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contractcourt: use the sweeper for HTLC offered remote timeout resolu…
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…tion

In this commit, we bring the timeout resolver more in line with the
success resolver by using the sweeper to handle the HTLC offered remote
timeout outputs. These are outputs that we can sweep directly from the
remote party's commitment transaction when they broadcast their version
of the commitment transaction.

With this change, we slim down the scope slightly by only doing this for
anchor channels. Non-anchor channels will continue to use the
utxonursery for this output type for now.
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@Roasbeef
Roasbeef committed Sep 12, 2024
1 parent 10d4f16 commit 2491692
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Showing 2 changed files with 122 additions and 34 deletions.
91 changes: 86 additions & 5 deletions contractcourt/htlc_timeout_resolver.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -538,7 +538,6 @@ func (h *htlcTimeoutResolver) sweepSecondLevelTx(immediate bool) error {
return err
}

// TODO(yy): checkpoint here?
return err
}

Expand All @@ -562,6 +561,59 @@ func (h *htlcTimeoutResolver) sendSecondLevelTxLegacy() error {
return h.Checkpoint(h)
}

// sweepDirectHtlcOutput sends the direct spend of the HTLC output to the
// sweeper. This is used when the remote party goes on chain, and we're able to
// sweep an HTLC we offered after a timeout. Only the CLTV encumbered outputs
// are resolved via this path.
func (h *htlcTimeoutResolver) sweepDirectHtlcOutput(immediate bool) error {
var htlcWitnessType input.StandardWitnessType
if h.isTaproot() {
htlcWitnessType = input.TaprootHtlcOfferedRemoteTimeout
} else {
htlcWitnessType = input.HtlcOfferedRemoteTimeout
}

sweepInput := input.NewCsvInputWithCltv(
&h.htlcResolution.ClaimOutpoint, htlcWitnessType,
&h.htlcResolution.SweepSignDesc, h.broadcastHeight,
h.htlcResolution.CsvDelay, h.htlcResolution.Expiry,
)

// Calculate the budget.
//
// TODO(yy): the budget is twice the output's value, which is needed as
// we don't force sweep the output now. To prevent cascading force
// closes, we use all its output value plus a wallet input as the
// budget. This is a temporary solution until we can optionally cancel
// the incoming HTLC, more details in,
// - https://github.com/lightningnetwork/lnd/issues/7969
budget := calculateBudget(
btcutil.Amount(sweepInput.SignDesc().Output.Value), 2, 0,
)

log.Infof("%T(%x): offering offered remote timeout HTLC output to "+
"sweeper with deadline %v and budget=%v at height=%v",
h, h.htlc.RHash[:], h.incomingHTLCExpiryHeight, budget,
h.broadcastHeight)

_, err := h.Sweeper.SweepInput(
sweepInput,
sweep.Params{
Budget: budget,

// This is an outgoing HTLC, so we want to make sure
// that we sweep it before the incoming HTLC expires.
DeadlineHeight: h.incomingHTLCExpiryHeight,
Immediate: immediate,
},
)
if err != nil {
return err
}

return nil
}

// spendHtlcOutput handles the initial spend of an HTLC output via the timeout
// clause. If this is our local commitment, the second-level timeout TX will be
// used to spend the output into the next stage. If this is the remote
Expand All @@ -582,6 +634,16 @@ func (h *htlcTimeoutResolver) spendHtlcOutput(
return nil, err
}

// If this is an anchor channel, and there's no second level txn (direct
// spend from remote commitment, which is the case for remote
// commitments), then we'll just send this directly to the sweeper.
case h.htlcResolution.SignedTimeoutTx == nil && !h.outputIncubating:
if err := h.sweepDirectHtlcOutput(immediate); err != nil {
log.Errorf("Sending direct spend to sweeper: %v", err)

return nil, err
}

// If we have no SignDetails, and we haven't already sent the output to
// the utxo nursery, then we'll do so now.
case h.htlcResolution.SignDetails == nil && !h.outputIncubating:
Expand Down Expand Up @@ -690,6 +752,13 @@ func (h *htlcTimeoutResolver) handleCommitSpend(
)

switch {

// If we swept an HTLC directly off the remote party's commitment
// transaction, then we can exit here as there's no second level sweep
// to do.
case h.htlcResolution.SignedTimeoutTx == nil:
break

