Merge pull request #9072 from lightningnetwork/extract-part3-from-staging-branch

[custom channels 3/5]: Extract PART3 from mega staging branch

chainreg/chainregistry.go

@@ -68,6 +68,10 @@ type Config struct {
 	// leaves for certain custom channel types.
 	AuxLeafStore fn.Option[lnwallet.AuxLeafStore]
 
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[lnwallet.AuxSigner]
+
 	// BlockCache is the main cache for storing block information.
 	BlockCache *blockcache.BlockCache
 

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

config_builder.go

@@ -34,6 +34,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/funding"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
@@ -167,6 +168,20 @@ type AuxComponents struct {
 	// MsgRouter is an optional message router that if set will be used in
 	// place of a new blank default message router.
 	MsgRouter fn.Option[msgmux.Router]
+
+	// AuxFundingController is an optional controller that can be used to
+	// modify the way we handle certain custom channel types. It's also
+	// able to automatically handle new custom protocol messages related to
+	// the funding process.
+	AuxFundingController fn.Option[funding.AuxFundingController]
+
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[lnwallet.AuxSigner]
+
+	// AuxDataParser is an optional data parser that can be used to parse
+	// auxiliary data for certain custom channel types.
+	AuxDataParser fn.Option[AuxDataParser]
 }
 
 // DefaultWalletImpl is the default implementation of our normal, btcwallet
@@ -573,6 +588,7 @@ func (d *DefaultWalletImpl) BuildWalletConfig(ctx context.Context,
 		ChanStateDB:                 dbs.ChanStateDB.ChannelStateDB(),
 		NeutrinoCS:                  neutrinoCS,
 		AuxLeafStore:                aux.AuxLeafStore,
+		AuxSigner:                   aux.AuxSigner,
 		ActiveNetParams:             d.cfg.ActiveNetParams,
 		FeeURL:                      d.cfg.FeeURL,
 		Fee: &lncfg.Fee{
@@ -730,6 +746,7 @@ func (d *DefaultWalletImpl) BuildChainControl(
 		NetParams:             *walletConfig.NetParams,
 		CoinSelectionStrategy: walletConfig.CoinSelectionStrategy,
 		AuxLeafStore:          partialChainControl.Cfg.AuxLeafStore,
+		AuxSigner:             partialChainControl.Cfg.AuxSigner,
 	}
 
 	// The broadcast is already always active for neutrino nodes, so we
@@ -912,10 +929,6 @@ type DatabaseInstances struct {
 	// for native SQL queries for tables that already support it. This may
 	// be nil if the use-native-sql flag was not set.
 	NativeSQLStore *sqldb.BaseDB
-
-	// AuxLeafStore is an optional data source that can be used by custom
-	// channels to fetch+store various data.
-	AuxLeafStore fn.Option[lnwallet.AuxLeafStore]
 }
 
 // DefaultDatabaseBuilder is a type that builds the default database backends

contractcourt/breach_arbitrator_test.go

@@ -2360,9 +2360,12 @@ func createInitChannels(t *testing.T) (
 	)
 	bobSigner := input.NewMockSigner([]*btcec.PrivateKey{bobKeyPriv}, nil)
 
+	signerMock := lnwallet.NewDefaultAuxSignerMock(t)
 	alicePool := lnwallet.NewSigPool(1, aliceSigner)
 	channelAlice, err := lnwallet.NewLightningChannel(
 		aliceSigner, aliceChannelState, alicePool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	if err != nil {
 		return nil, nil, err
@@ -2375,6 +2378,8 @@ func createInitChannels(t *testing.T) (
 	bobPool := lnwallet.NewSigPool(1, bobSigner)
 	channelBob, err := lnwallet.NewLightningChannel(
 		bobSigner, bobChannelState, bobPool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	if err != nil {
 		return nil, nil, err

contractcourt/chain_arbitrator.go

@@ -221,6 +221,10 @@ type ChainArbitratorConfig struct {
 	// AuxLeafStore is an optional store that can be used to store auxiliary
 	// leaves for certain custom channel types.
 	AuxLeafStore fn.Option[lnwallet.AuxLeafStore]
+
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[lnwallet.AuxSigner]
 }
 
 // ChainArbitrator is a sub-system that oversees the on-chain resolution of all
@@ -307,6 +311,9 @@ func (a *arbChannel) NewAnchorResolutions() (*lnwallet.AnchorResolutions,
 	a.c.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
 		chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
 	})
+	a.c.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
+		chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
+	})
 
 	chanMachine, err := lnwallet.NewLightningChannel(
 		a.c.cfg.Signer, channel, nil, chanOpts...,
@@ -357,6 +364,9 @@ func (a *arbChannel) ForceCloseChan() (*lnwallet.LocalForceCloseSummary, error)
 	a.c.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
 		chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
 	})
+	a.c.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
+		chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
+	})
 
 	// Finally, we'll force close the channel completing
 	// the force close workflow.

