lnd.xprv/lnwallet/wallet.go
2015-12-26 00:05:55 -06:00

772 lines
23 KiB
Go

package lnwallet
import (
"errors"
"fmt"
"math"
"os"
"path/filepath"
"sync"
"sync/atomic"
"li.lan/labs/plasma/shachain"
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcd/chaincfg"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/coinset"
"github.com/btcsuite/btcutil/txsort"
"github.com/btcsuite/btcwallet/chain"
"github.com/btcsuite/btcwallet/waddrmgr"
btcwallet "github.com/btcsuite/btcwallet/wallet"
"github.com/btcsuite/btcwallet/walletdb"
)
const (
msgBufferSize = 100
)
var (
// Error types
ErrInsufficientFunds = errors.New("not enough available outputs to " +
"create funding transaction")
// Which bitcoin network are we using?
ActiveNetParams = &chaincfg.TestNet3Params
)
type FundingType uint16
const (
// Use SegWit, assumes CSV+CLTV
SEGWIT FundingType = iota
// Use SIGHASH_NOINPUT, assumes CSV+CLTV
SIGHASH
// Use CSV without reserve
CSV
// Use CSV with reserve
// Reserve is a permanent amount of funds locked and the capacity.
CSV_RESERVE
// CLTV with reserve.
CLTV_RESERVE
)
// initFundingReserveReq...
type initFundingReserveMsg struct {
fundingAmount btcutil.Amount
fundingType FundingType
minFeeRate btcutil.Amount
nodeID [32]byte
// TODO(roasbeef): optional reserve for CLTV, etc.
// Insuffcient funds etc..
err chan error // Buffered
resp chan *ChannelReservation // Buffered
}
// FundingReserveCancelMsg...
type fundingReserveCancelMsg struct {
pendingFundingID uint64
// Buffered, used for optionally synchronization.
err chan error // Buffered
}
// addContributionMsg...
type addContributionMsg struct {
pendingFundingID uint64
// TODO(roasbeef): Should also carry SPV proofs in we're in SPV mode
contribution *ChannelContribution
err chan error // Buffered
}
// partiallySignedFundingState...
type partiallySignedFundingState struct {
// In order of sorted inputs that are ours. Sorting is done in accordance
// to BIP-69: https://github.com/bitcoin/bips/blob/master/bip-0069.mediawiki.
OurSigs [][]byte
NormalizedTxID wire.ShaHash
}
// addCounterPartySigsMsg...
type addCounterPartySigsMsg struct {
pendingFundingID uint64
// Should be order of sorted inputs that are theirs. Sorting is done in accordance
// to BIP-69: https://github.com/bitcoin/bips/blob/master/bip-0069.mediawiki.
theirFundingSigs [][]byte
// This should be 1/2 of the signatures needed to succesfully spend our
// version of the commitment transaction.
theirCommitmentSig []byte
err chan error // Buffered
}
// FundingCompleteResp...
type finalizedFundingState struct {
FundingTxId wire.ShaHash
NormalizedFundingTXID wire.ShaHash
CompletedFundingTx *btcutil.Tx
}
// LightningWallet....
// responsible for internal global (from the point of view of a user/node)
// channel state. Requests to modify this state come in via messages over
// channels, same with replies.
// Embedded wallet backed by boltdb...
type LightningWallet struct {
// TODO(roasbeef): add btcwallet/chain for notifications initially, then
// abstract out in order to accomodate zeroMQ/BitcoinCore
lmtx sync.RWMutex
DB walletdb.DB
// A wrapper around a namespace within boltdb reserved for ln-based
// wallet meta-data.
channelDB *ChannelDB
wallet *btcwallet.Wallet
rpc *chain.Client
msgChan chan interface{}
// TODO(roasbeef): zombie garbage collection routine to solve
// lost-object/starvation problem/attack.
limboMtx sync.RWMutex
nextFundingID uint64
fundingLimbo map[uint64]*ChannelReservation
started int32
shutdown int32
quit chan struct{}
wg sync.WaitGroup
// TODO(roasbeef): handle wallet lock/unlock
}
// NewLightningWallet...
