func mkGetKey(keys map[string]addressToKey) txscript.KeyDB {
if keys == nil {
return txscript.KeyClosure(func(addr btcutil.Address) (*btcec.PrivateKey,
bool, error) {
return nil, false, errors.New("nope")
})
}
return txscript.KeyClosure(func(addr btcutil.Address) (*btcec.PrivateKey,
bool, error) {
a2k, ok := keys[addr.EncodeAddress()]
if !ok {
return nil, false, errors.New("nope")
}
return a2k.key, a2k.compressed, nil
})
}
// This example demonstrates manually creating and signing a redeem transaction.
func ExampleSignTxOutput() {
// Ordinarily the private key would come from whatever storage mechanism
// is being used, but for this example just hard code it.
privKeyBytes, err := hex.DecodeString("22a47fa09a223f2aa079edf85a7c2" +
"d4f8720ee63e502ee2869afab7de234b80c")
if err != nil {
fmt.Println(err)
return
}
privKey, pubKey := btcec.PrivKeyFromBytes(btcec.S256(), privKeyBytes)
pubKeyHash := btcutil.Hash160(pubKey.SerializeCompressed())
addr, err := btcutil.NewAddressPubKeyHash(pubKeyHash,
&chaincfg.MainNetParams)
if err != nil {
fmt.Println(err)
return
}
// For this example, create a fake transaction that represents what
// would ordinarily be the real transaction that is being spent. It
// contains a single output that pays to address in the amount of 1 BTC.
originTx := wire.NewMsgTx()
prevOut := wire.NewOutPoint(&wire.ShaHash{}, ^uint32(0))
txIn := wire.NewTxIn(prevOut, []byte{txscript.OP_0, txscript.OP_0})
originTx.AddTxIn(txIn)
pkScript, err := txscript.PayToAddrScript(addr)
if err != nil {
fmt.Println(err)
return
}
txOut := wire.NewTxOut(100000000, pkScript)
originTx.AddTxOut(txOut)
originTxHash, err := originTx.TxSha()
if err != nil {
fmt.Println(err)
return
}
// Create the transaction to redeem the fake transaction.
redeemTx := wire.NewMsgTx()
// Add the input(s) the redeeming transaction will spend. There is no
// signature script at this point since it hasn't been created or signed
// yet, hence nil is provided for it.
prevOut = wire.NewOutPoint(&originTxHash, 0)
txIn = wire.NewTxIn(prevOut, nil)
redeemTx.AddTxIn(txIn)
// Ordinarily this would contain that actual destination of the funds,
// but for this example don't bother.
txOut = wire.NewTxOut(0, nil)
redeemTx.AddTxOut(txOut)
// Sign the redeeming transaction.
lookupKey := func(a btcutil.Address) (*btcec.PrivateKey, bool, error) {
// Ordinarily this function would involve looking up the private
// key for the provided address, but since the only thing being
// signed in this example uses the address associated with the
// private key from above, simply return it with the compressed
// flag set since the address is using the associated compressed
// public key.
//
// NOTE: If you want to prove the code is actually signing the
// transaction properly, uncomment the following line which
// intentionally returns an invalid key to sign with, which in
// turn will result in a failure during the script execution
// when verifying the signature.
//
// privKey.D.SetInt64(12345)
//
return privKey, true, nil
}
// Notice that the script database parameter is nil here since it isn't
// used. It must be specified when pay-to-script-hash transactions are
// being signed.
sigScript, err := txscript.SignTxOutput(&chaincfg.MainNetParams,
redeemTx, 0, originTx.TxOut[0].PkScript, txscript.SigHashAll,
txscript.KeyClosure(lookupKey), nil, nil)
if err != nil {
fmt.Println(err)
return
}
redeemTx.TxIn[0].SignatureScript = sigScript
// Prove that the transaction has been validly signed by executing the
// script pair.
flags := txscript.ScriptBip16 | txscript.ScriptVerifyDERSignatures |
txscript.ScriptStrictMultiSig |
txscript.ScriptDiscourageUpgradableNops
s, err := txscript.NewScript(redeemTx.TxIn[0].SignatureScript,
originTx.TxOut[0].PkScript, 0, redeemTx, flags)
if err != nil {
fmt.Println(err)
return
}
if err := s.Execute(); err != nil {
fmt.Println(err)
return
}
fmt.Println("Transaction successfully signed")
// Output:
// Transaction successfully signed
}
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
}