bug #19290 [HttpKernel] fixed internal subrequests having an if-modif…

…ied-since-header (MalteWunsch)

This PR was squashed before being merged into the 2.7 branch (closes #19290).

Discussion
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[HttpKernel] fixed internal subrequests having an if-modified-since-header

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

As the InlineFragmentRenderer has no access to a cached copy of a subrequest's target and hence couldn't handle a response with a HTTP status code of 304 (not modified), it makes no sense to send an if-not-modified-since header.

Commits
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e90038c [HttpKernel] fixed internal subrequests having an if-modified-since-header

src/Symfony/Component/HttpKernel/Fragment/InlineFragmentRenderer.php

@@ -129,6 +129,8 @@ protected function createSubRequest($uri, Request $request)
         }
 
         $server['REMOTE_ADDR'] = '127.0.0.1';
+        unset($server['HTTP_IF_MODIFIED_SINCE']);
+        unset($server['HTTP_IF_NONE_MATCH']);
 
         $subRequest = Request::create($uri, 'get', array(), $cookies, array(), $server);
         if ($request->headers->has('Surrogate-Capability')) {

src/Symfony/Component/HttpKernel/Tests/Fragment/InlineFragmentRendererTest.php

@@ -197,6 +197,19 @@ public function testESIHeaderIsKeptInSubrequestWithTrustedHeaderDisabled()
 
         Request::setTrustedHeaderName(Request::HEADER_CLIENT_IP, $trustedHeaderName);
     }
+
+    public function testHeadersPossiblyResultingIn304AreNotAssignedToSubrequest()
+    {
+        $expectedSubRequest = Request::create('/');
+        if (Request::getTrustedHeaderName(Request::HEADER_CLIENT_IP)) {
+            $expectedSubRequest->headers->set('x-forwarded-for', array('127.0.0.1'));
+            $expectedSubRequest->server->set('HTTP_X_FORWARDED_FOR', '127.0.0.1');
+        }
+
+        $strategy = new InlineFragmentRenderer($this->getKernelExpectingRequest($expectedSubRequest));
+        $request = Request::create('/', 'GET', array(), array(), array(), array('HTTP_IF_MODIFIED_SINCE' => 'Fri, 01 Jan 2016 00:00:00 GMT', 'HTTP_IF_NONE_MATCH' => '*'));
+        $strategy->render('/', $request);
+    }
 }
 
 class Bar