lnd.xprv/lnwallet/wallet.go

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package lnwallet
import (
"bytes"
"crypto/sha256"
"errors"
"fmt"
"math"
"net"
"sync"
"sync/atomic"
"github.com/btcsuite/btcd/blockchain"
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/txsort"
"github.com/davecgh/go-spew/spew"
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"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/keychain"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/shachain"
)
const (
// The size of the buffered queue of requests to the wallet from the
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// outside word.
msgBufferSize = 100
)
// ErrInsufficientFunds is a type matching the error interface which is
// returned when coin selection for a new funding transaction fails to due
// having an insufficient amount of confirmed funds.
type ErrInsufficientFunds struct {
amountAvailable btcutil.Amount
amountSelected btcutil.Amount
}
func (e *ErrInsufficientFunds) Error() string {
return fmt.Sprintf("not enough witness outputs to create funding transaction,"+
" need %v only have %v available", e.amountAvailable,
e.amountSelected)
}
// InitFundingReserveMsg is the first message sent to initiate the workflow
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// required to open a payment channel with a remote peer. The initial required
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// parameters are configurable across channels. These parameters are to be
// chosen depending on the fee climate within the network, and time value of
// funds to be locked up within the channel. Upon success a ChannelReservation
// will be created in order to track the lifetime of this pending channel.
// Outputs selected will be 'locked', making them unavailable, for any other
// pending reservations. Therefore, all channels in reservation limbo will be
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// periodically timed out after an idle period in order to avoid "exhaustion"
// attacks.
type InitFundingReserveMsg struct {
// ChainHash denotes that chain to be used to ultimately open the
// target channel.
ChainHash *chainhash.Hash
// NodeID is the ID of the remote node we would like to open a channel
// with.
NodeID *btcec.PublicKey
// NodeAddr is the address port that we used to either establish or
// accept the connection which led to the negotiation of this funding
// workflow.
NodeAddr net.Addr
// SubtractFees should be set if we intend to spend exactly
// LocalFundingAmt when opening the channel, subtracting the fees from
// the funding output. This can be used for instance to use all our
// remaining funds to open the channel, since it will take fees into
// account.
SubtractFees bool
// LocalFundingAmt is the amount of funds requested from us for this
// channel.
LocalFundingAmt btcutil.Amount
// RemoteFundingAmnt is the amount of funds the remote will contribute
// to this channel.
RemoteFundingAmt btcutil.Amount
// CommitFeePerKw is the starting accepted satoshis/Kw fee for the set
// of initial commitment transactions. In order to ensure timely
// confirmation, it is recommended that this fee should be generous,
// paying some multiple of the accepted base fee rate of the network.
CommitFeePerKw SatPerKWeight
// FundingFeePerKw is the fee rate in sat/kw to use for the initial
// funding transaction.
FundingFeePerKw SatPerKWeight
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// PushMSat is the number of milli-satoshis that should be pushed over
// the responder as part of the initial channel creation.
PushMSat lnwire.MilliSatoshi
// Flags are the channel flags specified by the initiator in the
// open_channel message.
Flags lnwire.FundingFlag
// MinConfs indicates the minimum number of confirmations that each
// output selected to fund the channel should satisfy.
MinConfs int32
// Tweakless indicates if the channel should use the new tweakless
// commitment format or not.
Tweakless bool
// err is a channel in which all errors will be sent across. Will be
// nil if this initial set is successful.
//
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// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error
// resp is channel in which a ChannelReservation with our contributions
// filled in will be sent across this channel in the case of a
// successfully reservation initiation. In the case of an error, this
// will read a nil pointer.
//
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// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
resp chan *ChannelReservation
}
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// fundingReserveCancelMsg is a message reserved for cancelling an existing
// channel reservation identified by its reservation ID. Cancelling a reservation
// frees its locked outputs up, for inclusion within further reservations.
type fundingReserveCancelMsg struct {
pendingFundingID uint64
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// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error // Buffered
}
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// addContributionMsg represents a message executing the second phase of the
// channel reservation workflow. This message carries the counterparty's
// "contribution" to the payment channel. In the case that this message is
// processed without generating any errors, then channel reservation will then
// be able to construct the funding tx, both commitment transactions, and
// finally generate signatures for all our inputs to the funding transaction,
// and for the remote node's version of the commitment transaction.
type addContributionMsg struct {
pendingFundingID uint64
// TODO(roasbeef): Should also carry SPV proofs in we're in SPV mode
contribution *ChannelContribution
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// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error
}
// addSingleContributionMsg represents a message executing the second phase of
// a single funder channel reservation workflow. This messages carries the
// counterparty's "contribution" to the payment channel. As this message is
// sent when on the responding side to a single funder workflow, no further
// action apart from storing the provided contribution is carried out.
type addSingleContributionMsg struct {
pendingFundingID uint64
contribution *ChannelContribution
// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error
}
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// addCounterPartySigsMsg represents the final message required to complete,
// and 'open' a payment channel. This message carries the counterparty's
// signatures for each of their inputs to the funding transaction, and also a
// signature allowing us to spend our version of the commitment transaction.
// If we're able to verify all the signatures are valid, the funding transaction
// will be broadcast to the network. After the funding transaction gains a
// configurable number of confirmations, the channel is officially considered
// 'open'.
type addCounterPartySigsMsg struct {
pendingFundingID uint64
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// 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.
theirFundingInputScripts []*input.Script
// This should be 1/2 of the signatures needed to successfully spend our
// version of the commitment transaction.
theirCommitmentSig []byte
// This channel is used to return the completed channel after the wallet
// has completed all of its stages in the funding process.
completeChan chan *channeldb.OpenChannel
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// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error
}
// addSingleFunderSigsMsg represents the next-to-last message required to
// complete a single-funder channel workflow. Once the initiator is able to
// construct the funding transaction, they send both the outpoint and a
// signature for our version of the commitment transaction. Once this message
// is processed we (the responder) are able to construct both commitment
// transactions, signing the remote party's version.
type addSingleFunderSigsMsg struct {
pendingFundingID uint64
// fundingOutpoint is the outpoint of the completed funding
// transaction as assembled by the workflow initiator.
fundingOutpoint *wire.OutPoint
// theirCommitmentSig are the 1/2 of the signatures needed to
// successfully spend our version of the commitment transaction.
theirCommitmentSig []byte
// This channel is used to return the completed channel after the wallet
// has completed all of its stages in the funding process.
completeChan chan *channeldb.OpenChannel
// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
err chan error
}
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// LightningWallet is a domain specific, yet general Bitcoin wallet capable of
// executing workflow required to interact with the Lightning Network. It is
// domain specific in the sense that it understands all the fancy scripts used
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// within the Lightning Network, channel lifetimes, etc. However, it embeds a
// general purpose Bitcoin wallet within it. Therefore, it is also able to
// serve as a regular Bitcoin wallet which uses HD keys. The wallet is highly
// concurrent internally. All communication, and requests towards the wallet
// are dispatched as messages over channels, ensuring thread safety across all
// operations. Interaction has been designed independent of any peer-to-peer
// communication protocol, allowing the wallet to be self-contained and
// embeddable within future projects interacting with the Lightning Network.
