multi: factor out sweep fee clamping function

instantout/actions.go

@@ -317,9 +317,16 @@ func (f *FSM) BuildHTLCAction(ctx context.Context,
 		return f.handleErrorAndUnlockReservations(ctx, err)
 	}
 
+	minRelayFee, err := f.cfg.Wallet.MinRelayFee(ctx)
+	if err != nil {
+		return f.handleErrorAndUnlockReservations(ctx, err)
+	}
+
 	// Now that our nonces are set, we can create and sign the htlc
 	// transaction.
-	htlcTx, err := f.InstantOut.createHtlcTransaction(f.cfg.Network)
+	htlcTx, err := f.InstantOut.createHtlcTransaction(
+		f.cfg.Network, minRelayFee,
+	)
 	if err != nil {
 		return f.handleErrorAndUnlockReservations(ctx, err)
 	}
@@ -382,6 +389,11 @@ func (f *FSM) PushPreimageAction(ctx context.Context,
 		return f.handleErrorAndUnlockReservations(ctx, err)
 	}
 
+	minRelayFee, err := f.cfg.Wallet.MinRelayFee(ctx)
+	if err != nil {
+		return f.handleErrorAndUnlockReservations(ctx, err)
+	}
+
 	pushPreImageRes, err := f.cfg.InstantOutClient.PushPreimage(
 		ctx,
 		&swapserverrpc.PushPreimageRequest{
@@ -400,7 +412,9 @@ func (f *FSM) PushPreimageAction(ctx context.Context,
 
 	// Now that we have the sweepless sweep signatures we can build and
 	// publish the sweepless sweep transaction.
-	sweepTx, err := f.InstantOut.createSweeplessSweepTx(feeRate)
+	sweepTx, err := f.InstantOut.createSweeplessSweepTx(
+		feeRate, minRelayFee,
+	)
 	if err != nil {
 		f.LastActionError = err
 		return OnErrorPublishHtlc

instantout/instantout.go

@@ -18,6 +18,7 @@ import (
 	"github.com/lightninglabs/loop/instantout/reservation"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
+	"github.com/lightninglabs/loop/utils"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -145,8 +146,8 @@ func (i *InstantOut) getInputReservations() (InputReservations, error) {
 }
 
 // createHtlcTransaction creates the htlc transaction for the instant out.
-func (i *InstantOut) createHtlcTransaction(network *chaincfg.Params) (
-	*wire.MsgTx, error) {
+func (i *InstantOut) createHtlcTransaction(network *chaincfg.Params,
+	minRelayFeeRate chainfee.SatPerKWeight) (*wire.MsgTx, error) {
 
 	if network == nil {
 		return nil, errors.New("no network provided")
@@ -170,7 +171,16 @@ func (i *InstantOut) createHtlcTransaction(network *chaincfg.Params) (
 	// Estimate the fee
 	weight := htlcWeight(len(inputReservations))
 	fee := i.htlcFeeRate.FeeForWeight(weight)
-	if fee > i.Value/5 {
+
+	// We cap the fee at 20% of the deposit value.
+	_, clamped, err := utils.ClampSweepFee(
+		fee, i.Value, utils.MaxFeeToAmountRatio, minRelayFeeRate,
+		weight,
+	)
+	if err != nil {
+		return nil, err
+	}
+	if clamped {
 		return nil, errors.New("fee is higher than 20% of " +
 			"sweep value")
 	}
@@ -193,8 +203,8 @@ func (i *InstantOut) createHtlcTransaction(network *chaincfg.Params) (
 