// TODO(roasbeef): fin...add config
func NewLightningWallet(privWalletPass, pubWalletPass, hdSeed []byte, dataDir string) (*LightningWallet, error) {
// Ensure the wallet exists or create it when the create flag is set.
netDir := networkDir(dataDir, ActiveNetParams)
dbPath := filepath.Join(netDir, walletDbName)
var pubPass []byte
if pubWalletPass == nil {
pubPass = defaultPubPassphrase
} else {
pubPass = pubWalletPass
}
// Wallet has never been created, perform initial set up.
if !fileExists(dbPath) {
// Ensure the data directory for the network exists.
if err := checkCreateDir(netDir); err != nil {
fmt.Fprintln(os.Stderr, err)
return nil, err
}
// Attempt to create a new wallet
if err := createWallet(privWalletPass, pubPass, hdSeed, dbPath); err != nil {
fmt.Fprintln(os.Stderr, err)
return nil, err
}
}
// Wallet has been created and been initialized at this point, open it
// along with all the required DB namepsaces, and the DB itself.
wallet, db, err := openWallet(pubPass, netDir)
if err != nil {
return nil, err
}
// Create a special namespace for our unique payment channel related
// meta-data. Subsequently initializing the channeldb around the
// created namespace.
lnNamespace, err := db.Namespace(lightningNamespaceKey)
if err != nil {
return nil, err
}
// TODO(roasbeef): logging
return &LightningWallet{
DB: db,
wallet: wallet,
channelDB: NewChannelDB(wallet.Manager, lnNamespace),
msgChan: make(chan interface{}, msgBufferSize),
// TODO(roasbeef): make this atomic.Uint32 instead? Which is
// faster, locks or CAS? I'm guessing CAS because assembly:
// * https://golang.org/src/sync/atomic/asm_amd64.s
nextFundingID: 0,
fundingLimbo: make(map[uint64]*ChannelReservation),
quit: make(chan struct{}),
}, nil
}
// Start...
func (l *LightningWallet) Start() error {
// Already started?
if atomic.AddInt32(&l.started, 1) != 1 {
return nil
}
// TODO(roasbeef): config...
rpcc, err := chain.NewClient(ActiveNetParams,
"host", "user", "pass", []byte("cert"), true)
if err != nil {
return err
}
// Start the goroutines in the underlying wallet.
l.rpc = rpcc
l.wallet.Start(rpcc)
l.wg.Add(1)
// TODO(roasbeef): multiple request handlers?
go l.requestHandler()
return nil
}
// Stop...
func (l *LightningWallet) Stop() error {
if atomic.AddInt32(&l.shutdown, 1) != 1 {
return nil
}
l.wallet.Stop()
close(l.quit)
l.wg.Wait()
return nil
}
// requestHandler....
func (l *LightningWallet) requestHandler() {
out:
for {
select {
case m := <-l.msgChan:
switch msg := m.(type) {
case *initFundingReserveMsg:
l.handleFundingReserveRequest(msg)
case *fundingReserveCancelMsg:
l.handleFundingCancelRequest(msg)
case *addContributionMsg:
l.handleContributionMsg(msg)
case *addCounterPartySigsMsg:
l.handleFundingCounterPartySigs(msg)
}
case <-l.quit:
// TODO: do some clean up
break out
}
}
l.wg.Done()
}
// InitChannelReservation...
// fields set after completion:
// * ourInputs
// * ourChange
// * ourMultisigKey
// * ourCommitKey
// * ourDeliveryAddress
// * ourShaChain
func (l *LightningWallet) InitChannelReservation(a btcutil.Amount, t FundingType, theirID [32]byte) (*ChannelReservation, error) {
errChan := make(chan error, 1)
respChan := make(chan *ChannelReservation, 1)
l.msgChan <- &initFundingReserveMsg{
fundingAmount: a,
fundingType: t,
nodeID: theirID,
err: errChan,
resp: respChan,
}
return <-respChan, <-errChan
}
// handleFundingReserveRequest...
func (l *LightningWallet) handleFundingReserveRequest(req *initFundingReserveMsg) {
// Create a limbo and record entry for this newly pending funding request.
l.limboMtx.Lock()
id := l.nextFundingID
reservation := newChannelReservation(req.fundingType, req.fundingAmount, req.minFeeRate, l, id)
l.nextFundingID++
l.fundingLimbo[id] = reservation
l.limboMtx.Unlock()
// Grab the mutex on the ChannelReservation to ensure thead-safety
reservation.Lock()
defer reservation.Unlock()
reservation.partialState.TheirLNID = req.nodeID
ourContribution := reservation.ourContribution
// Find all unlocked unspent outputs with greater than 6 confirmations.