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"
@@ -85,6 +86,7 @@ type optionalMsgFields struct {
 	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
@@ -2598,6 +2608,9 @@ 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())

funding/aux_funding.go

@@ -0,0 +1,51 @@
+package funding
+
+import (
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/msgmux"
+)
+
+// AuxFundingDescResult is a type alias for a function that returns an optional
+// aux funding desc.
+type AuxFundingDescResult = fn.Result[fn.Option[lnwallet.AuxFundingDesc]]
+
+// AuxTapscriptResult is a type alias for a function that returns an optional
+// tapscript root.
+type AuxTapscriptResult = fn.Result[fn.Option[chainhash.Hash]]
+
+// AuxFundingController permits the implementation of the funding of custom
+// channels types. The controller serves as a MsgEndpoint which allows it to
+// intercept custom messages, or even the regular funding messages. The
+// controller might also pass along an aux funding desc based on an existing
+// pending channel ID.
+type AuxFundingController interface {
+	// Endpoint is the embedded interface that signals that the funding
+	// controller is also a message endpoint. This'll allow it to handle
+	// custom messages specific to the funding type.
+	msgmux.Endpoint
+
+	// DescFromPendingChanID takes a pending channel ID, that may already be
+	// known due to prior custom channel messages, and maybe returns an aux
+	// funding desc which can be used to modify how a channel is funded.
+	DescFromPendingChanID(pid PendingChanID, openChan lnwallet.AuxChanState,
+		keyRing lntypes.Dual[lnwallet.CommitmentKeyRing],
+		initiator bool) AuxFundingDescResult
+
+	// DeriveTapscriptRoot takes a pending channel ID and maybe returns a
+	// tapscript root that should be used when creating any MuSig2 sessions
+	// for a channel.
+	DeriveTapscriptRoot(PendingChanID) AuxTapscriptResult
+
+	// ChannelReady is called when a channel has been fully opened (multiple
+	// confirmations) and is ready to be used. This can be used to perform
+	// any final setup or cleanup.
+	ChannelReady(openChan lnwallet.AuxChanState) error
+
+	// ChannelFinalized is called when a channel has been fully finalized.
+	// In this state, we've received the commitment sig from the remote
+	// party, so we are safe to broadcast the funding transaction.
+	ChannelFinalized(PendingChanID) error
+}

funding/manager.go

@@ -99,7 +99,6 @@ const (
 	// you and limitless channel size (apart from 21 million cap).
 	MaxBtcFundingAmountWumbo = btcutil.Amount(1000000000)
 
-	// TODO(roasbeef): tune.
 	msgBufferSize = 50
 
 	// MaxWaitNumBlocksFundingConf is the maximum number of blocks to wait
@@ -549,6 +548,16 @@ type Config struct {
 	// AuxLeafStore is an optional store that can be used to store auxiliary
 	// leaves for certain custom channel types.
 	AuxLeafStore fn.Option[lnwallet.AuxLeafStore]
+
+	// AuxFundingController is an optional controller that can be used to
+	// modify the way we handle certain custom channel types. It's also
+	// able to automatically handle new custom protocol messages related to
+	// the funding process.
+	AuxFundingController fn.Option[AuxFundingController]
+
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[lnwallet.AuxSigner]
 }
 
 // Manager acts as an orchestrator/bridge between the wallet's
@@ -1078,6 +1087,9 @@ func (f *Manager) advanceFundingState(channel *channeldb.OpenChannel,
 	f.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
 		chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
 	})
+	f.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
+		chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
+	})
 
 	// We create the state-machine object which wraps the database state.
 	lnChannel, err := lnwallet.NewLightningChannel(
@@ -1256,8 +1268,8 @@ func (f *Manager) stateStep(channel *channeldb.OpenChannel,
 
 // advancePendingChannelState waits for a pending channel's funding tx to
 // confirm, and marks it open in the database when that happens.
-func (f *Manager) advancePendingChannelState(
-	channel *channeldb.OpenChannel, pendingChanID PendingChanID) error {
+func (f *Manager) advancePendingChannelState(channel *channeldb.OpenChannel,
+	pendingChanID PendingChanID) error {
 
 	if channel.IsZeroConf() {
 		// Persist the alias to the alias database.
@@ -1626,6 +1638,23 @@ func (f *Manager) fundeeProcessOpenChannel(peer lnpeer.Peer,
 		return
 	}
 
