PageCacheTest.php

<?php

declare (strict_types=1);
namespace Drupal\Tests\page_cache\Functional;

use Drupal\Component\Datetime\DateTimePlus;
use Drupal\Core\Site\Settings;
use Drupal\Core\Url;
use Drupal\entity_test\Entity\EntityTest;
use Drupal\Core\Cache\Cache;
use Drupal\Tests\BrowserTestBase;
use Drupal\Tests\system\Functional\Cache\AssertPageCacheContextsAndTagsTrait;
use Drupal\user\RoleInterface;

/**
 * Enables the page cache and tests it with various HTTP requests.
 *
 * @group page_cache
 * @group #slow
 */
class PageCacheTest extends BrowserTestBase {
    use AssertPageCacheContextsAndTagsTrait;
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'test_page_test',
        'system_test',
        'entity_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * {@inheritdoc}
     */
    protected function setUp() : void {
        parent::setUp();
        $this->config('system.site')
            ->set('name', 'Drupal')
            ->set('page.front', '/test-page')
            ->save();
    }
    
    /**
     * Tests that cache tags are properly persisted.
     *
     * Since tag based invalidation works, we know that our tag properly
     * persisted.
     */
    public function testPageCacheTags() : void {
        $this->enablePageCaching();
        $path = 'system-test/cache_tags_page';
        $tags = [
            'system_test_cache_tags_page',
        ];
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        // Verify a cache hit, but also the presence of the correct cache tags.
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $cid_parts = [
            Url::fromRoute('system_test.cache_tags_page', [], [
                'absolute' => TRUE,
            ])->toString(),
            '',
        ];
        $cid = implode(':', $cid_parts);
        $cache_entry = \Drupal::cache('page')->get($cid);
        sort($cache_entry->tags);
        $expected_tags = [
            'config:user.role.anonymous',
            'http_response',
            'pre_render',
            'rendered',
            'system_test_cache_tags_page',
        ];
        $this->assertSame($expected_tags, $cache_entry->tags);
        Cache::invalidateTags($tags);
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    }
    
    /**
     * Tests that the page cache doesn't depend on cacheability headers.
     */
    public function testPageCacheTagsIndependentFromCacheabilityHeaders() : void {
        // Disable the cacheability headers.
        $this->setContainerParameter('http.response.debug_cacheability_headers', FALSE);
        $this->rebuildContainer();
        $this->resetAll();
        $path = 'system-test/cache_tags_page';
        $tags = [
            'system_test_cache_tags_page',
        ];
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        // Verify a cache hit, but also the presence of the correct cache tags.
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $cid_parts = [
            Url::fromRoute('system_test.cache_tags_page', [], [
                'absolute' => TRUE,
            ])->toString(),
            '',
        ];
        $cid = implode(':', $cid_parts);
        $cache_entry = \Drupal::cache('page')->get($cid);
        sort($cache_entry->tags);
        $expected_tags = [
            'config:user.role.anonymous',
            'http_response',
            'pre_render',
            'rendered',
            'system_test_cache_tags_page',
        ];
        $this->assertSame($expected_tags, $cache_entry->tags);
        Cache::invalidateTags($tags);
        $this->drupalGet($path);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    }
    
