code: func (cg *Consumergroup) FetchOffset(topic string, partition int32) (int64, error) {
  	node := fmt.Sprintf("%s/consumers/%s/offsets/%s/%d", cg.kz.conf.Chroot, cg.Name, topic, partition)
  	val, _, err := cg.kz.conn.Get(node)
  	if err == zk.ErrNoNode {
  		return -1, nil
  	} else if err != nil {
  		return -1, err
  	}
  	return strconv.ParseInt(string(val), 10, 64)
  }
docs: // FetchOffset retrieves an offset to a group/topic/partition