lnwallet: simplify fee calculation in evaluateHTLCView

This commit simplifies how we compute the commitment fee rate based
off of the live updates. Prior to this commit we processed all of
the FeeUpdate paymentDescriptors of both ChannelParty's. Now we only
process the last FeeUpdate of the OpeningParty

go.mod

@@ -35,7 +35,7 @@ require (
 	github.com/lightningnetwork/lightning-onion v1.2.1-0.20240712235311-98bd56499dfb
 	github.com/lightningnetwork/lnd/cert v1.2.2
 	github.com/lightningnetwork/lnd/clock v1.1.1
-	github.com/lightningnetwork/lnd/fn v1.2.1
+	github.com/lightningnetwork/lnd/fn v1.2.2
 	github.com/lightningnetwork/lnd/healthcheck v1.2.5
 	github.com/lightningnetwork/lnd/kvdb v1.4.10
 	github.com/lightningnetwork/lnd/queue v1.1.1

go.sum

@@ -453,8 +453,8 @@ github.com/lightningnetwork/lnd/cert v1.2.2 h1:71YK6hogeJtxSxw2teq3eGeuy4rHGKcFf
 github.com/lightningnetwork/lnd/cert v1.2.2/go.mod h1:jQmFn/Ez4zhDgq2hnYSw8r35bqGVxViXhX6Cd7HXM6U=
 github.com/lightningnetwork/lnd/clock v1.1.1 h1:OfR3/zcJd2RhH0RU+zX/77c0ZiOnIMsDIBjgjWdZgA0=
 github.com/lightningnetwork/lnd/clock v1.1.1/go.mod h1:mGnAhPyjYZQJmebS7aevElXKTFDuO+uNFFfMXK1W8xQ=
-github.com/lightningnetwork/lnd/fn v1.2.1 h1:pPsVGrwi9QBwdLJzaEGK33wmiVKOxs/zc8H7+MamFf0=
-github.com/lightningnetwork/lnd/fn v1.2.1/go.mod h1:SyFohpVrARPKH3XVAJZlXdVe+IwMYc4OMAvrDY32kw0=
+github.com/lightningnetwork/lnd/fn v1.2.2 h1:rVtmGW1cQTmYce2XdUbRcc5qLDxqu+aQ6IGRpyspakk=
+github.com/lightningnetwork/lnd/fn v1.2.2/go.mod h1:SyFohpVrARPKH3XVAJZlXdVe+IwMYc4OMAvrDY32kw0=
 github.com/lightningnetwork/lnd/healthcheck v1.2.5 h1:aTJy5xeBpcWgRtW/PGBDe+LMQEmNm/HQewlQx2jt7OA=
 github.com/lightningnetwork/lnd/healthcheck v1.2.5/go.mod h1:G7Tst2tVvWo7cx6mSBEToQC5L1XOGxzZTPB29g9Rv2I=
 github.com/lightningnetwork/lnd/kvdb v1.4.10 h1:vK89IVv1oVH9ubQWU+EmoCQFeVRaC8kfmOrqHbY5zoY=

lnwallet/channel.go

@@ -2906,6 +2906,19 @@ func (lc *LightningChannel) evaluateHTLCView(view *HtlcView, ourBalance,
 		NextHeight: nextHeight,
 	}
 
+	// The fee rate of our view is always the last UpdateFee message from
+	// the channel's OpeningParty.
+	openerUpdates := view.Updates.GetForParty(lc.channelState.Initiator())
+	feeUpdates := fn.Filter(func(u *paymentDescriptor) bool {
+		return u.EntryType == FeeUpdate
+	}, openerUpdates)
+	lastFeeUpdate := fn.Last(feeUpdates)
+	lastFeeUpdate.WhenSome(func(pd *paymentDescriptor) {
+		newView.FeePerKw = chainfee.SatPerKWeight(
+			pd.Amount.ToSatoshis(),
+		)
+	})
+
 	// We use two maps, one for the local log and one for the remote log to
 	// keep track of which entries we need to skip when creating the final
 	// htlc view. We skip an entry whenever we find a settle or a timeout
@@ -2921,21 +2934,8 @@ func (lc *LightningChannel) evaluateHTLCView(view *HtlcView, ourBalance,
 		case Add:
 			continue
 
-		// Process fee updates, updating the current feePerKw.
+		// Skip fee updates because we've already dealt with them above.
 		case FeeUpdate:
-			h := entry.addCommitHeights.GetForParty(
-				whoseCommitChain,
-			)
-
-			if h == 0 {
-				// If the update wasn't already locked in,
-				// update the current fee rate to reflect this
-				// update.
-				newView.FeePerKw = chainfee.SatPerKWeight(
-					entry.Amount.ToSatoshis(),
-				)
-			}
-
 			continue
 		}
 
@@ -2966,21 +2966,8 @@ func (lc *LightningChannel) evaluateHTLCView(view *HtlcView, ourBalance,
 		case Add:
 			continue
 
-		// Process fee updates, updating the current feePerKw.
+		// Skip fee updates because we've already dealt with them above.
 		case FeeUpdate:
-			h := entry.addCommitHeights.GetForParty(
-				whoseCommitChain,
-			)
-
-			if h == 0 {
-				// If the update wasn't already locked in,
-				// update the current fee rate to reflect this
-				// update.
-				newView.FeePerKw = chainfee.SatPerKWeight(
-					entry.Amount.ToSatoshis(),
-				)
-			}
-
 			continue
 		}
 

lnwallet/channel_test.go

@@ -8650,6 +8650,7 @@ func TestEvaluateView(t *testing.T) {
 		name             string
 		ourHtlcs         []*paymentDescriptor
 		theirHtlcs       []*paymentDescriptor
+		channelInitiator lntypes.ChannelParty
 		whoseCommitChain lntypes.ChannelParty
 		mutateState      bool
 
@@ -8679,6 +8680,7 @@ func TestEvaluateView(t *testing.T) {
 	}{
 		{
 			name:             "our fee update is applied",
+			channelInitiator: lntypes.Local,
 			whoseCommitChain: lntypes.Local,
 			mutateState:      false,
 			ourHtlcs: []*paymentDescriptor{
@@ -8696,6 +8698,7 @@ func TestEvaluateView(t *testing.T) {
 		},
 		{
 			name:             "their fee update is applied",
+			channelInitiator: lntypes.Remote,
 			whoseCommitChain: lntypes.Local,
 			mutateState:      false,
 			ourHtlcs:         []*paymentDescriptor{},
@@ -8911,8 +8914,10 @@ func TestEvaluateView(t *testing.T) {
 		test := test
 
 		t.Run(test.name, func(t *testing.T) {
+			isInitiator := test.channelInitiator == lntypes.Local
 			lc := LightningChannel{
 				channelState: &channeldb.OpenChannel{
+					IsInitiator:       isInitiator,
 					TotalMSatSent:     0,
 					TotalMSatReceived: 0,
 				},