    /**
     * Tests support for different cache items with different request formats.
     *
     * The request formats are specified via a query parameter.
     */
    public function testQueryParameterFormatRequests() : void {
        $this->enablePageCaching();
        $accept_header_cache_url = Url::fromRoute('system_test.page_cache_accept_header');
        $accept_header_cache_url_with_json = Url::fromRoute('system_test.page_cache_accept_header', [
            '_format' => 'json',
        ]);
        $accept_header_cache_url_with_ajax = Url::fromRoute('system_test.page_cache_accept_header', [
            '_format' => 'json',
        ], [
            'query' => [
                '_wrapper_format' => 'drupal_ajax',
            ],
        ]);
        $this->drupalGet($accept_header_cache_url);
        // Verify that HTML page was not yet cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->drupalGet($accept_header_cache_url);
        // Verify that HTML page was cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        // Verify that the correct HTML response was returned.
        $this->assertSession()
            ->responseContains('<p>oh hai this is html.</p>');
        $this->drupalGet($accept_header_cache_url_with_json);
        // Verify that JSON response was not yet cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->drupalGet($accept_header_cache_url_with_json);
        // Verify that JSON response was cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        // Verify that the correct JSON response was returned.
        $this->assertSession()
            ->responseContains('{"content":"oh hai this is json"}');
        $this->drupalGet($accept_header_cache_url_with_ajax);
        // Verify that AJAX response was not yet cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->drupalGet($accept_header_cache_url_with_ajax);
        // Verify that AJAX response was cached.
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        // Verify that the correct AJAX response was returned.
        $this->assertSession()
            ->responseContains('{"content":"oh hai this is ajax"}');
    }
    
    /**
     * Tests support of requests with If-Modified-Since and If-None-Match headers.
     */
    public function testConditionalRequests() : void {
        $this->enablePageCaching();
        // Fill the cache.
        $this->drupalGet('');
        // Verify the page is not printed twice when the cache is cold.
        $this->assertSession()
            ->responseNotMatches('#<html.*<html#');
        $this->drupalGet('');
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $etag = $this->getSession()
            ->getResponseHeader('ETag');
        $last_modified = $this->getSession()
            ->getResponseHeader('Last-Modified');
        // Ensure a conditional request returns 304 Not Modified.
        $this->drupalGet('', [], [
            'If-Modified-Since' => $last_modified,
            'If-None-Match' => $etag,
        ]);
        $this->assertSession()
            ->statusCodeEquals(304);
        // Ensure a conditional request with obsolete If-Modified-Since date
        // returns 304 Not Modified.
        $this->drupalGet('', [], [
            'If-Modified-Since' => gmdate(DATE_RFC822, strtotime($last_modified)),
            'If-None-Match' => $etag,
        ]);
        $this->assertSession()
            ->statusCodeEquals(304);
        // Ensure a conditional request with obsolete If-Modified-Since date
        // returns 304 Not Modified.
        $this->drupalGet('', [], [
            'If-Modified-Since' => gmdate(DATE_RFC850, strtotime($last_modified)),
            'If-None-Match' => $etag,
        ]);
        $this->assertSession()
            ->statusCodeEquals(304);
        // Ensure a conditional request without If-None-Match returns 200 OK.
        $this->drupalGet('', [], [
            'If-Modified-Since' => $last_modified,
            'If-None-Match' => NULL,
        ]);
        // Verify the page is not printed twice when the cache is warm.
        $this->assertSession()
            ->responseNotMatches('#<html.*<html#');
        $this->assertSession()
            ->statusCodeEquals(200);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        // Ensure a conditional request with If-Modified-Since newer than
        // Last-Modified returns 200 OK.
        $this->drupalGet('', [], [
            'If-Modified-Since' => gmdate(DateTimePlus::RFC7231, strtotime($last_modified) + 1),
            'If-None-Match' => $etag,
        ]);
        $this->assertSession()
            ->statusCodeEquals(200);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        // Ensure a conditional request by an authenticated user returns 200 OK.
        $user = $this->drupalCreateUser();
        $this->drupalLogin($user);
        $this->drupalGet('', [], [
            'If-Modified-Since' => $last_modified,
            'If-None-Match' => $etag,
        ]);
        $this->assertSession()
            ->statusCodeEquals(200);
        // Verify that absence of Page was not cached.
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
    }
    
