code: func updateTUFClient(client *tuf.Client) error {
  	_, err := client.Update()
  	if err == nil || tuf.IsLatestSnapshot(err) {
  		return nil
  	}
  	if err == tuf.ErrNoRootKeys {
  		if err := client.Init(tufconfig.RootKeys, len(tufconfig.RootKeys)); err != nil {
  			return err
  		}
  		return updateTUFClient(client)
  	}
  	return err
  }
docs: // updateTUFClient updates the given client, initializing and re-running the
  // update if ErrNoRootKeys is returned.