Golang MsgTx.AddTxOut方法代码示例

// fundTx attempts to fund a transaction sending amt bitcoin. The coins are
// selected such that the final amount spent pays enough fees as dictated by
// the passed fee rate. The passed fee rate should be expressed in
// satoshis-per-byte.
//
// NOTE: The memWallet's mutex must be held when this function is called.
func (m *memWallet) fundTx(tx *wire.MsgTx, amt btcutil.Amount, feeRate btcutil.Amount) error {
	const (
		// spendSize is the largest number of bytes of a sigScript
		// which spends a p2pkh output: OP_DATA_73 <sig> OP_DATA_33 <pubkey>
		spendSize = 1 + 73 + 1 + 33
	)

	var (
		amtSelected btcutil.Amount
		txSize      int
	)

	for outPoint, utxo := range m.utxos {
		// Skip any outputs that are still currently immature or are
		// currently locked.
		if !utxo.isMature(m.currentHeight) || utxo.isLocked {
			continue
		}

		amtSelected += utxo.value

		// Add the selected output to the transaction, updating the
		// current tx size while accounting for the size of the future
		// sigScript.
		tx.AddTxIn(wire.NewTxIn(&outPoint, nil, nil))
		txSize = tx.SerializeSize() + spendSize*len(tx.TxIn)

		// Calculate the fee required for the txn at this point
		// observing the specified fee rate. If we don't have enough
		// coins from he current amount selected to pay the fee, then
		// continue to grab more coins.
		reqFee := btcutil.Amount(txSize * int(feeRate))
		if amtSelected-reqFee < amt {
			continue
		}

		// If we have any change left over, then add an additional
		// output to the transaction reserved for change.
		changeVal := amtSelected - amt - reqFee
		if changeVal > 0 {
			addr, err := m.newAddress()
			if err != nil {
				return err
			}
			pkScript, err := txscript.PayToAddrScript(addr)
			if err != nil {
				return err
			}
			changeOutput := &wire.TxOut{
				Value:    int64(changeVal),
				PkScript: pkScript,
			}
			tx.AddTxOut(changeOutput)
		}

		return nil
	}

	// If we've reached this point, then coin selection failed due to an
	// insufficient amount of coins.
	return fmt.Errorf("not enough funds for coin selection")
}