// GetDoubleSpends takes a transaction and compares it with
// all transactions in the db. It returns a slice of all txids in the db
// which are double spent by the received tx.
func CheckDoubleSpends(
argTx *wire.MsgTx, txs []*wire.MsgTx) ([]*wire.ShaHash, error) {
var dubs []*wire.ShaHash // slice of all double-spent txs
argTxid := argTx.TxSha()
for _, compTx := range txs {
compTxid := compTx.TxSha()
// check if entire tx is dup
if argTxid.IsEqual(&compTxid) {
return nil, fmt.Errorf("tx %s is dup", argTxid.String())
}
// not dup, iterate through inputs of argTx
for _, argIn := range argTx.TxIn {
// iterate through inputs of compTx
for _, compIn := range compTx.TxIn {
if OutPointsEqual(
argIn.PreviousOutPoint, compIn.PreviousOutPoint) {
// found double spend
dubs = append(dubs, &compTxid)
break // back to argIn loop
}
}
}
}
return dubs, nil
}
// CalcPriority returns a transaction priority given a transaction and the sum
// of each of its input values multiplied by their age (# of confirmations).
// Thus, the final formula for the priority is:
// sum(inputValue * inputAge) / adjustedTxSize
func CalcPriority(tx *wire.MsgTx, utxoView *blockchain.UtxoViewpoint, nextBlockHeight int32) float64 {
// In order to encourage spending multiple old unspent transaction
// outputs thereby reducing the total set, don't count the constant
// overhead for each input as well as enough bytes of the signature
// script to cover a pay-to-script-hash redemption with a compressed
// pubkey. This makes additional inputs free by boosting the priority
// of the transaction accordingly. No more incentive is given to avoid
// encouraging gaming future transactions through the use of junk
// outputs. This is the same logic used in the reference
// implementation.
//
// The constant overhead for a txin is 41 bytes since the previous
// outpoint is 36 bytes + 4 bytes for the sequence + 1 byte the
// signature script length.
//
// A compressed pubkey pay-to-script-hash redemption with a maximum len
// signature is of the form:
// [OP_DATA_73 <73-byte sig> + OP_DATA_35 + {OP_DATA_33
// <33 byte compresed pubkey> + OP_CHECKSIG}]
//
// Thus 1 + 73 + 1 + 1 + 33 + 1 = 110
overhead := 0
for _, txIn := range tx.TxIn {
// Max inputs + size can't possibly overflow here.
overhead += 41 + minInt(110, len(txIn.SignatureScript))
}
serializedTxSize := tx.SerializeSize()
if overhead >= serializedTxSize {
return 0.0
}
inputValueAge := calcInputValueAge(tx, utxoView, nextBlockHeight)
return inputValueAge / float64(serializedTxSize-overhead)
}
// dbFetchTx looks up the passed transaction hash in the transaction index and
// loads it from the database.
func dbFetchTx(dbTx database.Tx, hash *chainhash.Hash) (*wire.MsgTx, error) {
// Look up the location of the transaction.
blockRegion, err := dbFetchTxIndexEntry(dbTx, hash)
if err != nil {
return nil, err
}
if blockRegion == nil {
return nil, fmt.Errorf("transaction %v not found", hash)
}
// Load the raw transaction bytes from the database.
txBytes, err := dbTx.FetchBlockRegion(blockRegion)
if err != nil {
return nil, err
}
// Deserialize the transaction.
var msgTx wire.MsgTx
err = msgTx.Deserialize(bytes.NewReader(txBytes))
if err != nil {
return nil, err
}
return &msgTx, nil
}
// AddSigHashes computes, then adds the partial sighashes for the passed
// transaction.
func (h *HashCache) AddSigHashes(tx *wire.MsgTx) {
h.Lock()
defer h.Unlock()
sigHashes := NewTxSigHashes(tx)
txid := tx.TxHash()
h.sigHashes[txid] = sigHashes
return
}
// TestCalcSignatureHash runs the Bitcoin Core signature hash calculation tests
// in sighash.json.