// TODO(roasbeef): make 6 a config paramter?
maxConfs := int32(math.MaxInt32)
unspentOutputs, err := l.wallet.ListUnspent(6, maxConfs, nil)
if err != nil {
req.err <- err
req.resp <- nil
return
}
// Convert the outputs to coins for coin selection below.
coins, err := outputsToCoins(unspentOutputs)
if err != nil {
req.err <- err
req.resp <- nil
return
}
// Peform coin selection over our available, unlocked unspent outputs
// in order to find enough coins to meet the funding amount requirements.
//
// TODO(roasbeef): Should extend coinset with optimal coin selection
// heuristics for our use case.
// TODO(roasbeef): factor in fees..
// TODO(roasbeef): possibly integrate the fee prediction project? if
// results hold up...
// NOTE: this current selection assumes "priority" is still a thing.
selector := &coinset.MaxValueAgeCoinSelector{
MaxInputs: 10,
MinChangeAmount: 10000,
}
selectedCoins, err := selector.CoinSelect(req.fundingAmount, coins)
if err != nil {
req.err <- err
req.resp <- nil
return
}
// Lock the selected coins. These coins are now "reserved", this
// prevents concurrent funding requests from referring to and this
// double-spending the same set of coins.
ourContribution.Inputs = make([]*wire.TxIn, len(selectedCoins.Coins()))
for i, coin := range selectedCoins.Coins() {
txout := wire.NewOutPoint(coin.Hash(), coin.Index())
l.wallet.LockOutpoint(*txout)
// Empty sig script, we'll actually sign if this reservation is
// queued up to be completed (the other side accepts).
outPoint := wire.NewOutPoint(coin.Hash(), coin.Index())
ourContribution.Inputs[i] = wire.NewTxIn(outPoint, nil)
}
// Create some possibly neccessary change outputs.
selectedTotalValue := coinset.NewCoinSet(selectedCoins.Coins()).TotalValue()
if selectedTotalValue > req.fundingAmount {
ourContribution.ChangeOutputs = make([]*wire.TxOut, 1)
// Change is necessary. Query for an available change address to
// send the remainder to.
changeAmount := selectedTotalValue - req.fundingAmount
addrs, err := l.wallet.Manager.NextInternalAddresses(waddrmgr.DefaultAccountNum, 1)
if err != nil {
req.err <- err
req.resp <- nil
return
}
changeAddrScript, err := txscript.PayToAddrScript(addrs[0].Address())
if err != nil {
req.err <- err
req.resp <- nil
return
}
// TODO(roasbeef): re-enable after tests are connected to real node.
// * or the change to btcwallet is made to reverse the dependancy
// between chain-client and wallet.
//changeAddr, err := l.wallet.NewChangeAddress(waddrmgr.DefaultAccountNum)
ourContribution.ChangeOutputs[0] = wire.NewTxOut(int64(changeAmount),
changeAddrScript)
}
// TODO(roasbeef): re-calculate fees here to minFeePerKB, may need more inputs
// TODO(roasbeef): use wallet.CurrentAddress() here instead? Solves the
// problem of 'wasted' unused addrtesses.
// Grab two fresh keys from out HD chain, one will be used for the
// multi-sig funding transaction, and the other for the commitment
// transaction.
multiSigKey, err := l.getNextRawKey()
if err != nil {
req.err <- err
req.resp <- nil
return
}
commitKey, err := l.getNextRawKey()
if err != nil {
req.err <- err
req.resp <- nil
return
}
reservation.partialState.MultiSigKey = multiSigKey
ourContribution.MultiSigKey = multiSigKey.PubKey()
reservation.partialState.OurCommitKey = commitKey
ourContribution.CommitKey = commitKey.PubKey()
// Generate a fresh address to be used in the case of a cooperative
// channel close.
