Adding 'related' link headers for entity references (#71)

* Adding 'related' link headers for entity references

(cherry picked from commit 10ac4e444b68c4fa8db13a04289acd68276b786b)

* Using event listener now so REST requests get the headers too

* Updating @covers annotation on test

* Coding standards

* Adding authZ test

* Caching properly now

islandora.module

@@ -181,47 +181,3 @@ function islandora_entity_delete(EntityInterface $entity) {
     }
   }
 }
-
-/**
- * Implements hook_node_view_alter().
- */
-function islandora_node_view_alter(&$build, EntityInterface $entity) {
-  // Return if memberof field does not exist.
-  if ($entity->hasField('field_memberof') == FALSE) {
-    return;
-  }
-
-  // Return if memberof field has no values.
-  $collection_members = $entity->get('field_memberof')->getValue();
-  if (count($collection_members) == 0) {
-    return;
-  }
-
-  // Loop through each member and add to the collection_links.
-  $collection_links = [];
-  foreach ($collection_members as $member_info) {
-    $collection_id = $member_info['target_id'];
-    $collection_entity = $entity->load($collection_id);
-
-    // If collection entity does not exist, skip.
-    if ($collection_entity == NULL) {
-      continue;
-    }
-
-    // If entity bundle type is not Collection, skip.
-    $collection_entity_bundle = $collection_entity->bundle();
-    if ($collection_entity_bundle != "islandora_collection") {
-      continue;
-    }
-
-    $collection_entity_url = $collection_entity->url('canonical', ['absolute' => TRUE]);
-    array_push($collection_links, "<" . $collection_entity_url . ">; rel='collection'");
-  }
-
-  if (count($collection_links) > 0) {
-    $collection_links_str = implode(", ", $collection_links);
-    $build['#attached']['http_header'] = [
-      ['Link', $collection_links_str],
-    ];
-  }
-}

islandora.services.yml

@@ -18,6 +18,11 @@ services:
     arguments: ['@entity_type.manager', '@current_user']
     tags:
       - { name: event_subscriber }
+  islandora.node_link_header_subscriber:
+    class: Drupal\islandora\EventSubscriber\NodeLinkHeaderSubscriber
+    arguments: ['@entity_field.manager', '@current_route_match']
+    tags:
+      - { name: event_subscriber }
   islandora.versioncounter:
     class: Drupal\islandora\VersionCounter\VersionCounter
     arguments: ['@database']