    /**
     * Tests cache headers.
     */
    public function testPageCache() : void {
        $this->enablePageCaching();
        // Fill the cache.
        $this->drupalGet('system-test/set-header', [
            'query' => [
                'name' => 'Foo',
                'value' => 'bar',
            ],
        ]);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->assertSession()
            ->responseHeaderContains('Vary', 'cookie');
        // Symfony's Response logic determines a specific order for the subvalues
        // of the Cache-Control header, even if they are explicitly passed in to
        // the response header bag in a different order.
        $this->assertCacheMaxAge(300);
        $this->assertSession()
            ->responseHeaderEquals('Expires', 'Sun, 19 Nov 1978 05:00:00 GMT');
        $this->assertSession()
            ->responseHeaderEquals('Foo', 'bar');
        // Check cache.
        $this->drupalGet('system-test/set-header', [
            'query' => [
                'name' => 'Foo',
                'value' => 'bar',
            ],
        ]);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $this->assertSession()
            ->responseHeaderContains('Vary', 'cookie');
        $this->assertCacheMaxAge(300);
        $this->assertSession()
            ->responseHeaderEquals('Expires', 'Sun, 19 Nov 1978 05:00:00 GMT');
        $this->assertSession()
            ->responseHeaderEquals('Foo', 'bar');
        // Check replacing default headers.
        $this->drupalGet('system-test/set-header', [
            'query' => [
                'name' => 'Expires',
                'value' => 'Fri, 19 Nov 2008 05:00:00 GMT',
            ],
        ]);
        $this->assertSession()
            ->responseHeaderEquals('Expires', 'Fri, 19 Nov 2008 05:00:00 GMT');
        $this->drupalGet('system-test/set-header', [
            'query' => [
                'name' => 'Vary',
                'value' => 'User-Agent',
            ],
        ]);
        $this->assertSession()
            ->responseHeaderContains('Vary', 'user-agent');
        // Check that authenticated users bypass the cache.
        $user = $this->drupalCreateUser();
        $this->drupalLogin($user);
        $this->drupalGet('system-test/set-header', [
            'query' => [
                'name' => 'Foo',
                'value' => 'bar',
            ],
        ]);
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
        $this->assertSession()
            ->responseHeaderNotContains('Vary', 'cookie');
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'must-revalidate, no-cache, private');
        $this->assertSession()
            ->responseHeaderEquals('Expires', 'Sun, 19 Nov 1978 05:00:00 GMT');
        $this->assertSession()
            ->responseHeaderEquals('Foo', 'bar');
        // Until bubbling of max-age up to the response is supported, verify that
        // a custom #cache max-age set on an element does not affect page max-age.
        $this->drupalLogout();
        $this->drupalGet('system-test/cache_max_age_page');
        $this->assertCacheMaxAge(300);
    }
    
    /**
     * Tests the automatic presence of the anonymous role's cache tag.
     *
     * The 'user.permissions' cache context ensures that if the permissions for a
     * role are modified, users are not served stale render cache content. But,
     * when entire responses are cached in reverse proxies, the value for the
     * cache context is never calculated, causing the stale response to not be
     * invalidated. Therefore, when varying by permissions and the current user is
     * the anonymous user, the cache tag for the 'anonymous' role must be added.
     *
     * This test verifies that, and it verifies that it does not happen for other
     * roles.
     */
    public function testPageCacheAnonymousRolePermissions() : void {
        $this->enablePageCaching();
        $content_url = Url::fromRoute('system_test.permission_dependent_content');
        $route_access_url = Url::fromRoute('system_test.permission_dependent_route_access');
        // 1. anonymous user, without permission.
        $this->drupalGet($content_url);
        $this->assertSession()
            ->pageTextContains('Permission to pet llamas: no!');
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderContains('X-Drupal-Cache-Tags', 'config:user.role.anonymous');
        $this->drupalGet($route_access_url);
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderContains('X-Drupal-Cache-Tags', 'config:user.role.anonymous');
        // 2. anonymous user, with permission.
        user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
            'pet llamas',
        ]);
        $this->drupalGet($content_url);
        $this->assertSession()
            ->pageTextContains('Permission to pet llamas: yes!');
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderContains('X-Drupal-Cache-Tags', 'config:user.role.anonymous');
        $this->drupalGet($route_access_url);
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderContains('X-Drupal-Cache-Tags', 'config:user.role.anonymous');
        // 3. authenticated user, without permission.
        $auth_user = $this->drupalCreateUser();
        $this->drupalLogin($auth_user);
        $this->drupalGet($content_url);
        $this->assertSession()
            ->pageTextContains('Permission to pet llamas: no!');
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:user.role.authenticated');
        $this->drupalGet($route_access_url);
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:user.role.authenticated');
        // 4. authenticated user, with permission.
        user_role_grant_permissions(RoleInterface::AUTHENTICATED_ID, [
            'pet llamas',
        ]);
        $this->drupalGet($content_url);
        $this->assertSession()
            ->pageTextContains('Permission to pet llamas: yes!');
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:user.role.authenticated');
        $this->drupalGet($route_access_url);
        $this->assertCacheContext('user.permissions');
        $this->assertSession()
            ->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:user.role.authenticated');
    }
    