// TODO(roasbeef): same here
//deliveryAddress, err := l.wallet.NewChangeAddress(waddrmgr.DefaultAccountNum)
addrs, err := l.wallet.Manager.NextInternalAddresses(waddrmgr.DefaultAccountNum, 1)
if err != nil {
// TODO(roasbeef): make into func sendErorr()
req.err <- err
req.resp <- nil
return
}
reservation.partialState.OurDeliveryAddress = addrs[0].Address()
ourContribution.DeliveryAddress = addrs[0].Address()
// Create a new shaChain for verifiable transaction revocations.
shaChain, err := shachain.NewFromSeed(nil, 0)
if err != nil {
req.err <- err
req.resp <- nil
return
}
reservation.partialState.OurShaChain = shaChain
ourContribution.RevocationHash = shaChain.CurrentRevocationHash()
// Funding reservation request succesfully handled. The funding inputs
// will be marked as unavailable until the reservation is either
// completed, or cancecled.
req.resp <- reservation
req.err <- nil
}
// handleFundingReserveCancel...
func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMsg) {
// TODO(roasbeef): holding lock too long
// RLOCK?
l.limboMtx.Lock()
defer l.limboMtx.Unlock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
if !ok {
// TODO(roasbeef): make new error, "unkown funding state" or something
req.err <- fmt.Errorf("attempted to cancel non-existant funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thead-safety
pendingReservation.Lock()
defer pendingReservation.Unlock()
// Mark all previously locked outpoints as usuable for future funding
// requests.
for _, unusedInput := range pendingReservation.ourContribution.Inputs {
l.wallet.UnlockOutpoint(unusedInput.PreviousOutPoint)
}
// TODO(roasbeef): is it even worth it to keep track of unsed keys?
// TODO(roasbeef): Is it possible to mark the unused change also as
// available?
delete(l.fundingLimbo, req.pendingFundingID)
req.err <- nil
}
// handleFundingCounterPartyFunds...
func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
l.limboMtx.Lock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
l.limboMtx.Unlock()
if !ok {
req.err <- fmt.Errorf("attempted to update non-existant funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thead-safety
pendingReservation.Lock()
defer pendingReservation.Unlock()
// Create a blank, fresh transaction. Soon to be a complete funding
// transaction which will allow opening a lightning channel.
pendingReservation.partialState.FundingTx = wire.NewMsgTx()
fundingTx := pendingReservation.partialState.FundingTx
pendingReservation.theirContribution = req.contribution
theirContribution := req.contribution
ourContribution := pendingReservation.ourContribution
// First, add all multi-party inputs to the transaction
// TODO(roasbeef); handle case that tx doesn't exist, fake input
// TODO(roasbeef): validate SPV proof from other side if in SPV mode.
// * actually, pure SPV would need fraud proofs right? must prove input
// is unspent
// * or, something like getutxo?
for _, ourInput := range ourContribution.Inputs {
fundingTx.AddTxIn(ourInput)
}
for _, theirInput := range theirContribution.Inputs {
fundingTx.AddTxIn(theirInput)
}
// Next, add all multi-party outputs to the transaction. This includes
// change outputs for both side.
for _, ourChangeOutput := range ourContribution.ChangeOutputs {
fundingTx.AddTxOut(ourChangeOutput)
}
for _, theirChangeOutput := range theirContribution.ChangeOutputs {
fundingTx.AddTxOut(theirChangeOutput)
}
// Finally, add the 2-of-2 multi-sig output which will set up the lightning
// channel.
ourKey := pendingReservation.partialState.MultiSigKey
theirKey := theirContribution.MultiSigKey
channelCapacity := int64(pendingReservation.partialState.Capacity)
redeemScript, multiSigOut, err := fundMultiSigOut(ourKey.PubKey().SerializeCompressed(),
theirKey.SerializeCompressed(), channelCapacity)
if err != nil {
req.err <- err
return
}
// TODO(roasbeef): do Manager.ImportScript(..) here, gives us a
// ManagedScriptAddress to play around with if we need it.
pendingReservation.partialState.FundingRedeemScript = redeemScript
fundingTx.AddTxOut(multiSigOut)
// Sort the transaction. Since both side agree to a cannonical
// ordering, by sorting we no longer need to send the entire
// transaction. Only signatures will be exchanged.
txsort.InPlaceSort(pendingReservation.partialState.FundingTx)
// Now that the transaction has been cannonically sorted, compute the
// normalized transation ID before we attach our signatures.
