lnd.xprv/contractcourt/contract_resolvers.go

1484 lines
47 KiB
Go
Raw Normal View History

package contractcourt
import (
"bytes"
"crypto/sha256"
"encoding/binary"
"fmt"
"io"
"io/ioutil"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/lightningnetwork/lnd/lnwire"
)
var (
endian = binary.BigEndian
)
// ContractResolver is an interface which packages a state machine which is
// able to carry out the necessary steps required to fully resolve a Bitcoin
// contract on-chain. Resolvers are fully encodable to ensure callers are able
// to persist them properly. A resolver may produce another resolver in the
// case that claiming an HTLC is a multi-stage process. In this case, we may
// partially resolve the contract, then persist, and set up for an additional
// resolution.
type ContractResolver interface {
// ResolverKey returns an identifier which should be globally unique
// for this particular resolver within the chain the original contract
// resides within.
ResolverKey() []byte
// Resolve instructs the contract resolver to resolve the output
// on-chain. Once the output has been *fully* resolved, the function
// should return immediately with a nil ContractResolver value for the
// first return value. In the case that the contract requires further
// resolution, then another resolve is returned.
//
// NOTE: This function MUST be run as a goroutine.
Resolve() (ContractResolver, error)
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
IsResolved() bool
// Encode writes an encoded version of the ContractResolver into the
// passed Writer.
Encode(w io.Writer) error
// Decode attempts to decode an encoded ContractResolver from the
// passed Reader instance, returning an active ContractResolver
// instance.
Decode(r io.Reader) error
// AttachResolverKit should be called once a resolved is successfully
// decoded from its stored format. This struct delivers a generic tool
// kit that resolvers need to complete their duty.
AttachResolverKit(ResolverKit)
// Stop signals the resolver to cancel any current resolution
// processes, and suspend.
Stop()
}
// ResolverKit is meant to be used as a mix-in struct to be embedded within a
// given ContractResolver implementation. It contains all the items that a
// resolver requires to carry out its duties.
type ResolverKit struct {
// ChannelArbitratorConfig contains all the interfaces and closures
// required for the resolver to interact with outside sub-systems.
ChannelArbitratorConfig
// Checkpoint allows a resolver to check point its state. This function
// should write the state of the resolver to persistent storage, and
// return a non-nil error upon success.
Checkpoint func(ContractResolver) error
Quit chan struct{}
}
// htlcTimeoutResolver is a ContractResolver that's capable of resolving an
// outgoing HTLC. The HTLC may be on our commitment transaction, or on the
// commitment transaction of the remote party. An output on our commitment
// transaction is considered fully resolved once the second-level transaction
// has been confirmed (and reached a sufficient depth). An output on the
// commitment transaction of the remote party is resolved once we detect a
// spend of the direct HTLC output using the timeout clause.
type htlcTimeoutResolver struct {
// htlcResolution contains all the information required to properly
// resolve this outgoing HTLC.
htlcResolution lnwallet.OutgoingHtlcResolution
// outputIncubating returns true if we've sent the output to the output
// incubator (utxo nursery).
outputIncubating bool
// resolved reflects if the contract has been fully resolved or not.
resolved bool
// broadcastHeight is the height that the original contract was
// broadcast to the main-chain at. We'll use this value to bound any
// historical queries to the chain for spends/confirmations.
//
// TODO(roasbeef): wrap above into definite resolution embedding?
broadcastHeight uint32
// htlcIndex is the index of this HTLC within the trace of the
// additional commitment state machine.
htlcIndex uint64
ResolverKit
}
// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) ResolverKey() []byte {
// The primary key for this resolver will be the outpoint of the HTLC
// on the commitment transaction itself. If this is our commitment,
// then the output can be found within the signed timeout tx,
// otherwise, it's just the ClaimOutpoint.
var op wire.OutPoint
if h.htlcResolution.SignedTimeoutTx != nil {
op = h.htlcResolution.SignedTimeoutTx.TxIn[0].PreviousOutPoint
} else {
op = h.htlcResolution.ClaimOutpoint
}
key := newResolverID(op)
return key[:]
}
// Resolve kicks off full resolution of an outgoing HTLC output. If it's our
// commitment, it isn't resolved until we see the second level HTLC txn
// confirmed. If it's the remote party's commitment, we don't resolve until we
// see a direct sweep via the timeout clause.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) Resolve() (ContractResolver, error) {
// If we're already resolved, then we can exit early.
if h.resolved {
return nil, nil
}
// If we haven't already sent the output to the utxo nursery, then
// we'll do so now.
if !h.outputIncubating {
log.Tracef("%T(%v): incubating htlc output", h,
h.htlcResolution.ClaimOutpoint)
err := h.IncubateOutputs(h.ChanPoint, nil, &h.htlcResolution, nil)
if err != nil {
return nil, err
}
h.outputIncubating = true
if err := h.Checkpoint(h); err != nil {
log.Errorf("unable to Checkpoint: %v", err)
}
}
// waitForOutputResolution waits for the HTLC output to be fully
// resolved. The output is considered fully resolved once it has been
// spent, and the spending transaction has been fully confirmed.
waitForOutputResolution := func() error {
// We first need to register to see when the HTLC output itself
// has been spent by a confirmed transaction.
spendNtfn, err := h.Notifier.RegisterSpendNtfn(
&h.htlcResolution.ClaimOutpoint,
h.htlcResolution.SweepSignDesc.Output.PkScript,
h.broadcastHeight,
)
if err != nil {
return err
}
select {
case _, ok := <-spendNtfn.Spend:
if !ok {
return fmt.Errorf("notifier quit")
}
case <-h.Quit:
return fmt.Errorf("quitting")
}
return nil
}
// With the output sent to the nursery, we'll now wait until the output
// has been fully resolved before sending the clean up message.