    /**
     * Tests the 4xx-response cache tag is added and invalidated.
     */
    public function testPageCacheAnonymous403404() : void {
        $admin_url = Url::fromRoute('system.admin');
        $invalid_url = 'foo/does_not_exist';
        $tests = [
            403 => $admin_url,
            404 => $invalid_url,
        ];
        $cache_ttl_4xx = Settings::get('cache_ttl_4xx', 3600);
        foreach ($tests as $code => $content_url) {
            // Anonymous user, without permissions.
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
            $this->assertSession()
                ->responseHeaderContains('X-Drupal-Cache-Tags', '4xx-response');
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
            $entity_values = [
                'name' => $this->randomMachineName(),
                'user_id' => 1,
                'field_test_text' => [
                    0 => [
                        'value' => $this->randomString(),
                        'format' => 'plain_text',
                    ],
                ],
            ];
            $entity = EntityTest::create($entity_values);
            $entity->save();
            // Saving an entity clears 4xx cache tag.
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
            // Rebuilding the router should invalidate the 4xx cache tag.
            $this->container
                ->get('router.builder')
                ->rebuild();
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
            // Ensure the 'expire' field on the cache entry uses cache_ttl_4xx.
            $cache_item = \Drupal::service('cache.page')->get($this->getUrl() . ':');
            $difference = $cache_item->expire - (int) $cache_item->created;
            // Given that a second might have passed we cannot be sure that
            // $difference will exactly equal the default cache_ttl_4xx setting.
            // Account for any timing difference or rounding errors by ensuring the
            // value is within 10 seconds.
            $this->assertTrue($difference > $cache_ttl_4xx - 10 && $difference < $cache_ttl_4xx + 10, "The cache entry expiry time uses the cache_ttl_4xx setting. Expire: {$cache_item->expire} Created: {$cache_item->created}");
        }
        // Disable 403 and 404 caching.
        $settings['settings']['cache_ttl_4xx'] = (object) [
            'value' => 0,
            'required' => TRUE,
        ];
        $this->writeSettings($settings);
        \Drupal::service('cache.page')->deleteAll();
        foreach ($tests as $code => $content_url) {
            // Getting the 404 page twice should still result in a cache miss.
            $this->drupalGet($content_url);
            $this->drupalGet($content_url);
            $this->assertSession()
                ->statusCodeEquals($code);
            $this->assertSession()
                ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        }
    }
    
    /**
     * Tests the omit_vary_cookie setting.
     */
    public function testPageCacheWithoutVaryCookie() : void {
        $this->enablePageCaching();
        $settings['settings']['omit_vary_cookie'] = (object) [
            'value' => TRUE,
            'required' => TRUE,
        ];
        $this->writeSettings($settings);
        // Fill the cache.
        $this->drupalGet('');
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->assertSession()
            ->responseHeaderNotContains('Vary', 'cookie');
        $this->assertCacheMaxAge(300);
        // Check cache.
        $this->drupalGet('');
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $this->assertSession()
            ->responseHeaderNotContains('Vary', 'cookie');
        $this->assertCacheMaxAge(300);
    }
    
