From 6d8bc63ad6cc6235711bee739451898bb84686ab Mon Sep 17 00:00:00 2001
From: Elle Mouton <elle.mouton@gmail.com>
Date: Wed, 4 Jun 2025 12:56:55 +0200
Subject: [PATCH] discovery+graph: get inbound fee directly from ChannelUpdate

Remove the previously added TODOs which would extract InboundFee info
from the ExtraOpaqueData of a ChannelUpdate at the time of
ChannelEdgePolicy construction. These can now be replaced by using the
newly added InboundFee record on the ChannelUpdate message.
---
 discovery/gossiper.go    | 21 +--------------------
 graph/builder.go         | 18 +-----------------
 netann/channel_update.go | 10 +++++++++-
 3 files changed, 11 insertions(+), 38 deletions(-)

diff --git a/discovery/gossiper.go b/discovery/gossiper.go
index d79fe7a74..d6855ae45 100644
--- a/discovery/gossiper.go
+++ b/discovery/gossiper.go
@@ -3257,29 +3257,10 @@ func (d *AuthenticatedGossiper) handleChanUpdate(ctx context.Context,
 		MaxHTLC:                   upd.HtlcMaximumMsat,
 		FeeBaseMSat:               lnwire.MilliSatoshi(upd.BaseFee),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(upd.FeeRate),
+		InboundFee:                upd.InboundFee.ValOpt(),
 		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 32aac9434..99fc73c17 100644
--- a/graph/builder.go
+++ b/graph/builder.go
@@ -11,7 +11,6 @@ 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"
@@ -955,25 +954,10 @@ func (b *Builder) ApplyChannelUpdate(msg *lnwire.ChannelUpdate1) bool {
 		MaxHTLC:                   msg.HtlcMaximumMsat,
 		FeeBaseMSat:               lnwire.MilliSatoshi(msg.BaseFee),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(msg.FeeRate),
+		InboundFee:                msg.InboundFee.ValOpt(),
 		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)
diff --git a/netann/channel_update.go b/netann/channel_update.go
index efc5cf61e..1bb509b08 100644
--- a/netann/channel_update.go
+++ b/netann/channel_update.go
@@ -13,6 +13,7 @@ import (
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/pkg/errors"
 )
 
@@ -138,7 +139,7 @@ func ExtractChannelUpdate(ownerPubKey []byte,
 func UnsignedChannelUpdateFromEdge(info *models.ChannelEdgeInfo,
 	policy *models.ChannelEdgePolicy) *lnwire.ChannelUpdate1 {
 
-	return &lnwire.ChannelUpdate1{
+	update := &lnwire.ChannelUpdate1{
 		ChainHash:       info.ChainHash,
 		ShortChannelID:  lnwire.NewShortChanIDFromInt(policy.ChannelID),
 		Timestamp:       uint32(policy.LastUpdate.Unix()),
@@ -151,6 +152,13 @@ func UnsignedChannelUpdateFromEdge(info *models.ChannelEdgeInfo,
 		FeeRate:         uint32(policy.FeeProportionalMillionths),
 		ExtraOpaqueData: policy.ExtraOpaqueData,
 	}
+	policy.InboundFee.WhenSome(func(fee lnwire.Fee) {
+		update.InboundFee = tlv.SomeRecordT(
+			tlv.NewRecordT[tlv.TlvType55555, lnwire.Fee](fee),
+		)
+	})
+
+	return update
 }
 
 // ChannelUpdateFromEdge reconstructs a signed ChannelUpdate from the given edge