//
// TODO(roasbeef): need to be able to cancel nursery?
// * if they pull on-chain while we're waiting
// If we don't have a second layer transaction, then this is a remote
// party's commitment, so we'll watch for a direct spend.
if h.htlcResolution.SignedTimeoutTx == nil {
// We'll block until: the HTLC output has been spent, and the
// transaction spending that output is sufficiently confirmed.
log.Infof("%T(%v): waiting for nursery to spend CLTV-locked "+
"output", h, h.htlcResolution.ClaimOutpoint)
if err := waitForOutputResolution(); err != nil {
return nil, err
}
} else {
// Otherwise, this is our commitment, so we'll watch for the
// second-level transaction to be sufficiently confirmed.
secondLevelTXID := h.htlcResolution.SignedTimeoutTx.TxHash()
sweepScript := h.htlcResolution.SignedTimeoutTx.TxOut[0].PkScript
confNtfn, err := h.Notifier.RegisterConfirmationsNtfn(
&secondLevelTXID, sweepScript, 1, h.broadcastHeight,
)
if err != nil {
return nil, err
}
log.Infof("%T(%v): waiting second-level tx (txid=%v) to be "+
"fully confirmed", h, h.htlcResolution.ClaimOutpoint,
secondLevelTXID)
select {
case _, ok := <-confNtfn.Confirmed:
if !ok {
return nil, fmt.Errorf("quitting")
}
case <-h.Quit:
return nil, fmt.Errorf("quitting")
}
}
// TODO(roasbeef): need to watch for remote party sweeping with pre-image?
// * have another waiting on spend above, will check the type, if it's
// pre-image, then we'll cancel, and send a clean up back with
// pre-image, also add to preimage cache
log.Infof("%T(%v): resolving htlc with incoming fail msg, fully "+
"confirmed", h, h.htlcResolution.ClaimOutpoint)
// At this point, the second-level transaction is sufficiently
// confirmed, or a transaction directly spending the output is.
// Therefore, we can now send back our clean up message.
failureMsg := &lnwire.FailPermanentChannelFailure{}
if err := h.DeliverResolutionMsg(ResolutionMsg{
SourceChan: h.ShortChanID,
HtlcIndex: h.htlcIndex,
Failure: failureMsg,
}); err != nil {
return nil, err
}
// Finally, if this was an output on our commitment transaction, we'll
// for the second-level HTLC output to be spent, and for that
// transaction itself to confirm.
if h.htlcResolution.SignedTimeoutTx != nil {
log.Infof("%T(%v): waiting for nursery to spend CSV delayed "+
"output", h, h.htlcResolution.ClaimOutpoint)
if err := waitForOutputResolution(); err != nil {
return nil, err
}
}
// With the clean up message sent, we'll now mark the contract
// resolved, and wait.
h.resolved = true
return nil, h.Checkpoint(h)
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) Stop() {
close(h.Quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) IsResolved() bool {
return h.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) Encode(w io.Writer) error {
// First, we'll write out the relevant fields of the
// OutgoingHtlcResolution to the writer.
if err := encodeOutgoingResolution(w, &h.htlcResolution); err != nil {
return err
}
// With that portion written, we can now write out the fields specific
// to the resolver itself.
if err := binary.Write(w, endian, h.outputIncubating); err != nil {
return err
}
if err := binary.Write(w, endian, h.resolved); err != nil {
return err
}
if err := binary.Write(w, endian, h.broadcastHeight); err != nil {
return err
}
if err := binary.Write(w, endian, h.htlcIndex); err != nil {
return err
}
return nil
}
// Decode attempts to decode an encoded ContractResolver from the passed Reader
// instance, returning an active ContractResolver instance.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) Decode(r io.Reader) error {
// First, we'll read out all the mandatory fields of the
// OutgoingHtlcResolution that we store.
if err := decodeOutgoingResolution(r, &h.htlcResolution); err != nil {
return err
}
// With those fields read, we can now read back the fields that are
// specific to the resolver itself.
if err := binary.Read(r, endian, &h.outputIncubating); err != nil {
return err
}
if err := binary.Read(r, endian, &h.resolved); err != nil {
return err
}
if err := binary.Read(r, endian, &h.broadcastHeight); err != nil {
return err
}
if err := binary.Read(r, endian, &h.htlcIndex); err != nil {
return err
}
return nil
}
// AttachResolverKit should be called once a resolved is successfully decoded
// from its stored format. This struct delivers a generic tool kit that
// resolvers need to complete their duty.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcTimeoutResolver) AttachResolverKit(r ResolverKit) {
h.ResolverKit = r
}
// A compile time assertion to ensure htlcTimeoutResolver meets the
// ContractResolver interface.
var _ ContractResolver = (*htlcTimeoutResolver)(nil)
// htlcSuccessResolver is a resolver that's capable of sweeping an incoming
// HTLC output on-chain. If this is the remote party's commitment, we'll sweep
// it directly from the commitment output *immediately*. If this is our
// commitment, we'll first broadcast the success transaction, then send it to
// the incubator for sweeping. That's it, no need to send any clean up
// messages.