//
// NOTE: At the moment the wallet requires a btcd full node, as it's dependent
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// on btcd's websockets notifications as event triggers during the lifetime of a
// channel. However, once the chainntnfs package is complete, the wallet will
// be compatible with multiple RPC/notification services such as Electrum,
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// Bitcoin Core + ZeroMQ, etc. Eventually, the wallet won't require a full-node
// at all, as SPV support is integrated into btcwallet.
type LightningWallet struct {
started int32 // To be used atomically.
shutdown int32 // To be used atomically.
nextFundingID uint64 // To be used atomically.
// Cfg is the configuration struct that will be used by the wallet to
// access the necessary interfaces and default it needs to carry on its
// duties.
Cfg Config
// WalletController is the core wallet, all non Lightning Network
// specific interaction is proxied to the internal wallet.
WalletController
// SecretKeyRing is the interface we'll use to derive any keys related
// to our purpose within the network including: multi-sig keys, node
// keys, revocation keys, etc.
keychain.SecretKeyRing
// This mutex MUST be held when performing coin selection in order to
// avoid inadvertently creating multiple funding transaction which
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// double spend inputs across each other.
coinSelectMtx sync.RWMutex
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// All messages to the wallet are to be sent across this channel.
msgChan chan interface{}
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// Incomplete payment channels are stored in the map below. An intent
// to create a payment channel is tracked as a "reservation" within
// limbo. Once the final signatures have been exchanged, a reservation
// is removed from limbo. Each reservation is tracked by a unique
// monotonically integer. All requests concerning the channel MUST
// carry a valid, active funding ID.
fundingLimbo map[uint64]*ChannelReservation
limboMtx sync.RWMutex
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// lockedOutPoints is a set of the currently locked outpoint. This
// information is kept in order to provide an easy way to unlock all
// the currently locked outpoints.
lockedOutPoints map[wire.OutPoint]struct{}
quit chan struct{}
wg sync.WaitGroup
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// TODO(roasbeef): handle wallet lock/unlock
}
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// NewLightningWallet creates/opens and initializes a LightningWallet instance.
// If the wallet has never been created (according to the passed dataDir), first-time
// setup is executed.
func NewLightningWallet(Cfg Config) (*LightningWallet, error) {
return &LightningWallet{
Cfg: Cfg,
SecretKeyRing: Cfg.SecretKeyRing,
WalletController: Cfg.WalletController,
msgChan: make(chan interface{}, msgBufferSize),
nextFundingID: 0,
fundingLimbo: make(map[uint64]*ChannelReservation),
lockedOutPoints: make(map[wire.OutPoint]struct{}),
quit: make(chan struct{}),
}, nil
}
// Startup establishes a connection to the RPC source, and spins up all
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// goroutines required to handle incoming messages.
func (l *LightningWallet) Startup() error {
// Already started?
if atomic.AddInt32(&l.started, 1) != 1 {
return nil
}
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// Start the underlying wallet controller.
if err := l.Start(); err != nil {
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return err
}
l.wg.Add(1)
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// TODO(roasbeef): multiple request handlers?
go l.requestHandler()
return nil
}
// Shutdown gracefully stops the wallet, and all active goroutines.
func (l *LightningWallet) Shutdown() error {
if atomic.AddInt32(&l.shutdown, 1) != 1 {
return nil
}
// Signal the underlying wallet controller to shutdown, waiting until
// all active goroutines have been shutdown.
if err := l.Stop(); err != nil {
return err
}
close(l.quit)
l.wg.Wait()
return nil
}
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// LockedOutpoints returns a list of all currently locked outpoint.
func (l *LightningWallet) LockedOutpoints() []*wire.OutPoint {
outPoints := make([]*wire.OutPoint, 0, len(l.lockedOutPoints))
for outPoint := range l.lockedOutPoints {
outPoints = append(outPoints, &outPoint)
}
return outPoints
}
// ResetReservations reset the volatile wallet state which tracks all currently
// active reservations.
func (l *LightningWallet) ResetReservations() {
l.nextFundingID = 0
l.fundingLimbo = make(map[uint64]*ChannelReservation)
for outpoint := range l.lockedOutPoints {
l.UnlockOutpoint(outpoint)
}
l.lockedOutPoints = make(map[wire.OutPoint]struct{})
}
// ActiveReservations returns a slice of all the currently active
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// (non-canceled) reservations.
func (l *LightningWallet) ActiveReservations() []*ChannelReservation {
reservations := make([]*ChannelReservation, 0, len(l.fundingLimbo))
for _, reservation := range l.fundingLimbo {
reservations = append(reservations, reservation)
}
return reservations
}
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// requestHandler is the primary goroutine(s) responsible for handling, and
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// dispatching replies to all messages.
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 *addSingleContributionMsg:
l.handleSingleContribution(msg)
case *addContributionMsg:
l.handleContributionMsg(msg)
case *addSingleFunderSigsMsg:
l.handleSingleFunderSigs(msg)
case *addCounterPartySigsMsg:
l.handleFundingCounterPartySigs(msg)
}
case <-l.quit:
// TODO: do some clean up
break out
}
}
l.wg.Done()
}
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// InitChannelReservation kicks off the 3-step workflow required to successfully
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// open a payment channel with a remote node. As part of the funding
// reservation, the inputs selected for the funding transaction are 'locked'.
// This ensures that multiple channel reservations aren't double spending the
// same inputs in the funding transaction. If reservation initialization is
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// successful, a ChannelReservation containing our completed contribution is
// returned. Our contribution contains all the items necessary to allow the
// counterparty to build the funding transaction, and both versions of the
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// commitment transaction. Otherwise, an error occurred and a nil pointer along
// with an error are returned.