 // createSweeplessSweepTx creates the sweepless sweep transaction for the
 // instant out.
-func (i *InstantOut) createSweeplessSweepTx(feerate chainfee.SatPerKWeight) (
-	*wire.MsgTx, error) {
+func (i *InstantOut) createSweeplessSweepTx(feerate,
+	minRelayFeeRate chainfee.SatPerKWeight) (*wire.MsgTx, error) {
 
 	inputReservations, err := i.getInputReservations()
 	if err != nil {
@@ -214,7 +224,14 @@ func (i *InstantOut) createSweeplessSweepTx(feerate chainfee.SatPerKWeight) (
 	// Estimate the fee
 	weight := sweeplessSweepWeight(len(inputReservations))
 	fee := feerate.FeeForWeight(weight)
-	if fee > i.Value/5 {
+	_, clamped, err := utils.ClampSweepFee(
+		fee, i.Value, utils.MaxFeeToAmountRatio, minRelayFeeRate,
+		weight,
+	)
+	if err != nil {
+		return nil, err
+	}
+	if clamped {
 		return nil, errors.New("fee is higher than 20% of " +
 			"sweep value")
 	}

staticaddr/deposit/actions.go

@@ -11,6 +11,7 @@ import (
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/loop/fsm"
 	"github.com/lightninglabs/loop/staticaddr/script"
+	"github.com/lightninglabs/loop/utils"
 	"github.com/lightningnetwork/lnd/lntypes"
 )
 
@@ -47,12 +48,25 @@ func (f *FSM) PublishDepositExpirySweepAction(ctx context.Context,
 			"estimation failed: %w", err))
 	}
 
+	minRelayFeeRate, err := f.cfg.WalletKit.MinRelayFee(ctx)
+	if err != nil {
+		return f.HandleError(fmt.Errorf("timeout sweep min relay "+
+			"query failed: %w", err))
+	}
+
 	weight := script.ExpirySpendWeight()
 
 	fee := feeRateEstimator.FeeForWeight(lntypes.WeightUnit(weight))
 
 	// We cap the fee at 20% of the deposit value.
-	if fee > f.deposit.Value/5 {
+	_, clamped, err := utils.ClampSweepFee(
+		fee, f.deposit.Value, utils.MaxFeeToAmountRatio,
+		minRelayFeeRate, lntypes.WeightUnit(weight),
+	)
+	if err != nil {
+		return f.HandleError(err)
+	}
+	if clamped {
 		return f.HandleError(errors.New("fee is greater than 20% of " +
 			"the deposit value"))
 	}

sweepbatcher/sweep_batch.go

@@ -46,10 +46,6 @@ const (
 	// transaction.
 	batchConfHeight = 3
 
-	// maxFeeToSwapAmtRatio is the maximum fee to swap amount ratio that
-	// we allow for a batch transaction.
-	maxFeeToSwapAmtRatio = 0.2
-
 	// MaxSweepsPerBatch is the maximum number of sweeps in a single batch.
 	// It is needed to prevent sweep tx from becoming non-standard. Max
 	// standard transaction is 400k wu, a non-cooperative input is 393 wu.
@@ -1414,9 +1410,9 @@ func constructUnsignedTx(sweeps []sweep, address btcutil.Address,
 	}
 
 	// Clamp the calculated fee to the max allowed fee amount for the batch.
-	fee, err := clampBatchFee(
+	fee, _, err := utils.ClampSweepFee(
 		feeForWeight, batchAmt-btcutil.Amount(sumChange),
-		minRelayFeeRate, weight,
+		utils.MaxFeeToAmountRatio, minRelayFeeRate, weight,
 	)
 	if err != nil {
 		return nil, 0, 0, 0, fmt.Errorf("failed to clamp batch "+
@@ -2644,28 +2640,3 @@ func (b *batch) persistConfirmedBatch(ctx context.Context,
 
 	return b.store.ConfirmBatchWithSweeps(ctx, b.dbBatch(), sweeps)
 }
-
-// clampBatchFee takes the fee amount and total amount of the sweeps in the
-// batch and makes sure the fee is not too high. If the fee is too high, it is
-// clamped to the maximum allowed fee. If the clamped fee results in a fee rate
-// below the minimum relay fee, an error is returned.
-func clampBatchFee(fee btcutil.Amount, totalAmount btcutil.Amount,
-	minRelayFeeRate chainfee.SatPerKWeight,
-	weight lntypes.WeightUnit) (btcutil.Amount, error) {
-
-	maxFeeAmount := btcutil.Amount(float64(totalAmount) *
-		maxFeeToSwapAmtRatio)
-
-	clampedFee := fee
-	if fee > maxFeeAmount {
-		clampedFee = maxFeeAmount
-	}
-
-	clampedFeeRate := chainfee.NewSatPerKWeight(clampedFee, weight)
-	if clampedFeeRate < minRelayFeeRate {
-		return 0, fmt.Errorf("clamped fee rate %v is less than "+
-			"minimum relay fee %v", clampedFeeRate, minRelayFeeRate)
-	}
-
-	return clampedFee, nil
-}