//
// TODO(roasbeef): don't need to broadcast?
type htlcSuccessResolver struct {
// htlcResolution is the incoming HTLC resolution for this HTLC. It
// contains everything we need to properly resolve this HTLC.
htlcResolution lnwallet.IncomingHtlcResolution
// outputIncubating returns true if we've sent the output to the output
// incubator (utxo nursery).
outputIncubating bool
// resolved reflects if the contract has been fully resolved or not.
resolved bool
// broadcastHeight is the height that the original contract was
// broadcast to the main-chain at. We'll use this value to bound any
// historical queries to the chain for spends/confirmations.
broadcastHeight uint32
// payHash is the payment hash of the original HTLC extended to us.
payHash [32]byte
// sweepTx will be non-nil if we've already crafted a transaction to
// sweep a direct HTLC output. This is only a concern if we're sweeping
// from the commitment transaction of the remote party.
//
// TODO(roasbeef): send off to utxobundler
sweepTx *wire.MsgTx
ResolverKit
}
// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) ResolverKey() []byte {
// The primary key for this resolver will be the outpoint of the HTLC
// on the commitment transaction itself. If this is our commitment,
// then the output can be found within the signed success tx,
// otherwise, it's just the ClaimOutpoint.
var op wire.OutPoint
if h.htlcResolution.SignedSuccessTx != nil {
op = h.htlcResolution.SignedSuccessTx.TxIn[0].PreviousOutPoint
} else {
op = h.htlcResolution.ClaimOutpoint
}
key := newResolverID(op)
return key[:]
}
// Resolve attempts to resolve an unresolved incoming HTLC that we know the
// preimage to. If the HTLC is on the commitment of the remote party, then
// we'll simply sweep it directly. Otherwise, we'll hand this off to the utxo
// nursery to do its duty.
//
// TODO(roasbeef): create multi to batch
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Resolve() (ContractResolver, error) {
// If we're already resolved, then we can exit early.
if h.resolved {
return nil, nil
}
// If we don't have a success transaction, then this means that this is
// an output on the remote party's commitment transaction.
if h.htlcResolution.SignedSuccessTx == nil {
// If we don't already have the sweep transaction constructed,
// we'll do so and broadcast it.
if h.sweepTx == nil {
log.Infof("%T(%x): crafting sweep tx for "+
"incoming+remote htlc confirmed", h,
h.payHash[:])
// In this case, we can sweep it directly from the
// commitment output. We'll first grab a fresh address
// from the wallet to sweep the output.
addr, err := h.NewSweepAddr()
if err != nil {
return nil, err
}
// With our address obtained, we'll query for an
// estimate to be confirmed at ease.
//
// TODO(roasbeef): signal up if fee would be too large
// to sweep singly, need to batch
feePerKw, err := h.FeeEstimator.EstimateFeePerKW(6)
if err != nil {
return nil, err
}
log.Debugf("%T(%x): using %v sat/kw to sweep htlc"+
"incoming+remote htlc confirmed", h,
h.payHash[:], int64(feePerKw))
// Using a weight estimator, we'll compute the total
// fee required, and from that the value we'll end up
// with.
totalWeight := (&lnwallet.TxWeightEstimator{}).
AddWitnessInput(lnwallet.OfferedHtlcSuccessWitnessSize).
AddP2WKHOutput().Weight()
totalFees := feePerKw.FeeForWeight(int64(totalWeight))
sweepAmt := h.htlcResolution.SweepSignDesc.Output.Value -
int64(totalFees)
// With the fee computation finished, we'll now
// construct the sweep transaction.
htlcPoint := h.htlcResolution.ClaimOutpoint
h.sweepTx = wire.NewMsgTx(2)
h.sweepTx.AddTxIn(&wire.TxIn{
PreviousOutPoint: htlcPoint,
})
h.sweepTx.AddTxOut(&wire.TxOut{
PkScript: addr,
Value: sweepAmt,
})
// With the transaction fully assembled, we can now
// generate a valid witness for the transaction.
h.htlcResolution.SweepSignDesc.SigHashes = txscript.NewTxSigHashes(
h.sweepTx,
)
h.sweepTx.TxIn[0].Witness, err = lnwallet.SenderHtlcSpendRedeem(
h.Signer, &h.htlcResolution.SweepSignDesc, h.sweepTx,
h.htlcResolution.Preimage[:],
)
if err != nil {
return nil, err
}
log.Infof("%T(%x): crafted sweep tx=%v", h,
h.payHash[:], spew.Sdump(h.sweepTx))
// With the sweep transaction confirmed, we'll now
// Checkpoint our state.
if err := h.Checkpoint(h); err != nil {
log.Errorf("unable to Checkpoint: %v", err)
}
// Finally, we'll broadcast the sweep transaction to
// the network.
//
// TODO(roasbeef): validate first?
if err := h.PublishTx(h.sweepTx); err != nil {
log.Infof("%T(%x): unable to publish tx: %v",
h, h.payHash[:], err)
return nil, err
}
}
// With the sweep transaction broadcast, we'll wait for its
// confirmation.
sweepTXID := h.sweepTx.TxHash()
sweepScript := h.sweepTx.TxOut[0].PkScript
confNtfn, err := h.Notifier.RegisterConfirmationsNtfn(
&sweepTXID, sweepScript, 1, h.broadcastHeight,
)
if err != nil {
return nil, err
}
log.Infof("%T(%x): waiting for sweep tx (txid=%v) to be "+
"confirmed", h, h.payHash[:], sweepTXID)
select {
case _, ok := <-confNtfn.Confirmed:
if !ok {
return nil, fmt.Errorf("quitting")
}
case <-h.Quit:
return nil, fmt.Errorf("quitting")
}
// Once the transaction has received a sufficient number of
// confirmations, we'll mark ourselves as fully resolved and exit.
h.resolved = true
return nil, h.Checkpoint(h)
}
log.Infof("%T(%x): broadcasting second-layer transition tx: %v",
h, h.payHash[:], spew.Sdump(h.htlcResolution.SignedSuccessTx))
// We'll now broadcast the second layer transaction so we can kick off
// the claiming process.
