class ContentDispositionFilenameParser

final class ContentDispositionFilenameParser {
    
    /**
     * The regex used to extract the filename from the content disposition header.
     */
    const REQUEST_HEADER_FILENAME_REGEX = '@\\bfilename(?<star>\\*?)=\\"(?<filename>.+)\\"@';
    
    /**
     * Private constructor to prevent instantiation.
     */
    private function __construct() {
    }
    
    /**
     * Parse the content disposition header and return the filename.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request.
     *
     * @return string
     *   The filename.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when the 'Content-Disposition' request header is invalid.
     */
    public static function parseFilename(Request $request) : string {
        // Firstly, check the header exists.
        if (!$request->headers
            ->has('content-disposition')) {
            throw new BadRequestHttpException('"Content-Disposition" header is required. A file name in the format "filename=FILENAME" must be provided.');
        }
        $content_disposition = $request->headers
            ->get('content-disposition');
        // Parse the header value. This regex does not allow an empty filename.
        // i.e. 'filename=""'. This also matches on a word boundary so other keys
        // like 'not_a_filename' don't work.
        if (!preg_match(static::REQUEST_HEADER_FILENAME_REGEX, $content_disposition, $matches)) {
            throw new BadRequestHttpException('No filename found in "Content-Disposition" header. A file name in the format "filename=FILENAME" must be provided.');
        }
        // Check for the "filename*" format. This is currently unsupported.
        if (!empty($matches['star'])) {
            throw new BadRequestHttpException('The extended "filename*" format is currently not supported in the "Content-Disposition" header.');
        }
        // Don't validate the actual filename here, that will be done by the upload
        // validators in validate().
        // @see \Drupal\file\Plugin\rest\resource\FileUploadResource::validate()
        $filename = $matches['filename'];
        // Make sure only the filename component is returned. Path information is
        // stripped as per https://tools.ietf.org/html/rfc6266#section-4.3.
        // We do not need to use Drupal's FileSystem service here as we are not
        // dealing with StreamWrappers.
        return \basename($filename);
    }

}