Issue #2752325 by Wim Leers, marthinal, dawehner, ericpugh: Automatically...

Issue #2752325 by Wim Leers, marthinal, dawehner, ericpugh: Automatically provide HEAD support when a REST resource supports GET

core/modules/rest/src/RequestHandler.php

@@ -62,6 +62,21 @@ public static function create(ContainerInterface $container) {
   public function handle(RouteMatchInterface $route_match, Request $request) {
     $method = strtolower($request->getMethod());
 
+    // Symfony is built to transparently map HEAD requests to a GET request. In
+    // the case of the REST module's RequestHandler though, we essentially have
+    // our own light-weight routing system on top of the Drupal/symfony routing
+    // system. So, we have to do the same as what the UrlMatcher does: map HEAD
+    // requests to the logic for GET. This also guarantees response headers for
+    // HEAD requests are identical to those for GET requests, because we just
+    // return a GET response. Response::prepare() will transform it to a HEAD
+    // response at the very last moment.
+    // @see https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.4
+    // @see \Symfony\Component\Routing\Matcher\UrlMatcher::matchCollection()
+    // @see \Symfony\Component\HttpFoundation\Response::prepare()
+    if ($method === 'head') {
+      $method = 'get';
+    }
+
     $resource_config_id = $route_match->getRouteObject()->getDefault('_rest_resource_config');
     /** @var \Drupal\rest\RestResourceConfigInterface $resource_config */
     $resource_config = $this->resourceStorage->load($resource_config_id);

core/modules/rest/src/Tests/PageCacheTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\rest\Tests;
 
+use Drupal\Component\Serialization\Json;
 use Drupal\Core\Url;
 use Drupal\system\Tests\Cache\AssertPageCacheContextsAndTagsTrait;
 
@@ -19,7 +20,7 @@ class PageCacheTest extends RESTTestBase {
    *
    * @var array
    */
-  public static $modules = array('hal', 'rest', 'entity_test');
+  public static $modules = array('hal');
 
   /**
    * The 'serializer' service.
@@ -135,4 +136,31 @@ public function testConfigChangePageCache() {
     }
   }
 
+  /**
+   * Tests HEAD support when a REST resource supports GET.
+   */
+  public function testHeadSupport() {
+    user_role_grant_permissions('anonymous', ['view test entity', 'restful get entity:entity_test']);
+
+    // Create an entity programatically.
+    $this->entityCreate('entity_test')->save();
+
+    $url = Url::fromUri('internal:/entity_test/1?_format=' . $this->defaultFormat);
+
+    $this->enableService('entity:entity_test', 'GET');
+
+    $this->httpRequest($url, 'HEAD', NULL, $this->defaultMimeType);
+    $this->assertResponse(200, 'HTTP response code is correct.');
+    $this->assertHeader('X-Drupal-Cache', 'MISS');
+    $this->assertResponseBody('');
+
+    $response = $this->httpRequest($url, 'GET', NULL, $this->defaultMimeType);
+    $this->assertResponse(200, 'HTTP response code is correct.');
+    $this->assertHeader('X-Drupal-Cache', 'HIT');
+    $this->assertCacheTag('config:rest.resource.entity.entity_test');
+    $this->assertCacheTag('entity_test:1');
+    $data = Json::decode($response);
+    $this->assertEqual($data['type'][0]['value'], 'entity_test');
+  }
+
 }

core/modules/rest/src/Tests/ReadTest.php

@@ -55,9 +55,28 @@ public function testRead() {
       // Create an entity programmatically.
       $entity = $this->entityCreate($entity_type);
       $entity->save();
+
+      // Verify that it exists: use a HEAD request.
+      $this->httpRequest($this->getReadUrl($entity), 'HEAD');
+      $this->assertResponseBody('');
+      $head_headers = $this->drupalGetHeaders();
+
       // Read it over the REST API.
       $response = $this->httpRequest($this->getReadUrl($entity), 'GET');
+      $get_headers = $this->drupalGetHeaders();
       $this->assertResponse('200', 'HTTP response code is correct.');
+
+      // Verify that the GET and HEAD responses are the same, that the only
+      // difference is that there's no body.
+      unset($get_headers['date']);
+      unset($head_headers['date']);
+      unset($get_headers['content-length']);
+      unset($head_headers['content-length']);
+      unset($get_headers['x-drupal-dynamic-cache']);
+      unset($head_headers['x-drupal-dynamic-cache']);
+      $this->assertIdentical($get_headers, $head_headers);
+      $this->assertResponse('200', 'HTTP response code is correct.');
+
       $this->assertHeader('content-type', $this->defaultMimeType);
       $data = Json::decode($response);
       // Only assert one example property here, other properties should be