// TODO(roasbeef): this isn't the normalized txid, this isn't recursive...
// pendingReservation.normalizedTxID = pendingReservation.fundingTx.TxSha()
// Now, sign all inputs that are ours, collecting the signatures in
// order of the inputs.
pendingReservation.ourFundingSigs = make([][]byte, 0, len(ourContribution.Inputs))
for i, txIn := range fundingTx.TxIn {
// Does the wallet know about the txin?
txDetail, _ := l.wallet.TxStore.TxDetails(&txIn.PreviousOutPoint.Hash)
if txDetail == nil {
continue
}
// Is this our txin? TODO(roasbeef): assumes all inputs are P2PKH...
prevIndex := txIn.PreviousOutPoint.Index
prevOut := txDetail.TxRecord.MsgTx.TxOut[prevIndex]
_, addrs, _, _ := txscript.ExtractPkScriptAddrs(prevOut.PkScript, ActiveNetParams)
apkh, ok := addrs[0].(*btcutil.AddressPubKeyHash)
if !ok {
req.err <- btcwallet.ErrUnsupportedTransactionType
return
}
ai, err := l.wallet.Manager.Address(apkh)
if err != nil {
req.err <- fmt.Errorf("cannot get address info: %v", err)
return
}
pka := ai.(waddrmgr.ManagedPubKeyAddress)
privkey, err := pka.PrivKey()
if err != nil {
req.err <- fmt.Errorf("cannot get private key: %v", err)
return
}
sigscript, err := txscript.SignatureScript(pendingReservation.partialState.FundingTx, i,
prevOut.PkScript, txscript.SigHashAll, privkey,
ai.Compressed())
if err != nil {
req.err <- fmt.Errorf("cannot create sigscript: %s", err)
return
}
fundingTx.TxIn[i].SignatureScript = sigscript
pendingReservation.ourFundingSigs = append(pendingReservation.ourFundingSigs, sigscript)
}
// Initialize an empty sha-chain for them, tracking the current pending
// revocation hash (we don't yet know the pre-image so we can't add it
// to the chain).
pendingReservation.partialState.TheirShaChain = shachain.New()
pendingReservation.partialState.TheirCurrentRevocation = theirContribution.RevocationHash
// Grab the hash of the current pre-image in our chain, this is needed
// for out commitment tx.
// TODO(roasbeef): grab partial state above to avoid long attr chain
ourCurrentRevokeHash := pendingReservation.partialState.OurShaChain.CurrentRevocationHash()
ourContribution.RevocationHash = ourCurrentRevokeHash
// Create the txIn to our commitment transaction. In the process, we
// need to locate the index of the multi-sig output on the funding tx
// since the outputs are cannonically sorted.
fundingNTxid := fundingTx.TxSha() // NOTE: assumes testnet-L
_, multiSigIndex := findScriptOutputIndex(fundingTx, multiSigOut.PkScript)
fundingTxIn := wire.NewTxIn(wire.NewOutPoint(&fundingNTxid, multiSigIndex), nil)
// With the funding tx complete, create both commitment transactions.
initialBalance := ourContribution.FundingAmount
pendingReservation.fundingLockTime = theirContribution.CsvDelay
ourCommitKey := ourContribution.CommitKey
theirCommitKey := theirContribution.CommitKey
ourCommitTx, err := createCommitTx(fundingTxIn, ourCommitKey, theirCommitKey,
ourCurrentRevokeHash, theirContribution.CsvDelay, initialBalance)
if err != nil {
req.err <- err
return
}
theirCommitTx, err := createCommitTx(fundingTxIn, theirCommitKey, ourCommitKey,
theirContribution.RevocationHash, theirContribution.CsvDelay, initialBalance)
if err != nil {
req.err <- err
return
}
pendingReservation.partialState.CsvDelay = theirContribution.CsvDelay
pendingReservation.partialState.TheirDeliveryAddress = theirContribution.DeliveryAddress
pendingReservation.partialState.ChanID = fundingNTxid
pendingReservation.partialState.TheirCommitKey = theirCommitKey
pendingReservation.partialState.TheirCommitTx = theirCommitTx
pendingReservation.partialState.OurCommitTx = ourCommitTx
// Generate a signature for their version of the initial commitment
// transaction.