// https://github.com/bitcoin/bitcoin/blob/master/src/test/data/sighash.json
func TestCalcSignatureHash(t *testing.T) {
file, err := ioutil.ReadFile("data/sighash.json")
if err != nil {
t.Errorf("TestCalcSignatureHash: %v\n", err)
return
}
var tests [][]interface{}
err = json.Unmarshal(file, &tests)
if err != nil {
t.Errorf("TestCalcSignatureHash couldn't Unmarshal: %v\n",
err)
return
}
for i, test := range tests {
if i == 0 {
// Skip first line -- contains comments only.
continue
}
if len(test) != 5 {
t.Fatalf("TestCalcSignatureHash: Test #%d has "+
"wrong length.", i)
}
var tx wire.MsgTx
rawTx, _ := hex.DecodeString(test[0].(string))
err := tx.Deserialize(bytes.NewReader(rawTx))
if err != nil {
t.Errorf("TestCalcSignatureHash failed test #%d: "+
"Failed to parse transaction: %v", i, err)
continue
}
subScript, _ := hex.DecodeString(test[1].(string))
parsedScript, err := parseScript(subScript)
if err != nil {
t.Errorf("TestCalcSignatureHash failed test #%d: "+
"Failed to parse sub-script: %v", i, err)
continue
}
hashType := SigHashType(testVecF64ToUint32(test[3].(float64)))
hash := calcSignatureHash(parsedScript, hashType, &tx,
int(test[2].(float64)))
expectedHash, _ := chainhash.NewHashFromStr(test[4].(string))
if !bytes.Equal(hash, expectedHash[:]) {
t.Errorf("TestCalcSignatureHash failed test #%d: "+
"Signature hash mismatch.", i)
}
}
}
func spendOutput(txHash *wire.ShaHash, index uint32, outputValues ...int64) *wire.MsgTx {
tx := wire.MsgTx{
TxIn: []*wire.TxIn{
&wire.TxIn{
PreviousOutPoint: wire.OutPoint{Hash: *txHash, Index: index},
},
},
}
for _, val := range outputValues {
tx.TxOut = append(tx.TxOut, &wire.TxOut{Value: val})
}
return &tx
}
func newCoinBase(outputValues ...int64) *wire.MsgTx {
tx := wire.MsgTx{
TxIn: []*wire.TxIn{
&wire.TxIn{
PreviousOutPoint: wire.OutPoint{Index: ^uint32(0)},
},
},
}
for _, val := range outputValues {
tx.TxOut = append(tx.TxOut, &wire.TxOut{Value: val})
}
return &tx
}
// receiverHtlcSpendRedeem constructs a valid witness allowing the receiver of
// an HTLC to redeem the conditional payment in the event that their commitment
// transaction is broadcast. Since this is a pay out to the receiving party as
// an output on their commitment transaction, a relative time delay is required
// before the output can be spent.
func receiverHtlcSpendRedeem(commitScript []byte, outputAmt btcutil.Amount,
reciverKey *btcec.PrivateKey, sweepTx *wire.MsgTx,
paymentPreimage []byte, relativeTimeout uint32) (wire.TxWitness, error) {
// In order to properly spend the transaction, we need to set the
// sequence number. We do this by convering the relative block delay
// into a sequence number value able to be interpeted by
// OP_CHECKSEQUENCEVERIFY.
sweepTx.TxIn[0].Sequence = lockTimeToSequence(false, relativeTimeout)
// Additionally, OP_CSV requires that the version of the transaction
// spending a pkscript with OP_CSV within it *must* be >= 2.
sweepTx.Version = 2
hashCache := txscript.NewTxSigHashes(sweepTx)
sweepSig, err := txscript.RawTxInWitnessSignature(
sweepTx, hashCache, 0, int64(outputAmt), commitScript,
txscript.SigHashAll, reciverKey)
if err != nil {
return nil, err
}
// Place a one as the first item in the evaluated witness stack to
// force script execution to the HTLC redemption clause.
