Merge pull request #8824 from Crypt-iQ/precise_dust_limit

multi: include commitment fees in dust calculation

htlcswitch/interfaces.go

@@ -3,9 +3,11 @@ package htlcswitch
 import (
 	"context"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
@@ -59,8 +61,10 @@ type packetHandler interface {
 // whether a link has too much dust exposure.
 type dustHandler interface {
 	// getDustSum returns the dust sum on either the local or remote
-	// commitment.
-	getDustSum(remote bool) lnwire.MilliSatoshi
+	// commitment. An optional fee parameter can be passed in which is used
+	// to calculate the dust sum.
+	getDustSum(remote bool,
+		fee fn.Option[chainfee.SatPerKWeight]) lnwire.MilliSatoshi
 
 	// getFeeRate returns the current channel feerate.
 	getFeeRate() chainfee.SatPerKWeight
@@ -68,6 +72,10 @@ type dustHandler interface {
 	// getDustClosure returns a closure that can evaluate whether a passed
 	// HTLC is dust.
 	getDustClosure() dustClosure
+
+	// getCommitFee returns the commitment fee in satoshis from either the
+	// local or remote commitment. This does not include dust.
+	getCommitFee(remote bool) btcutil.Amount
 }
 
 // scidAliasHandler is an interface that the ChannelLink implements so it can

htlcswitch/link.go

@@ -21,6 +21,7 @@ import (
 	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/htlcswitch/hodl"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
+	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lnpeer"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -278,6 +279,10 @@ type ChannelLinkConfig struct {
 	// by failing back any blinding-related payloads as if they were
 	// invalid.
 	DisallowRouteBlinding bool
+
+	// MaxFeeExposure is the threshold in milli-satoshis after which we'll
+	// restrict the flow of HTLCs and fee updates.
+	MaxFeeExposure lnwire.MilliSatoshi
 }
 
 // channelLink is the service which drives a channel's commitment update
@@ -447,6 +452,11 @@ func NewChannelLink(cfg ChannelLinkConfig,
 
 	logPrefix := fmt.Sprintf("ChannelLink(%v):", channel.ChannelPoint())
 
+	// If the max fee exposure isn't set, use the default.
+	if cfg.MaxFeeExposure == 0 {
+		cfg.MaxFeeExposure = DefaultMaxFeeExposure
+	}
+
 	return &channelLink{
 		cfg:                 cfg,
 		channel:             channel,
@@ -1591,6 +1601,20 @@ func (l *channelLink) handleDownstreamUpdateAdd(pkt *htlcPacket) error {
 		return nil
 	}
 
+	// Check if we can add the HTLC here without exceededing the max fee
+	// exposure threshold.
+	if l.isOverexposedWithHtlc(htlc, false) {
+		l.log.Debugf("Unable to handle downstream HTLC - max fee " +
+			"exposure exceeded")
+
+		l.mailBox.FailAdd(pkt)
+
+		return NewDetailedLinkError(
+			lnwire.NewTemporaryChannelFailure(nil),
+			OutgoingFailureDownstreamHtlcAdd,
+		)
+	}
+
 	// A new payment has been initiated via the downstream channel,
 	// so we add the new HTLC to our local log, then update the
 	// commitment chains.
@@ -1958,6 +1982,18 @@ func (l *channelLink) handleUpstreamMsg(msg lnwire.Message) {
 			return
 		}
 
+		// We have to check the limit here rather than later in the
+		// switch because the counterparty can keep sending HTLC's
+		// without sending a revoke. This would mean that the switch
+		// check would only occur later.
+		if l.isOverexposedWithHtlc(msg, true) {
+			l.fail(LinkFailureError{code: ErrInternalError},
+				"peer sent us an HTLC that exceeded our max "+
+					"fee exposure")
+
+			return
+		}
+
 		// We just received an add request from an upstream peer, so we
 		// add it to our state machine, then add the HTLC to our
 		// "settle" list in the event that we know the preimage.
@@ -2375,9 +2411,32 @@ func (l *channelLink) handleUpstreamMsg(msg lnwire.Message) {
 		l.RWMutex.Unlock()
 
