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);
  }

}