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//
// Once a ChannelReservation has been obtained, two additional steps must be
// processed before a payment channel can be considered 'open'. The second step
// validates, and processes the counterparty's channel contribution. The third,
// and final step verifies all signatures for the inputs of the funding
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// transaction, and that the signature we record for our version of the
// commitment transaction is valid.
func (l *LightningWallet) InitChannelReservation(
req *InitFundingReserveMsg) (*ChannelReservation, error) {
req.resp = make(chan *ChannelReservation, 1)
req.err = make(chan error, 1)
select {
case l.msgChan <- req:
case <-l.quit:
return nil, errors.New("wallet shutting down")
}
return <-req.resp, <-req.err
}
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// handleFundingReserveRequest processes a message intending to create, and
// validate a funding reservation request.
func (l *LightningWallet) handleFundingReserveRequest(req *InitFundingReserveMsg) {
// It isn't possible to create a channel with zero funds committed.
if req.LocalFundingAmt+req.RemoteFundingAmt == 0 {
err := ErrZeroCapacity()
req.err <- err
req.resp <- nil
return
}
// If the funding request is for a different chain than the one the
// wallet is aware of, then we'll reject the request.
if !bytes.Equal(l.Cfg.NetParams.GenesisHash[:], req.ChainHash[:]) {
err := ErrChainMismatch(
l.Cfg.NetParams.GenesisHash, req.ChainHash,
)
req.err <- err
req.resp <- nil
return
}
localFundingAmt := req.LocalFundingAmt
var (
selected *coinSelection
err error
)
// If we're on the receiving end of a single funder channel then we
// don't need to perform any coin selection, and the remote contributes
// all funds. Otherwise, attempt to obtain enough coins to meet the
// required funding amount.
if req.LocalFundingAmt != 0 {
// Coin selection is done on the basis of sat/kw, so we'll use
// the fee rate passed in to perform coin selection.
var err error
selected, err = l.selectCoinsAndChange(
req.FundingFeePerKw, req.LocalFundingAmt, req.MinConfs,
req.SubtractFees,
)
if err != nil {
req.err <- err
req.resp <- nil
return
}
localFundingAmt = selected.fundingAmt
}
// The total channel capacity will be the size of the funding output we
// created plus the remote contribution.
capacity := localFundingAmt + req.RemoteFundingAmt
id := atomic.AddUint64(&l.nextFundingID, 1)
reservation, err := NewChannelReservation(
capacity, localFundingAmt, req.CommitFeePerKw, l, id,
req.PushMSat, l.Cfg.NetParams.GenesisHash, req.Flags,
req.Tweakless,
)
if err != nil {
selected.unlockCoins()
req.err <- err
req.resp <- nil
return
}
err = l.initOurContribution(
reservation, selected, req.NodeAddr, req.NodeID,
)
if err != nil {
selected.unlockCoins()
req.err <- err
req.resp <- nil
return
}
// Create a limbo and record entry for this newly pending funding
// request.
l.limboMtx.Lock()
l.fundingLimbo[id] = reservation
l.limboMtx.Unlock()
// Funding reservation request successfully handled. The funding inputs
// will be marked as unavailable until the reservation is either
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// completed, or canceled.
req.resp <- reservation
req.err <- nil
}
// initOurContribution initializes the given ChannelReservation with our coins
// and change reserved for the channel, and derives the keys to use for this
// channel.
func (l *LightningWallet) initOurContribution(reservation *ChannelReservation,
selected *coinSelection, nodeAddr net.Addr, nodeID *btcec.PublicKey) error {
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// Grab the mutex on the ChannelReservation to ensure thread-safety
reservation.Lock()
defer reservation.Unlock()
if selected != nil {
reservation.ourContribution.Inputs = selected.coins
reservation.ourContribution.ChangeOutputs = selected.change
}
reservation.nodeAddr = nodeAddr
reservation.partialState.IdentityPub = nodeID
// Next, we'll grab a series of keys from the wallet which will be used
// for the duration of the channel. The keys include: our multi-sig
// key, the base revocation key, the base htlc key,the base payment
// key, and the delayed payment key.
//
// TODO(roasbeef): "salt" each key as well?
var err error
reservation.ourContribution.MultiSigKey, err = l.DeriveNextKey(
keychain.KeyFamilyMultiSig,
)
if err != nil {
return err
}
reservation.ourContribution.RevocationBasePoint, err = l.DeriveNextKey(
keychain.KeyFamilyRevocationBase,
)
if err != nil {
return err
}
reservation.ourContribution.HtlcBasePoint, err = l.DeriveNextKey(
keychain.KeyFamilyHtlcBase,
)
if err != nil {
return err
}
reservation.ourContribution.PaymentBasePoint, err = l.DeriveNextKey(
keychain.KeyFamilyPaymentBase,
)
if err != nil {
return err
}
reservation.ourContribution.DelayBasePoint, err = l.DeriveNextKey(
keychain.KeyFamilyDelayBase,
)
if err != nil {
return err
}
// With the above keys created, we'll also need to initialization our
// initial revocation tree state.
nextRevocationKeyDesc, err := l.DeriveNextKey(
keychain.KeyFamilyRevocationRoot,
)
if err != nil {
return err
}
revocationRoot, err := l.DerivePrivKey(nextRevocationKeyDesc)
if err != nil {
return err
}
// Once we have the root, we can then generate our shachain producer
// and from that generate the per-commitment point.
revRoot, err := chainhash.NewHash(revocationRoot.Serialize())
if err != nil {
return err
}
producer := shachain.NewRevocationProducer(*revRoot)
firstPreimage, err := producer.AtIndex(0)
if err != nil {
return err
}
reservation.ourContribution.FirstCommitmentPoint = input.ComputeCommitmentPoint(
firstPreimage[:],
)
reservation.partialState.RevocationProducer = producer
reservation.ourContribution.ChannelConstraints = l.Cfg.DefaultConstraints
return nil
}
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// handleFundingReserveCancel cancels an existing channel reservation. As part
// of the cancellation, outputs previously selected as inputs for the funding
// transaction via coin selection are freed allowing future reservations to
// include them.
func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMsg) {
// TODO(roasbeef): holding lock too long
l.limboMtx.Lock()
defer l.limboMtx.Unlock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
if !ok {
// TODO(roasbeef): make new error, "unknown funding state" or something
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req.err <- fmt.Errorf("attempted to cancel non-existent funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thread-safety
pendingReservation.Lock()
defer pendingReservation.Unlock()
// Mark all previously locked outpoints as useable for future funding
// requests.
for _, unusedInput := range pendingReservation.ourContribution.Inputs {
delete(l.lockedOutPoints, unusedInput.PreviousOutPoint)
l.UnlockOutpoint(unusedInput.PreviousOutPoint)
}
// TODO(roasbeef): is it even worth it to keep track of unused keys?