//
// TODO(roasbeef): after changing sighashes send to tx bundler
if err := h.PublishTx(h.htlcResolution.SignedSuccessTx); err != nil {
return nil, err
}
// Otherwise, this is an output on our commitment transaction. In this
// case, we'll send it to the incubator, but only if we haven't already
// done so.
if !h.outputIncubating {
log.Infof("%T(%x): incubating incoming htlc output",
h, h.payHash[:])
err := h.IncubateOutputs(h.ChanPoint, nil, nil, &h.htlcResolution)
if err != nil {
return nil, err
}
h.outputIncubating = true
if err := h.Checkpoint(h); err != nil {
log.Errorf("unable to Checkpoint: %v", err)
}
}
// To wrap this up, we'll wait until the second-level transaction has
// been spent, then fully resolve the contract.
spendNtfn, err := h.Notifier.RegisterSpendNtfn(
&h.htlcResolution.ClaimOutpoint,
h.htlcResolution.SweepSignDesc.Output.PkScript,
h.broadcastHeight,
)
if err != nil {
return nil, err
}
log.Infof("%T(%x): waiting for second-level HTLC output to be spent "+
"after csv_delay=%v", h, h.payHash[:], h.htlcResolution.CsvDelay)
select {
case _, ok := <-spendNtfn.Spend:
if !ok {
return nil, fmt.Errorf("quitting")
}
case <-h.Quit:
return nil, fmt.Errorf("quitting")
}
h.resolved = true
return nil, h.Checkpoint(h)
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Stop() {
close(h.Quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) IsResolved() bool {
return h.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Encode(w io.Writer) error {
// First we'll encode our inner HTLC resolution.
if err := encodeIncomingResolution(w, &h.htlcResolution); err != nil {
return err
}
// Next, we'll write out the fields that are specified to the contract
// resolver.
if err := binary.Write(w, endian, h.outputIncubating); err != nil {
return err
}
if err := binary.Write(w, endian, h.resolved); err != nil {
return err
}
if err := binary.Write(w, endian, h.broadcastHeight); err != nil {
return err
}
if _, err := w.Write(h.payHash[:]); err != nil {
return err
}
return nil
}
// Decode attempts to decode an encoded ContractResolver from the passed Reader
// instance, returning an active ContractResolver instance.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Decode(r io.Reader) error {
// First we'll decode our inner HTLC resolution.
if err := decodeIncomingResolution(r, &h.htlcResolution); err != nil {
return err
}
// Next, we'll read all the fields that are specified to the contract
// resolver.
if err := binary.Read(r, endian, &h.outputIncubating); err != nil {
return err
}
if err := binary.Read(r, endian, &h.resolved); err != nil {
return err
}
if err := binary.Read(r, endian, &h.broadcastHeight); err != nil {
return err
}
if _, err := io.ReadFull(r, h.payHash[:]); err != nil {
return err
}
return nil
}
// AttachResolverKit should be called once a resolved is successfully decoded
// from its stored format. This struct delivers a generic tool kit that
// resolvers need to complete their duty.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) AttachResolverKit(r ResolverKit) {
h.ResolverKit = r
}
// A compile time assertion to ensure htlcSuccessResolver meets the
// ContractResolver interface.
var _ ContractResolver = (*htlcSuccessResolver)(nil)
// htlcOutgoingContestResolver is a ContractResolver that's able to resolve an
// outgoing HTLC that is still contested. An HTLC is still contested, if at the
// time that we broadcast the commitment transaction, it isn't able to be fully
2018-04-18 05:03:27 +03:00
// resolved. In this case, we'll either wait for the HTLC to timeout, or for
// us to learn of the preimage.
type htlcOutgoingContestResolver struct {
// htlcTimeoutResolver is the inner solver that this resolver may turn
// into. This only happens if the HTLC expires on-chain.
htlcTimeoutResolver
}
// Resolve commences the resolution of this contract. As this contract hasn't
// yet timed out, we'll wait for one of two things to happen
//
// 1. The HTLC expires. In this case, we'll sweep the funds and send a clean
// up cancel message to outside sub-systems.
//
// 2. The remote party sweeps this HTLC on-chain, in which case we'll add the
// pre-image to our global cache, then send a clean up settle message
// backwards.
//
// When either of these two things happens, we'll create a new resolver which
// is able to handle the final resolution of the contract. We're only the pivot
// point.
func (h *htlcOutgoingContestResolver) Resolve() (ContractResolver, error) {
// If we're already full resolved, then we don't have anything further
// to do.
if h.resolved {
return nil, nil
}
// claimCleanUp is a helper function that's called once the HTLC output
// is spent by the remote party. It'll extract the preimage, add it to
// the global cache, and finally send the appropriate clean up message.
claimCleanUp := func(commitSpend *chainntnfs.SpendDetail) (ContractResolver, error) {
// Depending on if this is our commitment or not, then we'll be
// looking for a different witness pattern.
spenderIndex := commitSpend.SpenderInputIndex
spendingInput := commitSpend.SpendingTx.TxIn[spenderIndex]
log.Infof("%T(%v): extracting preimage! remote party spent "+
"HTLC with tx=%v", h, h.htlcResolution.ClaimOutpoint,
spew.Sdump(commitSpend.SpendingTx))
// If this is the remote party's commitment, then we'll be
// looking for them to spend using the second-level success
// transaction.
