class ImageStyleDownloadController

class ImageStyleDownloadController extends FileDownloadController {
    
    /**
     * The lock backend.
     *
     * @var \Drupal\Core\Lock\LockBackendInterface
     */
    protected $lock;
    
    /**
     * The image factory.
     *
     * @var \Drupal\Core\Image\ImageFactory
     */
    protected $imageFactory;
    
    /**
     * A logger instance.
     *
     * @var \Psr\Log\LoggerInterface
     */
    protected $logger;
    
    /**
     * Constructs a ImageStyleDownloadController object.
     *
     * @param \Drupal\Core\Lock\LockBackendInterface $lock
     *   The lock backend.
     * @param \Drupal\Core\Image\ImageFactory $image_factory
     *   The image factory.
     * @param \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $stream_wrapper_manager
     *   The stream wrapper manager.
     */
    public function __construct(LockBackendInterface $lock, ImageFactory $image_factory, StreamWrapperManagerInterface $stream_wrapper_manager = NULL) {
        parent::__construct($stream_wrapper_manager);
        $this->lock = $lock;
        $this->imageFactory = $image_factory;
        $this->logger = $this->getLogger('image');
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('lock'), $container->get('image.factory'), $container->get('stream_wrapper_manager'));
    }
    
    /**
     * Generates a derivative, given a style and image path.
     *
     * After generating an image, transfer it to the requesting agent.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param string $scheme
     *   The file scheme, defaults to 'private'.
     * @param \Drupal\image\ImageStyleInterface $image_style
     *   The image style to deliver.
     *
     * @return \Symfony\Component\HttpFoundation\BinaryFileResponse|\Symfony\Component\HttpFoundation\Response
     *   The transferred file as response or some error response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
     *   Thrown when the file request is invalid.
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Thrown when the user does not have access to the file.
     * @throws \Symfony\Component\HttpKernel\Exception\ServiceUnavailableHttpException
     *   Thrown when the file is still being generated.
     */
    public function deliver(Request $request, $scheme, ImageStyleInterface $image_style) {
        $target = $request->query
            ->get('file');
        $image_uri = $scheme . '://' . $target;
        // Check that the style is defined, the scheme is valid, and the image
        // derivative token is valid. Sites which require image derivatives to be
        // generated without a token can set the
        // 'image.settings:allow_insecure_derivatives' configuration to TRUE to
        // bypass the latter check, but this will increase the site's vulnerability
        // to denial-of-service attacks. To prevent this variable from leaving the
        // site vulnerable to the most serious attacks, a token is always required
        // when a derivative of a style is requested.
        // The $target variable for a derivative of a style has
        // styles/<style_name>/... as structure, so we check if the $target variable
        // starts with styles/.
        $valid = !empty($image_style) && $this->streamWrapperManager
            ->isValidScheme($scheme);
        if (!$this->config('image.settings')
            ->get('allow_insecure_derivatives') || strpos(ltrim($target, '\\/'), 'styles/') === 0) {
            $valid &= hash_equals($image_style->getPathToken($image_uri), $request->query
                ->get(IMAGE_DERIVATIVE_TOKEN, ''));
        }
        if (!$valid) {
            // Return a 404 (Page Not Found) rather than a 403 (Access Denied) as the
            // image token is for DDoS protection rather than access checking. 404s
            // are more likely to be cached (e.g. at a proxy) which enhances
            // protection from DDoS.
            throw new NotFoundHttpException();
        }
        $derivative_uri = $image_style->buildUri($image_uri);
        $headers = [];
        // If using the private scheme, let other modules provide headers and
        // control access to the file.
        if ($scheme == 'private') {
            $headers = $this->moduleHandler()
                ->invokeAll('file_download', [
                $image_uri,
            ]);
            if (in_array(-1, $headers) || empty($headers)) {
                throw new AccessDeniedHttpException();
            }
        }
        // Don't try to generate file if source is missing.
        if (!file_exists($image_uri)) {
            // If the image style converted the extension, it has been added to the
            // original file, resulting in filenames like image.png.jpeg. So to find
            // the actual source image, we remove the extension and check if that
            // image exists.
            $path_info = pathinfo($image_uri);
            $converted_image_uri = $path_info['dirname'] . DIRECTORY_SEPARATOR . $path_info['filename'];
            if (!file_exists($converted_image_uri)) {
                $this->logger
                    ->notice('Source image at %source_image_path not found while trying to generate derivative image at %derivative_path.', [
                    '%source_image_path' => $image_uri,
                    '%derivative_path' => $derivative_uri,
                ]);
                return new Response($this->t('Error generating image, missing source file.'), 404);
            }
            else {
                // The converted file does exist, use it as the source.
                $image_uri = $converted_image_uri;
            }
        }
        // Don't start generating the image if the derivative already exists or if
        // generation is in progress in another thread.
        if (!file_exists($derivative_uri)) {
            $lock_name = 'image_style_deliver:' . $image_style->id() . ':' . Crypt::hashBase64($image_uri);
            $lock_acquired = $this->lock
                ->acquire($lock_name);
            if (!$lock_acquired) {
                // Tell client to retry again in 3 seconds. Currently no browsers are
                // known to support Retry-After.
                throw new ServiceUnavailableHttpException(3, 'Image generation in progress. Try again shortly.');
            }
        }
        // Try to generate the image, unless another thread just did it while we
        // were acquiring the lock.
        $success = file_exists($derivative_uri) || $image_style->createDerivative($image_uri, $derivative_uri);
        if (!empty($lock_acquired)) {
            $this->lock
                ->release($lock_name);
        }
        if ($success) {
            $image = $this->imageFactory
                ->get($derivative_uri);
            $uri = $image->getSource();
            $headers += [
                'Content-Type' => $image->getMimeType(),
                'Content-Length' => $image->getFileSize(),
            ];
            // \Drupal\Core\EventSubscriber\FinishResponseSubscriber::onRespond()
            // sets response as not cacheable if the Cache-Control header is not
            // already modified. We pass in FALSE for non-private schemes for the
            // $public parameter to make sure we don't change the headers.
            return new BinaryFileResponse($uri, 200, $headers, $scheme !== 'private');
        }
        else {
            $this->logger
                ->notice('Unable to generate the derived image located at %path.', [
                '%path' => $derivative_uri,
            ]);
            return new Response($this->t('Error generating image.'), 500);
        }
    }

}