// If the sweeper is handling the second level transaction, wait for
// the CSV and possible CLTV lock to expire, before sweeping the output
// on the second-level.
Expand Down Expand Up @@ -763,6 +832,7 @@ func (h *htlcTimeoutResolver) handleCommitSpend(
h.htlcResolution.CsvDelay,
uint32(commitSpend.SpendingHeight), h.htlc.RHash,
)

// Calculate the budget for this sweep.
budget := calculateBudget(
btcutil.Amount(inp.SignDesc().Output.Value),
Expand Down Expand Up @@ -800,6 +870,7 @@ func (h *htlcTimeoutResolver) handleCommitSpend(
case h.htlcResolution.SignedTimeoutTx != nil:
log.Infof("%T(%v): waiting for nursery/sweeper to spend CSV "+
"delayed output", h, claimOutpoint)

sweepTx, err := waitForSpend(
&claimOutpoint,
h.htlcResolution.SweepSignDesc.Output.PkScript,
Expand Down Expand Up @@ -866,9 +937,12 @@ func (h *htlcTimeoutResolver) IsResolved() bool {

// report returns a report on the resolution state of the contract.
func (h *htlcTimeoutResolver) report() *ContractReport {
// If the sign details are nil, the report will be created by handled
// by the nursery.
if h.htlcResolution.SignDetails == nil {
// If the sign details are nil, the report will be created by handled by
// the nursery.Sign details are only non-nil for anchor channels. We
// then further restrict this path by ensuring we'll only return nil for
// non-anchor local commitmetn sweeps.
if h.htlcResolution.SignDetails == nil && h.
htlcResolution.SignedTimeoutTx != nil {
return nil
}

Expand All @@ -888,13 +962,20 @@ func (h *htlcTimeoutResolver) initReport() {
)
}

// If there's no timeout transaction, then we're already effectively in
// level two.
stage := uint32(1)
if h.htlcResolution.SignedTimeoutTx == nil {
stage = 2
}

h.currentReport = ContractReport{
Outpoint: h.htlcResolution.ClaimOutpoint,
Type: ReportOutputOutgoingHtlc,
Amount: finalAmt,
MaturityHeight: h.htlcResolution.Expiry,
LimboBalance: finalAmt,
Stage: 1,
Stage: stage,
}
}

Expand Down
65 changes: 36 additions & 29 deletions contractcourt/htlc_timeout_resolver_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -294,12 +294,13 @@ func testHtlcTimeoutResolver(t *testing.T, testCase htlcTimeoutTestCase) {
chainCfg := ChannelArbitratorConfig{
ChainArbitratorConfig: ChainArbitratorConfig{
Notifier: notifier,
Sweeper: newMockSweeper(),
PreimageDB: witnessBeacon,
IncubateOutputs: func(wire.OutPoint,
fn.Option[lnwallet.OutgoingHtlcResolution],
fn.Option[lnwallet.IncomingHtlcResolution],
uint32, fn.Option[int32],
) error {
uint32, fn.Option[int32]) error {

incubateChan <- struct{}{}
return nil
},
Expand All @@ -311,26 +312,28 @@ func testHtlcTimeoutResolver(t *testing.T, testCase htlcTimeoutTestCase) {
}

resolutionChan <- msgs[0]

return nil
},
Budget: *DefaultBudgetConfig(),
QueryIncomingCircuit: func(circuit models.CircuitKey,
) *models.CircuitKey {

return nil
},
},
PutResolverReport: func(_ kvdb.RwTx,
_ *channeldb.ResolverReport,
) error {
_ *channeldb.ResolverReport) error {

return nil
},
}

cfg := ResolverConfig{
ChannelArbitratorConfig: chainCfg,
Checkpoint: func(_ ContractResolver,
reports ...*channeldb.ResolverReport,
) error {
reports ...*channeldb.ResolverReport) error {

checkPointChan <- struct{}{}

// Send all of our reports into the channel.
Expand Down Expand Up @@ -367,13 +370,15 @@ func testHtlcTimeoutResolver(t *testing.T, testCase htlcTimeoutTestCase) {