+	// At this point, if we have an AuxFundingController active, we'll
+	// check to see if we have a special tapscript root to use in our
+	// MuSig funding output.
+	tapscriptRoot, err := fn.MapOptionZ(
+		f.cfg.AuxFundingController,
+		func(c AuxFundingController) AuxTapscriptResult {
+			return c.DeriveTapscriptRoot(msg.PendingChannelID)
+		},
+	).Unpack()
+	if err != nil {
+		err = fmt.Errorf("error deriving tapscript root: %w", err)
+		log.Error(err)
+		f.failFundingFlow(peer, cid, err)
+
+		return
+	}
+
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:        &msg.ChainHash,
 		PendingChanID:    msg.PendingChannelID,
@@ -1642,6 +1671,7 @@ func (f *Manager) fundeeProcessOpenChannel(peer lnpeer.Peer,
 		ZeroConf:         zeroConf,
 		OptionScidAlias:  scid,
 		ScidAliasFeature: scidFeatureVal,
+		TapscriptRoot:    tapscriptRoot,
 	}
 
 	reservation, err := f.cfg.Wallet.InitChannelReservation(req)
@@ -1898,6 +1928,8 @@ func (f *Manager) fundeeProcessOpenChannel(peer lnpeer.Peer,
 	log.Debugf("Remote party accepted commitment rendering params: %v",
 		lnutils.SpewLogClosure(params))
 
+	reservation.SetState(lnwallet.SentAcceptChannel)
+
 	// With the initiator's contribution recorded, respond with our
 	// contribution in the next message of the workflow.
 	fundingAccept := lnwire.AcceptChannel{
@@ -1958,6 +1990,10 @@ func (f *Manager) funderProcessAcceptChannel(peer lnpeer.Peer,
 	// Update the timestamp once the fundingAcceptMsg has been handled.
 	defer resCtx.updateTimestamp()
 
+	if resCtx.reservation.State() != lnwallet.SentOpenChannel {
+		return
+	}
+
 	log.Infof("Recv'd fundingResponse for pending_id(%x)",
 		pendingChanID[:])
 
@@ -2261,10 +2297,34 @@ func (f *Manager) waitForPsbt(intent *chanfunding.PsbtIntent,
 			return
 		}
 
+		// At this point, we'll see if there's an AuxFundingDesc we
+		// need to deliver so the funding process can continue
+		// properly.
+		auxFundingDesc, err := fn.MapOptionZ(
+			f.cfg.AuxFundingController,
+			func(c AuxFundingController) AuxFundingDescResult {
+				return c.DescFromPendingChanID(
+					cid.tempChanID,
+					lnwallet.NewAuxChanState(
+						resCtx.reservation.ChanState(),
+					),
+					resCtx.reservation.CommitmentKeyRings(),
+					true,
+				)
+			},
+		).Unpack()
+		if err != nil {
+			failFlow("error continuing PSBT flow", err)
+			return
+		}
+
 		// A non-nil error means we can continue the funding flow.
 		// Notify the wallet so it can prepare everything we need to
 		// continue.
-		err = resCtx.reservation.ProcessPsbt()
+		//
+		// We'll also pass along the aux funding controller as well,
+		// which may be used to help process the finalized PSBT.
+		err = resCtx.reservation.ProcessPsbt(auxFundingDesc)
 		if err != nil {
 			failFlow("error continuing PSBT flow", err)
 			return
@@ -2359,6 +2419,8 @@ func (f *Manager) continueFundingAccept(resCtx *reservationWithCtx,
 		}
 	}
 
+	resCtx.reservation.SetState(lnwallet.SentFundingCreated)
+
 	if err := resCtx.peer.SendMessage(true, fundingCreated); err != nil {
 		log.Errorf("Unable to send funding complete message: %v", err)
 		f.failFundingFlow(resCtx.peer, cid, err)
@@ -2390,11 +2452,14 @@ func (f *Manager) fundeeProcessFundingCreated(peer lnpeer.Peer,
 	// final funding transaction, as well as a signature for our version of
 	// the commitment transaction. So at this point, we can validate the
 	// initiator's commitment transaction, then send our own if it's valid.
-	// TODO(roasbeef): make case (p vs P) consistent throughout
 	fundingOut := msg.FundingPoint
 	log.Infof("completing pending_id(%x) with ChannelPoint(%v)",
 		pendingChanID[:], fundingOut)
 
+	if resCtx.reservation.State() != lnwallet.SentAcceptChannel {
+		return
+	}
+
 	// Create the channel identifier without setting the active channel ID.
 	cid := newChanIdentifier(pendingChanID)
 
