code: func (*ArchiveHandler) Stat(u *url.URL) (os.FileInfo, error) {
  	switch u.Query().Get("format") {
  	case "", "tar", "tgz":
  		// ok
  	default:
  		log.Printf("unknown archive format: %q", u)
  		return nil, vix.Error(vix.InvalidArg)
  	}
  
  	return &archive{
  		name: u.Path,
  		size: math.MaxInt64,
  	}, nil
  }
docs: // Stat implements FileHandler.Stat