 	case *lnwire.UpdateFee:
+		// Check and see if their proposed fee-rate would make us
+		// exceed the fee threshold.
+		fee := chainfee.SatPerKWeight(msg.FeePerKw)
+
+		isDust, err := l.exceedsFeeExposureLimit(fee)
+		if err != nil {
+			// This shouldn't typically happen. If it does, it
+			// indicates something is wrong with our channel state.
+			l.log.Errorf("Unable to determine if fee threshold " +
+				"exceeded")
+			l.fail(LinkFailureError{code: ErrInternalError},
+				"error calculating fee exposure: %v", err)
+
+			return
+		}
+
+		if isDust {
+			// The proposed fee-rate makes us exceed the fee
+			// threshold.
+			l.fail(LinkFailureError{code: ErrInternalError},
+				"fee threshold exceeded: %v", err)
+			return
+		}
+
 		// We received fee update from peer. If we are the initiator we
 		// will fail the channel, if not we will apply the update.
-		fee := chainfee.SatPerKWeight(msg.FeePerKw)
 		if err := l.channel.ReceiveUpdateFee(fee); err != nil {
 			l.fail(LinkFailureError{code: ErrInvalidUpdate},
 				"error receiving fee update: %v", err)
@@ -2668,8 +2727,10 @@ func (l *channelLink) MayAddOutgoingHtlc(amt lnwire.MilliSatoshi) error {
 // method.
 //
 // NOTE: Part of the dustHandler interface.
-func (l *channelLink) getDustSum(remote bool) lnwire.MilliSatoshi {
-	return l.channel.GetDustSum(remote)
+func (l *channelLink) getDustSum(remote bool,
+	dryRunFee fn.Option[chainfee.SatPerKWeight]) lnwire.MilliSatoshi {
+
+	return l.channel.GetDustSum(remote, dryRunFee)
 }
 
 // getFeeRate is a wrapper method that retrieves the underlying channel's
@@ -2692,6 +2753,130 @@ func (l *channelLink) getDustClosure() dustClosure {
 	return dustHelper(chanType, localDustLimit, remoteDustLimit)
 }
 
