);
+        $response = new Response();
+        $listener->onKernelResponse(new FilterResponseEvent($kernel, $request, HttpKernelInterface::MASTER_REQUEST, $response));
+
+        $this->assertTrue($response->headers->hasCacheControlDirective('private'));
+        $this->assertTrue($response->headers->hasCacheControlDirective('must-revalidate'));
+        $this->assertSame('0', $response->headers->getCacheControlDirective('max-age'));
+    }
+}