tapchannel: add stxo support for aux leaves

We also add stxo support for the aux leaf creation. This is crucial and
needs to be the same across both channel parties. We rely on the
consistency of the feature bit for whether we'll include the stxo alt
leaves or not. A disagreement here could lead to a force close.

Author: GeorgeTsagk

server.go

@@ -868,7 +868,9 @@ func (s *Server) FetchLeavesFromView(
 
 	// The aux leaf creator is fully stateless, and we don't need to wait
 	// for the server to be started before being able to use it.
-	return tapchannel.FetchLeavesFromView(s.chainParams, in)
+	return tapchannel.FetchLeavesFromView(
+		s.chainParams, in, s.cfg.AuxChanNegotiator,
+	)
 }
 
 // FetchLeavesFromCommit attempts to fetch the auxiliary leaves that
@@ -924,7 +926,9 @@ func (s *Server) ApplyHtlcView(
 
 	// The aux leaf creator is fully stateless, and we don't need to wait
 	// for the server to be started before being able to use it.
-	return tapchannel.ApplyHtlcView(s.chainParams, in)
+	return tapchannel.ApplyHtlcView(
+		s.chainParams, in, s.cfg.AuxChanNegotiator,
+	)
 }
 
 // InlineParseCustomData replaces any custom data binary blob in the given RPC

tapchannel/aux_leaf_creator.go

@@ -10,11 +10,13 @@ import (
 	"github.com/lightninglabs/taproot-assets/address"
 	"github.com/lightninglabs/taproot-assets/fn"
 	cmsg "github.com/lightninglabs/taproot-assets/tapchannelmsg"
+	"github.com/lightninglabs/taproot-assets/tapfeatures"
 	"github.com/lightningnetwork/lnd/channeldb"
 	lfn "github.com/lightningnetwork/lnd/fn/v2"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lntypes"
 	lnwl "github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -24,10 +26,19 @@ const (
 	DefaultTimeout = 30 * time.Second
 )
 
+// FeatureBitFetcher is responsible for fetching feature bits by referencing a
+// channel ID.
+type FeatureBitFetcher interface {
+	// GetChannelFeatures returns the negotiated features that are active
+	// over the channel identifier by the provided channelID.
+	GetChannelFeatures(cid lnwire.ChannelID) lnwire.FeatureVector
+}
+
 // FetchLeavesFromView attempts to fetch the auxiliary leaves that correspond to
 // the passed aux blob, and pending fully evaluated HTLC view.
 func FetchLeavesFromView(chainParams *address.ChainParams,
-	in lnwl.CommitDiffAuxInput) lfn.Result[lnwl.CommitDiffAuxResult] {
+	in lnwl.CommitDiffAuxInput,
+	bitFetcher FeatureBitFetcher) lfn.Result[lnwl.CommitDiffAuxResult] {
 
 	type returnType = lnwl.CommitDiffAuxResult
 
@@ -50,10 +61,18 @@ func FetchLeavesFromView(chainParams *address.ChainParams,
 			"commit state: %w", err))
 	}
 
+	features := bitFetcher.GetChannelFeatures(
+		lnwire.NewChanIDFromOutPoint(
+			in.ChannelState.FundingOutpoint,
+		),
+	)
+
+	supportsSTXO := features.HasFeature(tapfeatures.STXOOptional)
+
 	allocations, newCommitment, err := GenerateCommitmentAllocations(
 		prevState, in.ChannelState, chanAssetState, in.WhoseCommit,
 		in.OurBalance, in.TheirBalance, in.UnfilteredView, chainParams,
-		in.KeyRing, false,
+		in.KeyRing, supportsSTXO,
 	)
 	if err != nil {
 		return lfn.Err[returnType](fmt.Errorf("unable to generate "+
@@ -98,6 +117,8 @@ func FetchLeavesFromCommit(chainParams *address.ChainParams,
 			"commitment: %w", err))
 	}
 
+	supportSTXO := commitment.STXO.Val
+
 	incomingHtlcs := commitment.IncomingHtlcAssets.Val.HtlcOutputs
 	incomingHtlcLeaves := commitment.AuxLeaves.Val.IncomingHtlcLeaves.
 		Val.HtlcAuxLeaves
@@ -129,7 +150,7 @@ func FetchLeavesFromCommit(chainParams *address.ChainParams,
 			leaf, err := CreateSecondLevelHtlcTx(
 				chanState, com.CommitTx, htlc.Amt.ToSatoshis(),
 				keys, chainParams, htlcOutputs, cltvTimeout,
-				htlc.HtlcIndex, false,
+				htlc.HtlcIndex, supportSTXO,
 			)
 			if err != nil {
 				return lfn.Err[returnType](fmt.Errorf("unable "+
@@ -170,7 +191,7 @@ func FetchLeavesFromCommit(chainParams *address.ChainParams,
 			leaf, err := CreateSecondLevelHtlcTx(
 				chanState, com.CommitTx, htlc.Amt.ToSatoshis(),
 				keys, chainParams, htlcOutputs, cltvTimeout,
-				htlc.HtlcIndex, false,
+				htlc.HtlcIndex, supportSTXO,
 			)
 			if err != nil {
 				return lfn.Err[returnType](fmt.Errorf("unable "+
@@ -225,7 +246,8 @@ func FetchLeavesFromRevocation(
 // channel's blob. Given the old blob, and an HTLC view, then a new
 // blob should be returned that reflects the pending updates.
 func ApplyHtlcView(chainParams *address.ChainParams,
-	in lnwl.CommitDiffAuxInput) lfn.Result[lfn.Option[tlv.Blob]] {
+	in lnwl.CommitDiffAuxInput,
+	bitFetcher FeatureBitFetcher) lfn.Result[lfn.Option[tlv.Blob]] {
 
 	type returnType = lfn.Option[tlv.Blob]
 
@@ -248,10 +270,20 @@ func ApplyHtlcView(chainParams *address.ChainParams,
 			"commit state: %w", err))
 	}
 
+	features := bitFetcher.GetChannelFeatures(
+		lnwire.NewChanIDFromOutPoint(
+			in.ChannelState.FundingOutpoint,
+		),
+	)
+
+	supportSTXO := features.HasFeature(
+		tapfeatures.STXOOptional,
+	)
+
 	_, newCommitment, err := GenerateCommitmentAllocations(
 		prevState, in.ChannelState, chanAssetState, in.WhoseCommit,
 		in.OurBalance, in.TheirBalance, in.UnfilteredView, chainParams,
-		in.KeyRing, false,
+		in.KeyRing, supportSTXO,
 	)
 	if err != nil {
 		return lfn.Err[returnType](fmt.Errorf("unable to generate "+