+// getCommitFee returns either the local or remote CommitFee in satoshis. This
+// is used so that the Switch can have access to the commitment fee without
+// needing to have a *LightningChannel. This doesn't include dust.
+//
+// NOTE: Part of the dustHandler interface.
+func (l *channelLink) getCommitFee(remote bool) btcutil.Amount {
+	if remote {
+		return l.channel.State().RemoteCommitment.CommitFee
+	}
+
+	return l.channel.State().LocalCommitment.CommitFee
+}
+
+// exceedsFeeExposureLimit returns whether or not the new proposed fee-rate
+// increases the total dust and fees within the channel past the configured
+// fee threshold. It first calculates the dust sum over every update in the
+// update log with the proposed fee-rate and taking into account both the local
+// and remote dust limits. It uses every update in the update log instead of
+// what is actually on the local and remote commitments because it is assumed
+// that in a worst-case scenario, every update in the update log could
+// theoretically be on either commitment transaction and this needs to be
+// accounted for with this fee-rate. It then calculates the local and remote
+// commitment fees given the proposed fee-rate. Finally, it tallies the results
+// and determines if the fee threshold has been exceeded.
+func (l *channelLink) exceedsFeeExposureLimit(
+	feePerKw chainfee.SatPerKWeight) (bool, error) {
+
+	dryRunFee := fn.Some[chainfee.SatPerKWeight](feePerKw)
+
+	// Get the sum of dust for both the local and remote commitments using
+	// this "dry-run" fee.
+	localDustSum := l.getDustSum(false, dryRunFee)
+	remoteDustSum := l.getDustSum(true, dryRunFee)
+
+	// Calculate the local and remote commitment fees using this dry-run
+	// fee.
+	localFee, remoteFee, err := l.channel.CommitFeeTotalAt(feePerKw)
+	if err != nil {
+		return false, err
+	}
+
+	// Finally, check whether the max fee exposure was exceeded on either
+	// future commitment transaction with the fee-rate.
+	totalLocalDust := localDustSum + lnwire.NewMSatFromSatoshis(localFee)
+	if totalLocalDust > l.cfg.MaxFeeExposure {
+		return true, nil
+	}
+
+	totalRemoteDust := remoteDustSum + lnwire.NewMSatFromSatoshis(
+		remoteFee,
+	)
+
+	return totalRemoteDust > l.cfg.MaxFeeExposure, nil
+}
+
+// isOverexposedWithHtlc calculates whether the proposed HTLC will make the
+// channel exceed the fee threshold. It first fetches the largest fee-rate that
+// may be on any unrevoked commitment transaction. Then, using this fee-rate,
+// determines if the to-be-added HTLC is dust. If the HTLC is dust, it adds to
+// the overall dust sum. If it is not dust, it contributes to weight, which
+// also adds to the overall dust sum by an increase in fees. If the dust sum on
+// either commitment exceeds the configured fee threshold, this function
+// returns true.
+func (l *channelLink) isOverexposedWithHtlc(htlc *lnwire.UpdateAddHTLC,
+	incoming bool) bool {
+
+	dustClosure := l.getDustClosure()
+
+	feeRate := l.channel.WorstCaseFeeRate()
+
+	amount := htlc.Amount.ToSatoshis()
+
+	// See if this HTLC is dust on both the local and remote commitments.
+	isLocalDust := dustClosure(feeRate, incoming, true, amount)
+	isRemoteDust := dustClosure(feeRate, incoming, false, amount)
+
+	// Calculate the dust sum for the local and remote commitments.
+	localDustSum := l.getDustSum(false, fn.None[chainfee.SatPerKWeight]())
+	remoteDustSum := l.getDustSum(true, fn.None[chainfee.SatPerKWeight]())
+
+	// Grab the larger of the local and remote commitment fees w/o dust.
+	commitFee := l.getCommitFee(false)
+
+	if l.getCommitFee(true) > commitFee {
+		commitFee = l.getCommitFee(true)
+	}
+
+	localDustSum += lnwire.NewMSatFromSatoshis(commitFee)
+	remoteDustSum += lnwire.NewMSatFromSatoshis(commitFee)
+
+	// Calculate the additional fee increase if this is a non-dust HTLC.
+	weight := lntypes.WeightUnit(input.HTLCWeight)
+	additional := lnwire.NewMSatFromSatoshis(
+		feeRate.FeeForWeight(weight),
+	)
+
+	if isLocalDust {
+		// If this is dust, it doesn't contribute to weight but does
+		// contribute to the overall dust sum.
+		localDustSum += lnwire.NewMSatFromSatoshis(amount)
+	} else {
+		// Account for the fee increase that comes with an increase in
+		// weight.
+		localDustSum += additional
+	}
+
+	if localDustSum > l.cfg.MaxFeeExposure {
+		// The max fee exposure was exceeded.
+		return true
+	}
+
+	if isRemoteDust {
+		// If this is dust, it doesn't contribute to weight but does
+		// contribute to the overall dust sum.
+		remoteDustSum += lnwire.NewMSatFromSatoshis(amount)
+	} else {
+		// Account for the fee increase that comes with an increase in
+		// weight.
+		remoteDustSum += additional
+	}
+
+	return remoteDustSum > l.cfg.MaxFeeExposure
+}
+
 // dustClosure is a function that evaluates whether an HTLC is dust. It returns
 // true if the HTLC is dust. It takes in a feerate, a boolean denoting whether
 // the HTLC is incoming (i.e. one that the remote sent), a boolean denoting
@@ -3060,6 +3245,19 @@ func (l *channelLink) updateChannelFee(feePerKw chainfee.SatPerKWeight) error {
 		return nil
 	}
 
+	// Check and see if our proposed fee-rate would make us exceed the fee
+	// threshold.
+	thresholdExceeded, err := l.exceedsFeeExposureLimit(feePerKw)
+	if err != nil {
+		// This shouldn't typically happen. If it does, it indicates
+		// something is wrong with our channel state.
+		return err
+	}
+
+	if thresholdExceeded {
+		return fmt.Errorf("link fee threshold exceeded")
+	}
+
 	// First, we'll update the local fee on our commitment.
 	if err := l.channel.UpdateFee(feePerKw); err != nil {
 		return err

htlcswitch/link_test.go

@@ -4471,10 +4471,20 @@ func TestChannelLinkUpdateCommitFee(t *testing.T) {
 
 	// Triggering the link to update the fee of the channel with a fee rate
 	// that exceeds its maximum fee allocation should result in a fee rate
-	// corresponding to the maximum fee allocation.
+	// corresponding to the maximum fee allocation. Increase the dust
+	// threshold so that we don't trigger that logic.
+	highFeeExposure := lnwire.NewMSatFromSatoshis(
+		2 * btcutil.SatoshiPerBitcoin,
+	)
 	const maxFeeRate chainfee.SatPerKWeight = 207180182
+	n.aliceChannelLink.cfg.MaxFeeExposure = highFeeExposure
+	n.firstBobChannelLink.cfg.MaxFeeExposure = highFeeExposure
 	triggerFeeUpdate(maxFeeRate+1, minRelayFee, maxFeeRate, true)
 