var preimage [32]byte
if h.htlcResolution.SignedTimeoutTx == nil {
// The witness stack when the remote party sweeps the
// output to them looks like:
//
// * <sender sig> <recvr sig> <preimage> <witness script>
copy(preimage[:], spendingInput.Witness[3])
} else {
// Otherwise, they'll be spending directly from our
// commitment output. In which case the witness stack
// looks like:
//
// * <sig> <preimage> <witness script>
copy(preimage[:], spendingInput.Witness[1])
}
log.Infof("%T(%v): extracting preimage=%x from on-chain "+
"spend!", h, h.htlcResolution.ClaimOutpoint, preimage[:])
// With the preimage obtained, we can now add it to the global
// cache.
if err := h.PreimageDB.AddPreimage(preimage[:]); err != nil {
log.Errorf("%T(%v): unable to add witness to cache",
h, h.htlcResolution.ClaimOutpoint)
}
// Finally, we'll send the clean up message, mark ourselves as
// resolved, then exit.
if err := h.DeliverResolutionMsg(ResolutionMsg{
SourceChan: h.ShortChanID,
HtlcIndex: h.htlcIndex,
PreImage: &preimage,
}); err != nil {
return nil, err
}
h.resolved = true
return nil, h.Checkpoint(h)
}
// Otherwise, we'll watch for two external signals to decide if we'll
// morph into another resolver, or fully resolve the contract.
// The output we'll be watching for is the *direct* spend from the HTLC
// output. If this isn't our commitment transaction, it'll be right on
// the resolution. Otherwise, we fetch this pointer from the input of
// the time out transaction.
var (
outPointToWatch wire.OutPoint
scriptToWatch []byte
err error
)
if h.htlcResolution.SignedTimeoutTx == nil {
outPointToWatch = h.htlcResolution.ClaimOutpoint
scriptToWatch = h.htlcResolution.SweepSignDesc.Output.PkScript
} else {
// If this is the remote party's commitment, then we'll need to
// grab watch the output that our timeout transaction points
// to. We can directly grab the outpoint, then also extract the
// witness script (the last element of the witness stack) to
// re-construct the pkScipt we need to watch.
outPointToWatch = h.htlcResolution.SignedTimeoutTx.TxIn[0].PreviousOutPoint
witness := h.htlcResolution.SignedTimeoutTx.TxIn[0].Witness
scriptToWatch, err = lnwallet.WitnessScriptHash(
witness[len(witness)-1],
)
if err != nil {
return nil, err
}
}
// First, we'll register for a spend notification for this output. If
// the remote party sweeps with the pre-image, we'll be notified.
spendNtfn, err := h.Notifier.RegisterSpendNtfn(
&outPointToWatch, scriptToWatch, h.broadcastHeight,
)
if err != nil {
return nil, err
}
// We'll quickly check to see if the output has already been spent.
select {
// If the output has already been spent, then we can stop early and
// sweep the pre-image from the output.
case commitSpend, ok := <-spendNtfn.Spend:
if !ok {
return nil, fmt.Errorf("quitting")
}
// TODO(roasbeef): Checkpoint?
return claimCleanUp(commitSpend)
// If it hasn't, then we'll watch for both the expiration, and the
// sweeping out this output.
default:
}
// We'll check the current height, if the HTLC has already expired,
// then we'll morph immediately into a resolver that can sweep the
// HTLC.
//
// TODO(roasbeef): use grace period instead?
_, currentHeight, err := h.ChainIO.GetBestBlock()
if err != nil {
return nil, err
}
if uint32(currentHeight) >= h.htlcResolution.Expiry {
log.Infof("%T(%v): HTLC has expired (height=%v, expiry=%v), "+
"transforming into timeout resolver", h,
h.htlcResolution.ClaimOutpoint)
return &h.htlcTimeoutResolver, nil
}
// If we reach this point, then we can't fully act yet, so we'll await
// either of our signals triggering: the HTLC expires, or we learn of
// the preimage.
blockEpochs, err := h.Notifier.RegisterBlockEpochNtfn(nil)
if err != nil {
return nil, err
}
defer blockEpochs.Cancel()
for {
select {
// A new block has arrived, we'll check to see if this leads to
// HTLC expiration.
case newBlock, ok := <-blockEpochs.Epochs:
if !ok {
return nil, fmt.Errorf("quitting")
}
// If this new height expires the HTLC, then we can
// exit early and create a resolver that's capable of
// handling the time locked output.
newHeight := uint32(newBlock.Height)
if newHeight >= h.htlcResolution.Expiry-1 {
log.Infof("%T(%v): HTLC has expired "+
"(height=%v, expiry=%v), transforming "+
"into timeout resolver", h,
h.htlcResolution.ClaimOutpoint,
newHeight, h.htlcResolution.Expiry)
return &h.htlcTimeoutResolver, nil
}
// The output has been spent! This means the preimage has been
// revealed on-chain.
case commitSpend, ok := <-spendNtfn.Spend:
if !ok {
return nil, fmt.Errorf("quitting")
}
// The only way this output can be spent by the remote
// party is by revealing the preimage. So we'll perform
// our duties to clean up the contract once it has been
// claimed.