    /**
     * Tests the setting of forms to be immutable.
     */
    public function testFormImmutability() : void {
        // Install the module that provides the test form.
        $this->container
            ->get('module_installer')
            ->install([
            'page_cache_form_test',
        ]);
        // Uninstall the page_cache module to verify that form is immutable
        // regardless of the internal page cache module.
        $this->container
            ->get('module_installer')
            ->uninstall([
            'page_cache',
        ]);
        $this->drupalGet('page_cache_form_test_immutability');
        $this->assertSession()
            ->pageTextContains("Immutable: TRUE");
        // The immutable flag is set unconditionally by system_form_alter(), set
        // a flag to tell page_cache_form_test_module_implements_alter() to disable
        // that implementation.
        \Drupal::state()->set('page_cache_bypass_form_immutability', TRUE);
        \Drupal::moduleHandler()->resetImplementations();
        Cache::invalidateTags([
            'rendered',
        ]);
        $this->drupalGet('page_cache_form_test_immutability');
        $this->assertSession()
            ->pageTextContains("Immutable: FALSE");
    }
    
    /**
     * Tests cacheability of a CacheableResponse.
     *
     * Tests the difference between having a controller return a plain Symfony
     * Response object versus returning a Response object that implements the
     * CacheableResponseInterface.
     */
    public function testCacheableResponseResponses() : void {
        $this->enablePageCaching();
        // GET a URL, which would be marked as a cache miss if it were cacheable.
        $this->drupalGet('/system-test/respond-response');
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'must-revalidate, no-cache, private');
        // GET it again, verify it's still not cached.
        $this->drupalGet('/system-test/respond-response');
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'must-revalidate, no-cache, private');
        // GET a URL, which would be marked as a cache miss if it were cacheable.
        $this->drupalGet('/system-test/respond-public-response');
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'max-age=60, public');
        // GET it again, verify it's still not cached.
        $this->drupalGet('/system-test/respond-public-response');
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'max-age=60, public');
        // GET a URL, which should be marked as a cache miss.
        $this->drupalGet('/system-test/respond-cacheable-response');
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->assertCacheMaxAge(300);
        // GET it again, it should now be a cache hit.
        $this->drupalGet('/system-test/respond-cacheable-response');
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $this->assertCacheMaxAge(300);
        // Uninstall page cache. This should flush all caches so the next call to a
        // previously cached page should be a miss now.
        $this->container
            ->get('module_installer')
            ->uninstall([
            'page_cache',
        ]);
        // GET a URL that was cached by Page Cache before, it should not be now.
        $this->drupalGet('/respond-cacheable-response');
        $this->assertSession()
            ->responseHeaderDoesNotExist('X-Drupal-Cache');
    }
    
    /**
     * Tests that HEAD requests are treated the same as GET requests.
     */
    public function testHead() : void {
        
        /** @var \GuzzleHttp\ClientInterface $client */
        $client = $this->getSession()
            ->getDriver()
            ->getClient()
            ->getClient();
        // GET, then HEAD.
        $url_a = $this->buildUrl('system-test/set-header', [
            'query' => [
                'name' => 'Foo',
                'value' => 'bar',
            ],
        ]);
        $response_body = $this->drupalGet($url_a);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
        $this->assertSession()
            ->responseHeaderEquals('Foo', 'bar');
        $this->assertEquals('The following header was set: <em class="placeholder">Foo</em>: <em class="placeholder">bar</em>', $response_body);
        $response = $client->request('HEAD', $url_a);
        $this->assertEquals('HIT', $response->getHeaderLine('X-Drupal-Cache'), 'Page was cached.');
        $this->assertEquals('bar', $response->getHeaderLine('Foo'), 'Custom header was sent.');
        $this->assertEquals('', $response->getBody()
            ->getContents());
        // HEAD, then GET.
        $url_b = $this->buildUrl('system-test/set-header', [
            'query' => [
                'name' => 'Foo',
                'value' => 'baz',
            ],
        ]);
        $response = $client->request('HEAD', $url_b);
        $this->assertEquals('MISS', $response->getHeaderLine('X-Drupal-Cache'), 'Page was not cached.');
        $this->assertEquals('baz', $response->getHeaderLine('Foo'), 'Custom header was sent.');
        $this->assertEquals('', $response->getBody()
            ->getContents());
        $response_body = $this->drupalGet($url_b);
        $this->assertSession()
            ->responseHeaderEquals('X-Drupal-Cache', 'HIT');
        $this->assertSession()
            ->responseHeaderEquals('Foo', 'baz');
        $this->assertEquals('The following header was set: <em class="placeholder">Foo</em>: <em class="placeholder">baz</em>', $response_body);
    }
    
