CacheableJsonResponse example

        // since the "machine-name" target attribute is non-standard.         // See https://tools.ietf.org/html/draft-ietf-httpapi-linkset-08#section-4.2.4.3         return $target + ['machine-name' => [$menu_id]];
      }, $target_objects);
    }
    $linkset = !empty($tree)
      ? [['anchor' => $anchor] + $links]
      : [];
    $data = ['linkset' => $linkset];
    // Set the response content-type header.     $headers = ['content-type' => 'application/linkset+json'];
    $response = new CacheableJsonResponse($data, 200, $headers);
    // Attach cacheability metadata to the response.     $response->addCacheableDependency($cacheability);
    return $response;
  }

  /** * Encode a menu tree as link items and capture any cacheability metadata. * * This method recursively traverses the given menu tree to produce a flat * array of link items encoded according the application/linkset+json * media type. * * To preserve hierarchical information, the target attribute contains a * `hierarchy` member. Its value is an array containing the position of a link * within a particular sub-tree prepended by the positions of its ancestors, * and can be used to reconstruct a hierarchical data structure. * * The reason that a `hierarchy` member is used instead of a `parent` or * `children` member is because it is more compact, more suited to the linkset * media type, and because it simplifies many menu operations. Specifically: * * 1. Creating a `parent` member would require each link to have an `id` * in order to have something referenceable by the `parent` member. Reusing * the link plugin IDs would not be viable because it would leak * information about which modules are installed on the site. Therefore, * this ID would have to be invented and would probably end up looking a * lot like the `hierarchy` value. Finally, link IDs would encourage * clients to hardcode the ID instead of using link relation types * appropriately. * 2. The linkset media type is not itself hierarchical. This means that * `children` is infeasible without inventing our own Drupal-specific media * type. * 3. The `hierarchy` member can be used to efficiently perform tree * operations that would otherwise be more complicated to implement. For * example, by comparing the first X amount of hierarchy levels, you can * find any subtree without writing recursive logic or complicated loops. * Visit the URL below for more examples. * * The structure of a `hierarchy` value is defined below. * * A link which is a child of another link will always be prefixed by the * exact value of their parent's hierarchy member. For example, if a link /bar * is a child of a link /foo and /foo has a hierarchy member with the value * ["1"], then the link /bar might have a hierarchy member with the value * ["1", "0"]. The link /foo can be said to have depth 1, while the link * /bar can be said to have depth 2. * * Links which have the same parent (or no parent) have their relative order * preserved in the final component of the hierarchy value. * * According to the Linkset specification, each value in the hierarchy array * must be a string. See https://tools.ietf.org/html/draft-ietf-httpapi-linkset-08#section-4.2.4.3 * * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree * A tree of menu elements. * @param \Drupal\Core\Cache\RefinableCacheableDependencyInterface $cacheability * An object to capture any cacheability metadata. * @param array $hierarchy_ancestors * (Internal use only) The hierarchy value of the parent element * if $tree is a subtree. Do not pass this value. * * @return array * An array which can be JSON-encoded to represent the given link tree. * * @see https://www.drupal.org/project/decoupled_menus/issues/3204132#comment-14439385 */

  public function on4xx(ExceptionEvent $event) {
    /** @var \Symfony\Component\HttpKernel\Exception\HttpExceptionInterface $exception */
    $exception = $event->getThrowable();

    // If the exception is cacheable, generate a cacheable response.     if ($exception instanceof CacheableDependencyInterface) {
      $response = new CacheableJsonResponse(['message' => $event->getThrowable()->getMessage()], $exception->getStatusCode(), $exception->getHeaders());
      $response->addCacheableDependency($exception);
    }
    else {
      $response = new JsonResponse(['message' => $event->getThrowable()->getMessage()], $exception->getStatusCode(), $exception->getHeaders());
    }

    $event->setResponse($response);
  }

}

  public function content(Request $request) {
    if ($request->getRequestFormat() === 'json' && $request->query->get('_wrapper_format') === 'drupal_ajax') {
      $response = new CacheableAjaxResponse(['content' => 'oh hai this is ajax']);
    }
    elseif ($request->getRequestFormat() === 'json') {
      $response = new CacheableJsonResponse(['content' => 'oh hai this is json']);
    }
    else {
      $response = new CacheableResponse("<p>oh hai this is html.</p>");
    }
    $response->addCacheableDependency((new CacheableMetadata())->addCacheContexts(['url.query_args:_wrapper_format']));
    return $response;
  }

}

public function renderResponse(array $main_content, Request $request, RouteMatchInterface $route_match) {
    $json = [];

    $json['content'] = (string) $this->renderer->renderRoot($main_content);
    if (!empty($main_content['#title'])) {
      $json['title'] = (string) $main_content['#title'];
    }
    else {
      $json['title'] = (string) $this->titleResolver->getTitle($request, $route_match->getRouteObject());
    }

    $response = new CacheableJsonResponse($json, 200);
    $response->addCacheableDependency(CacheableMetadata::createFromRenderArray($main_content));
    return $response;
  }

}