@@ -2422,16 +2487,38 @@ func (f *Manager) fundeeProcessFundingCreated(peer lnpeer.Peer,
 		}
 	}
 
+	// At this point, we'll see if there's an AuxFundingDesc we need to
+	// deliver so the funding process can continue properly.
+	auxFundingDesc, err := fn.MapOptionZ(
+		f.cfg.AuxFundingController,
+		func(c AuxFundingController) AuxFundingDescResult {
+			return c.DescFromPendingChanID(
+				cid.tempChanID, lnwallet.NewAuxChanState(
+					resCtx.reservation.ChanState(),
+				), resCtx.reservation.CommitmentKeyRings(),
+				true,
+			)
+		},
+	).Unpack()
+	if err != nil {
+		log.Errorf("error continuing PSBT flow: %v", err)
+		f.failFundingFlow(peer, cid, err)
+		return
+	}
+
 	// With all the necessary data available, attempt to advance the
 	// funding workflow to the next stage. If this succeeds then the
 	// funding transaction will broadcast after our next message.
 	// CompleteReservationSingle will also mark the channel as 'IsPending'
 	// in the database.
+	//
+	// We'll also directly pass in the AuxFunding controller as well,
+	// which may be used by the reservation system to finalize funding our
+	// side.
 	completeChan, err := resCtx.reservation.CompleteReservationSingle(
-		&fundingOut, commitSig,
+		&fundingOut, commitSig, auxFundingDesc,
 	)
 	if err != nil {
-		// TODO(roasbeef): better error logging: peerID, channelID, etc.
 		log.Errorf("unable to complete single reservation: %v", err)
 		f.failFundingFlow(peer, cid, err)
 		return
@@ -2632,6 +2719,14 @@ func (f *Manager) funderProcessFundingSigned(peer lnpeer.Peer,
 		return
 	}
 
+	if resCtx.reservation.State() != lnwallet.SentFundingCreated {
+		err := fmt.Errorf("unable to find reservation for chan_id=%x",
+			msg.ChanID)
+		f.failFundingFlow(peer, cid, err)
+
+		return
+	}
+
 	// Create an entry in the local discovery map so we can ensure that we
 	// process the channel confirmation fully before we receive a
 	// channel_ready message.
@@ -2727,6 +2822,21 @@ func (f *Manager) funderProcessFundingSigned(peer lnpeer.Peer,
 		}
 	}
 
+	// Before we proceed, if we have a funding hook that wants a
+	// notification that it's safe to broadcast the funding transaction,
+	// then we'll send that now.
+	err = fn.MapOptionZ(
+		f.cfg.AuxFundingController,
+		func(controller AuxFundingController) error {
+			return controller.ChannelFinalized(cid.tempChanID)
+		},
+	)
+	if err != nil {
+		log.Errorf("Failed to inform aux funding controller about "+
+			"ChannelPoint(%v) being finalized: %v", fundingPoint,
+			err)
+	}
+
 	// Now that we have a finalized reservation for this funding flow,
 	// we'll send the to be active channel to the ChainArbitrator so it can
 	// watch for any on-chain actions before the channel has fully
@@ -2742,9 +2852,6 @@ func (f *Manager) funderProcessFundingSigned(peer lnpeer.Peer,
 
 	// Send an update to the upstream client that the negotiation process
 	// is over.
-	//
-	// TODO(roasbeef): add abstraction over updates to accommodate
-	// long-polling, or SSE, etc.
 	upd := &lnrpc.OpenStatusUpdate{
 		Update: &lnrpc.OpenStatusUpdate_ChanPending{
 			ChanPending: &lnrpc.PendingUpdate{
@@ -3450,6 +3557,7 @@ 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:
@@ -3646,7 +3754,7 @@ func (f *Manager) annAfterSixConfs(completeChan *channeldb.OpenChannel,
 
 // waitForZeroConfChannel is called when the state is addedToGraph with
 // a zero-conf channel. This will wait for the real confirmation, add the
-// confirmed SCID to the graph, and then announce after six confs.
+// confirmed SCID to the router graph, and then announce after six confs.
 func (f *Manager) waitForZeroConfChannel(c *channeldb.OpenChannel) error {
 	// First we'll check whether the channel is confirmed on-chain. If it
 	// is already confirmed, the chainntnfs subsystem will return with the
@@ -3977,6 +4085,26 @@ func (f *Manager) handleChannelReady(peer lnpeer.Peer, //nolint:funlen
 				PubNonce: remoteNonce,
 			}),
 		)
+
+		// Inform the aux funding controller that the liquidity in the
+		// custom channel is now ready to be advertised. We potentially
+		// haven't sent our own channel ready message yet, but other
+		// than that the channel is ready to count toward available
+		// liquidity.
+		err = fn.MapOptionZ(
+			f.cfg.AuxFundingController,
+			func(controller AuxFundingController) error {
+				return controller.ChannelReady(
+					lnwallet.NewAuxChanState(channel),
+				)
+			},
+		)
+		if err != nil {
+			cid := newChanIdentifier(msg.ChanID)
+			f.sendWarning(peer, cid, err)
+
+			return
+		}
 	}
 