return claimCleanUp(commitSpend)
case <-h.Quit:
return nil, fmt.Errorf("resolver cancelled")
}
}
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcOutgoingContestResolver) Stop() {
close(h.Quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcOutgoingContestResolver) IsResolved() bool {
return h.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcOutgoingContestResolver) Encode(w io.Writer) error {
return h.htlcTimeoutResolver.Encode(w)
}
// Decode attempts to decode an encoded ContractResolver from the passed Reader
// instance, returning an active ContractResolver instance.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcOutgoingContestResolver) Decode(r io.Reader) error {
return h.htlcTimeoutResolver.Decode(r)
}
// AttachResolverKit should be called once a resolved is successfully decoded
// from its stored format. This struct delivers a generic tool kit that
// resolvers need to complete their duty.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcOutgoingContestResolver) AttachResolverKit(r ResolverKit) {
h.ResolverKit = r
}
// A compile time assertion to ensure htlcOutgoingContestResolver meets the
// ContractResolver interface.
var _ ContractResolver = (*htlcOutgoingContestResolver)(nil)
// htlcIncomingContestResolver is a ContractResolver that's able to resolve an
// incoming HTLC that is still contested. An HTLC is still contested, if at the
// time of commitment broadcast, we don't know of the preimage for it yet, and
// it hasn't expired. In this case, we can resolve the HTLC if we learn of the
// preimage, otherwise the remote party will sweep it after it expires.
//
// TODO(roasbeef): just embed the other resolver?
type htlcIncomingContestResolver struct {
// htlcExpiry is the absolute expiry of this incoming HTLC. We use this
// value to determine if we can exit early as if the HTLC times out,
// before we learn of the preimage then we can't claim it on chain
// successfully.
htlcExpiry uint32
// htlcSuccessResolver is the inner resolver that may be utilized if we
// learn of the preimage.
htlcSuccessResolver
}
// Resolve attempts to resolve this contract. As we don't yet know of the
// preimage for the contract, we'll wait for one of two things to happen:
//
// 1. We learn of the preimage! In this case, we can sweep the HTLC incoming
// and ensure that if this was a multi-hop HTLC we are made whole. In this
// case, an additional ContractResolver will be returned to finish the
// job.
//
// 2. The HTLC expires. If this happens, then the contract is fully resolved
// as we have no remaining actions left at our disposal.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Resolve() (ContractResolver, error) {
// If we're already full resolved, then we don't have anything further
// to do.
if h.resolved {
return nil, nil
}
// We'll first check if this HTLC has been timed out, if so, we can
// return now and mark ourselves as resolved.
_, currentHeight, err := h.ChainIO.GetBestBlock()
if err != nil {
return nil, err
}
// If we're past the point of expiry of the HTLC, then at this point
// the sender can sweep it, so we'll end our lifetime.
if uint32(currentHeight) >= h.htlcExpiry {
// TODO(roasbeef): should also somehow check if outgoing is
// resolved or not
// * may need to hook into the circuit map
// * can't timeout before the outgoing has been
log.Infof("%T(%v): HTLC has timed out (expiry=%v, height=%v), "+
"abandoning", h, h.htlcResolution.ClaimOutpoint,
h.htlcExpiry, currentHeight)
h.resolved = true
return nil, h.Checkpoint(h)
}
// applyPreimage is a helper function that will populate our internal
// resolver with the preimage we learn of. This should be called once
// the preimage is revealed so the inner resolver can properly complete
// its duties.
applyPreimage := func(preimage []byte) {
copy(h.htlcResolution.Preimage[:], preimage)
log.Infof("%T(%v): extracted preimage=%x from beacon!", h,
h.htlcResolution.ClaimOutpoint, preimage[:])
// If this our commitment transaction, then we'll need to
// populate the witness for the second-level HTLC transaction.
if h.htlcResolution.SignedSuccessTx != nil {
// Within the witness for the success transaction, the
// preimage is the 4th element as it looks like:
//
// * <sender sig> <recvr sig> <preimage> <witness script>
//
// We'll populate it within the witness, as since this
// was a "contest" resolver, we didn't yet know of the
// preimage.
h.htlcResolution.SignedSuccessTx.TxIn[0].Witness[3] = preimage[:]
}
copy(h.htlcResolution.Preimage[:], preimage[:])
}
// If the HTLC hasn't expired yet, then we may still be able to claim
// it if we learn of the pre-image, so we'll subscribe to the preimage
// database to see if it turns up, or the HTLC times out.
//
// NOTE: This is done BEFORE opportunistically querying the db, to
// ensure the preimage can't be delivered between querying and
// registering for the preimage subscription.
preimageSubscription := h.PreimageDB.SubscribeUpdates()
blockEpochs, err := h.Notifier.RegisterBlockEpochNtfn(nil)
if err != nil {
return nil, err
}
defer func() {
preimageSubscription.CancelSubscription()
blockEpochs.Cancel()
}()
// With the epochs and preimage subscriptions initialized, we'll query
// to see if we already know the preimage.
preimage, ok := h.PreimageDB.LookupPreimage(h.payHash[:])
if ok {
// If we do, then this means we can claim the HTLC! However,
// we don't know how to ourselves, so we'll return our inner
// resolver which has the knowledge to do so.
applyPreimage(preimage[:])
return &h.htlcSuccessResolver, nil
}
for {
select {
case preimage := <-preimageSubscription.WitnessUpdates:
// If this isn't our preimage, then we'll continue
// onwards.
newHash := sha256.Sum256(preimage)
preimageMatches := bytes.Equal(newHash[:], h.payHash[:])
if !preimageMatches {
continue
}
// Otherwise, we've learned of the preimage! We'll add
// this information to our inner resolver, then return
// it so it can continue contract resolution.