if testCase.timeout {
timeoutTxID := timeoutTx.TxHash()
reports = append(reports, &channeldb.ResolverReport{
OutPoint: timeoutTx.TxIn[0].PreviousOutPoint,
report := &channeldb.ResolverReport{
OutPoint: timeoutTx.TxIn[0].PreviousOutPoint, //nolint:lll
Amount: testHtlcAmt.ToSatoshis(),
ResolverType: channeldb.ResolverTypeOutgoingHtlc,
ResolverOutcome: channeldb.ResolverOutcomeFirstStage,
ResolverType: channeldb.ResolverTypeOutgoingHtlc, //nolint:lll
ResolverOutcome: channeldb.ResolverOutcomeFirstStage, //nolint:lll
SpendTxID: &timeoutTxID,
})
}

reports = append(reports, report)
}
}

Expand All @@ -391,10 +396,21 @@ func testHtlcTimeoutResolver(t *testing.T, testCase htlcTimeoutTestCase) {
}
}()

// As the output isn't yet in the nursery, we expect that we
// should receive an incubation request.
// If this is a remote commit, then we expct the outputs should receive
// an incubation request to go through the sweeper, otherwise the
// nursery.
var sweepChan chan input.Input
if testCase.remoteCommit {
mockSweeper, ok := resolver.Sweeper.(*mockSweeper)
require.True(t, ok)
sweepChan = mockSweeper.sweptInputs
}

// The output should be offered to either the sweeper or
// the nursery.
select {
case <-incubateChan:
case <-sweepChan:
case err := <-resolveErr:
t.Fatalf("unable to resolve HTLC: %v", err)
case <-time.After(time.Second * 5):
Expand Down Expand Up @@ -450,7 +466,6 @@ func testHtlcTimeoutResolver(t *testing.T, testCase htlcTimeoutTestCase) {
t.Fatalf("resolution not sent")
}
} else {

// Otherwise, the HTLC should now timeout. First, we
// should get a resolution message with a populated
// failure message.
Expand Down Expand Up @@ -559,10 +574,6 @@ func TestHtlcTimeoutSingleStage(t *testing.T) {
}

checkpoints := []checkpoint{
{
// Output should be handed off to the nursery.
incubating: true,
},
{
// We send a confirmation the sweep tx from published
// by the nursery.
Expand Down Expand Up @@ -594,7 +605,7 @@ func TestHtlcTimeoutSingleStage(t *testing.T) {
// After the sweep has confirmed, we expect the
// checkpoint to be resolved, and with the above
// report.
incubating: true,
incubating: false,
resolved: true,
reports: []*channeldb.ResolverReport{
claim,
Expand Down Expand Up @@ -849,9 +860,9 @@ func TestHtlcTimeoutSingleStageRemoteSpend(t *testing.T) {
)
}

// TestHtlcTimeoutSecondStageRemoteSpend tests that when a remite commitment
// confirms, and the remote spends the output using the success tx, we
// properly detect this and extract the preimage.
// TestHtlcTimeoutSecondStageRemoteSpend tests that when a remote commitment
// confirms, and the remote spends the output using the success tx, we properly
// detect this and extract the preimage.
func TestHtlcTimeoutSecondStageRemoteSpend(t *testing.T) {
commitOutpoint := wire.OutPoint{Index: 2}

Expand Down Expand Up @@ -895,10 +906,6 @@ func TestHtlcTimeoutSecondStageRemoteSpend(t *testing.T) {
}

checkpoints := []checkpoint{
{
// Output should be handed off to the nursery.
incubating: true,
},
{
// We send a confirmation for the remote's second layer
// success transcation.
Expand Down Expand Up @@ -944,7 +951,7 @@ func TestHtlcTimeoutSecondStageRemoteSpend(t *testing.T) {
// After the sweep has confirmed, we expect the
// checkpoint to be resolved, and with the above
// report.
incubating: true,
incubating: false,
resolved: true,
reports: []*channeldb.ResolverReport{
claim,
Expand Down Expand Up @@ -1321,8 +1328,8 @@ func TestHtlcTimeoutSecondStageSweeperRemoteSpend(t *testing.T) {
}

func testHtlcTimeout(t *testing.T, resolution lnwallet.OutgoingHtlcResolution,
checkpoints []checkpoint,
) {
checkpoints []checkpoint) {

t.Helper()

defer timeout()()
Expand Down

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