// TODO(roasbeef): Is it possible to mark the unused change also as
// available?
delete(l.fundingLimbo, req.pendingFundingID)
req.err <- nil
}
// CreateCommitmentTxns is a helper function that creates the initial
// commitment transaction for both parties. This function is used during the
// initial funding workflow as both sides must generate a signature for the
// remote party's commitment transaction, and verify the signature for their
// version of the commitment transaction.
func CreateCommitmentTxns(localBalance, remoteBalance btcutil.Amount,
ourChanCfg, theirChanCfg *channeldb.ChannelConfig,
localCommitPoint, remoteCommitPoint *btcec.PublicKey,
fundingTxIn wire.TxIn,
tweaklessCommit bool) (*wire.MsgTx, *wire.MsgTx, error) {
localCommitmentKeys := DeriveCommitmentKeys(
localCommitPoint, true, tweaklessCommit, ourChanCfg,
theirChanCfg,
)
remoteCommitmentKeys := DeriveCommitmentKeys(
remoteCommitPoint, false, tweaklessCommit, ourChanCfg,
theirChanCfg,
)
ourCommitTx, err := CreateCommitTx(fundingTxIn, localCommitmentKeys,
uint32(ourChanCfg.CsvDelay), localBalance, remoteBalance,
ourChanCfg.DustLimit)
if err != nil {
return nil, nil, err
}
otxn := btcutil.NewTx(ourCommitTx)
if err := blockchain.CheckTransactionSanity(otxn); err != nil {
return nil, nil, err
}
theirCommitTx, err := CreateCommitTx(fundingTxIn, remoteCommitmentKeys,
uint32(theirChanCfg.CsvDelay), remoteBalance, localBalance,
theirChanCfg.DustLimit)
if err != nil {
return nil, nil, err
}
ttxn := btcutil.NewTx(theirCommitTx)
if err := blockchain.CheckTransactionSanity(ttxn); err != nil {
return nil, nil, err
}
return ourCommitTx, theirCommitTx, nil
}
// handleContributionMsg processes the second workflow step for the lifetime of
// a channel reservation. Upon completion, the reservation will carry a
// completed funding transaction (minus the counterparty's input signatures),
// both versions of the commitment transaction, and our signature for their
// version of the commitment transaction.
func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
l.limboMtx.Lock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
l.limboMtx.Unlock()
if !ok {
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req.err <- fmt.Errorf("attempted to update non-existent funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thread-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.fundingTx = wire.NewMsgTx(1)
fundingTx := pendingReservation.fundingTx
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// Some temporary variables to cut down on the resolution verbosity.
pendingReservation.theirContribution = req.contribution
theirContribution := req.contribution
ourContribution := pendingReservation.ourContribution
// Add all multi-party inputs and outputs to the transaction.
for _, ourInput := range ourContribution.Inputs {
fundingTx.AddTxIn(ourInput)
}
for _, theirInput := range theirContribution.Inputs {
fundingTx.AddTxIn(theirInput)
}
for _, ourChangeOutput := range ourContribution.ChangeOutputs {
fundingTx.AddTxOut(ourChangeOutput)
}
for _, theirChangeOutput := range theirContribution.ChangeOutputs {
fundingTx.AddTxOut(theirChangeOutput)
}
ourKey := pendingReservation.ourContribution.MultiSigKey
theirKey := theirContribution.MultiSigKey
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// Finally, add the 2-of-2 multi-sig output which will set up the lightning
// channel.
channelCapacity := int64(pendingReservation.partialState.Capacity)
witnessScript, multiSigOut, err := input.GenFundingPkScript(
ourKey.PubKey.SerializeCompressed(),
theirKey.PubKey.SerializeCompressed(), channelCapacity,
)
if err != nil {
req.err <- err
return
}
// Sort the transaction. Since both side agree to a canonical ordering,
// by sorting we no longer need to send the entire transaction. Only
// signatures will be exchanged.
fundingTx.AddTxOut(multiSigOut)
txsort.InPlaceSort(pendingReservation.fundingTx)
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// Next, sign all inputs that are ours, collecting the signatures in
// order of the inputs.
pendingReservation.ourFundingInputScripts = make([]*input.Script, 0,
len(ourContribution.Inputs))
signDesc := input.SignDescriptor{
HashType: txscript.SigHashAll,
SigHashes: txscript.NewTxSigHashes(fundingTx),
}
for i, txIn := range fundingTx.TxIn {
info, err := l.FetchInputInfo(&txIn.PreviousOutPoint)
if err == ErrNotMine {
continue
} else if err != nil {
req.err <- err
return
}
signDesc.Output = &wire.TxOut{
PkScript: info.PkScript,
Value: int64(info.Value),
}
signDesc.InputIndex = i
inputScript, err := l.Cfg.Signer.ComputeInputScript(
fundingTx, &signDesc,
)
if err != nil {
req.err <- err
return
}
txIn.SignatureScript = inputScript.SigScript
txIn.Witness = inputScript.Witness
pendingReservation.ourFundingInputScripts = append(
pendingReservation.ourFundingInputScripts,
inputScript,
)
}
// Locate the index of the multi-sig outpoint in order to record it
// since the outputs are canonically sorted. If this is a single funder
// workflow, then we'll also need to send this to the remote node.
fundingTxID := fundingTx.TxHash()
_, multiSigIndex := input.FindScriptOutputIndex(fundingTx, multiSigOut.PkScript)
fundingOutpoint := wire.NewOutPoint(&fundingTxID, multiSigIndex)
pendingReservation.partialState.FundingOutpoint = *fundingOutpoint
walletLog.Debugf("Funding tx for ChannelPoint(%v) generated: %v",
fundingOutpoint, spew.Sdump(fundingTx))
// Initialize an empty sha-chain for them, tracking the current pending
// revocation hash (we don't yet know the preimage so we can't add it
// to the chain).
s := shachain.NewRevocationStore()
pendingReservation.partialState.RevocationStore = s
// Store their current commitment point. We'll need this after the
// first state transition in order to verify the authenticity of the
// revocation.
chanState := pendingReservation.partialState
chanState.RemoteCurrentRevocation = theirContribution.FirstCommitmentPoint
// Create the txin to our commitment transaction; required to construct
// the commitment transactions.
fundingTxIn := wire.TxIn{
PreviousOutPoint: wire.OutPoint{
Hash: fundingTxID,
Index: multiSigIndex,
},
}
// With the funding tx complete, create both commitment transactions.
localBalance := pendingReservation.partialState.LocalCommitment.LocalBalance.ToSatoshis()
remoteBalance := pendingReservation.partialState.LocalCommitment.RemoteBalance.ToSatoshis()
tweaklessCommits := pendingReservation.partialState.ChanType.IsTweakless()
ourCommitTx, theirCommitTx, err := CreateCommitmentTxns(
localBalance, remoteBalance, ourContribution.ChannelConfig,
theirContribution.ChannelConfig,
ourContribution.FirstCommitmentPoint,
theirContribution.FirstCommitmentPoint, fundingTxIn,
tweaklessCommits,
)
if err != nil {
req.err <- err
return
}
// With both commitment transactions constructed, generate the state
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// obfuscator then use it to encode the current state number within
// both commitment transactions.
