// NewUnsignedTransaction creates an unsigned transaction paying to one or more
// non-change outputs. An appropriate transaction fee is included based on the
// transaction size.
//
// Transaction inputs are chosen from repeated calls to fetchInputs with
// increasing targets amounts.
//
// If any remaining output value can be returned to the wallet via a change
// output without violating mempool dust rules, a P2PKH change output is
// appended to the transaction outputs. Since the change output may not be
// necessary, fetchChange is called zero or one times to generate this script.
// This function must return a P2PKH script or smaller, otherwise fee estimation
// will be incorrect.
//
// If successful, the transaction, total input value spent, and all previous
// output scripts are returned. If the input source was unable to provide
// enough input value to pay for every output any any necessary fees, an
// InputSourceError is returned.
//
// BUGS: Fee estimation may be off when redeeming non-compressed P2PKH outputs.
func NewUnsignedTransaction(outputs []*wire.TxOut, relayFeePerKb btcutil.Amount,
fetchInputs InputSource, fetchChange ChangeSource) (*AuthoredTx, error) {
targetAmount := h.SumOutputValues(outputs)
estimatedSize := txsizes.EstimateSerializeSize(1, outputs, true)
targetFee := txrules.FeeForSerializeSize(relayFeePerKb, estimatedSize)
for {
inputAmount, inputs, scripts, err := fetchInputs(targetAmount + targetFee)
if err != nil {
return nil, err
}
if inputAmount < targetAmount+targetFee {
return nil, insufficientFundsError{}
}
maxSignedSize := txsizes.EstimateSerializeSize(len(inputs), outputs, true)
maxRequiredFee := txrules.FeeForSerializeSize(relayFeePerKb, maxSignedSize)
remainingAmount := inputAmount - targetAmount
if remainingAmount < maxRequiredFee {
targetFee = maxRequiredFee
continue
}
unsignedTransaction := &wire.MsgTx{
Version: wire.TxVersion,
TxIn: inputs,
TxOut: outputs,
LockTime: 0,
}
changeIndex := -1
changeAmount := inputAmount - targetAmount - maxRequiredFee
if changeAmount != 0 && !txrules.IsDustAmount(changeAmount,
txsizes.P2PKHPkScriptSize, relayFeePerKb) {
changeScript, err := fetchChange()
if err != nil {
return nil, err
}
if len(changeScript) > txsizes.P2PKHPkScriptSize {
return nil, errors.New("fee estimation requires change " +
"scripts no larger than P2PKH output scripts")
}
change := wire.NewTxOut(int64(changeAmount), changeScript)
l := len(outputs)
unsignedTransaction.TxOut = append(outputs[:l:l], change)
changeIndex = l
}
return &AuthoredTx{
Tx: unsignedTransaction,
PrevScripts: scripts,
TotalInput: inputAmount,
ChangeIndex: changeIndex,
}, nil
}
}
func (w *LibbitcoinWallet) Spend(amount int64, addr btc.Address, feeLevel bitcoin.FeeLevel) error {
// Check for dust
script, _ := txscript.PayToAddrScript(addr)
if txrules.IsDustAmount(btc.Amount(amount), len(script), txrules.DefaultRelayFeePerKb) {
return errors.New("Amount is below dust threshold")
}
var additionalPrevScripts map[wire.OutPoint][]byte
var additionalKeysByAddress map[string]*btc.WIF
// Create input source
coinMap := w.gatherCoins()
coins := make([]coinset.Coin, 0, len(coinMap))
for k := range coinMap {
coins = append(coins, k)
}
inputSource := func(target btc.Amount) (total btc.Amount, inputs []*wire.TxIn, scripts [][]byte, err error) {
// TODO: maybe change the coin selection algorithm? We're using min coins right now because
// TODO: we don't know the number of confirmations on each coin without querying the libbitcoin server.
coinSelector := coinset.MinNumberCoinSelector{MaxInputs: 10000, MinChangeAmount: btc.Amount(10000)}
coins, err := coinSelector.CoinSelect(target, coins)
if err != nil {
return total, inputs, scripts, errors.New("insuffient funds")
}
additionalPrevScripts = make(map[wire.OutPoint][]byte)
additionalKeysByAddress = make(map[string]*btc.WIF)
for _, c := range coins.Coins() {
total += c.Value()
outpoint := wire.NewOutPoint(c.Hash(), c.Index())
in := wire.NewTxIn(outpoint, []byte{})
in.Sequence = 0 // Opt-in RBF so we can bump fees
inputs = append(inputs, in)
additionalPrevScripts[*outpoint] = c.PkScript()
key := coinMap[c]
addr, _ := btc.NewAddressPubKey(key.PublicKey().Key, w.params)
pk, _ := btcec.PrivKeyFromBytes(btcec.S256(), key.Key)
wif, _ := btc.NewWIF(pk, w.params, true)
additionalKeysByAddress[addr.AddressPubKeyHash().EncodeAddress()] = wif
}
return total, inputs, scripts, nil
}
// Get the fee per kilobyte
feePerKB := int64(w.getFeePerByte(feeLevel)) * 1000
// outputs
out := wire.NewTxOut(amount, script)
// Create change source
changeSource := func() ([]byte, error) {
addr := w.GetCurrentAddress(bitcoin.CHANGE)
script, err := txscript.PayToAddrScript(addr)
if err != nil {
return []byte{}, err
}
return script, nil
}
authoredTx, err := txauthor.NewUnsignedTransaction([]*wire.TxOut{out}, btc.Amount(feePerKB), inputSource, changeSource)
if err != nil {
return err
}
// BIP 69 sorting
txsort.InPlaceSort(authoredTx.Tx)
// Sign tx
getKey := txscript.KeyClosure(func(addr btc.Address) (
*btcec.PrivateKey, bool, error) {
addrStr := addr.EncodeAddress()
wif := additionalKeysByAddress[addrStr]
return wif.PrivKey, wif.CompressPubKey, nil
})
getScript := txscript.ScriptClosure(func(
addr btc.Address) ([]byte, error) {
return []byte{}, nil
})
for i, txIn := range authoredTx.Tx.TxIn {
prevOutScript := additionalPrevScripts[txIn.PreviousOutPoint]
script, err := txscript.SignTxOutput(w.params,
authoredTx.Tx, i, prevOutScript, txscript.SigHashAll, getKey,
getScript, txIn.SignatureScript)
if err != nil {
return errors.New("Failed to sign transaction")
}
txIn.SignatureScript = script
}
// Broadcast tx to bitcoin network
serializedTx := new(bytes.Buffer)
authoredTx.Tx.Serialize(serializedTx)
w.Client.Broadcast(serializedTx.Bytes(), func(i interface{}, err error) {
if err == nil {
log.Infof("Broadcast tx %s to bitcoin network\n", authoredTx.Tx.TxSha().String())
} else {
log.Errorf("Failed to broadcast tx, reason: %s\n", err)
}
})
// Update the db
w.ProcessTransaction(btc.NewTx(authoredTx.Tx), 0)
return nil
}