From 9890d74622f4b62821c61dfc2aa8da033f1461a5 Mon Sep 17 00:00:00 2001
From: Elle Mouton <elle.mouton@gmail.com>
Date: Wed, 4 Jun 2025 12:48:59 +0200
Subject: [PATCH] multi: set the InboundFee on ChannelEdgePolicy

In this commit, we make sure to set the new field wherever appropriate.
This will be any place where the ChannelEdgePolicy is constructed other
than its disk deserialisation.
---
 discovery/gossiper.go         | 20 ++++++++++++++++++++
 graph/builder.go              | 23 +++++++++++++++++++++--
 graph/notifications_test.go   |  1 +
 routing/localchans/manager.go | 10 +++++-----
 4 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/discovery/gossiper.go b/discovery/gossiper.go
index 0b59c8af9..d79fe7a74 100644
--- a/discovery/gossiper.go
+++ b/discovery/gossiper.go
@@ -3260,6 +3260,26 @@ func (d *AuthenticatedGossiper) handleChanUpdate(ctx context.Context,
 		ExtraOpaqueData:           upd.ExtraOpaqueData,
 	}
 
+	// Extract the inbound fee from the ExtraOpaqueData, if present.
+	//
+	// TODO(elle): this can be removed once we define the optional TLV
+	// field on the lnwire.ChannelUpdate itself.
+	var inboundFee lnwire.Fee
+	typeMap, err := upd.ExtraOpaqueData.ExtractRecords(&inboundFee)
+	if err != nil {
+		rErr := fmt.Errorf("%w: %w", graphdb.ErrParsingExtraTLVBytes,
+			err)
+
+		log.Error(rErr)
+		nMsg.err <- rErr
+		return nil, false
+	}
+
+	val, ok := typeMap[lnwire.FeeRecordType]
+	if ok && val == nil {
+		update.InboundFee = fn.Some(inboundFee)
+	}
+
 	if err := d.cfg.Graph.UpdateEdge(update, ops...); err != nil {
 		if graph.IsError(
 			err, graph.ErrOutdated,
diff --git a/graph/builder.go b/graph/builder.go
index 3350eeb33..32aac9434 100644
--- a/graph/builder.go
+++ b/graph/builder.go
@@ -11,6 +11,7 @@ import (
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/batch"
 	"github.com/lightningnetwork/lnd/chainntnfs"
+	"github.com/lightningnetwork/lnd/fn/v2"
 	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/lnutils"
@@ -943,7 +944,7 @@ func (b *Builder) ApplyChannelUpdate(msg *lnwire.ChannelUpdate1) bool {
 		return false
 	}
 
-	err = b.UpdateEdge(&models.ChannelEdgePolicy{
+	update := &models.ChannelEdgePolicy{
 		SigBytes:                  msg.Signature.ToSignatureBytes(),
 		ChannelID:                 msg.ShortChannelID.ToUint64(),
 		LastUpdate:                time.Unix(int64(msg.Timestamp), 0),
@@ -955,7 +956,25 @@ func (b *Builder) ApplyChannelUpdate(msg *lnwire.ChannelUpdate1) bool {
 		FeeBaseMSat:               lnwire.MilliSatoshi(msg.BaseFee),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(msg.FeeRate),
 		ExtraOpaqueData:           msg.ExtraOpaqueData,
-	})
+	}
+
+	// Extract the inbound fee from the ExtraOpaqueData, if present.
+	//
+	// TODO(elle): this can be removed once we define the optional TLV
+	// field on the lnwire.ChannelUpdate itself.
+	var inboundFee lnwire.Fee
+	typeMap, err := update.ExtraOpaqueData.ExtractRecords(&inboundFee)
+	if err != nil {
+		log.Errorf("%v: %v", graphdb.ErrParsingExtraTLVBytes, err)
+		return false
+	}
+
+	val, ok := typeMap[lnwire.FeeRecordType]
+	if ok && val == nil {
+		update.InboundFee = fn.Some(inboundFee)
+	}
+
+	err = b.UpdateEdge(update)
 	if err != nil && !IsError(err, ErrIgnored, ErrOutdated) {
 		log.Errorf("Unable to apply channel update: %v", err)
 		return false
diff --git a/graph/notifications_test.go b/graph/notifications_test.go
index 71c6f4a34..2f2ec1b4b 100644
--- a/graph/notifications_test.go
+++ b/graph/notifications_test.go
@@ -121,6 +121,7 @@ func randEdgePolicy(chanID *lnwire.ShortChannelID,
 		FeeBaseMSat:               lnwire.MilliSatoshi(prand.Int31()),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(prand.Int31()),
 		ToNode:                    node.PubKeyBytes,
+		InboundFee:                fn.Some(inboundFee),
 		ExtraOpaqueData:           extraOpaqueData,
 	}, nil
 }
diff --git a/routing/localchans/manager.go b/routing/localchans/manager.go
index 3beb28525..492f8f18c 100644
--- a/routing/localchans/manager.go
+++ b/routing/localchans/manager.go
@@ -127,12 +127,10 @@ func (r *Manager) UpdatePolicy(newSchema routing.ChannelPolicy,
 			Edge: edge,
 		})
 
-		// Extract inbound fees from the ExtraOpaqueData.
 		var inboundWireFee lnwire.Fee
-		_, err = edge.ExtraOpaqueData.ExtractRecords(&inboundWireFee)
-		if err != nil {
-			return err
-		}
+		edge.InboundFee.WhenSome(func(fee lnwire.Fee) {
+			inboundWireFee = fee
+		})
 		inboundFee := models.NewInboundFeeFromWire(inboundWireFee)
 
 		// Add updated policy to list of policies to send to switch.
@@ -372,6 +370,8 @@ func (r *Manager) updateEdge(chanPoint wire.OutPoint,
 	err = fn.MapOptionZ(newSchema.InboundFee,
 		func(f models.InboundFee) error {
 			inboundWireFee := f.ToWire()
+			edge.InboundFee = fn.Some(inboundWireFee)
+
 			return edge.ExtraOpaqueData.PackRecords(
 				&inboundWireFee,
 			)