 	// The channel_ready message contains the next commitment point we'll
@@ -4063,6 +4191,19 @@ func (f *Manager) handleChannelReadyReceived(channel *channeldb.OpenChannel,
 	log.Debugf("Channel(%v) with ShortChanID %v: successfully "+
 		"added to graph", chanID, scid)
 
+	err = fn.MapOptionZ(
+		f.cfg.AuxFundingController,
+		func(controller AuxFundingController) error {
+			return controller.ChannelReady(
+				lnwallet.NewAuxChanState(channel),
+			)
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("failed notifying aux funding controller "+
+			"about channel ready: %w", err)
+	}
+
 	// Give the caller a final update notifying them that the channel is
 	fundingPoint := channel.FundingOutpoint
 	cp := &lnrpc.ChannelPoint{
@@ -4376,9 +4517,9 @@ 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)
@@ -4444,7 +4585,6 @@ func (f *Manager) announceChannel(localIDKey, remoteIDKey *btcec.PublicKey,
 
 // InitFundingWorkflow sends a message to the funding manager instructing it
 // to initiate a single funder workflow with the source peer.
-// TODO(roasbeef): re-visit blocking nature..
 func (f *Manager) InitFundingWorkflow(msg *InitFundingMsg) {
 	f.fundingRequests <- msg
 }
@@ -4634,6 +4774,23 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 		scidFeatureVal = true
 	}
 
+	// At this point, if we have an AuxFundingController active, we'll check
+	// to see if we have a special tapscript root to use in our MuSig2
+	// funding output.
+	tapscriptRoot, err := fn.MapOptionZ(
+		f.cfg.AuxFundingController,
+		func(c AuxFundingController) AuxTapscriptResult {
+			return c.DeriveTapscriptRoot(chanID)
+		},
+	).Unpack()
+	if err != nil {
+		err = fmt.Errorf("error deriving tapscript root: %w", err)
+		log.Error(err)
+		msg.Err <- err
+
+		return
+	}
+
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:         &msg.ChainHash,
 		PendingChanID:     chanID,
@@ -4673,6 +4830,7 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 		OptionScidAlias:  scid,
 		ScidAliasFeature: scidFeatureVal,
 		Memo:             msg.Memo,
+		TapscriptRoot:    tapscriptRoot,
 	}
 
 	reservation, err := f.cfg.Wallet.InitChannelReservation(req)
@@ -4824,6 +4982,8 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 	log.Infof("Starting funding workflow with %v for pending_id(%x), "+
 		"committype=%v", msg.Peer.Address(), chanID, commitType)
 
+	reservation.SetState(lnwallet.SentOpenChannel)
+
 	fundingOpen := lnwire.OpenChannel{
 		ChainHash:             *f.cfg.Wallet.Cfg.NetParams.GenesisHash,
 		PendingChannelID:      chanID,

funding/manager_test.go

@@ -567,6 +567,9 @@ func createTestFundingManager(t *testing.T, privKey *btcec.PrivateKey,
 		AuxLeafStore: fn.Some[lnwallet.AuxLeafStore](
 			&lnwallet.MockAuxLeafStore{},
 		),
+		AuxSigner: fn.Some[lnwallet.AuxSigner](
+			&lnwallet.MockAuxSigner{},
+		),
 	}
 
 	for _, op := range options {
@@ -677,6 +680,7 @@ func recreateAliceFundingManager(t *testing.T, alice *testNode) {
 		DeleteAliasEdge:       oldCfg.DeleteAliasEdge,
 		AliasManager:          oldCfg.AliasManager,
 		AuxLeafStore:          oldCfg.AuxLeafStore,
+		AuxSigner:             oldCfg.AuxSigner,
 	})
 	require.NoError(t, err, "failed recreating aliceFundingManager")
 

graph/builder.go

@@ -1093,8 +1093,8 @@ 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(
@@ -1141,7 +1141,7 @@ 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
@@ -1275,7 +1275,7 @@ 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