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var stateObfuscator [StateHintSize]byte
if chanState.ChanType.IsSingleFunder() {
stateObfuscator = DeriveStateHintObfuscator(
ourContribution.PaymentBasePoint.PubKey,
theirContribution.PaymentBasePoint.PubKey,
)
} else {
ourSer := ourContribution.PaymentBasePoint.PubKey.SerializeCompressed()
theirSer := theirContribution.PaymentBasePoint.PubKey.SerializeCompressed()
switch bytes.Compare(ourSer, theirSer) {
case -1:
stateObfuscator = DeriveStateHintObfuscator(
ourContribution.PaymentBasePoint.PubKey,
theirContribution.PaymentBasePoint.PubKey,
)
default:
stateObfuscator = DeriveStateHintObfuscator(
theirContribution.PaymentBasePoint.PubKey,
ourContribution.PaymentBasePoint.PubKey,
)
}
}
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err = initStateHints(ourCommitTx, theirCommitTx, stateObfuscator)
if err != nil {
req.err <- err
return
}
// Sort both transactions according to the agreed upon canonical
// ordering. This lets us skip sending the entire transaction over,
// instead we'll just send signatures.
txsort.InPlaceSort(ourCommitTx)
txsort.InPlaceSort(theirCommitTx)
walletLog.Debugf("Local commit tx for ChannelPoint(%v): %v",
fundingOutpoint, spew.Sdump(ourCommitTx))
walletLog.Debugf("Remote commit tx for ChannelPoint(%v): %v",
fundingOutpoint, spew.Sdump(theirCommitTx))
// Record newly available information within the open channel state.
chanState.FundingOutpoint = *fundingOutpoint
chanState.LocalCommitment.CommitTx = ourCommitTx
chanState.RemoteCommitment.CommitTx = theirCommitTx
// Generate a signature for their version of the initial commitment
// transaction.
signDesc = input.SignDescriptor{
WitnessScript: witnessScript,
KeyDesc: ourKey,
Output: multiSigOut,
HashType: txscript.SigHashAll,
SigHashes: txscript.NewTxSigHashes(theirCommitTx),
InputIndex: 0,
}
sigTheirCommit, err := l.Cfg.Signer.SignOutputRaw(theirCommitTx, &signDesc)
if err != nil {
req.err <- err
return
}
pendingReservation.ourCommitmentSig = sigTheirCommit
req.err <- nil
}
// handleSingleContribution is called as the second step to a single funder
// workflow to which we are the responder. It simply saves the remote peer's
// contribution to the channel, as solely the remote peer will contribute any
// funds to the channel.
func (l *LightningWallet) handleSingleContribution(req *addSingleContributionMsg) {
l.limboMtx.Lock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
l.limboMtx.Unlock()
if !ok {
req.err <- fmt.Errorf("attempted to update non-existent funding state")
return
}
// Grab the mutex on the channelReservation to ensure thread-safety.
pendingReservation.Lock()
defer pendingReservation.Unlock()
// TODO(roasbeef): verify sanity of remote party's parameters, fail if
// disagree
// Simply record the counterparty's contribution into the pending
// reservation data as they'll be solely funding the channel entirely.
pendingReservation.theirContribution = req.contribution
theirContribution := pendingReservation.theirContribution
chanState := pendingReservation.partialState
// Initialize an empty sha-chain for them, tracking the current pending
// revocation hash (we don't yet know the preimage so we can't add it
// to the chain).
remotePreimageStore := shachain.NewRevocationStore()
chanState.RevocationStore = remotePreimageStore
// Now that we've received their first commitment point, we'll store it
// within the channel state so we can sync it to disk once the funding
// process is complete.
chanState.RemoteCurrentRevocation = theirContribution.FirstCommitmentPoint
req.err <- nil
return
}
// openChanDetails contains a "finalized" channel which can be considered
// "open" according to the requested confirmation depth at reservation
// initialization. Additionally, the struct contains additional details
// pertaining to the exact location in the main chain in-which the transaction
// was confirmed.
type openChanDetails struct {
}
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// handleFundingCounterPartySigs is the final step in the channel reservation
// workflow. During this step, we validate *all* the received signatures for
2015-12-28 23:14:00 +03:00
// inputs to the funding transaction. If any of these are invalid, we bail,
// and forcibly cancel this funding request. Additionally, we ensure that the
// signature we received from the counterparty for our version of the commitment
// transaction allows us to spend from the funding output with the addition of
// our signature.
func (l *LightningWallet) handleFundingCounterPartySigs(msg *addCounterPartySigsMsg) {
l.limboMtx.RLock()
res, ok := l.fundingLimbo[msg.pendingFundingID]
l.limboMtx.RUnlock()
if !ok {
msg.err <- fmt.Errorf("attempted to update non-existent funding state")
return
}
// Grab the mutex on the ChannelReservation to ensure thread-safety
res.Lock()
defer res.Unlock()
// Now we can complete the funding transaction by adding their
// signatures to their inputs.
res.theirFundingInputScripts = msg.theirFundingInputScripts
inputScripts := msg.theirFundingInputScripts
fundingTx := res.fundingTx
sigIndex := 0
fundingHashCache := txscript.NewTxSigHashes(fundingTx)
for i, txin := range fundingTx.TxIn {
if len(inputScripts) != 0 && len(txin.Witness) == 0 {
// Attach the input scripts so we can verify it below.
txin.Witness = inputScripts[sigIndex].Witness
txin.SignatureScript = inputScripts[sigIndex].SigScript
// Fetch the alleged previous output along with the
// pkscript referenced by this input.