+	// Decrease the max fee exposure back to normal.
+	n.aliceChannelLink.cfg.MaxFeeExposure = DefaultMaxFeeExposure
+	n.firstBobChannelLink.cfg.MaxFeeExposure = DefaultMaxFeeExposure
+
 	// Triggering the link to update the fee of the channel with a fee rate
 	// that is below the current min relay fee rate should result in a fee
 	// rate corresponding to the minimum relay fee.

htlcswitch/mock.go

@@ -26,6 +26,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/contractcourt"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lnpeer"
@@ -200,7 +201,7 @@ func initSwitchWithDB(startingHeight uint32, db *channeldb.DB) (*Switch, error)
 		HtlcNotifier:           &mockHTLCNotifier{},
 		Clock:                  clock.NewDefaultClock(),
 		MailboxDeliveryTimeout: time.Hour,
-		DustThreshold:          DefaultDustThreshold,
+		MaxFeeExposure:         DefaultMaxFeeExposure,
 		SignAliasUpdate:        signAliasUpdate,
 		IsAlias:                isAlias,
 	}
@@ -813,7 +814,9 @@ func (f *mockChannelLink) handleSwitchPacket(pkt *htlcPacket) error {
 	return nil
 }
 
-func (f *mockChannelLink) getDustSum(remote bool) lnwire.MilliSatoshi {
+func (f *mockChannelLink) getDustSum(remote bool,
+	dryRunFee fn.Option[chainfee.SatPerKWeight]) lnwire.MilliSatoshi {
+
 	return 0
 }
 
@@ -828,6 +831,10 @@ func (f *mockChannelLink) getDustClosure() dustClosure {
 	)
 }
 
+func (f *mockChannelLink) getCommitFee(remote bool) btcutil.Amount {
+	return 0
+}
+
 func (f *mockChannelLink) HandleChannelUpdate(lnwire.Message) {
 }
 

htlcswitch/switch.go

@@ -18,6 +18,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/contractcourt"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -75,14 +76,15 @@ var (
 	// failed to be processed.
 	ErrLocalAddFailed = errors.New("local add HTLC failed")
 
-	// errDustThresholdExceeded is only surfaced to callers of SendHTLC and
-	// signals that sending the HTLC would exceed the outgoing link's dust
-	// threshold.
-	errDustThresholdExceeded = errors.New("dust threshold exceeded")
+	// errFeeExposureExceeded is only surfaced to callers of SendHTLC and
+	// signals that sending the HTLC would exceed the outgoing link's fee
+	// exposure threshold.
+	errFeeExposureExceeded = errors.New("fee exposure exceeded")
 
-	// DefaultDustThreshold is the default threshold after which we'll fail
-	// payments if they are dust. This is currently set to 500m msats.
-	DefaultDustThreshold = lnwire.MilliSatoshi(500_000_000)
+	// DefaultMaxFeeExposure is the default threshold after which we'll
+	// fail payments if they increase our fee exposure. This is currently
+	// set to 500m msats.
+	DefaultMaxFeeExposure = lnwire.MilliSatoshi(500_000_000)
 )
 
 // plexPacket encapsulates switch packet and adds error channel to receive
@@ -210,9 +212,9 @@ type Config struct {
 	// a mailbox via AddPacket.
 	MailboxDeliveryTimeout time.Duration
 
-	// DustThreshold is the threshold in milli-satoshis after which we'll
-	// fail incoming or outgoing dust payments for a particular channel.
-	DustThreshold lnwire.MilliSatoshi
+	// MaxFeeExposure is the threshold in milli-satoshis after which we'll
+	// fail incoming or outgoing payments for a particular channel.
+	MaxFeeExposure lnwire.MilliSatoshi
 
 	// SignAliasUpdate is used when sending FailureMessages backwards for
 	// option_scid_alias channels. This avoids a potential privacy leak by
@@ -559,9 +561,9 @@ func (s *Switch) SendHTLC(firstHop lnwire.ShortChannelID, attemptID uint64,
 		return linkErr
 	}
 
