From 5c854a2f53fbc661f1505f5a8b50cc5f8d02e0fa Mon Sep 17 00:00:00 2001
From: Oliver Gugger <gugger@gmail.com>
Date: Fri, 17 May 2024 12:39:12 +0200
Subject: [PATCH] multi: add tapscript root to gossip message

---
 channeldb/models/channel_edge_info.go |  6 ++++++
 discovery/gossiper.go                 | 19 ++++++++++++++++---
 funding/manager.go                    |  7 ++++---
 graph/builder.go                      |  8 ++++----
 4 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/channeldb/models/channel_edge_info.go b/channeldb/models/channel_edge_info.go
index 1afa2d627..0f91e2bbe 100644
--- a/channeldb/models/channel_edge_info.go
+++ b/channeldb/models/channel_edge_info.go
@@ -8,6 +8,7 @@ import (
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/fn"
 )
 
 // ChannelEdgeInfo represents a fully authenticated channel along with all its
@@ -62,6 +63,11 @@ type ChannelEdgeInfo struct {
 	// the value output in the outpoint that created this channel.
 	Capacity btcutil.Amount
 
+	// TapscriptRoot is the optional Merkle root of the tapscript tree if
+	// this channel is a taproot channel that also commits to a tapscript
+	// tree (custom channel).
+	TapscriptRoot fn.Option[chainhash.Hash]
+
 	// ExtraOpaqueData is the set of data that was appended to this
 	// message, some of which we may not actually know how to iterate or
 	// parse. By holding onto this data, we ensure that we're able to
diff --git a/discovery/gossiper.go b/discovery/gossiper.go
index 84fae767f..1d3051de5 100644
--- a/discovery/gossiper.go
+++ b/discovery/gossiper.go
@@ -20,6 +20,7 @@ import (
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/graph"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
@@ -82,9 +83,10 @@ var (
 // can provide that serve useful when processing a specific network
 // announcement.
 type optionalMsgFields struct {
-	capacity     *btcutil.Amount
-	channelPoint *wire.OutPoint
-	remoteAlias  *lnwire.ShortChannelID
+	capacity      *btcutil.Amount
+	channelPoint  *wire.OutPoint
+	remoteAlias   *lnwire.ShortChannelID
+	tapscriptRoot fn.Option[chainhash.Hash]
 }
 
 // apply applies the optional fields within the functional options.
@@ -115,6 +117,14 @@ func ChannelPoint(op wire.OutPoint) OptionalMsgField {
 	}
 }
 
+// TapscriptRoot is an optional field that lets the gossiper know of the root of
+// the tapscript tree for a custom channel.
+func TapscriptRoot(root fn.Option[chainhash.Hash]) OptionalMsgField {
+	return func(f *optionalMsgFields) {
+		f.tapscriptRoot = root
+	}
+}
+
 // RemoteAlias is an optional field that lets the gossiper know that a locally
 // sent channel update is actually an update for the peer that should replace
 // the ShortChannelID field with the remote's alias. This is only used for
@@ -2578,6 +2588,9 @@ func (d *AuthenticatedGossiper) handleChanAnnouncement(nMsg *networkMsg,
 			cp := *nMsg.optionalMsgFields.channelPoint
 			edge.ChannelPoint = cp
 		}
+
+		// Optional tapscript root for custom channels.
+		edge.TapscriptRoot = nMsg.optionalMsgFields.tapscriptRoot
 	}
 
 	log.Debugf("Adding edge for short_chan_id: %v", scid.ToUint64())
diff --git a/funding/manager.go b/funding/manager.go
index cb1ec04b9..7c8309e93 100644
--- a/funding/manager.go
+++ b/funding/manager.go
@@ -3515,6 +3515,7 @@ func (f *Manager) addToGraph(completeChan *channeldb.OpenChannel,
 	errChan := f.cfg.SendAnnouncement(
 		ann.chanAnn, discovery.ChannelCapacity(completeChan.Capacity),
 		discovery.ChannelPoint(completeChan.FundingOutpoint),
+		discovery.TapscriptRoot(completeChan.TapscriptRoot),
 	)
 	select {
 	case err := <-errChan:
@@ -4441,9 +4442,9 @@ func (f *Manager) announceChannel(localIDKey, remoteIDKey *btcec.PublicKey,
 	//
 	// We can pass in zeroes for the min and max htlc policy, because we
 	// only use the channel announcement message from the returned struct.
-	ann, err := f.newChanAnnouncement(localIDKey, remoteIDKey,
-		localFundingKey, remoteFundingKey, shortChanID, chanID,
-		0, 0, nil, chanType,
+	ann, err := f.newChanAnnouncement(
+		localIDKey, remoteIDKey, localFundingKey, remoteFundingKey,
+		shortChanID, chanID, 0, 0, nil, chanType,
 	)
 	if err != nil {
 		log.Errorf("can't generate channel announcement: %v", err)
diff --git a/graph/builder.go b/graph/builder.go
index 717d3e5ad..3c882058b 100644
--- a/graph/builder.go
+++ b/graph/builder.go
@@ -1092,8 +1092,8 @@ func (b *Builder) addZombieEdge(chanID uint64) error {
 // segwit v1 (taproot) channels.
 //
 // TODO(roasbeef: export and use elsewhere?
-func makeFundingScript(bitcoinKey1, bitcoinKey2 []byte,
-	chanFeatures []byte) ([]byte, error) {
+func makeFundingScript(bitcoinKey1, bitcoinKey2 []byte, chanFeatures []byte,
+	tapscriptRoot fn.Option[chainhash.Hash]) ([]byte, error) {
 
 	legacyFundingScript := func() ([]byte, error) {
 		witnessScript, err := input.GenMultiSigScript(
@@ -1140,7 +1140,7 @@ func makeFundingScript(bitcoinKey1, bitcoinKey2 []byte,
 		}
 
 		fundingScript, _, err := input.GenTaprootFundingScript(
-			pubKey1, pubKey2, 0, fn.None[chainhash.Hash](),
+			pubKey1, pubKey2, 0, tapscriptRoot,
 		)
 		if err != nil {
 			return nil, err
@@ -1272,7 +1272,7 @@ func (b *Builder) processUpdate(msg interface{},
 		// reality.
 		fundingPkScript, err := makeFundingScript(
 			msg.BitcoinKey1Bytes[:], msg.BitcoinKey2Bytes[:],
-			msg.Features,
+			msg.Features, msg.TapscriptRoot,
 		)
 		if err != nil {
 			return err