class DefaultExceptionSubscriber

class DefaultExceptionSubscriber extends SerializationDefaultExceptionSubscriber {
  
  /**
   * {@inheritdoc}
   */
  protected static function getPriority() {
    return parent::getPriority() + 25;
  }
  
  /**
   * {@inheritdoc}
   */
  protected function getHandledFormats() {
    return [
      'api_json',
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function onException(ExceptionEvent $event) {
    if (!$this->isJsonApiExceptionEvent($event)) {
      return;
    }
    if (($exception = $event->getThrowable()) && !$exception instanceof HttpException) {
      $exception = new HttpException(500, $exception->getMessage(), $exception);
      $event->setThrowable($exception);
    }
    $this->setEventResponse($event, $exception->getStatusCode());
  }
  
  /**
   * {@inheritdoc}
   */
  protected function setEventResponse(ExceptionEvent $event, $status) {
    /** @var \Symfony\Component\HttpKernel\Exception\HttpException $exception */
    $exception = $event->getThrowable();
    $document = new JsonApiDocumentTopLevel(new ErrorCollection([
      $exception,
    ]), new NullIncludedData(), new LinkCollection([]));
    if ($event->getRequest()
      ->isMethodCacheable()) {
      $response = new CacheableResourceResponse($document, $exception->getStatusCode(), $exception->getHeaders());
      $response->addCacheableDependency($exception);
    }
    else {
      $response = new ResourceResponse($document, $exception->getStatusCode(), $exception->getHeaders());
    }
    $event->setResponse($response);
  }
  
  /**
   * Check if the error should be formatted using JSON:API.
   *
   * The JSON:API format is supported if the format is explicitly set or the
   * request is for a known JSON:API route.
   *
   * @param \Symfony\Component\HttpKernel\Event\ExceptionEvent $exception_event
   *   The exception event.
   *
   * @return bool
   *   TRUE if it needs to be formatted using JSON:API. FALSE otherwise.
   */
  protected function isJsonApiExceptionEvent(ExceptionEvent $exception_event) {
    $request = $exception_event->getRequest();
    $parameters = $request->attributes
      ->all();
    return $request->getRequestFormat() === 'api_json' || (bool) Routes::getResourceTypeNameFromParameters($parameters);
  }

}