-	// Evaluate whether this HTLC would increase our exposure to dust. If
-	// it does, don't send it out and instead return an error.
-	if s.evaluateDustThreshold(link, htlc.Amount, false) {
+	// Evaluate whether this HTLC would bypass our fee exposure. If it
+	// does, don't send it out and instead return an error.
+	if s.dustExceedsFeeThreshold(link, htlc.Amount, false) {
 		// Notify the htlc notifier of a link failure on our outgoing
 		// link. We use the FailTemporaryChannelFailure in place of a
 		// more descriptive error message.
@@ -579,7 +581,7 @@ func (s *Switch) SendHTLC(firstHop lnwire.ShortChannelID, attemptID uint64,
 			false,
 		)
 
-		return errDustThresholdExceeded
+		return errFeeExposureExceeded
 	}
 
 	circuit := newPaymentCircuit(&htlc.PaymentHash, packet)
@@ -1247,9 +1249,10 @@ func (s *Switch) handlePacketForward(packet *htlcPacket) error {
 			return s.failAddPacket(packet, linkErr)
 		}
 
-		// Evaluate whether this HTLC would increase our exposure to
-		// dust on the incoming link. If it does, fail it backwards.
-		if s.evaluateDustThreshold(
+		// Evaluate whether this HTLC would increase our fee exposure
+		// over the threshold on the incoming link. If it does, fail it
+		// backwards.
+		if s.dustExceedsFeeThreshold(
 			incomingLink, packet.incomingAmount, true,
 		) {
 			// The incoming dust exceeds the threshold, so we fail
@@ -1261,9 +1264,10 @@ func (s *Switch) handlePacketForward(packet *htlcPacket) error {
 			return s.failAddPacket(packet, linkErr)
 		}
 
-		// Also evaluate whether this HTLC would increase our exposure
-		// to dust on the destination link. If it does, fail it back.
-		if s.evaluateDustThreshold(
+		// Also evaluate whether this HTLC would increase our fee
+		// exposure over the threshold on the destination link. If it
+		// does, fail it back.
+		if s.dustExceedsFeeThreshold(
 			destination, packet.amount, false,
 		) {
 			// The outgoing dust exceeds the threshold, so we fail
@@ -2768,14 +2772,15 @@ func (s *Switch) BestHeight() uint32 {
 	return atomic.LoadUint32(&s.bestHeight)
 }
 
-// evaluateDustThreshold takes in a ChannelLink, HTLC amount, and a boolean to
-// determine whether the default dust threshold has been exceeded. This
+// dustExceedsFeeThreshold takes in a ChannelLink, HTLC amount, and a boolean
+// to determine whether the default fee threshold has been exceeded. This
 // heuristic takes into account the trimmed-to-dust mechanism. The sum of the
 // commitment's dust with the mailbox's dust with the amount is checked against
-// the default threshold. If incoming is true, then the amount is not included
-// in the sum as it was already included in the commitment's dust. A boolean is
-// returned telling the caller whether the HTLC should be failed back.
-func (s *Switch) evaluateDustThreshold(link ChannelLink,
+// the fee exposure threshold. If incoming is true, then the amount is not
+// included in the sum as it was already included in the commitment's dust. A
+// boolean is returned telling the caller whether the HTLC should be failed
+// back.
+func (s *Switch) dustExceedsFeeThreshold(link ChannelLink,
 	amount lnwire.MilliSatoshi, incoming bool) bool {
 
 	// Retrieve the link's current commitment feerate and dustClosure.
@@ -2801,7 +2806,9 @@ func (s *Switch) evaluateDustThreshold(link ChannelLink,
 	// If the htlc is dust on the local commitment, we'll obtain the dust
 	// sum for it.
 	if isLocalDust {
-		localSum := link.getDustSum(false)
+		localSum := link.getDustSum(
+			false, fn.None[chainfee.SatPerKWeight](),
+		)
 		localSum += localMailDust
 
 		// Optionally include the HTLC amount only for outgoing
@@ -2810,8 +2817,8 @@ func (s *Switch) evaluateDustThreshold(link ChannelLink,
 			localSum += amount
 		}
 