witnessStack := wire.TxWitness(make([][]byte, 4))
witnessStack[0] = sweepSig
witnessStack[1] = paymentPreimage
witnessStack[2] = []byte{1}
witnessStack[3] = commitScript
return witnessStack, nil
}
// receiverHtlcSpendTimeout constructs a valid witness allowing the sender of
// an HTLC to recover the pending funds after an absolute timeout in the
// scenario that the receiver of the HTLC broadcasts their version of the
// commitment transaction.
func receiverHtlcSpendTimeout(commitScript []byte, outputAmt btcutil.Amount,
senderKey *btcec.PrivateKey, sweepTx *wire.MsgTx,
absoluteTimeout uint32) (wire.TxWitness, error) {
// The HTLC output has an absolute time period before we are permitted
// to recover the pending funds. Therefore we need to set the locktime
// on this sweeping transaction in order to pass Script verification.
sweepTx.LockTime = absoluteTimeout
hashCache := txscript.NewTxSigHashes(sweepTx)
sweepSig, err := txscript.RawTxInWitnessSignature(
sweepTx, hashCache, 0, int64(outputAmt), commitScript,
txscript.SigHashAll, senderKey)
if err != nil {
return nil, err
}
witnessStack := wire.TxWitness(make([][]byte, 4))
witnessStack[0] = sweepSig
witnessStack[1] = []byte{0}
witnessStack[2] = []byte{0}
witnessStack[3] = commitScript
return witnessStack, nil
}
func equalTxs(t *testing.T, got, exp *wire.MsgTx) {
var bufGot, bufExp bytes.Buffer
err := got.Serialize(&bufGot)
if err != nil {
t.Fatal(err)
}
err = exp.Serialize(&bufExp)
if err != nil {
t.Fatal(err)
}
if !bytes.Equal(bufGot.Bytes(), bufExp.Bytes()) {
t.Errorf("Found unexpected wire.MsgTx:")
t.Errorf("Got: %v", got)
t.Errorf("Expected: %v", exp)
}
}
// BUGS:
// - The transaction is not inspected to be relevant before publishing using
// sendrawtransaction, so connection errors to btcd could result in the tx
// never being added to the wallet database.
// - Once the above bug is fixed, wallet will require a way to purge invalid
// transactions from the database when they are rejected by the network, other
// than double spending them.
func (s *walletServer) PublishTransaction(ctx context.Context, req *pb.PublishTransactionRequest) (
*pb.PublishTransactionResponse, error) {
var msgTx wire.MsgTx
err := msgTx.Deserialize(bytes.NewReader(req.SignedTransaction))
if err != nil {
return nil, grpc.Errorf(codes.InvalidArgument,
"Bytes do not represent a valid raw transaction: %v", err)
}
err = s.wallet.PublishTransaction(&msgTx)
if err != nil {
return nil, translateError(err)
}
return &pb.PublishTransactionResponse{}, nil
}
// TxToString prints out some info about a transaction. for testing / debugging
func TxToString(tx *wire.MsgTx) string {
str := fmt.Sprintf("size %d vsize %d wsize %d locktime %d txid %s\n",
tx.SerializeSize(), blockchain.GetTxVirtualSize(btcutil.NewTx(tx)),
tx.SerializeSize(), tx.LockTime, tx.TxSha().String())
for i, in := range tx.TxIn {
str += fmt.Sprintf("Input %d spends %s\n", i, in.PreviousOutPoint.String())
str += fmt.Sprintf("\tSigScript: %x\n", in.SignatureScript)
for j, wit := range in.Witness {
str += fmt.Sprintf("\twitness %d: %x\n", j, wit)
}
}
for i, out := range tx.TxOut {
if out != nil {
str += fmt.Sprintf("output %d script: %x amt: %d\n",
i, out.PkScript, out.Value)
} else {
str += fmt.Sprintf("output %d nil (WARNING)\n", i)
}
}
return str
}
func (s *SPVCon) NewOutgoingTx(tx *wire.MsgTx) error {
txid := tx.TxSha()
// assign height of zero for txs we create
err := s.TS.AddTxid(&txid, 0)
if err != nil {
return err
}
_, err = s.TS.Ingest(tx, 0) // our own tx; don't keep track of false positives
if err != nil {
return err
}
// make an inv message instead of a tx message to be polite
iv1 := wire.NewInvVect(wire.InvTypeWitnessTx, &txid)
invMsg := wire.NewMsgInv()
err = invMsg.AddInvVect(iv1)
if err != nil {
return err
}
s.outMsgQueue <- invMsg
return nil
}
// htlcSpendTimeout constructs a valid witness allowing the sender of an HTLC
// to recover the pending funds after an absolute, then relative locktime
// period.