src/EventSubscriber/NodeLinkHeaderSubscriber.php

@@ -0,0 +1,136 @@
+<?php
+
+namespace Drupal\islandora\EventSubscriber;
+
+use Drupal\Core\Entity\EntityFieldManager;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
+use Symfony\Component\HttpKernel\KernelEvents;
+
+/**
+ * Class NodeLinkHeaderSubscriber.
+ *
+ * @package Drupal\islandora\EventSubscriber
+ */
+class NodeLinkHeaderSubscriber implements EventSubscriberInterface {
+
+  /**
+   * The entity field manager.
+   *
+   * @var \Drupal\Core\Entity\EntityFieldManager
+   */
+  protected $entityFieldManager;
+
+  /**
+   * The route match object.
+   *
+   * @var \Drupal\Core\Routing\RouteMatchInterface
+   */
+  protected $routeMatch;
+
+  /**
+   * Constructor.
+   *
+   * @param \Drupal\Core\Entity\EntityFieldManager $entity_field_manager
+   *   The entity field manager.
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The route match object.
+   */
+  public function __construct(
+    EntityFieldManager $entity_field_manager,
+    RouteMatchInterface $route_match
+  ) {
+    $this->entityFieldManager = $entity_field_manager;
+    $this->routeMatch = $route_match;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    // Run this early so the headers get cached.
+    $events[KernelEvents::RESPONSE][] = ['onResponse', 129];
+
+    return $events;
+  }
+
+  /**
+   * Adds node-specific link headers to appropriate responses.
+   *
+   * @param \Symfony\Component\HttpKernel\Event\FilterResponseEvent $event
+   *   Event containing the response.
+   */
+  public function onResponse(FilterResponseEvent $event) {
+    $response = $event->getResponse();
+
+    // Exit early if the response is already cached.
+    if ($response->headers->get('X-Drupal-Dynamic-Cache') == 'HIT') {
+      return;
+    }
+
+    if (!$response->isOk()) {
+      return;
+    }
+
+    // Hack the node out of the route.
+    $route_object = $this->routeMatch->getRouteObject();
+    if (!$route_object) {
+      return;
+    }
+
+    $methods = $route_object->getMethods();
+    $is_get = in_array('GET', $methods);
+    $is_head = in_array('HEAD', $methods);
+    if (!($is_get || $is_head)) {
+      return;
+    }
+
+    $route_contexts = $route_object->getOption('parameters');
+    if (!$route_contexts) {
+      return;
+    }
+    if (!isset($route_contexts['node'])) {
+      return;
+    }
+
+    $node = $this->routeMatch->getParameter('node');
+
+    if (!$node) {
+      return;
+    }
+
+    // Use the node to add link headers for each entity reference.
+    $bundle = $node->bundle();
+
+    // Get all fields for the entity.
+    $fields = $this->entityFieldManager->getFieldDefinitions('node', $bundle);
+
+    // Strip out everything but entity references that are not base fields.
+    $entity_reference_fields = array_filter($fields, function ($field) {
+      return $field->getFieldStorageDefinition()->isBaseField() == FALSE && $field->getType() == "entity_reference";
+    });
+
+    // Collect links for referenced entities.
+    $links = [];
+    foreach ($entity_reference_fields as $field_name => $field_definition) {
+      foreach ($node->get($field_name)->referencedEntities() as $referencedEntity) {
+        // Headers are subject to an access check.
+        if ($referencedEntity->access('view')) {
+          $entity_url = $referencedEntity->url('canonical', ['absolute' => TRUE]);
+          $field_label = $field_definition->label();
+          $links[] = "<$entity_url>; rel=\"related\"; title=\"$field_label\"";
+        }
+      }
+    }
+
+    // Exit early if there aren't any.
+    if (empty($links)) {
+      return;
+    }
+
+    // Add the link headers to the response.
+    $response->headers->set('Link', $links, FALSE);
+  }
+
+}

tests/src/Functional/IslandoraFunctionalTestBase.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\islandora\Functional;
 
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\TestFileCreationTrait;
 
@@ -120,4 +121,64 @@ class IslandoraFunctionalTestBase extends BrowserTestBase {
     $this->assertResponse(200);
   }
 
+  /**
+   * Utility function to check if a link header is included in the response.
+   *
+   * @param string $rel
+   *   The relation to search for.
+   *
+   * @return bool
+   *   TRUE if link header with relation is included in the response.
+   */
+  protected function doesNotHaveLinkHeader($rel) {
+    $headers = $this->getSession()->getResponseHeaders();
+
+    foreach ($headers['Link'] as $link_header) {
+      if (strpos($link_header, "rel=\"$rel\"") !== FALSE) {
+        return FALSE;
+      }
+    }
+
+    return TRUE;
+  }
+
+  /**
+   * Checks if the collection link header contains the correct uri.
+   *
+   * @param string $rel
+   *   The expected relation type of the link header.
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity whose uri is expected in the link header.
+   * @param string $title
+   *   The expected title of the link header.
+   *
+   * @return int
+   *   The number of times the correct header appears.
+   */
+  protected function validateLinkHeader($rel, EntityInterface $entity, $title = '') {
+    $entity_url = $entity->url('canonical', ['absolute' => TRUE]);
+
+    $regex = '/<(.*)>; rel="' . preg_quote($rel) . '"';
+    if (!empty($title)) {
+      $regex .= '; title="' . preg_quote($title) . '"';
+    }
+    $regex .= '/';
+
+    $count = 0;
+
+    $headers = $this->getSession()->getResponseHeaders();
+
+    foreach ($headers['Link'] as $link_headers) {
+      $split = explode(',', $link_headers);
+      foreach ($split as $link_header) {
+        $matches = [];
+        if (preg_match($regex, $link_header, $matches) && $matches[1] == $entity_url) {
+          $count++;
+        }
+      }
+    }
+
+    return $count;
+  }
+
 }