-		// Finally check against the defined dust threshold.
-		if localSum > s.cfg.DustThreshold {
+		// Finally check against the defined fee threshold.
+		if localSum > s.cfg.MaxFeeExposure {
 			return true
 		}
 	}
@@ -2819,7 +2826,9 @@ func (s *Switch) evaluateDustThreshold(link ChannelLink,
 	// Also check if the htlc is dust on the remote commitment, if we've
 	// reached this point.
 	if isRemoteDust {
-		remoteSum := link.getDustSum(true)
+		remoteSum := link.getDustSum(
+			true, fn.None[chainfee.SatPerKWeight](),
+		)
 		remoteSum += remoteMailDust
 
 		// Optionally include the HTLC amount only for outgoing
@@ -2828,8 +2837,8 @@ func (s *Switch) evaluateDustThreshold(link ChannelLink,
 			remoteSum += amount
 		}
 
-		// Finally check against the defined dust threshold.
-		if remoteSum > s.cfg.DustThreshold {
+		// Finally check against the defined fee threshold.
+		if remoteSum > s.cfg.MaxFeeExposure {
 			return true
 		}
 	}

htlcswitch/switch_test.go

@@ -18,10 +18,12 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/contractcourt"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/htlcswitch/hodl"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/lntest/mock"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/ticker"
 	"github.com/stretchr/testify/require"
@@ -4259,7 +4261,7 @@ func TestInterceptableSwitchWatchDog(t *testing.T) {
 }
 
 // TestSwitchDustForwarding tests that the switch properly fails HTLC's which
-// have incoming or outgoing links that breach their dust thresholds.
+// have incoming or outgoing links that breach their fee thresholds.
 func TestSwitchDustForwarding(t *testing.T) {
 	t.Parallel()
 
@@ -4288,14 +4290,15 @@ func TestSwitchDustForwarding(t *testing.T) {
 	// We'll test that once the default threshold is exceeded on the
 	// Alice -> Bob channel, either side's calls to SendHTLC will fail.
 	//
-	// Alice will send 357 HTLC's of 700sats. Bob will also send 357 HTLC's
-	// of 700sats. If either side attempts to send a dust HTLC, it will
-	// fail so amounts below 800sats will breach the dust threshold.
+	// Alice will send 354 HTLC's of 700sats. Bob will also send 354 HTLC's
+	// of 700sats.
+	numHTLCs := 354
+	aliceAttemptID, bobAttemptID := numHTLCs, numHTLCs
 	amt := lnwire.NewMSatFromSatoshis(700)
 	aliceBobFirstHop := n.aliceChannelLink.ShortChanID()
 
-	sendDustHtlcs(t, n, true, amt, aliceBobFirstHop)
-	sendDustHtlcs(t, n, false, amt, aliceBobFirstHop)
+	sendDustHtlcs(t, n, true, amt, aliceBobFirstHop, numHTLCs)
+	sendDustHtlcs(t, n, false, amt, aliceBobFirstHop, numHTLCs)
 
 	// Generate the parameters needed for Bob to send another dust HTLC.
 	_, timelock, hops := generateHops(
@@ -4320,7 +4323,7 @@ func TestSwitchDustForwarding(t *testing.T) {
 
 		timeout := time.After(15 * time.Second)
 		pollInterval := 300 * time.Millisecond
-		expectedDust := 357 * 2 * amt
+		expectedDust := 354 * 2 * amt
 
 		for {
 			<-time.After(pollInterval)
@@ -4331,7 +4334,9 @@ func TestSwitchDustForwarding(t *testing.T) {
 			default:
 			}
 
-			linkDust := link.getDustSum(remote)
+			linkDust := link.getDustSum(
+				remote, fn.None[chainfee.SatPerKWeight](),
+			)
 			localMailDust, remoteMailDust := mbox.DustPackets()
 
 			totalDust := linkDust
@@ -4349,18 +4354,34 @@ func TestSwitchDustForwarding(t *testing.T) {
 		return true
 	}
 
-	// Wait until Bob is almost at the dust threshold.
+	// Wait until Bob is almost at the fee threshold.
 	bobMbox := n.bobServer.htlcSwitch.mailOrchestrator.GetOrCreateMailBox(
 		n.firstBobChannelLink.ChanID(),
 		n.firstBobChannelLink.ShortChanID(),
 	)
 	require.True(t, checkAlmostDust(n.firstBobChannelLink, bobMbox, false))
 