applyPreimage(preimage)
return &h.htlcSuccessResolver, nil
case newBlock, ok := <-blockEpochs.Epochs:
if !ok {
return nil, fmt.Errorf("quitting")
}
// If this new height expires the HTLC, then this means
// we never found out the preimage, so we can mark
// resolved and
// exit.
newHeight := uint32(newBlock.Height)
if newHeight >= h.htlcExpiry {
log.Infof("%T(%v): HTLC has timed out "+
"(expiry=%v, height=%v), abandoning", h,
h.htlcResolution.ClaimOutpoint,
h.htlcExpiry, currentHeight)
h.resolved = true
return nil, h.Checkpoint(h)
}
case <-h.Quit:
return nil, fmt.Errorf("resolver stopped")
}
}
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Stop() {
close(h.Quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) IsResolved() bool {
return h.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Encode(w io.Writer) error {
// We'll first write out the one field unique to this resolver.
if err := binary.Write(w, endian, h.htlcExpiry); err != nil {
return err
}
// Then we'll write out our internal resolver.
return h.htlcSuccessResolver.Encode(w)
}
// Decode attempts to decode an encoded ContractResolver from the passed Reader
// instance, returning an active ContractResolver instance.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Decode(r io.Reader) error {
// We'll first read the one field unique to this resolver.
if err := binary.Read(r, endian, &h.htlcExpiry); err != nil {
return err
}
// Then we'll decode our internal resolver.
return h.htlcSuccessResolver.Decode(r)
}
// AttachResolverKit should be called once a resolved is successfully decoded
// from its stored format. This struct delivers a generic tool kit that
// resolvers need to complete their duty.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) AttachResolverKit(r ResolverKit) {
h.ResolverKit = r
}
// A compile time assertion to ensure htlcIncomingContestResolver meets the
// ContractResolver interface.
var _ ContractResolver = (*htlcIncomingContestResolver)(nil)
// commitSweepResolver is a resolver that will attempt to sweep the commitment
// output paying to us, in the case that the remote party broadcasts their
// version of the commitment transaction. We can sweep this output immediately,
// as it doesn't have a time-lock delay.
type commitSweepResolver struct {
// commitResolution contains all data required to successfully sweep
// this HTLC on-chain.
commitResolution lnwallet.CommitOutputResolution
// resolved reflects if the contract has been fully resolved or not.
resolved bool
// broadcastHeight is the height that the original contract was
// broadcast to the main-chain at. We'll use this value to bound any
// historical queries to the chain for spends/confirmations.
broadcastHeight uint32
// chanPoint is the channel point of the original contract.
chanPoint wire.OutPoint
// sweepTx is the fully signed transaction which when broadcast, will
// sweep the commitment output into an output under control by the
// source wallet.
sweepTx *wire.MsgTx
ResolverKit
}
// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
func (c *commitSweepResolver) ResolverKey() []byte {
key := newResolverID(c.commitResolution.SelfOutPoint)
return key[:]
}
// Resolve instructs the contract resolver to resolve the output on-chain. Once
// the output has been *fully* resolved, the function should return immediately
// with a nil ContractResolver value for the first return value. In the case
// that the contract requires further resolution, then another resolve is
// returned.
//
// NOTE: This function MUST be run as a goroutine.
func (c *commitSweepResolver) Resolve() (ContractResolver, error) {
// If we're already resolved, then we can exit early.
if c.resolved {
return nil, nil
}
// First, we'll register for a notification once the commitment output
// itself has been confirmed.
//
// TODO(roasbeef): instead sweep asap if remote commit? yeh
commitTXID := c.commitResolution.SelfOutPoint.Hash
sweepScript := c.commitResolution.SelfOutputSignDesc.Output.PkScript
confNtfn, err := c.Notifier.RegisterConfirmationsNtfn(
&commitTXID, sweepScript, 1, c.broadcastHeight,
)
if err != nil {
return nil, err
}
log.Debugf("%T(%v): waiting for commit tx to confirm", c, c.chanPoint)
select {
case _, ok := <-confNtfn.Confirmed:
if !ok {
return nil, fmt.Errorf("quitting")
}
case <-c.Quit:
return nil, fmt.Errorf("quitting")
}
// TODO(roasbeef): checkpoint tx confirmed?
// We're dealing with our commitment transaction if the delay on the
// resolution isn't zero.
isLocalCommitTx := c.commitResolution.MaturityDelay != 0
switch {
// If the sweep transaction isn't already generated, and the remote
// party broadcast the commitment transaction then we'll create it now.
case c.sweepTx == nil && !isLocalCommitTx:
// Now that the commitment transaction has confirmed, we'll
// craft a transaction to sweep this output into the wallet.
signDesc := c.commitResolution.SelfOutputSignDesc
// First, we'll estimate the total weight so we can compute
// fees properly. We'll use a lax estimate, as this output is
// in no immediate danger.
feePerKw, err := c.FeeEstimator.EstimateFeePerKW(6)
if err != nil {
return nil, err
}
log.Debugf("%T(%v): using %v sat/kw for sweep tx", c,
c.chanPoint, int64(feePerKw))
totalWeight := (&lnwallet.TxWeightEstimator{}).
AddP2WKHInput().
