[anchors] HTLC update fee clamp

config.go

@@ -33,6 +33,7 @@ import (
 	"github.com/lightningnetwork/lnd/lncfg"
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/signrpc"
+	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/tor"
 )
@@ -289,6 +290,8 @@ type Config struct {
 
 	MaxChannelFeeAllocation float64 `long:"max-channel-fee-allocation" description:"The maximum percentage of total funds that can be allocated to a channel's commitment fee. This only applies for the initiator of the channel. Valid values are within [0.1, 1]."`
 
+	MaxCommitFeeRateAnchors uint64 `long:"max-commit-fee-rate-anchors" description:"The maximum fee rate in sat/vbyte that will be used for commitments of channels of the anchors type"`
+
 	DryRunMigration bool `long:"dry-run-migration" description:"If true, lnd will abort committing a migration if it would otherwise have been successful. This leaves the database unmodified, and still compatible with the previously active version of lnd."`
 
 	net tor.Net
@@ -475,6 +478,7 @@ func DefaultConfig() Config {
 		},
 		MaxOutgoingCltvExpiry:   htlcswitch.DefaultMaxOutgoingCltvExpiry,
 		MaxChannelFeeAllocation: htlcswitch.DefaultMaxLinkFeeAllocation,
+		MaxCommitFeeRateAnchors: lnwallet.DefaultAnchorsCommitMaxFeeRateSatPerVByte,
 		LogWriter:               build.NewRotatingLogWriter(),
 		DB:                      lncfg.DefaultDB(),
 		registeredChains:        chainreg.NewChainRegistry(),
@@ -735,6 +739,12 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 			cfg.MaxChannelFeeAllocation)
 	}
 
+	if cfg.MaxCommitFeeRateAnchors < 1 {
+		return nil, fmt.Errorf("invalid max commit fee rate anchors: "+
+			"%v, must be at least 1 sat/vbyte",
+			cfg.MaxCommitFeeRateAnchors)
+	}
+
 	// Validate the Tor config parameters.
 	socks, err := lncfg.ParseAddressString(
 		cfg.Tor.SOCKS, strconv.Itoa(defaultTorSOCKSPort),

fundingmanager.go

@@ -366,6 +366,10 @@ type fundingConfig struct {
 	// RegisteredChains keeps track of all chains that have been registered
 	// with the daemon.
 	RegisteredChains *chainreg.ChainRegistry
+
+	// MaxAnchorsCommitFeeRate is the max commitment fee rate we'll use as
+	// the initiator for channels of the anchor type.
+	MaxAnchorsCommitFeeRate chainfee.SatPerKWeight
 }
 
 // fundingManager acts as an orchestrator/bridge between the wallet's
@@ -3123,16 +3127,6 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 		msg.pushAmt, msg.chainHash, peerKey.SerializeCompressed(),
 		ourDustLimit, msg.minConfs)
 
-	// First, we'll query the fee estimator for a fee that should get the
-	// commitment transaction confirmed by the next few blocks (conf target
-	// of 3). We target the near blocks here to ensure that we'll be able
-	// to execute a timely unilateral channel closure if needed.
-	commitFeePerKw, err := f.cfg.FeeEstimator.EstimateFeePerKW(3)
-	if err != nil {
-		msg.err <- err
-		return
-	}
-
 	// We set the channel flags to indicate whether we want this channel to
 	// be announced to the network.
 	var channelFlags lnwire.FundingFlag
@@ -3192,6 +3186,25 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 	commitType := commitmentType(
 		msg.peer.LocalFeatures(), msg.peer.RemoteFeatures(),
 	)
+
+	// First, we'll query the fee estimator for a fee that should get the
+	// commitment transaction confirmed by the next few blocks (conf target
+	// of 3). We target the near blocks here to ensure that we'll be able
+	// to execute a timely unilateral channel closure if needed.
+	commitFeePerKw, err := f.cfg.FeeEstimator.EstimateFeePerKW(3)
+	if err != nil {
+		msg.err <- err
+		return
+	}
+
+	// For anchor channels cap the initial commit fee rate at our defined
+	// maximum.
+	if commitType == lnwallet.CommitmentTypeAnchors &&
+		commitFeePerKw > f.cfg.MaxAnchorsCommitFeeRate {
+
+		commitFeePerKw = f.cfg.MaxAnchorsCommitFeeRate
+	}
+
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:        &msg.chainHash,
 		PendingChanID:    chanID,
@@ -3224,6 +3237,36 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 	// SubtractFees=true.
 	capacity := reservation.Capacity()
 
