code: func (l *httpFileSystem) CreateFile(filePath string, length uint64) (io.WriteCloser, error) {
  	_, filename := filepath.Split(filePath)
  	contentLength := strconv.FormatUint(length, 10)
  	header := l.writer.Header()
  
  	httplib.SetNoCacheHeaders(header)
  	httplib.SetNoSniff(header)
  	header.Set("Content-Length", contentLength)
  	header.Set("Content-Type", "application/octet-stream")
  	filename = url.QueryEscape(filename)
  	header.Set("Content-Disposition", fmt.Sprintf(`attachment;filename="%v"`, filename))
  
  	return &nopWriteCloser{Writer: l.writer}, nil
  }
docs: // CreateFile sets proper HTTP headers and returns HTTP writer to stream incoming
  // file content