code: func getChannelVersion(configDir string, client *tuf.Client, log log15.Logger) (string, error) {
  	log.Info("getting configured release channel")
  	data, err := ioutil.ReadFile(filepath.Join(configDir, "channel.txt"))
  	if err != nil {
  		log.Error("error getting configured release channel", "err", err)
  		return "", err
  	}
  	channel := strings.TrimSpace(string(data))
  
  	log.Info(fmt.Sprintf("determining latest version of %s release channel", channel))
  	version, err := tufutil.DownloadString(client, path.Join("channels", channel))
  	if err != nil {
  		log.Error("error determining latest version", "err", err)
  		return "", err
  	}
  	version = strings.TrimSpace(version)
  	log.Info(fmt.Sprintf("latest %s version is %s", channel, version))
  	return version, nil
  }
docs: // getChannelVersion reads the locally configured release channel from
  // <configDir>/channel.txt then gets the latest version for that channel
  // using the TUF client.