func senderHtlcSpendTimeout(commitScript []byte, outputAmt btcutil.Amount,
senderKey *btcec.PrivateKey, sweepTx *wire.MsgTx,
absoluteTimeout, relativeTimeout uint32) (wire.TxWitness, error) {
// Since the HTLC output has an absolute timeout before we're permitted
// to sweep the output, we need to set the locktime of this sweepign
// transaction to that aboslute value in order to pass Script
// verification.
sweepTx.LockTime = absoluteTimeout
// Additionally, we're required to wait a relative period of time
// before we can sweep the output in order to allow the other party to
// contest our claim of validity to this version of the commitment
// transaction.
sweepTx.TxIn[0].Sequence = lockTimeToSequence(false, relativeTimeout)
// Finally, OP_CSV requires that the version of the transaction
// spending a pkscript with OP_CSV within it *must* be >= 2.
sweepTx.Version = 2
hashCache := txscript.NewTxSigHashes(sweepTx)
sweepSig, err := txscript.RawTxInWitnessSignature(
sweepTx, hashCache, 0, int64(outputAmt), commitScript,
txscript.SigHashAll, senderKey)
if err != nil {
return nil, err
}
// We place a zero as the first item of the evaluated witness stack in
// order to force Script execution to the HTLC timeout clause.
witnessStack := wire.TxWitness(make([][]byte, 3))
witnessStack[0] = sweepSig
witnessStack[1] = []byte{0}
witnessStack[2] = commitScript
return witnessStack, nil
}
// EstFee gives a fee estimate based on a tx and a sat/Byte target.
// The TX should have all outputs, including the change address already
// populated (with potentially 0 amount. Also it should have all inputs
// populated, but inputs don't need to have sigscripts or witnesses
// (it'll guess the sizes of sigs/wits that arent' filled in).
func EstFee(otx *wire.MsgTx, spB int64) int64 {
mtsig := make([]byte, 72)
mtpub := make([]byte, 33)
tx := otx.Copy()
// iterate through txins, replacing subscript sigscripts with noise
// sigs or witnesses
for _, txin := range tx.TxIn {
// check wpkh
if len(txin.SignatureScript) == 22 &&
txin.SignatureScript[0] == 0x00 && txin.SignatureScript[1] == 0x14 {
txin.SignatureScript = nil
txin.Witness = make([][]byte, 2)
txin.Witness[0] = mtsig
txin.Witness[1] = mtpub
} else if len(txin.SignatureScript) == 34 &&
txin.SignatureScript[0] == 0x00 && txin.SignatureScript[1] == 0x20 {
// p2wsh -- sig lenght is a total guess!
txin.SignatureScript = nil
txin.Witness = make([][]byte, 3)
// 3 sigs? totally guessing here
txin.Witness[0] = mtsig
txin.Witness[1] = mtsig
txin.Witness[2] = mtsig
} else {
// assume everything else is p2pkh. Even though it's not
txin.Witness = nil
txin.SignatureScript = make([]byte, 105) // len of p2pkh sigscript
}
}
fmt.Printf(TxToString(tx))
size := int64(blockchain.GetTxVirtualSize(btcutil.NewTx(tx)))
fmt.Printf("%d spB, est vsize %d, fee %d\n", spB, size, size*spB)
return size * spB
}
// TxHandler takes in transaction messages that come in from either a request
// after an inv message or after a merkle block message.
