code: func (msg *MsgCFHeaders) AddCFHash(hash *chainhash.Hash) error {
  	if len(msg.FilterHashes)+1 > MaxCFHeadersPerMsg {
  		str := fmt.Sprintf("too many block headers in message [max %v]",
  			MaxBlockHeadersPerMsg)
  		return messageError("MsgCFHeaders.AddCFHash", str)
  	}
  
  	msg.FilterHashes = append(msg.FilterHashes, hash)
  	return nil
  }
docs: // AddCFHash adds a new filter hash to the message.