class WebprofilerEventSubscriber

class WebprofilerEventSubscriber implements EventSubscriberInterface {
    
    /**
     * @var \Drupal\Core\Session\AccountInterface
     */
    private $currentUser;
    
    /**
     * @var \Drupal\Core\Routing\UrlGeneratorInterface
     */
    protected $urlGenerator;
    
    /**
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * @param \Drupal\Core\Session\AccountInterface $currentUser
     * @param \Drupal\Core\Routing\UrlGeneratorInterface $urlGenerator
     * @param \Drupal\Core\Render\RendererInterface $renderer
     */
    public function __construct(AccountInterface $currentUser, UrlGeneratorInterface $urlGenerator, RendererInterface $renderer) {
        $this->currentUser = $currentUser;
        $this->urlGenerator = $urlGenerator;
        $this->renderer = $renderer;
    }
    
    /**
     * @param \Symfony\Component\HttpKernel\Event\FilterResponseEvent $event
     */
    public function onKernelResponse(FilterResponseEvent $event) {
        $response = $event->getResponse();
        $request = $event->getRequest();
        if ($response->headers
            ->has('X-Debug-Token') && NULL !== $this->urlGenerator) {
            $response->headers
                ->set('X-Debug-Token-Link', $this->urlGenerator
                ->generate('webprofiler.dashboard', [
                'profile' => $response->headers
                    ->get('X-Debug-Token'),
            ]));
        }
        // do not capture redirects or modify XML HTTP Requests
        if ($request->isXmlHttpRequest()) {
            return;
        }
        if ($this->currentUser
            ->hasPermission('view webprofiler toolbar')) {
            $this->injectToolbar($response);
        }
    }
    
    /**
     * @param \Symfony\Component\HttpFoundation\Response $response
     */
    protected function injectToolbar(Response $response) {
        $content = $response->getContent();
        $pos = mb_strripos($content, '</body>');
        if (FALSE !== $pos) {
            if ($token = $response->headers
                ->get('X-Debug-Token')) {
                $loader = [
                    '#theme' => 'webprofiler_loader',
                    '#token' => $token,
                    '#profiler_url' => $this->urlGenerator
                        ->generate('webprofiler.toolbar', [
                        'profile' => $token,
                    ]),
                ];
                $content = mb_substr($content, 0, $pos) . $this->renderer
                    ->renderRoot($loader) . mb_substr($content, $pos);
                $response->setContent($content);
            }
        }
    }
    
    /**
     * @return array
     */
    public static function getSubscribedEvents() {
        return [
            KernelEvents::RESPONSE => [
                'onKernelResponse',
                -128,
            ],
        ];
    }

}