AddP2WKHOutput().Weight()
totalFees := feePerKw.FeeForWeight(int64(totalWeight))
sweepAmt := signDesc.Output.Value - int64(totalFees)
c.sweepTx = wire.NewMsgTx(2)
c.sweepTx.AddTxIn(&wire.TxIn{
PreviousOutPoint: c.commitResolution.SelfOutPoint,
})
sweepAddr, err := c.NewSweepAddr()
if err != nil {
return nil, err
}
c.sweepTx.AddTxOut(&wire.TxOut{
PkScript: sweepAddr,
Value: sweepAmt,
})
// With the transaction fully assembled, we can now generate a
// valid witness for the transaction.
signDesc.SigHashes = txscript.NewTxSigHashes(c.sweepTx)
c.sweepTx.TxIn[0].Witness, err = lnwallet.CommitSpendNoDelay(
c.Signer, &signDesc, c.sweepTx,
)
if err != nil {
return nil, err
}
log.Infof("%T(%v): sweeping commit output with tx=%v", c,
c.chanPoint, spew.Sdump(c.sweepTx))
// Finally, we'll broadcast the sweep transaction to the
// network.
if err := c.PublishTx(c.sweepTx); err != nil {
log.Errorf("%T(%v): unable to publish sweep tx: %v",
c, c.chanPoint, err)
return nil, err
}
// With the sweep transaction confirmed, we'll now Checkpoint
// our state.
if err := c.Checkpoint(c); err != nil {
log.Errorf("unable to Checkpoint: %v", err)
}
// Otherwise, this is our commitment transaction, So we'll obtain the
// sweep transaction once the commitment output has been spent.
case c.sweepTx == nil && isLocalCommitTx:
// Otherwise, if we're dealing with our local commitment
// transaction, then the output we need to sweep has been sent
// to the nursery for incubation. In this case, we'll wait
// until the commitment output has been spent.
spendNtfn, err := c.Notifier.RegisterSpendNtfn(
&c.commitResolution.SelfOutPoint,
c.commitResolution.SelfOutputSignDesc.Output.PkScript,
c.broadcastHeight,
)
if err != nil {
return nil, err
}
log.Infof("%T(%v): waiting for commit output to be swept", c,
c.chanPoint)
select {
case commitSpend, ok := <-spendNtfn.Spend:
if !ok {
return nil, fmt.Errorf("quitting")
}
// Once we detect the commitment output has been spent,
// we'll extract the spending transaction itself, as we
// now consider this to be our sweep transaction.
c.sweepTx = commitSpend.SpendingTx
log.Infof("%T(%v): commit output swept by txid=%v",
c, c.chanPoint, c.sweepTx.TxHash())
if err := c.Checkpoint(c); err != nil {
log.Errorf("unable to Checkpoint: %v", err)
}
case <-c.Quit:
return nil, fmt.Errorf("quitting")
}
}
log.Infof("%T(%v): waiting for commit sweep txid=%v conf", c, c.chanPoint,
c.sweepTx.TxHash())
// Now we'll wait until the sweeping transaction has been fully
// confirmed. Once it's confirmed, we can mark this contract resolved.
sweepTXID := c.sweepTx.TxHash()
sweepingScript := c.sweepTx.TxOut[0].PkScript
confNtfn, err = c.Notifier.RegisterConfirmationsNtfn(
&sweepTXID, sweepingScript, 1, c.broadcastHeight,
)
if err != nil {
return nil, err
}
select {
case confInfo, ok := <-confNtfn.Confirmed:
if !ok {
return nil, fmt.Errorf("quitting")
}
log.Infof("ChannelPoint(%v) commit tx is fully resolved, at height: %v",
c.chanPoint, confInfo.BlockHeight)
case <-c.Quit:
return nil, fmt.Errorf("quitting")
}
// Once the transaction has received a sufficient number of
// confirmations, we'll mark ourselves as fully resolved and exit.
c.resolved = true
return nil, c.Checkpoint(c)
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) Stop() {
close(c.Quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) IsResolved() bool {
return c.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) Encode(w io.Writer) error {
if err := encodeCommitResolution(w, &c.commitResolution); err != nil {
return err
}
if err := binary.Write(w, endian, c.resolved); err != nil {
return err
}
if err := binary.Write(w, endian, c.broadcastHeight); err != nil {
return err
}
if _, err := w.Write(c.chanPoint.Hash[:]); err != nil {
return err
}
err := binary.Write(w, endian, c.chanPoint.Index)
if err != nil {
return err
}
if c.sweepTx != nil {
return c.sweepTx.Serialize(w)
}
return nil
}
// Decode attempts to decode an encoded ContractResolver from the passed Reader
// instance, returning an active ContractResolver instance.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) Decode(r io.Reader) error {
if err := decodeCommitResolution(r, &c.commitResolution); err != nil {
return err
}
if err := binary.Read(r, endian, &c.resolved); err != nil {
return err
}
if err := binary.Read(r, endian, &c.broadcastHeight); err != nil {
return err
}
_, err := io.ReadFull(r, c.chanPoint.Hash[:])
if err != nil {
return err
}
err = binary.Read(r, endian, &c.chanPoint.Index)
if err != nil {
return err
}
txBytes, err := ioutil.ReadAll(r)
if err != nil {
return err
}
if len(txBytes) == 0 {
return nil
}
txReader := bytes.NewReader(txBytes)
tx := &wire.MsgTx{}
if err := tx.Deserialize(txReader); err != nil {
return nil
}
c.sweepTx = tx
return nil
}
// AttachResolverKit should be called once a resolved is successfully decoded
// from its stored format. This struct delivers a generic tool kit that
// resolvers need to complete their duty.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) AttachResolverKit(r ResolverKit) {
c.ResolverKit = r
}
// A compile time assertion to ensure commitSweepResolver meets the
// ContractResolver interface.
var _ ContractResolver = (*commitSweepResolver)(nil)