func (s *SPVCon) TxHandler(m *wire.MsgTx) {
s.TS.OKMutex.Lock()
height, ok := s.TS.OKTxids[m.TxSha()]
s.TS.OKMutex.Unlock()
if !ok {
log.Printf("Tx %s unknown, will not ingest\n", m.TxSha().String())
return
}
// check for double spends
// allTxs, err := s.TS.GetAllTxs()
// if err != nil {
// log.Printf("Can't get txs from db: %s", err.Error())
// return
// }
// dubs, err := CheckDoubleSpends(m, allTxs)
// if err != nil {
// log.Printf("CheckDoubleSpends error: %s", err.Error())
// return
// }
// if len(dubs) > 0 {
// for i, dub := range dubs {
// fmt.Printf("dub %d known tx %s and new tx %s are exclusive!!!\n",
// i, dub.String(), m.TxSha().String())
// }
// }
utilTx := btcutil.NewTx(m)
if !s.HardMode || s.TS.localFilter.MatchTxAndUpdate(utilTx) {
hits, err := s.TS.Ingest(m, height)
if err != nil {
log.Printf("Incoming Tx error: %s\n", err.Error())
return
}
if hits == 0 && !s.HardMode {
log.Printf("tx %s had no hits, filter false positive.",
m.TxSha().String())
s.fPositives <- 1 // add one false positive to chan
return
}
log.Printf("tx %s ingested and matches %d utxo/adrs.",
m.TxSha().String(), hits)
}
}
// BUGS:
// - InputIndexes request field is ignored.
func (s *walletServer) SignTransaction(ctx context.Context, req *pb.SignTransactionRequest) (
*pb.SignTransactionResponse, error) {
defer zero.Bytes(req.Passphrase)
var tx wire.MsgTx
err := tx.Deserialize(bytes.NewReader(req.SerializedTransaction))
if err != nil {
return nil, grpc.Errorf(codes.InvalidArgument,
"Bytes do not represent a valid raw transaction: %v", err)
}
lock := make(chan time.Time, 1)
defer func() {
lock <- time.Time{} // send matters, not the value
}()
err = s.wallet.Unlock(req.Passphrase, lock)
if err != nil {
return nil, translateError(err)
}
invalidSigs, err := s.wallet.SignTransaction(&tx, txscript.SigHashAll, nil, nil, nil)
if err != nil {
return nil, translateError(err)
}
invalidInputIndexes := make([]uint32, len(invalidSigs))
for i, e := range invalidSigs {
invalidInputIndexes[i] = e.InputIndex
}
var serializedTransaction bytes.Buffer
serializedTransaction.Grow(tx.SerializeSize())
err = tx.Serialize(&serializedTransaction)
if err != nil {
return nil, translateError(err)
}
resp := &pb.SignTransactionResponse{
Transaction: serializedTransaction.Bytes(),
UnsignedInputIndexes: invalidInputIndexes,
}
return resp, nil
}
// NewTxRecordFromMsgTx creates a new transaction record that may be inserted
// into the store.
func NewTxRecordFromMsgTx(msgTx *wire.MsgTx, received time.Time) (*TxRecord, error) {
buf := bytes.NewBuffer(make([]byte, 0, msgTx.SerializeSize()))
err := msgTx.Serialize(buf)
if err != nil {
str := "failed to serialize transaction"
return nil, storeError(ErrInput, str, err)
}
rec := &TxRecord{
MsgTx: *msgTx,
Received: received,
SerializedTx: buf.Bytes(),
Hash: msgTx.TxSha(),
}
return rec, nil
}
// Ingest puts a tx into the DB atomically. This can result in a
// gain, a loss, or no result. Gain or loss in satoshis is returned.
func (ts *TxStore) Ingest(tx *wire.MsgTx, height int32) (uint32, error) {
var hits uint32
var err error
var nUtxoBytes [][]byte
// tx has been OK'd by SPV; check tx sanity
utilTx := btcutil.NewTx(tx) // convert for validation
// checks basic stuff like there are inputs and ouputs
err = blockchain.CheckTransactionSanity(utilTx)
if err != nil {
return hits, err
}
// note that you can't check signatures; this is SPV.
