class AjaxResponseSubscriber

class AjaxResponseSubscriber implements EventSubscriberInterface {
    
    /**
     * The AJAX response attachments processor service.
     *
     * @var \Drupal\Core\Render\AttachmentsResponseProcessorInterface
     */
    protected $ajaxResponseAttachmentsProcessor;
    
    /**
     * Constructs an AjaxResponseSubscriber object.
     *
     * @param \Drupal\Core\Render\AttachmentsResponseProcessorInterface $ajax_response_attachments_processor
     *   The AJAX response attachments processor service.
     */
    public function __construct(AttachmentsResponseProcessorInterface $ajax_response_attachments_processor) {
        $this->ajaxResponseAttachmentsProcessor = $ajax_response_attachments_processor;
    }
    
    /**
     * Request parameter to indicate that a request is a Drupal Ajax request.
     */
    const AJAX_REQUEST_PARAMETER = '_drupal_ajax';
    
    /**
     * Sets the AJAX parameter from the current request.
     *
     * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
     *   The response event, which contains the current request.
     */
    public function onRequest(RequestEvent $event) {
        // Pass to the Html class that the current request is an Ajax request.
        if ($event->getRequest()->request
            ->get(static::AJAX_REQUEST_PARAMETER)) {
            Html::setIsAjax(TRUE);
        }
    }
    
    /**
     * Renders the ajax commands right before preparing the result.
     *
     * @param \Symfony\Component\HttpKernel\Event\ResponseEvent $event
     *   The response event, which contains the possible AjaxResponse object.
     */
    public function onResponse(ResponseEvent $event) {
        $response = $event->getResponse();
        if ($response instanceof AjaxResponse) {
            $this->ajaxResponseAttachmentsProcessor
                ->processAttachments($response);
            // IE 9 does not support XHR 2 (http://caniuse.com/#feat=xhr2), so
            // for that browser, jquery.form submits requests containing a file upload
            // via an IFRAME rather than via XHR. Since the response is being sent to
            // an IFRAME, it must be formatted as HTML. Specifically:
            // - It must use the text/html content type or else the browser will
            //   present a download prompt. Note: This applies to both file uploads
            //   as well as any ajax request in a form with a file upload form.
            // - It must place the JSON data into a textarea to prevent browser
            //   extensions such as Linkification and Skype's Browser Highlighter
            //   from applying HTML transformations such as URL or phone number to
            //   link conversions on the data values.
            //
            // Since this affects the format of the output, it could be argued that
            // this should be implemented as a separate Accept MIME type. However,
            // that would require separate variants for each type of AJAX request
            // (e.g., drupal-ajax, drupal-dialog, drupal-modal), so for expediency,
            // this browser workaround is implemented via a GET or POST parameter.
            //
            // @see http://malsup.com/jquery/form/#file-upload
            // @see https://www.drupal.org/node/1009382
            // @see https://www.drupal.org/node/2339491
            // @see Drupal.ajax.prototype.beforeSend()
            $accept = $event->getRequest()->headers
                ->get('accept', '');
            if (strpos($accept, 'text/html') !== FALSE) {
                $response->headers
                    ->set('Content-Type', 'text/html; charset=utf-8');
                // Browser IFRAMEs expect HTML. Browser extensions, such as Linkification
                // and Skype's Browser Highlighter, convert URLs, phone numbers, etc.
                // into links. This corrupts the JSON response. Protect the integrity of
                // the JSON data by making it the value of a textarea.
                // @see http://malsup.com/jquery/form/#file-upload
                // @see https://www.drupal.org/node/1009382
                $response->setContent('<textarea>' . $response->getContent() . '</textarea>');
            }
            // User-uploaded files cannot set any response headers, so a custom header
            // is used to indicate to ajax.js that this response is safe. Note that
            // most Ajax requests bound using the Form API will be protected by having
            // the URL flagged as trusted in Drupal.settings, so this header is used
            // only for things like custom markup that gets Ajax behaviors attached.
            $response->headers
                ->set('X-Drupal-Ajax-Token', 1);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        $events[KernelEvents::RESPONSE][] = [
            'onResponse',
            -100,
        ];
        $events[KernelEvents::REQUEST][] = [
            'onRequest',
            50,
        ];
        return $events;
    }

}