class JsonApiRequestValidator

class JsonApiRequestValidator implements EventSubscriberInterface {
    
    /**
     * Validates JSON:API requests.
     *
     * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
     *   The event to process.
     */
    public function onRequest(RequestEvent $event) {
        $request = $event->getRequest();
        if ($request->getRequestFormat() !== 'api_json') {
            return;
        }
        $this->validateQueryParams($request);
    }
    
    /**
     * Validates custom (implementation-specific) query parameter names.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request for which to validate JSON:API query parameters.
     *
     * @return \Drupal\jsonapi\ResourceResponse|null
     *   A JSON:API resource response.
     *
     * @see http://jsonapi.org/format/#query-parameters
     */
    protected function validateQueryParams(Request $request) {
        $invalid_query_params = [];
        foreach (array_keys($request->query
            ->all()) as $query_parameter_name) {
            // Ignore reserved (official) query parameters.
            if (in_array($query_parameter_name, JsonApiSpec::getReservedQueryParameters())) {
                continue;
            }
            if (!JsonApiSpec::isValidCustomQueryParameter($query_parameter_name)) {
                $invalid_query_params[] = $query_parameter_name;
            }
        }
        // Drupal uses the `_format` query parameter for Content-Type negotiation.
        // Using it violates the JSON:API spec. Nudge people nicely in the correct
        // direction. (This is special cased because using it is pretty common.)
        if (in_array('_format', $invalid_query_params, TRUE)) {
            $uri_without_query_string = $request->getSchemeAndHttpHost() . $request->getBaseUrl() . $request->getPathInfo();
            $exception = new CacheableBadRequestHttpException((new CacheableMetadata())->addCacheContexts([
                'url.query_args:_format',
            ]), 'JSON:API does not need that ugly \'_format\' query string! 🤘 Use the URL provided in \'links\' 🙏');
            $exception->setHeaders([
                'Link' => $uri_without_query_string,
            ]);
            throw $exception;
        }
        if (empty($invalid_query_params)) {
            return NULL;
        }
        $message = sprintf('The following query parameters violate the JSON:API spec: \'%s\'.', implode("', '", $invalid_query_params));
        $exception = new CacheableBadRequestHttpException((new CacheableMetadata())->addCacheContexts([
            'url.query_args',
        ]), $message);
        $exception->setHeaders([
            'Link' => 'http://jsonapi.org/format/#query-parameters',
        ]);
        throw $exception;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        $events[KernelEvents::REQUEST][] = [
            'onRequest',
        ];
        return $events;
    }

}