tests/src/Functional/RelatedLinkHeaderTest.php

@@ -0,0 +1,147 @@
+<?php
+
+namespace Drupal\Tests\islandora\Functional;
+
+use Drupal\field\Tests\EntityReference\EntityReferenceTestTrait;
+use Drupal\Tests\media_entity\Functional\MediaEntityFunctionalTestTrait;
+
+/**
+ * Tests the RelatedLinkHeader view alter.
+ *
+ * @group islandora
+ */
+class RelatedLinkHeaderTest extends IslandoraFunctionalTestBase {
+
+  use EntityReferenceTestTrait;
+  use MediaEntityFunctionalTestTrait;
+
+  /**
+   * Node that has entity reference field.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $referencer;
+
+  /**
+   * Node that has entity reference field, but it's empty.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $referenced;
+
+  /**
+   * Media to be referenced (to check authZ).
+   *
+   * @var \Drupal\media\MediaInterface
+   */
+  protected $media;
+
+  /**
+   * Node of a bundle that does _not_ have an entity reference field.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $other;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    // Create a test content type with an entity reference field.
+    $test_type_with_reference = $this->container->get('entity_type.manager')->getStorage('node_type')->create([
+      'type' => 'test_type_with_reference',
+      'label' => 'Test Type With Reference',
+    ]);
+    $test_type_with_reference->save();
+
+    // Add two entity reference fields.
+    // One for nodes and one for media.
+    $this->createEntityReferenceField('node', 'test_type_with_reference', 'field_reference', 'Referenced Entity', 'node', 'default', [], 2);
+    $this->createEntityReferenceField('node', 'test_type_with_reference', 'field_media', 'Media Entity', 'media', 'default', [], 2);
+
+    $this->other = $this->container->get('entity_type.manager')->getStorage('node')->create([
+      'type' => 'test_type',
+      'title' => 'Test object w/o entity reference field',
+    ]);
+    $this->other->save();
+
+    $this->referenced = $this->container->get('entity_type.manager')->getStorage('node')->create([
+      'type' => 'test_type_with_reference',
+      'title' => 'Referenced',
+    ]);
+    $this->referenced->save();
+
+    $media_bundle = $this->drupalCreateMediaBundle();
+    $this->media = $this->container->get('entity_type.manager')->getStorage('media')->create([
+      'bundle' => $media_bundle->id(),
+      'name' => 'Media',
+    ]);
+    $this->media->save();
+
+    $this->referencer = $this->container->get('entity_type.manager')->getStorage('node')->create([
+      'type' => 'test_type_with_reference',
+      'title' => 'Referencer',
+      'field_reference' => [$this->referenced->id()],
+      'field_media' => [$this->media->id()],
+    ]);
+    $this->referencer->save();
+  }
+
+  /**
+   * @covers \Drupal\islandora\EventSubscriber\NodeLinkHeaderSubscriber::onResponse
+   */
+  public function testRelatedLinkHeader() {
+    // Create a test user that can see media.
+    $account = $this->drupalCreateUser([
+      'view media',
+    ]);
+    $this->drupalLogin($account);
+
+    // Visit the other, there should not be a header since it does not even
+    // have the field.
+    $this->drupalGet('node/' . $this->other->id());
+    $this->assertTrue(
+      $this->doesNotHaveLinkHeader('related'),
+      "Node that does not have entity reference field must not return related link header."
+    );
+
+    // Visit the referenced node, there should not be a header since its
+    // entity reference field is empty.
+    $this->drupalGet('node/' . $this->referenced->id());
+    $this->assertTrue(
+      $this->doesNotHaveLinkHeader('related'),
+      "Node that has empty entity reference field must not return link header."
+    );
+
+    // Visit the referencer. It should return a rel="related" link header
+    // for both the referenced node and media entity.
+    $this->drupalGet('node/' . $this->referencer->id());
+    $this->assertTrue(
+      $this->validateLinkHeader('related', $this->referenced, 'Referenced Entity') == 1,
+      "Malformed related link header"
+    );
+    $this->assertTrue(
+      $this->validateLinkHeader('related', $this->media, 'Media Entity') == 1,
+      "Malformed related link header"
+    );
+
+    // Log in as anonymous.
+    $account = $this->drupalCreateUser();
+    $this->drupalLogin($account);
+
+    // Visit the referencer. It should return a rel="related" link header
+    // for both the referenced node and media entity.
+    $this->drupalGet('node/' . $this->referencer->id());
+    $this->assertTrue(
+      $this->validateLinkHeader('related', $this->referenced, 'Referenced Entity') == 1,
+      "Malformed related link header"
+    );
+    $this->assertTrue(
+      $this->validateLinkHeader('related', $this->media, 'Media Entity') == 0,
+      "Anonymous should not be able to see media link header"
+    );
+  }
+
+}