code: func (dht *DHT) id(target string) string {
  	if dht.IsStandardMode() || target == "" {
  		return dht.node.id.RawString()
  	}
  	return target[:15] + dht.node.id.RawString()[15:]
  }
docs: // id returns a id near to target if target is not null, otherwise it returns
  // the dht's node id.