htlcswitch/link.go

@@ -2192,10 +2192,20 @@ func (l *channelLink) handleUpstreamMsg(msg lnwire.Message) {
 		// We just received a new updates to our local commitment
 		// chain, validate this new commitment, closing the link if
 		// invalid.
+		auxSigBlob, err := msg.CustomRecords.Serialize()
+		if err != nil {
+			l.failf(
+				LinkFailureError{code: ErrInvalidCommitment},
+				"unable to serialize custom records: %v", err,
+			)
+
+			return
+		}
 		err = l.channel.ReceiveNewCommitment(&lnwallet.CommitSigs{
 			CommitSig:  msg.CommitSig,
 			HtlcSigs:   msg.HtlcSigs,
 			PartialSig: msg.PartialSig,
+			AuxSigBlob: auxSigBlob,
 		})
 		if err != nil {
 			// If we were unable to reconstruct their proposed
@@ -2622,11 +2632,17 @@ func (l *channelLink) updateCommitTx() error {
 	default:
 	}
 
+	auxBlobRecords, err := lnwire.ParseCustomRecords(newCommit.AuxSigBlob)
+	if err != nil {
+		return fmt.Errorf("error parsing aux sigs: %w", err)
+	}
+
 	commitSig := &lnwire.CommitSig{
 		ChanID:        l.ChanID(),
 		CommitSig:     newCommit.CommitSig,
 		HtlcSigs:      newCommit.HtlcSigs,
 		PartialSig:    newCommit.PartialSig,
+		CustomRecords: auxBlobRecords,
 	}
 	l.cfg.Peer.SendMessage(false, commitSig)
 
@@ -3778,7 +3794,18 @@ func (l *channelLink) processExitHop(add lnwire.UpdateAddHTLC,
 	// As we're the exit hop, we'll double check the hop-payload included in
 	// the HTLC to ensure that it was crafted correctly by the sender and
 	// is compatible with the HTLC we were extended.
-	if add.Amount < fwdInfo.AmountToForward {
+	//
+	// For a special case, if the fwdInfo doesn't have any blinded path
+	// information, and the incoming HTLC had special extra data, then
+	// we'll skip this amount check. The invoice acceptor will make sure we
+	// reject the HTLC if it's not containing the correct amount after
+	// examining the custom data.
+	hasBlindedPath := fwdInfo.NextBlinding.IsSome()
+	customHTLC := len(add.CustomRecords) > 0 && !hasBlindedPath
+	log.Tracef("Exit hop has_blinded_path=%v custom_htlc_bypass=%v",
+		hasBlindedPath, customHTLC)
+
+	if !customHTLC && add.Amount < fwdInfo.AmountToForward {
 		l.log.Errorf("onion payload of incoming htlc(%x) has "+
 			"incompatible value: expected <=%v, got %v",
 			add.PaymentHash, add.Amount, fwdInfo.AmountToForward)

htlcswitch/link_test.go

@@ -268,9 +268,12 @@ func TestChannelLinkRevThenSig(t *testing.T) {
 
 	// Restart Bob as well by calling NewLightningChannel.
 	bobSigner := harness.bobChannel.Signer
+	signerMock := lnwallet.NewDefaultAuxSignerMock(t)
 	bobPool := lnwallet.NewSigPool(runtime.NumCPU(), bobSigner)
 	bobChannel, err := lnwallet.NewLightningChannel(
 		bobSigner, harness.bobChannel.State(), bobPool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	require.NoError(t, err)
 	err = bobPool.Start()
@@ -403,9 +406,12 @@ func TestChannelLinkSigThenRev(t *testing.T) {
 
 	// Restart Bob as well by calling NewLightningChannel.
 	bobSigner := harness.bobChannel.Signer
+	signerMock := lnwallet.NewDefaultAuxSignerMock(t)
 	bobPool := lnwallet.NewSigPool(runtime.NumCPU(), bobSigner)
 	bobChannel, err := lnwallet.NewLightningChannel(
 		bobSigner, harness.bobChannel.State(), bobPool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	require.NoError(t, err)
 	err = bobPool.Start()

htlcswitch/test_utils.go

@@ -353,8 +353,11 @@ func createTestChannel(t *testing.T, alicePrivKey, bobPrivKey []byte,
 	)
 