sigTheirCommit, err := txscript.RawTxInSignature(theirCommitTx, 0, multiSigOut.PkScript,
txscript.SigHashAll, ourKey)
if err != nil {
req.err <- err
return
}
pendingReservation.ourCommitmentSig = sigTheirCommit
req.err <- nil
}
// handleFundingCounterPartySigs...
func (l *LightningWallet) handleFundingCounterPartySigs(msg *addCounterPartySigsMsg) {
l.limboMtx.RLock()
pendingReservation, ok := l.fundingLimbo[msg.pendingFundingID]
l.limboMtx.RUnlock()
if !ok {
msg.err <- fmt.Errorf("attempted to update non-existant funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thead-safety
pendingReservation.Lock()
defer pendingReservation.Unlock()
// Now we can complete the funding transaction by adding their
// signatures to their inputs.
pendingReservation.theirFundingSigs = msg.theirFundingSigs
fundingTx := pendingReservation.partialState.FundingTx
for i, txin := range fundingTx.TxIn {
if txin.SignatureScript == nil {
txin.SignatureScript = pendingReservation.theirFundingSigs[i]
/*// Fetch the alleged previous output along with the
// pkscript referenced by this input.
prevOut := txin.PreviousOutPoint
output, err := l.rpc.GetTxOut(&prevOut.Hash, prevOut.Index, false)
if err != nil {
// TODO(roasbeef): do this at the start to avoid wasting out time?
// 8 or a set of nodes "we" run with exposed unauthenticated RPC?
msg.err <- err
return
}
pkscript, err := hex.DecodeString(output.ScriptPubKey.Hex)
if err != nil {
msg.err <- err
return
}
// Ensure that the signature is valid.
vm, err := txscript.NewEngine(pkscript,
fundingTx, i, txscript.StandardVerifyFlags, nil)
if err != nil {
// TODO(roasbeef): cancel at this stage if invalid sigs?
msg.err <- fmt.Errorf("cannot create script engine: %s", err)
return
}
if err = vm.Execute(); err != nil {
msg.err <- fmt.Errorf("cannot validate transaction: %s", err)
return
}*/
}
}
// At this point, wen calso record and verify their isgnature for our
// commitment transaction.
pendingReservation.partialState.TheirCommitSig = msg.theirCommitmentSig
// TODO(roasbeef): verify
//commitSig := msg.theirCommitmentSig
// Funding complete, this entry can be removed from limbo.
l.limboMtx.Lock()
delete(l.fundingLimbo, pendingReservation.reservationID)
// TODO(roasbeef): unlock outputs here, Store.InsertTx will handle marking
// input in unconfirmed tx, so future coin selects don't pick it up
// * also record location of change address so can use AddCredit
l.limboMtx.Unlock()
// Add the complete funding transaction to the DB, in it's open bucket
// which will be used for the lifetime of this channel.
err := l.channelDB.PutOpenChannel(pendingReservation.partialState)
// TODO(roasbeef): broadcast now?
// * create goroutine, listens on blockconnected+blockdisconnected channels
// * after six blocks, then will create an LightningChannel struct and
// send over reservation.
// * will need a multi-plexer to fan out, to listen on ListenConnectedBlocks
// * should prob be a separate struct/modele
// * use NotifySpent in order to catch non-cooperative spends of revoked
// * NotifySpent(outpoints []*wire.OutPoint)
// commitment txns. Hmm using p2sh or bare multi-sig?
// * record partialState.CreationTime once tx is 'open'
msg.err <- err
}
// nextMultiSigKey...
// TODO(roasbeef): on shutdown, write state of pending keys, then read back?
func (l *LightningWallet) getNextRawKey() (*btcec.PrivateKey, error) {
l.lmtx.Lock()
defer l.lmtx.Unlock()
nextAddr, err := l.wallet.Manager.NextExternalAddresses(waddrmgr.DefaultAccountNum, 1)
if err != nil {
return nil, err
}
pkAddr := nextAddr[0].(waddrmgr.ManagedPubKeyAddress)
return pkAddr.PrivKey()
}