utils/fees.go

@@ -0,0 +1,44 @@
+package utils
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+)
+
+const (
+	// MaxFeeToAmountRatio is the maximum fee to total amount ratio allowed
+	// for a sweep transaction.
+	MaxFeeToAmountRatio = 0.2
+)
+
+// ClampSweepFee caps a fee to a percentage of the provided total amount and
+// verifies the resulting fee rate is not below the minimum relay fee. It
+// returns the clamped fee, whether it was clamped, or an error if the clamped
+// fee would fall below the minimum relay fee.
+func ClampSweepFee(fee btcutil.Amount, totalAmount btcutil.Amount,
+	ratio float64, minRelayFeeRate chainfee.SatPerKWeight,
+	weight lntypes.WeightUnit) (btcutil.Amount, bool, error) {
+
+	maxFeeAmount := btcutil.Amount(float64(totalAmount) * ratio)
+
+	clampedFee := fee
+	clamped := false
+	if fee > maxFeeAmount {
+		clampedFee = maxFeeAmount
+		clamped = true
+	}
+
+	if minRelayFeeRate > 0 {
+		clampedFeeRate := chainfee.NewSatPerKWeight(clampedFee, weight)
+		if clampedFeeRate < minRelayFeeRate {
+			return 0, clamped, fmt.Errorf("clamped fee rate %v is "+
+				"less than minimum relay fee %v",
+				clampedFeeRate, minRelayFeeRate)
+		}
+	}
+
+	return clampedFee, clamped, nil
+}

utils/fees_test.go

@@ -0,0 +1,53 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+	"github.com/stretchr/testify/require"
+)
+
+// TestClampSweepFee verifies clamping still respects min relay fee
+// requirements and reports clamping.
+func TestClampSweepFee(t *testing.T) {
+	weight := lntypes.WeightUnit(400)
+	minRelay := chainfee.SatPerKWeight(253)
+	total := btcutil.Amount(100_000)
+
+	// Fee below the clamp threshold and above min relay should pass
+	// through.
+	fee := chainfee.SatPerKWeight(1_000).FeeForWeight(weight)
+	clamped, clampedFlag, err := ClampSweepFee(
+		fee, total, MaxFeeToAmountRatio, minRelay, weight,
+	)
+	require.NoError(t, err)
+	require.Equal(t, fee, clamped)
+	require.False(t, clampedFlag)
+
+	// A clamped fee that would fall below min relay should error.
+	// The fee will be clamped to 20 sats.
+	fee = btcutil.Amount(10_000)
+	total = btcutil.Amount(100)
+	_, clampedFlag, err = ClampSweepFee(
+		fee, total, MaxFeeToAmountRatio, minRelay, weight,
+	)
+	require.True(t, clampedFlag)
+	require.Error(t, err)
+
+	// A fee above the clamp threshold should be clamped without error when
+	// still above min relay. The fee is 30% of total, will clamp to 20%.
+	fee = btcutil.Amount(30_000)
+	total = btcutil.Amount(100_000)
+	clamped, clampedFlag, err = ClampSweepFee(
+		fee, total, MaxFeeToAmountRatio, minRelay, weight,
+	)
+	require.NoError(t, err)
+	require.True(t, clampedFlag)
+
+	expectedClampedFee := btcutil.Amount(
+		float64(total) * MaxFeeToAmountRatio,
+	)
+	require.Equal(t, expectedClampedFee, clamped)
+}