code: func getTempFile(rootDir, prefix string) (*os.File, error) {
  	tmpFile, err := ioutil.TempFile(rootDir, prefix)
  	if err != nil {
  		return nil, err
  	}
  	if err := util.WriteInt(tmpFile, fileVersion); err != nil {
  		return nil, err
  	}
  	return tmpFile, nil
  }
docs: // Return a temporary file (including file version)