//
// TODO(roasbeef): when dual funder pass actual
// height-hint
pkScript, err := input.WitnessScriptHash(
txin.Witness[len(txin.Witness)-1],
)
if err != nil {
msg.err <- fmt.Errorf("cannot create script: "+
"%v", err)
msg.completeChan <- nil
return
}
output, err := l.Cfg.ChainIO.GetUtxo(
&txin.PreviousOutPoint,
pkScript, 0, l.quit,
)
if output == nil {
msg.err <- fmt.Errorf("input to funding tx "+
"does not exist: %v", err)
msg.completeChan <- nil
return
}
// Ensure that the witness+sigScript combo is valid.
vm, err := txscript.NewEngine(output.PkScript,
fundingTx, i, txscript.StandardVerifyFlags, nil,
fundingHashCache, output.Value)
if err != nil {
msg.err <- fmt.Errorf("cannot create script "+
"engine: %s", err)
msg.completeChan <- nil
return
}
if err = vm.Execute(); err != nil {
msg.err <- fmt.Errorf("cannot validate "+
"transaction: %s", err)
msg.completeChan <- nil
return
}
sigIndex++
}
}
// At this point, we can also record and verify their signature for our
// commitment transaction.
res.theirCommitmentSig = msg.theirCommitmentSig
commitTx := res.partialState.LocalCommitment.CommitTx
ourKey := res.ourContribution.MultiSigKey
theirKey := res.theirContribution.MultiSigKey
// Re-generate both the witnessScript and p2sh output. We sign the
// witnessScript script, but include the p2sh output as the subscript
// for verification.
witnessScript, _, err := input.GenFundingPkScript(
ourKey.PubKey.SerializeCompressed(),
theirKey.PubKey.SerializeCompressed(),
int64(res.partialState.Capacity),
)
if err != nil {
msg.err <- err
msg.completeChan <- nil
return
}
// Next, create the spending scriptSig, and then verify that the script
// is complete, allowing us to spend from the funding transaction.
channelValue := int64(res.partialState.Capacity)
hashCache := txscript.NewTxSigHashes(commitTx)
sigHash, err := txscript.CalcWitnessSigHash(witnessScript, hashCache,
txscript.SigHashAll, commitTx, 0, channelValue)
if err != nil {
msg.err <- err
msg.completeChan <- nil
return
}
// Verify that we've received a valid signature from the remote party
// for our version of the commitment transaction.
theirCommitSig := msg.theirCommitmentSig
sig, err := btcec.ParseSignature(theirCommitSig, btcec.S256())
if err != nil {
msg.err <- err
msg.completeChan <- nil
return
} else if !sig.Verify(sigHash, theirKey.PubKey) {
msg.err <- fmt.Errorf("counterparty's commitment signature is invalid")
msg.completeChan <- nil
return
}
res.partialState.LocalCommitment.CommitSig = theirCommitSig
// Funding complete, this entry can be removed from limbo.
l.limboMtx.Lock()
delete(l.fundingLimbo, res.reservationID)
l.limboMtx.Unlock()
// As we're about to broadcast the funding transaction, we'll take note
// of the current height for record keeping purposes.
//
// TODO(roasbeef): this info can also be piped into light client's
// basic fee estimation?
_, bestHeight, err := l.Cfg.ChainIO.GetBestBlock()
if err != nil {
msg.err <- err
msg.completeChan <- nil
return
}
// As we've completed the funding process, we'll no convert the
// contribution structs into their underlying channel config objects to
// he stored within the database.
res.partialState.LocalChanCfg = res.ourContribution.toChanConfig()
res.partialState.RemoteChanCfg = res.theirContribution.toChanConfig()
// We'll also record the finalized funding txn, which will allow us to
// rebroadcast on startup in case we fail.
res.partialState.FundingTxn = fundingTx
// Add the complete funding transaction to the DB, in its open bucket
// which will be used for the lifetime of this channel.
nodeAddr := res.nodeAddr
err = res.partialState.SyncPending(nodeAddr, uint32(bestHeight))
if err != nil {
msg.err <- err
msg.completeChan <- nil
return
}
msg.completeChan <- res.partialState
msg.err <- nil
}
// handleSingleFunderSigs is called once the remote peer who initiated the
// single funder workflow has assembled the funding transaction, and generated
// a signature for our version of the commitment transaction. This method
// progresses the workflow by generating a signature for the remote peer's
// version of the commitment transaction.
func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
l.limboMtx.RLock()
pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
l.limboMtx.RUnlock()
if !ok {
2017-09-25 21:25:58 +03:00
req.err <- fmt.Errorf("attempted to update non-existent funding state")
req.completeChan <- nil
return
}
// Grab the mutex on the ChannelReservation to ensure thread-safety
pendingReservation.Lock()
defer pendingReservation.Unlock()
chanState := pendingReservation.partialState
chanState.FundingOutpoint = *req.fundingOutpoint
fundingTxIn := wire.NewTxIn(req.fundingOutpoint, nil, nil)
// Now that we have the funding outpoint, we can generate both versions
// of the commitment transaction, and generate a signature for the
// remote node's commitment transactions.
localBalance := pendingReservation.partialState.LocalCommitment.LocalBalance.ToSatoshis()
remoteBalance := pendingReservation.partialState.LocalCommitment.RemoteBalance.ToSatoshis()
tweaklessCommits := pendingReservation.partialState.ChanType.IsTweakless()
ourCommitTx, theirCommitTx, err := CreateCommitmentTxns(
localBalance, remoteBalance,
pendingReservation.ourContribution.ChannelConfig,
pendingReservation.theirContribution.ChannelConfig,
pendingReservation.ourContribution.FirstCommitmentPoint,
pendingReservation.theirContribution.FirstCommitmentPoint,
*fundingTxIn, tweaklessCommits,
)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
// With both commitment transactions constructed, we can now use the
// generator state obfuscator to encode the current state number within
// both commitment transactions.
stateObfuscator := DeriveStateHintObfuscator(
pendingReservation.theirContribution.PaymentBasePoint.PubKey,
pendingReservation.ourContribution.PaymentBasePoint.PubKey,
)
2017-09-25 21:25:58 +03:00
err = initStateHints(ourCommitTx, theirCommitTx, stateObfuscator)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
// Sort both transactions according to the agreed upon canonical
// ordering. This ensures that both parties sign the same sighash
// without further synchronization.
txsort.InPlaceSort(ourCommitTx)
txsort.InPlaceSort(theirCommitTx)
chanState.LocalCommitment.CommitTx = ourCommitTx
chanState.RemoteCommitment.CommitTx = theirCommitTx
walletLog.Debugf("Local commit tx for ChannelPoint(%v): %v",
req.fundingOutpoint, spew.Sdump(ourCommitTx))
walletLog.Debugf("Remote commit tx for ChannelPoint(%v): %v",
req.fundingOutpoint, spew.Sdump(theirCommitTx))
channelValue := int64(pendingReservation.partialState.Capacity)
hashCache := txscript.NewTxSigHashes(ourCommitTx)
theirKey := pendingReservation.theirContribution.MultiSigKey
ourKey := pendingReservation.ourContribution.MultiSigKey
witnessScript, _, err := input.GenFundingPkScript(
ourKey.PubKey.SerializeCompressed(),
theirKey.PubKey.SerializeCompressed(), channelValue,
)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
sigHash, err := txscript.CalcWitnessSigHash(witnessScript, hashCache,
txscript.SigHashAll, ourCommitTx, 0, channelValue)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
// Verify that we've received a valid signature from the remote party
// for our version of the commitment transaction.
