code: func (c *Client) SendRawTransactionAsync(tx *wire.MsgTx, allowHighFees bool) FutureSendRawTransactionResult {
  	txHex := ""
  	if tx != nil {
  		// Serialize the transaction and convert to hex string.
  		buf := bytes.NewBuffer(make([]byte, 0, tx.SerializeSize()))
  		if err := tx.Serialize(buf); err != nil {
  			return newFutureError(err)
  		}
  		txHex = hex.EncodeToString(buf.Bytes())
  	}
  
  	cmd := btcjson.NewSendRawTransactionCmd(txHex, &allowHighFees)
  	return c.sendCmd(cmd)
  }
docs: // SendRawTransactionAsync returns an instance of a type that can be used to get
  // the result of the RPC at some future time by invoking the Receive function on
  // the returned instance.
  //
  // See SendRawTransaction for the blocking version and more details.