-	// Assert that the HTLC is failed due to the dust threshold.
+	// Sending one more HTLC should fail. SendHTLC won't error, but the
+	// HTLC should be failed backwards.
 	err = n.bobServer.htlcSwitch.SendHTLC(
-		aliceBobFirstHop, uint64(357), failingHtlc,
+		aliceBobFirstHop, uint64(bobAttemptID), failingHtlc,
 	)
-	require.ErrorIs(t, err, errDustThresholdExceeded)
+	require.Nil(t, err)
+
+	// Use the network result store to ensure the HTLC was failed
+	// backwards.
+	bobResultChan, err := n.bobServer.htlcSwitch.GetAttemptResult(
+		uint64(bobAttemptID), failingHash, newMockDeobfuscator(),
+	)
+	require.NoError(t, err)
+
+	result, ok := <-bobResultChan
+	require.True(t, ok)
+	assertFailureCode(
+		t, result.Error, lnwire.CodeTemporaryChannelFailure,
+	)
+
+	bobAttemptID++
 
 	// Generate the parameters needed for bob to send a non-dust HTLC.
 	nondustAmt := lnwire.NewMSatFromSatoshis(10_000)
@@ -4371,8 +4392,9 @@ func TestSwitchDustForwarding(t *testing.T) {
 	blob, err = generateRoute(hops...)
 	require.NoError(t, err)
 
-	// Now attempt to send an HTLC above Bob's dust limit. It should
-	// succeed.
+	// Now attempt to send an HTLC above Bob's dust limit. Even though this
+	// is not a dust HTLC, it should fail because the increase in weight
+	// pushes us over the threshold.
 	nondustPreimage := lntypes.Preimage{0, 0, 4}
 	nondustHash := nondustPreimage.Hash()
 	nondustHtlc := &lnwire.UpdateAddHTLC{
@@ -4382,12 +4404,23 @@ func TestSwitchDustForwarding(t *testing.T) {
 		OnionBlob:   blob,
 	}
 
-	// Assert that SendHTLC succeeds and evaluateDustThreshold returns
-	// false.
 	err = n.bobServer.htlcSwitch.SendHTLC(
-		aliceBobFirstHop, uint64(358), nondustHtlc,
+		aliceBobFirstHop, uint64(bobAttemptID), nondustHtlc,
 	)
 	require.NoError(t, err)
+	require.True(t, checkAlmostDust(n.firstBobChannelLink, bobMbox, false))
+
+	// Check that the HTLC failed.
+	bobResultChan, err = n.bobServer.htlcSwitch.GetAttemptResult(
+		uint64(bobAttemptID), nondustHash, newMockDeobfuscator(),
+	)
+	require.NoError(t, err)
+
+	result, ok = <-bobResultChan
+	require.True(t, ok)
+	assertFailureCode(
+		t, result.Error, lnwire.CodeTemporaryChannelFailure,
+	)
 
 	// Introduce Carol into the mix and assert that sending a multi-hop
 	// dust HTLC to Alice will fail. Bob should fail back the HTLC with a
@@ -4417,21 +4450,19 @@ func TestSwitchDustForwarding(t *testing.T) {
 		carolHtlc,
 	)
 	require.NoError(t, err)
-	carolAttemptID++
 
 	carolResultChan, err := n.carolServer.htlcSwitch.GetAttemptResult(
-		uint64(carolAttemptID-1), carolHash, newMockDeobfuscator(),
+		uint64(carolAttemptID), carolHash, newMockDeobfuscator(),
 	)
 	require.NoError(t, err)
 
-	result, ok := <-carolResultChan
+	result, ok = <-carolResultChan
 	require.True(t, ok)
 	assertFailureCode(
 		t, result.Error, lnwire.CodeTemporaryChannelFailure,
 	)
 
-	// Send an HTLC from Alice to Carol and assert that it is failed at the
-	// call to SendHTLC.
+	// Send an HTLC from Alice to Carol and assert that it gets failed.
 	htlcAmt, totalTimelock, aliceHops := generateHops(
 		amt, testStartingHeight, n.firstBobChannelLink,
 		n.carolChannelLink,
@@ -4450,7 +4481,7 @@ func TestSwitchDustForwarding(t *testing.T) {
 	}
 
