watchtower/wtclient: add anchor backup tasks

watchtower/wtclient/backup_task.go

@@ -39,6 +39,7 @@ import (
 type backupTask struct {
 	id         wtdb.BackupID
 	breachInfo *lnwallet.BreachRetribution
+	chanType   channeldb.ChannelType
 
 	// state-dependent variables
 
@@ -90,18 +91,33 @@ func newBackupTask(chanID *lnwire.ChannelID,
 	if breachInfo.LocalOutputSignDesc != nil {
 		var witnessType input.WitnessType
 		switch {
+		case chanType.HasAnchors():
+			witnessType = input.CommitmentToRemoteConfirmed
 		case chanType.IsTweakless():
 			witnessType = input.CommitSpendNoDelayTweakless
 		default:
 			witnessType = input.CommitmentNoDelay
 		}
 
+		// Anchor channels have a CSV-encumbered to-remote output. We'll
+		// construct a CSV input in that case and assign the proper CSV
+		// delay of 1, otherwise we fallback to the a regular P2WKH
+		// to-remote output for tweaked or tweakless channels.
+		if chanType.HasAnchors() {
+			toRemoteInput = input.NewCsvInput(
+				&breachInfo.LocalOutpoint,
+				witnessType,
+				breachInfo.LocalOutputSignDesc,
+				0, 1,
+			)
+		} else {
 			toRemoteInput = input.NewBaseInput(
 				&breachInfo.LocalOutpoint,
 				witnessType,
 				breachInfo.LocalOutputSignDesc,
 				0,
 			)
+		}
 
 		totalAmt += breachInfo.LocalOutputSignDesc.Output.Value
 	}
@@ -112,6 +128,7 @@ func newBackupTask(chanID *lnwire.ChannelID,
 			CommitHeight: breachInfo.RevokedStateNum,
 		},
 		breachInfo:    breachInfo,
+		chanType:      chanType,
 		toLocalInput:  toLocalInput,
 		toRemoteInput: toRemoteInput,
 		totalAmt:      btcutil.Amount(totalAmt),
@@ -151,14 +168,29 @@ func (t *backupTask) bindSession(session *wtdb.ClientSessionBody) error {
 		// underestimate the size by one byte. The diferrence in weight
 		// can cause different output values on the sweep transaction,
 		// so we mimic the original bug and create signatures using the
-		// original weight estimate.
+		// original weight estimate. For anchor channels we'll go ahead
+		// an use the correct penalty witness when signing our justice
+		// transactions.
+		if t.chanType.HasAnchors() {
+			weightEstimate.AddWitnessInput(
+				input.ToLocalPenaltyWitnessSize,
+			)
+		} else {
 			weightEstimate.AddWitnessInput(
 				input.ToLocalPenaltyWitnessSize - 1,
 			)
 		}
+	}
 	if t.toRemoteInput != nil {
+		// Legacy channels (both tweaked and non-tweaked) spend from
+		// P2WKH output. Anchor channels spend a to-remote confirmed
+		// P2WSH  output.
+		if t.chanType.HasAnchors() {
+			weightEstimate.AddWitnessInput(input.ToRemoteConfirmedWitnessSize)
+		} else {
 			weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
 		}
+	}
 
 	// All justice transactions have a p2wkh output paying to the victim.
 	weightEstimate.AddP2WKHOutput()
@@ -169,6 +201,12 @@ func (t *backupTask) bindSession(session *wtdb.ClientSessionBody) error {
 		weightEstimate.AddP2WKHOutput()
 	}
 
+	if t.chanType.HasAnchors() != session.Policy.IsAnchorChannel() {
+		log.Criticalf("Invalid task (has_anchors=%t) for session "+
+			"(has_anchors=%t)", t.chanType.HasAnchors(),
+			session.Policy.IsAnchorChannel())
+	}
+
 	// Now, compute the output values depending on whether FlagReward is set
 	// in the current session's policy.
 	outputs, err := session.Policy.ComputeJusticeTxOuts(
@@ -225,9 +263,10 @@ func (t *backupTask) craftSessionPayload(
 	// information. This will either be contain both the to-local and
 	// to-remote outputs, or only be the to-local output.
 	inputs := t.inputs()
-	for prevOutPoint := range inputs {
+	for prevOutPoint, input := range inputs {
 		justiceTxn.AddTxIn(&wire.TxIn{
 			PreviousOutPoint: prevOutPoint,
+			Sequence:         input.BlocksToMaturity(),
 		})
 	}
 
@@ -294,6 +333,8 @@ func (t *backupTask) craftSessionPayload(
 		case input.CommitSpendNoDelayTweakless:
 			fallthrough
 		case input.CommitmentNoDelay:
+			fallthrough
+		case input.CommitmentToRemoteConfirmed:
 			copy(justiceKit.CommitToRemoteSig[:], signature[:])
 		default:
 			return hint, nil, fmt.Errorf("invalid witness type: %v",

watchtower/wtclient/backup_task_internal_test.go

@@ -95,6 +95,12 @@ func genTaskTest(
 	bindErr error,
 	chanType channeldb.ChannelType) backupTaskTest {
 
+	// Set the anchor flag in the blob type if the session needs to support
+	// anchor channels.
+	if chanType.HasAnchors() {
+		blobType |= blob.Type(blob.FlagAnchorChannel)
+	}
+
 	// Parse the key pairs for all keys used in the test.
 	revSK, revPK := btcec.PrivKeyFromBytes(
 		btcec.S256(), revPrivBytes,
@@ -195,12 +201,22 @@ func genTaskTest(
 
 		var witnessType input.WitnessType
 		switch {
+		case chanType.HasAnchors():
+			witnessType = input.CommitmentToRemoteConfirmed
 		case chanType.IsTweakless():
 			witnessType = input.CommitSpendNoDelayTweakless
 		default:
 			witnessType = input.CommitmentNoDelay
 		}
 
