Add support for filtering out response attributes to reduce payload size

Closes #3350524

src/Resource/MenuItemsResource.php

@@ -71,7 +71,7 @@ final class MenuItemsResource extends ResourceBase {
     ];
     $tree = $menu_tree->transform($tree, $manipulators);
 
-    $this->getMenuItems($tree, $this->menuItems, $cacheability);
+    $this->getMenuItems($request, $tree, $this->menuItems, $cacheability);
 
     $data = new ResourceObjectData($this->menuItems);
     $response = $this->createJsonapiResponse($data, $request, 200, [] /* , $pagination_links */);
@@ -142,6 +142,8 @@ final class MenuItemsResource extends ResourceBase {
   /**
    * Generate the menu items.
    *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request.
    * @param array $tree
    *   The menu tree.
    * @param array $items
@@ -149,7 +151,7 @@ final class MenuItemsResource extends ResourceBase {
    * @param \Drupal\Core\Cache\CacheableMetadata $cache
    *   The cacheable metadata.
    */
-  protected function getMenuItems(array $tree, array &$items, CacheableMetadata $cache) {
+  protected function getMenuItems(Request $request, array $tree, array &$items, CacheableMetadata $cache) {
     foreach ($tree as $menu_link) {
       if ($menu_link->access !== NULL && !$menu_link->access instanceof AccessResultInterface) {
         throw new \DomainException('MenuLinkTreeElement::access must be either NULL or an AccessResultInterface object.');
@@ -198,6 +200,14 @@ final class MenuItemsResource extends ResourceBase {
         'url' => $url->getGeneratedUrl(),
         'weight' => (int) $menu_link->link->getWeight(),
       ];
+
+      // Apply field filter if required on each field
+      foreach ($fields as $field_name => $field) {
+        if (!$this->checkFieldPresence($request, $field_name)) {
+          unset($fields[$field_name]);
+        }
+      }
+
       $links = new LinkCollection([]);
 
       $resource_object_cacheability = new CacheableMetadata();
@@ -206,9 +216,38 @@ final class MenuItemsResource extends ResourceBase {
       $items[$id] = new ResourceObject($resource_object_cacheability, $resource_type, $id, NULL, $fields, $links);
 
       if ($menu_link->subtree) {
-        $this->getMenuItems($menu_link->subtree, $items, $cache);
+        $this->getMenuItems($request, $menu_link->subtree, $items, $cache);
       }
     }
   }
 
+  /**
+   * Check the request object to see if we need to return a specific field.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request.
+   * @param string $field_name
+   *   The field to check.
+   *
+   * @return bool
+   *   Return true if we are including the field in results.
+   */
+  private function checkFieldPresence(Request $request, string $field_name): bool {
+    if (!$request->query->has('filter') ) {
+      return true;
+    }
+
+    $filters = $request->query->all('filter');
+    if (empty($filters['fields'])) {
+      return true;
+    }
+
+    $requested_fields = explode(',', preg_replace("/\s+/", "", $filters['fields']));
+    if (in_array($field_name, $requested_fields)) {
+      return true;
+    }
+
+    return false;
+  }
+
 }