// 0 conf SPV means pretty much nothing. Anyone can say anything.
spentOPs := make([][]byte, len(tx.TxIn))
// before entering into db, serialize all inputs of the ingested tx
for i, txin := range tx.TxIn {
spentOPs[i], err = outPointToBytes(&txin.PreviousOutPoint)
if err != nil {
return hits, err
}
}
// go through txouts, and then go through addresses to match
// generate PKscripts for all addresses
wPKscripts := make([][]byte, len(ts.Adrs))
aPKscripts := make([][]byte, len(ts.Adrs))
for i, _ := range ts.Adrs {
// iterate through all our addresses
// convert regular address to witness address. (split adrs later)
wa, err := btcutil.NewAddressWitnessPubKeyHash(
ts.Adrs[i].PkhAdr.ScriptAddress(), ts.Param)
if err != nil {
return hits, err
}
wPKscripts[i], err = txscript.PayToAddrScript(wa)
if err != nil {
return hits, err
}
aPKscripts[i], err = txscript.PayToAddrScript(ts.Adrs[i].PkhAdr)
if err != nil {
return hits, err
}
}
cachedSha := tx.TxSha()
// iterate through all outputs of this tx, see if we gain
for i, out := range tx.TxOut {
for j, ascr := range aPKscripts {
// detect p2wpkh
witBool := false
if bytes.Equal(out.PkScript, wPKscripts[j]) {
witBool = true
}
if bytes.Equal(out.PkScript, ascr) || witBool { // new utxo found
var newu Utxo // create new utxo and copy into it
newu.AtHeight = height
newu.KeyIdx = ts.Adrs[j].KeyIdx
newu.Value = out.Value
newu.IsWit = witBool // copy witness version from pkscript
var newop wire.OutPoint
newop.Hash = cachedSha
newop.Index = uint32(i)
newu.Op = newop
b, err := newu.ToBytes()
if err != nil {
return hits, err
}
nUtxoBytes = append(nUtxoBytes, b)
hits++
break // txos can match only 1 script
}
}
}
err = ts.StateDB.Update(func(btx *bolt.Tx) error {
// get all 4 buckets
duf := btx.Bucket(BKTUtxos)
// sta := btx.Bucket(BKTState)
old := btx.Bucket(BKTStxos)
txns := btx.Bucket(BKTTxns)
if duf == nil || old == nil || txns == nil {
return fmt.Errorf("error: db not initialized")
}
// iterate through duffel bag and look for matches
// this makes us lose money, which is regrettable, but we need to know.
for _, nOP := range spentOPs {
v := duf.Get(nOP)
if v != nil {
hits++
// do all this just to figure out value we lost
x := make([]byte, len(nOP)+len(v))
copy(x, nOP)
copy(x[len(nOP):], v)
lostTxo, err := UtxoFromBytes(x)
if err != nil {
return err
}
// after marking for deletion, save stxo to old bucket
var st Stxo // generate spent txo
st.Utxo = lostTxo // assign outpoint
st.SpendHeight = height // spent at height
st.SpendTxid = cachedSha // spent by txid
stxb, err := st.ToBytes() // serialize
if err != nil {
return err
}
err = old.Put(nOP, stxb) // write nOP:v outpoint:stxo bytes
if err != nil {
return err
}
err = duf.Delete(nOP)
if err != nil {
return err
}
}
}
// done losing utxos, next gain utxos
// next add all new utxos to db, this is quick as the work is above
for _, ub := range nUtxoBytes {
err = duf.Put(ub[:36], ub[36:])
if err != nil {
return err
}
}
// if hits is nonzero it's a relevant tx and we should store it
var buf bytes.Buffer
tx.Serialize(&buf)
err = txns.Put(cachedSha.Bytes(), buf.Bytes())
if err != nil {
return err
}
return nil
})
return hits, err
}
// 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")
}