sig, err := btcec.ParseSignature(req.theirCommitmentSig, btcec.S256())
if err != nil {
req.err <- err
req.completeChan <- nil
return
} else if !sig.Verify(sigHash, theirKey.PubKey) {
req.err <- fmt.Errorf("counterparty's commitment signature " +
"is invalid")
req.completeChan <- nil
return
}
chanState.LocalCommitment.CommitSig = req.theirCommitmentSig
// With their signature for our version of the commitment transactions
// verified, we can now generate a signature for their version,
// allowing the funding transaction to be safely broadcast.
p2wsh, err := input.WitnessScriptHash(witnessScript)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
signDesc := input.SignDescriptor{
WitnessScript: witnessScript,
KeyDesc: ourKey,
Output: &wire.TxOut{
PkScript: p2wsh,
Value: channelValue,
},
HashType: txscript.SigHashAll,
SigHashes: txscript.NewTxSigHashes(theirCommitTx),
InputIndex: 0,
}
sigTheirCommit, err := l.Cfg.Signer.SignOutputRaw(theirCommitTx, &signDesc)
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
pendingReservation.ourCommitmentSig = sigTheirCommit
_, bestHeight, err := l.Cfg.ChainIO.GetBestBlock()
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
// Add the complete funding transaction to the DB, in it's open bucket
// which will be used for the lifetime of this channel.
chanState.LocalChanCfg = pendingReservation.ourContribution.toChanConfig()
chanState.RemoteChanCfg = pendingReservation.theirContribution.toChanConfig()
err = chanState.SyncPending(pendingReservation.nodeAddr, uint32(bestHeight))
if err != nil {
req.err <- err
req.completeChan <- nil
return
}
req.completeChan <- chanState
req.err <- nil
l.limboMtx.Lock()
delete(l.fundingLimbo, req.pendingFundingID)
l.limboMtx.Unlock()
}
// WithCoinSelectLock will execute the passed function closure in a
// synchronized manner preventing any coin selection operations from proceeding
// while the closure if executing. This can be seen as the ability to execute a
// function closure under an exclusive coin selection lock.
func (l *LightningWallet) WithCoinSelectLock(f func() error) error {
l.coinSelectMtx.Lock()
defer l.coinSelectMtx.Unlock()
return f()
}
// coinSelection holds the result from selectCoinsAndChange.
type coinSelection struct {
coins []*wire.TxIn
change []*wire.TxOut
fundingAmt btcutil.Amount
unlockCoins func()
}
// selectCoinsAndChange performs coin selection in order to obtain witness
// outputs which sum to at least 'amt' amount of satoshis. If necessary,
// a change address will also be generated. If coin selection is
// successful/possible, then the selected coins and change outputs are
// returned, and the value of the resulting funding output. This method locks
// the selected outputs, and a function closure to unlock them in case of an
// error is returned.
func (l *LightningWallet) selectCoinsAndChange(feeRate SatPerKWeight,
amt btcutil.Amount, minConfs int32, subtractFees bool) (
*coinSelection, error) {
// We hold the coin select mutex while querying for outputs, and
// performing coin selection in order to avoid inadvertent double
// spends across funding transactions.
l.coinSelectMtx.Lock()
defer l.coinSelectMtx.Unlock()
walletLog.Infof("Performing funding tx coin selection using %v "+
"sat/kw as fee rate", int64(feeRate))
// Find all unlocked unspent witness outputs that satisfy the minimum
// number of confirmations required.
coins, err := l.ListUnspentWitness(minConfs, math.MaxInt32)
if err != nil {
return nil, err
}
var (
selectedCoins []*Utxo
fundingAmt btcutil.Amount
changeAmt btcutil.Amount
)
// Perform coin selection over our available, unlocked unspent outputs
// in order to find enough coins to meet the funding amount
// requirements.
switch {
// In case this request want the fees subtracted from the local amount,
// we'll call the specialized method for that. This ensures that we
// won't deduct more that the specified balance from our wallet.
case subtractFees:
dustLimit := l.Cfg.DefaultConstraints.DustLimit
selectedCoins, fundingAmt, changeAmt, err = coinSelectSubtractFees(
feeRate, amt, dustLimit, coins,
)
if err != nil {
return nil, err
}
// Ótherwise do a normal coin selection where we target a given funding
// amount.
default:
fundingAmt = amt
selectedCoins, changeAmt, err = coinSelect(feeRate, amt, coins)
if err != nil {
return nil, err
}
}
// Record any change output(s) generated as a result of the coin
// selection, but only if the addition of the output won't lead to the
// creation of dust.
var changeOutputs []*wire.TxOut
if changeAmt != 0 && changeAmt > DefaultDustLimit() {
changeAddr, err := l.NewAddress(WitnessPubKey, true)
if err != nil {
return nil, err
}
changeScript, err := txscript.PayToAddrScript(changeAddr)
if err != nil {
return nil, err
}
changeOutputs = make([]*wire.TxOut, 1)
changeOutputs[0] = &wire.TxOut{
Value: int64(changeAmt),
PkScript: changeScript,
}
}
// 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.
inputs := make([]*wire.TxIn, len(selectedCoins))
for i, coin := range selectedCoins {
outpoint := &coin.OutPoint
l.lockedOutPoints[*outpoint] = struct{}{}
l.LockOutpoint(*outpoint)
// Empty sig script, we'll actually sign if this reservation is
// queued up to be completed (the other side accepts).
inputs[i] = wire.NewTxIn(outpoint, nil, nil)
}
unlock := func() {
l.coinSelectMtx.Lock()
defer l.coinSelectMtx.Unlock()
for _, coin := range selectedCoins {
outpoint := &coin.OutPoint
delete(l.lockedOutPoints, *outpoint)
l.UnlockOutpoint(*outpoint)
}
}
return &coinSelection{
coins: inputs,
change: changeOutputs,
fundingAmt: fundingAmt,
unlockCoins: unlock,
}, nil
}
// DeriveStateHintObfuscator derives the bytes to be used for obfuscating the
// state hints from the root to be used for a new channel. The obfuscator is
// generated via the following computation:
//
// * sha256(initiatorKey || responderKey)[26:]
// * where both keys are the multi-sig keys of the respective parties
//
// The first 6 bytes of the resulting hash are used as the state hint.