+	// We'll use the current value of the channels and our default policy
+	// to determine of required commitment constraints for the remote
+	// party.
+	chanReserve := f.cfg.RequiredRemoteChanReserve(capacity, ourDustLimit)
+
+	// As a sanity check, we ensure that the user is not trying to open a
+	// tiny anchor channel that would be unusable because of the fee siphon
+	// check we do.
+	if commitType == lnwallet.CommitmentTypeAnchors {
+		timeoutFee := lnwallet.HtlcTimeoutFee(
+			channeldb.AnchorOutputsBit,
+			f.cfg.MaxAnchorsCommitFeeRate,
+		)
+
+		maxNumHtlcs := chanReserve / timeoutFee
+		if maxNumHtlcs < lnwallet.MinAnchorHtlcSlots {
+			if err := reservation.Cancel(); err != nil {
+				fndgLog.Errorf("unable to cancel "+
+					"reservation: %v", err)
+			}
+
+			maxHtlcErr := fmt.Errorf("tiny channel, only room "+
+				"for %d HTLCs. Consider making a larger "+
+				"channel or reducing the max commit fee rate",
+				maxNumHtlcs)
+			msg.err <- maxHtlcErr
+			return
+		}
+	}
+
 	fndgLog.Infof("Target commit tx sat/kw for pendingID(%x): %v", chanID,
 		int64(commitFeePerKw))
 
@@ -3279,11 +3322,6 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 	// request to the remote peer, kicking off the funding workflow.
 	ourContribution := reservation.OurContribution()
 
-	// Finally, we'll use the current value of the channels and our default
-	// policy to determine of required commitment constraints for the
-	// remote party.
-	chanReserve := f.cfg.RequiredRemoteChanReserve(capacity, ourDustLimit)
-
 	fndgLog.Infof("Starting funding workflow with %v for pending_id(%x), "+
 		"committype=%v", msg.peer.Address(), chanID, commitType)
 

htlcswitch/link.go

@@ -269,6 +269,10 @@ type ChannelLinkConfig struct {
 	// initiator of the channel.
 	MaxFeeAllocation float64
 
+	// MaxAnchorsCommitFeeRate is the max commitment fee rate we'll use as
+	// the initiator for channels of the anchor type.
+	MaxAnchorsCommitFeeRate chainfee.SatPerKWeight
+
 	// NotifyActiveLink allows the link to tell the ChannelNotifier when a
 	// link is first started.
 	NotifyActiveLink func(wire.OutPoint)
@@ -1083,7 +1087,10 @@ func (l *channelLink) htlcManager() {
 			// based on our current set fee rate. We'll cap the new
 			// fee rate to our max fee allocation.
 			commitFee := l.channel.CommitFeeRate()
-			maxFee := l.channel.MaxFeeRate(l.cfg.MaxFeeAllocation)
+			maxFee := l.channel.MaxFeeRate(
+				l.cfg.MaxFeeAllocation,
+				l.cfg.MaxAnchorsCommitFeeRate,
+			)
 			newCommitFee := chainfee.SatPerKWeight(
 				math.Min(float64(netFee), float64(maxFee)),
 			)

htlcswitch/test_utils.go

@@ -1185,6 +1185,7 @@ func (h *hopNetwork) createChannelLink(server, peer *mockServer,
 			OutgoingCltvRejectDelta: 3,
 			MaxOutgoingCltvExpiry:   DefaultMaxOutgoingCltvExpiry,
 			MaxFeeAllocation:        DefaultMaxLinkFeeAllocation,
+			MaxAnchorsCommitFeeRate: chainfee.SatPerKVByte(10 * 1000).FeePerKWeight(),
 			NotifyActiveLink:        func(wire.OutPoint) {},
 			NotifyActiveChannel:     func(wire.OutPoint) {},
 			NotifyInactiveChannel:   func(wire.OutPoint) {},