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htlcswitch+lnwallet: calculate fee exposure as commit fees + dust

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This commit expands the definition of the dust limit to take into
account commitment fees as well as dust HTLCs. The dust limit is now
known as a fee exposure threshold. Dust HTLCs are fees anyways so it
makes sense to account for commitment fees as well. The link has
been modified slightly to calculate dust. In the future, the switch
dust calculations can be removed.
This commit is contained in:
Eugene Siegel
2024-06-03 12:43:33 -04:00
parent b7c59b36a7
commit d6001d033b
11 changed files with 456 additions and 88 deletions
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73
htlcswitch/switch.go
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@@ -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
}
}