 	alicePool := lnwallet.NewSigPool(runtime.NumCPU(), aliceSigner)
+	signerMock := lnwallet.NewDefaultAuxSignerMock(t)
 	channelAlice, err := lnwallet.NewLightningChannel(
 		aliceSigner, aliceChannelState, alicePool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	if err != nil {
 		return nil, nil, err
@@ -364,6 +367,8 @@ func createTestChannel(t *testing.T, alicePrivKey, bobPrivKey []byte,
 	bobPool := lnwallet.NewSigPool(runtime.NumCPU(), bobSigner)
 	channelBob, err := lnwallet.NewLightningChannel(
 		bobSigner, bobChannelState, bobPool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(signerMock),
 	)
 	if err != nil {
 		return nil, nil, err
@@ -425,6 +430,8 @@ func createTestChannel(t *testing.T, alicePrivKey, bobPrivKey []byte,
 
 		newAliceChannel, err := lnwallet.NewLightningChannel(
 			aliceSigner, aliceStoredChannel, alicePool,
+			lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+			lnwallet.WithAuxSigner(signerMock),
 		)
 		if err != nil {
 			return nil, errors.Errorf("unable to create new channel: %v",
@@ -471,6 +478,8 @@ func createTestChannel(t *testing.T, alicePrivKey, bobPrivKey []byte,
 
 		newBobChannel, err := lnwallet.NewLightningChannel(
 			bobSigner, bobStoredChannel, bobPool,
+			lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+			lnwallet.WithAuxSigner(signerMock),
 		)
 		if err != nil {
 			return nil, errors.Errorf("unable to create new channel: %v",

itest/lnd_psbt_test.go

@@ -177,6 +177,17 @@ func runPsbtChanFunding(ht *lntest.HarnessTest, carol, dave *node.HarnessNode,
 		},
 	)
 
+	// If this is a taproot channel, then we'll decode the PSBT to assert
+	// that an internal key is included.
+	if commitType == lnrpc.CommitmentType_SIMPLE_TAPROOT {
+		decodedPSBT, err := psbt.NewFromRawBytes(
+			bytes.NewReader(tempPsbt), false,
+		)
+		require.NoError(ht, err)
+
+		require.Len(ht, decodedPSBT.Outputs[0].TaprootInternalKey, 32)
+	}
+
 	// Let's add a second channel to the batch. This time between Carol and
 	// Alice. We will publish the batch TX once this channel funding is
 	// complete.

lnrpc/lightning.pb.go

@@ -4703,6 +4703,8 @@ type Channel struct {
 	// useful information. This is only ever stored locally and in no way impacts
 	// the channel's operation.
 	Memo string `protobuf:"bytes,36,opt,name=memo,proto3" json:"memo,omitempty"`
+	// Custom channel data that might be populated in custom channels.
+	CustomChannelData []byte `protobuf:"bytes,37,opt,name=custom_channel_data,json=customChannelData,proto3" json:"custom_channel_data,omitempty"`
 }
 
 func (x *Channel) Reset() {
@@ -4993,6 +4995,13 @@ func (x *Channel) GetMemo() string {
 	return ""
 }
 
+func (x *Channel) GetCustomChannelData() []byte {
+	if x != nil {
+		return x.CustomChannelData
+	}
+	return nil
+}
+
 type ListChannelsRequest struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -9505,6 +9514,9 @@ type ChannelBalanceResponse struct {
 	PendingOpenLocalBalance *Amount `protobuf:"bytes,7,opt,name=pending_open_local_balance,json=pendingOpenLocalBalance,proto3" json:"pending_open_local_balance,omitempty"`
 	// Sum of channels pending remote balances.
 	PendingOpenRemoteBalance *Amount `protobuf:"bytes,8,opt,name=pending_open_remote_balance,json=pendingOpenRemoteBalance,proto3" json:"pending_open_remote_balance,omitempty"`
+	// Custom channel data that might be populated if there are custom channels
+	// present.
+	CustomChannelData []byte `protobuf:"bytes,9,opt,name=custom_channel_data,json=customChannelData,proto3" json:"custom_channel_data,omitempty"`
 }
 
 func (x *ChannelBalanceResponse) Reset() {
@@ -9597,6 +9609,13 @@ func (x *ChannelBalanceResponse) GetPendingOpenRemoteBalance() *Amount {
 	return nil
 }
 
+func (x *ChannelBalanceResponse) GetCustomChannelData() []byte {
+	if x != nil {
+		return x.CustomChannelData
+	}
+	return nil
+}
+
 type QueryRoutesRequest struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -17642,6 +17661,8 @@ type PendingChannelsResponse_PendingChannel struct {
 	// useful information. This is only ever stored locally and in no way
 	// impacts the channel's operation.
 	Memo string `protobuf:"bytes,13,opt,name=memo,proto3" json:"memo,omitempty"`
+	// Custom channel data that might be populated in custom channels.
+	CustomChannelData []byte `protobuf:"bytes,34,opt,name=custom_channel_data,json=customChannelData,proto3" json:"custom_channel_data,omitempty"`
 }
 
 func (x *PendingChannelsResponse_PendingChannel) Reset() {
@@ -17767,6 +17788,13 @@ func (x *PendingChannelsResponse_PendingChannel) GetMemo() string {
 	return ""
 }
 