func DeriveStateHintObfuscator(key1, key2 *btcec.PublicKey) [StateHintSize]byte {
h := sha256.New()
h.Write(key1.SerializeCompressed())
h.Write(key2.SerializeCompressed())
sha := h.Sum(nil)
var obfuscator [StateHintSize]byte
copy(obfuscator[:], sha[26:])
return obfuscator
}
// initStateHints properly sets the obfuscated state hints on both commitment
2017-09-25 21:25:58 +03:00
// transactions using the passed obfuscator.
func initStateHints(commit1, commit2 *wire.MsgTx,
obfuscator [StateHintSize]byte) error {
if err := SetStateNumHint(commit1, 0, obfuscator); err != nil {
return err
}
if err := SetStateNumHint(commit2, 0, obfuscator); err != nil {
return err
}
return nil
}
// selectInputs selects a slice of inputs necessary to meet the specified
2018-04-18 05:03:27 +03:00
// selection amount. If input selection is unable to succeed due to insufficient
// funds, a non-nil error is returned. Additionally, the total amount of the
// selected coins are returned in order for the caller to properly handle
// change+fees.
func selectInputs(amt btcutil.Amount, coins []*Utxo) (btcutil.Amount, []*Utxo, error) {
satSelected := btcutil.Amount(0)
for i, coin := range coins {
satSelected += coin.Value
if satSelected >= amt {
return satSelected, coins[:i+1], nil
}
}
return 0, nil, &ErrInsufficientFunds{amt, satSelected}
}
// coinSelect attempts to select a sufficient amount of coins, including a
// change output to fund amt satoshis, adhering to the specified fee rate. The
// specified fee rate should be expressed in sat/kw for coin selection to
// function properly.
func coinSelect(feeRate SatPerKWeight, amt btcutil.Amount,
coins []*Utxo) ([]*Utxo, btcutil.Amount, error) {
amtNeeded := amt
for {
// First perform an initial round of coin selection to estimate
// the required fee.
totalSat, selectedUtxos, err := selectInputs(amtNeeded, coins)
if err != nil {
return nil, 0, err
}
var weightEstimate input.TxWeightEstimator
for _, utxo := range selectedUtxos {
switch utxo.AddressType {
case WitnessPubKey:
weightEstimate.AddP2WKHInput()
case NestedWitnessPubKey:
weightEstimate.AddNestedP2WKHInput()
default:
return nil, 0, fmt.Errorf("unsupported address type: %v",
utxo.AddressType)
}
}
// Channel funding multisig output is P2WSH.
weightEstimate.AddP2WSHOutput()
// Assume that change output is a P2WKH output.
//
// TODO: Handle wallets that generate non-witness change
// addresses.
2019-07-11 14:14:36 +03:00
// TODO(halseth): make coinSelect not estimate change output
// for dust change.
weightEstimate.AddP2WKHOutput()
// The difference between the selected amount and the amount
// requested will be used to pay fees, and generate a change
// output with the remaining.
overShootAmt := totalSat - amt
// Based on the estimated size and fee rate, if the excess
// amount isn't enough to pay fees, then increase the requested
// coin amount by the estimate required fee, performing another
// round of coin selection.
totalWeight := int64(weightEstimate.Weight())
requiredFee := feeRate.FeeForWeight(totalWeight)
if overShootAmt < requiredFee {
amtNeeded = amt + requiredFee
continue
}
// If the fee is sufficient, then calculate the size of the
// change output.
changeAmt := overShootAmt - requiredFee
return selectedUtxos, changeAmt, nil
}
}
// coinSelectSubtractFees attempts to select coins such that we'll spend up to
// amt in total after fees, adhering to the specified fee rate. The selected
// coins, the final output and change values are returned.
func coinSelectSubtractFees(feeRate SatPerKWeight, amt,
dustLimit btcutil.Amount, coins []*Utxo) ([]*Utxo, btcutil.Amount,
btcutil.Amount, error) {
// First perform an initial round of coin selection to estimate
// the required fee.
totalSat, selectedUtxos, err := selectInputs(amt, coins)
if err != nil {
return nil, 0, 0, err
}
var weightEstimate input.TxWeightEstimator
for _, utxo := range selectedUtxos {
switch utxo.AddressType {
case WitnessPubKey:
weightEstimate.AddP2WKHInput()
case NestedWitnessPubKey:
weightEstimate.AddNestedP2WKHInput()
default:
return nil, 0, 0, fmt.Errorf("unsupported "+
"address type: %v", utxo.AddressType)
}
}
// Channel funding multisig output is P2WSH.
weightEstimate.AddP2WSHOutput()
// At this point we've got two possibilities, either create a
// change output, or not. We'll first try without creating a
// change output.
//
// Estimate the fee required for a transaction without a change
// output.
totalWeight := int64(weightEstimate.Weight())
requiredFee := feeRate.FeeForWeight(totalWeight)
// For a transaction without a change output, we'll let everything go
// to our multi-sig output after subtracting fees.
outputAmt := totalSat - requiredFee
changeAmt := btcutil.Amount(0)
// If the the output is too small after subtracting the fee, the coin
// selection cannot be performed with an amount this small.
if outputAmt <= dustLimit {
return nil, 0, 0, fmt.Errorf("output amount(%v) after "+
"subtracting fees(%v) below dust limit(%v)", outputAmt,
requiredFee, dustLimit)
}
// We were able to create a transaction with no change from the
// selected inputs. We'll remember the resulting values for
// now, while we try to add a change output. Assume that change output
// is a P2WKH output.
weightEstimate.AddP2WKHOutput()
// Now that we have added the change output, redo the fee
// estimate.
totalWeight = int64(weightEstimate.Weight())
requiredFee = feeRate.FeeForWeight(totalWeight)
// For a transaction with a change output, everything we don't spend
// will go to change.
newChange := totalSat - amt
newOutput := amt - requiredFee
// If adding a change output leads to both outputs being above
// the dust limit, we'll add the change output. Otherwise we'll
// go with the no change tx we originally found.
if newChange > dustLimit && newOutput > dustLimit {
outputAmt = newOutput
changeAmt = newChange
}
// Sanity check the resulting output values to make sure we
// don't burn a great part to fees.
totalOut := outputAmt + changeAmt
fee := totalSat - totalOut
// Fail if more than 20% goes to fees.
// TODO(halseth): smarter fee limit. Make configurable or dynamic wrt
// total funding size?
if fee > totalOut/5 {
return nil, 0, 0, fmt.Errorf("fee %v on total output"+
"value %v", fee, totalOut)
}
return selectedUtxos, outputAmt, changeAmt, nil
}