 	// Wait until Alice's expected dust for the remote commitment is just
-	// under the dust threshold.
+	// under the fee threshold.
 	aliceOrch := n.aliceServer.htlcSwitch.mailOrchestrator
 	aliceMbox := aliceOrch.GetOrCreateMailBox(
 		n.aliceChannelLink.ChanID(), n.aliceChannelLink.ShortChanID(),
@@ -4458,23 +4489,36 @@ func TestSwitchDustForwarding(t *testing.T) {
 	require.True(t, checkAlmostDust(n.aliceChannelLink, aliceMbox, true))
 
 	err = n.aliceServer.htlcSwitch.SendHTLC(
-		n.aliceChannelLink.ShortChanID(), uint64(357),
+		n.aliceChannelLink.ShortChanID(), uint64(aliceAttemptID),
 		aliceMultihopHtlc,
 	)
-	require.ErrorIs(t, err, errDustThresholdExceeded)
+	require.Nil(t, err)
+
+	aliceResultChan, err := n.aliceServer.htlcSwitch.GetAttemptResult(
+		uint64(aliceAttemptID), aliceMultihopHash,
+		newMockDeobfuscator(),
+	)
+	require.NoError(t, err)
+
+	result, ok = <-aliceResultChan
+	require.True(t, ok)
+	assertFailureCode(
+		t, result.Error, lnwire.CodeTemporaryChannelFailure,
+	)
+
+	// Check that there are numHTLCs circuits open for both Alice and Bob.
+	require.Equal(t, numHTLCs, n.aliceServer.htlcSwitch.circuits.NumOpen())
+	require.Equal(t, numHTLCs, n.bobServer.htlcSwitch.circuits.NumOpen())
 }
 
 // sendDustHtlcs is a helper function used to send many dust HTLC's to test the
 // Switch's dust-threshold logic. It takes a boolean denoting whether or not
 // Alice is the sender.
 func sendDustHtlcs(t *testing.T, n *threeHopNetwork, alice bool,
-	amt lnwire.MilliSatoshi, sid lnwire.ShortChannelID) {
+	amt lnwire.MilliSatoshi, sid lnwire.ShortChannelID, numHTLCs int) {
 
 	t.Helper()
 
-	// The number of dust HTLC's we'll send for both Alice and Bob.
-	numHTLCs := 357
-
 	// Extract the destination into a variable. If alice is the sender, the
 	// destination is Bob.
 	destLink := n.aliceChannelLink
@@ -4527,8 +4571,8 @@ func sendDustHtlcs(t *testing.T, n *threeHopNetwork, alice bool,
 		}
 
 		for {
-			// It may be the case that the dust threshold is hit
-			// before all 357*2 HTLC's are sent due to double
+			// It may be the case that the fee threshold is hit
+			// before all numHTLCs*2 HTLC's are sent due to double
 			// counting. Get around this by continuing to send
 			// until successful.
 			err = sendingSwitch.SendHTLC(sid, attemptID, htlc)
@@ -4542,7 +4586,7 @@ func sendDustHtlcs(t *testing.T, n *threeHopNetwork, alice bool,
 }
 
 // TestSwitchMailboxDust tests that the switch takes into account the mailbox
-// dust when evaluating the dust threshold. The mockChannelLink does not have
+// dust when evaluating the fee threshold. The mockChannelLink does not have
 // channel state, so this only tests the switch-mailbox interaction.
 func TestSwitchMailboxDust(t *testing.T) {
 	t.Parallel()
@@ -4612,7 +4656,7 @@ func TestSwitchMailboxDust(t *testing.T) {
 	var carolHTLCID uint64
 
 	// It will take aliceCount HTLC's of 350sats to fill up Alice's mailbox
-	// to the point where another would put Alice over the dust threshold.
+	// to the point where another would put Alice over the fee threshold.
 	aliceCount := 1428
 
 	mailbox := s.mailOrchestrator.GetOrCreateMailBox(chanID1, aliceChanID)
@@ -4634,10 +4678,10 @@ func TestSwitchMailboxDust(t *testing.T) {
 		carolHTLCID++
 	}
 
-	// Sending one more HTLC to Alice should result in the dust threshold
+	// Sending one more HTLC to Alice should result in the fee threshold
 	// being breached.
 	err = s.SendHTLC(aliceChanID, 0, addMsg)
-	require.ErrorIs(t, err, errDustThresholdExceeded)
+	require.ErrorIs(t, err, errFeeExposureExceeded)
 
 	// We'll now call ForwardPackets from Bob to ensure that the mailbox
 	// sum is also accounted for in the forwarding case.