    /**
     * Tests a cacheable response with custom cache control.
     */
    public function testCacheableWithCustomCacheControl() : void {
        $this->enablePageCaching();
        $this->drupalGet('/system-test/custom-cache-control');
        $this->assertSession()
            ->statusCodeEquals(200);
        $this->assertSession()
            ->responseHeaderEquals('Cache-Control', 'bar, private');
    }
    
    /**
     * Tests that the Cache-Control header is added by FinishResponseSubscriber.
     */
    public function testCacheabilityOfRedirectResponses() : void {
        $this->enablePageCaching();
        $this->getSession()
            ->getDriver()
            ->getClient()
            ->followRedirects(FALSE);
        $this->maximumMetaRefreshCount = 0;
        foreach ([
            301,
            302,
            303,
            307,
            308,
        ] as $status_code) {
            foreach ([
                'local',
                'cacheable',
                'trusted',
            ] as $type) {
                $this->drupalGet("/system-test/redirect/{$type}/{$status_code}");
                $this->assertSession()
                    ->statusCodeEquals($status_code);
                $this->assertCacheMaxAge(300);
            }
        }
    }
    
    /**
     * Tests that URLs are cached in a not normalized form.
     */
    public function testNoUrlNormalization() : void {
        // Use absolute URLs to avoid any processing.
        $url = Url::fromRoute('<front>')->setAbsolute()
            ->toString();
        // In each test, the first array value is raw URL, the second one is the
        // possible normalized URL.
        $tests = [
            [
                $url . '?z=z&a=a',
                $url . '?a=a&z=z',
            ],
            [
                $url . '?a=b+c',
                $url . '?a=b%20c',
            ],
        ];
        foreach ($tests as [
            $url_raw,
            $url_normalized,
        ]) {
            // Initialize cache on raw URL.
            $headers = $this->getHeaders($url_raw);
            $this->assertEquals('MISS', $headers['X-Drupal-Cache']);
            // Ensure cache was set.
            $headers = $this->getHeaders($url_raw);
            $this->assertEquals('HIT', $headers['X-Drupal-Cache'], "Cache was set for {$url_raw} URL.");
            // Check if the normalized URL is not cached.
            $headers = $this->getHeaders($url_normalized);
            $this->assertEquals('MISS', $headers['X-Drupal-Cache'], "Cache is missing for {$url_normalized} URL.");
        }
    }
    
    /**
     * Retrieves only the headers for an absolute path.
     *
     * Executes a cURL request without any modifications to the given URL.
     * Note that Guzzle always normalizes URLs which prevents testing all
     * possible edge cases.
     *
     * @param string $url
     *   URL to request.
     *
     * @return array
     *   Array of headers.
     */
    protected function getHeaders($url) {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_HEADER, TRUE);
        curl_setopt($ch, CURLOPT_NOBODY, TRUE);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_USERAGENT, drupal_generate_test_ua($this->databasePrefix));
        $output = curl_exec($ch);
        curl_close($ch);
        $headers = [];
        foreach (explode("\n", $output) as $header) {
            if (strpos($header, ':')) {
                [
                    $key,
                    $value,
                ] = explode(':', $header, 2);
                $headers[trim($key)] = trim($value);
            }
        }
        return $headers;
    }

}