+		if chanType.HasAnchors() {
+			toRemoteInput = input.NewCsvInput(
+				&breachInfo.LocalOutpoint,
+				witnessType,
+				breachInfo.LocalOutputSignDesc,
+				0, 1,
+			)
+		} else {
 			toRemoteInput = input.NewBaseInput(
 				&breachInfo.LocalOutpoint,
 				witnessType,
@@ -208,6 +224,7 @@ func genTaskTest(
 				0,
 			)
 		}
+	}
 
 	return backupTaskTest{
 		name:             name,
@@ -260,10 +277,42 @@ func TestBackupTask(t *testing.T) {
 	chanTypes := []channeldb.ChannelType{
 		channeldb.SingleFunderBit,
 		channeldb.SingleFunderTweaklessBit,
+		channeldb.AnchorOutputsBit,
 	}
 
 	var backupTaskTests []backupTaskTest
 	for _, chanType := range chanTypes {
+		// Depending on whether the test is for anchor channels or
+		// legacy (tweaked and non-tweaked) channels, adjust the
+		// expected sweep amount to accommodate. These are different for
+		// several reasons:
+		//   - anchor to-remote outputs require a P2WSH sweep rather
+		//     than a P2WKH sweep.
+		//   - the to-local weight estimate fixes an off-by-one.
+		// In tests related to the dust threshold, the size difference
+		// between the channel types makes it so that the threshold fee
+		// rate is slightly lower (since the transactions are heavier).
+		var (
+			expSweepCommitNoRewardBoth     int64                  = 299241
+			expSweepCommitNoRewardLocal    int64                  = 199514
+			expSweepCommitNoRewardRemote   int64                  = 99561
+			expSweepCommitRewardBoth       int64                  = 296117
+			expSweepCommitRewardLocal      int64                  = 197390
+			expSweepCommitRewardRemote     int64                  = 98437
+			sweepFeeRateNoRewardRemoteDust chainfee.SatPerKWeight = 227500
+			sweepFeeRateRewardRemoteDust   chainfee.SatPerKWeight = 175000
+		)
+		if chanType.HasAnchors() {
+			expSweepCommitNoRewardBoth = 299236
+			expSweepCommitNoRewardLocal = 199513
+			expSweepCommitNoRewardRemote = 99557
+			expSweepCommitRewardBoth = 296112
+			expSweepCommitRewardLocal = 197389
+			expSweepCommitRewardRemote = 98433
+			sweepFeeRateNoRewardRemoteDust = 225000
+			sweepFeeRateRewardRemoteDust = 173750
+		}
+
 		backupTaskTests = append(backupTaskTests, []backupTaskTest{
 			genTaskTest(
 				"commit no-reward, both outputs",
@@ -273,7 +322,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitNoReward,     // blobType
 				1000,                       // sweepFeeRate
 				nil,                        // rewardScript
-				299241,                 // expSweepAmt
+				expSweepCommitNoRewardBoth, // expSweepAmt
 				0,                          // expRewardAmt
 				nil,                        // bindErr
 				chanType,
@@ -286,7 +335,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitNoReward,      // blobType
 				1000,                        // sweepFeeRate
 				nil,                         // rewardScript
-				199514,                 // expSweepAmt
+				expSweepCommitNoRewardLocal, // expSweepAmt
 				0,                           // expRewardAmt
 				nil,                         // bindErr
 				chanType,
@@ -299,7 +348,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitNoReward,       // blobType
 				1000,                         // sweepFeeRate
 				nil,                          // rewardScript
-				99561,                  // expSweepAmt
+				expSweepCommitNoRewardRemote, // expSweepAmt
 				0,                            // expRewardAmt
 				nil,                          // bindErr
 				chanType,
@@ -310,7 +359,7 @@ func TestBackupTask(t *testing.T) {
 				0,                              // toLocalAmt
 				100000,                         // toRemoteAmt
 				blobTypeCommitNoReward,         // blobType
-				227500,                  // sweepFeeRate
+				sweepFeeRateNoRewardRemoteDust, // sweepFeeRate
 				nil,                            // rewardScript
 				0,                              // expSweepAmt
 				0,                              // expRewardAmt
@@ -351,7 +400,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitReward,     // blobType
 				1000,                     // sweepFeeRate
 				addrScript,               // rewardScript
-				296117,               // expSweepAmt
+				expSweepCommitRewardBoth, // expSweepAmt
 				3000,                     // expRewardAmt
 				nil,                      // bindErr
 				chanType,
@@ -364,7 +413,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitReward,      // blobType
 				1000,                      // sweepFeeRate
 				addrScript,                // rewardScript
-				197390,               // expSweepAmt
+				expSweepCommitRewardLocal, // expSweepAmt
 				2000,                      // expRewardAmt
 				nil,                       // bindErr
 				chanType,
@@ -377,7 +426,7 @@ func TestBackupTask(t *testing.T) {
 				blobTypeCommitReward,       // blobType
 				1000,                       // sweepFeeRate
 				addrScript,                 // rewardScript
-				98437,                // expSweepAmt
+				expSweepCommitRewardRemote, // expSweepAmt
 				1000,                       // expRewardAmt
 				nil,                        // bindErr
 				chanType,
@@ -388,7 +437,7 @@ func TestBackupTask(t *testing.T) {
 				0,                            // toLocalAmt
 				100000,                       // toRemoteAmt
 				blobTypeCommitReward,         // blobType
-				175000,                  // sweepFeeRate
+				sweepFeeRateRewardRemoteDust, // sweepFeeRate
 				addrScript,                   // rewardScript
 				0,                            // expSweepAmt
 				0,                            // expRewardAmt