+func (x *PendingChannelsResponse_PendingChannel) GetCustomChannelData() []byte {
+	if x != nil {
+		return x.CustomChannelData
+	}
+	return nil
+}
+
 type PendingChannelsResponse_PendingOpenChannel struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -18652,7 +18680,7 @@ var file_lightning_proto_rawDesc = []byte{
 	0x61, 0x74, 0x12, 0x2c, 0x0a, 0x12, 0x6d, 0x61, 0x78, 0x5f, 0x61, 0x63, 0x63, 0x65, 0x70, 0x74,
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@@ -18743,6 +18771,9 @@ var file_lightning_proto_rawDesc = []byte{
 	0x69, 0x61, 0x73, 0x18, 0x23, 0x20, 0x01, 0x28, 0x04, 0x42, 0x02, 0x30, 0x01, 0x52, 0x0d, 0x70,
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+	0x65, 0x6c, 0x5f, 0x64, 0x61, 0x74, 0x61, 0x18, 0x25, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x11, 0x63,
+	0x75, 0x73, 0x74, 0x6f, 0x6d, 0x43, 0x68, 0x61, 0x6e, 0x6e, 0x65, 0x6c, 0x44, 0x61, 0x74, 0x61,
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@@ -19326,7 +19357,7 @@ var file_lightning_proto_rawDesc = []byte{
 	0x61, 0x6e, 0x6e, 0x65, 0x6c, 0x73, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x24, 0x0a,
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@@ -19358,7 +19389,7 @@ var file_lightning_proto_rawDesc = []byte{
 	0x6c, 0x73, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x2e, 0x57, 0x61, 0x69, 0x74, 0x69,
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@@ -19393,7 +19424,10 @@ var file_lightning_proto_rawDesc = []byte{
 	0x6e, 0x53, 0x74, 0x61, 0x74, 0x75, 0x73, 0x46, 0x6c, 0x61, 0x67, 0x73, 0x12, 0x18, 0x0a, 0x07,
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@@ -19571,7 +19605,7 @@ var file_lightning_proto_rawDesc = []byte{
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-	0x65, 0x73, 0x74, 0x22, 0x80, 0x04, 0x0a, 0x16, 0x43, 0x68, 0x61, 0x6e, 0x6e, 0x65, 0x6c, 0x42,
+	0x65, 0x73, 0x74, 0x22, 0xb0, 0x04, 0x0a, 0x16, 0x43, 0x68, 0x61, 0x6e, 0x6e, 0x65, 0x6c, 0x42,
 	0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12, 0x1c,
 	0x0a, 0x07, 0x62, 0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x18, 0x01, 0x20, 0x01, 0x28, 0x03, 0x42,
 	0x02, 0x18, 0x01, 0x52, 0x07, 0x62, 0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x12, 0x34, 0x0a, 0x14,
@@ -19603,7 +19637,10 @@ var file_lightning_proto_rawDesc = []byte{
 	0x62, 0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x18, 0x08, 0x20, 0x01, 0x28, 0x0b, 0x32, 0x0d, 0x2e,
 	0x6c, 0x6e, 0x72, 0x70, 0x63, 0x2e, 0x41, 0x6d, 0x6f, 0x75, 0x6e, 0x74, 0x52, 0x18, 0x70, 0x65,
 	0x6e, 0x64, 0x69, 0x6e, 0x67, 0x4f, 0x70, 0x65, 0x6e, 0x52, 0x65, 0x6d, 0x6f, 0x74, 0x65, 0x42,
-	0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x22, 0x9a, 0x07, 0x0a, 0x12, 0x51, 0x75, 0x65, 0x72, 0x79,
+	0x61, 0x6c, 0x61, 0x6e, 0x63, 0x65, 0x12, 0x2e, 0x0a, 0x13, 0x63, 0x75, 0x73, 0x74, 0x6f, 0x6d,
+	0x5f, 0x63, 0x68, 0x61, 0x6e, 0x6e, 0x65, 0x6c, 0x5f, 0x64, 0x61, 0x74, 0x61, 0x18, 0x09, 0x20,
+	0x01, 0x28, 0x0c, 0x52, 0x11, 0x63, 0x75, 0x73, 0x74, 0x6f, 0x6d, 0x43, 0x68, 0x61, 0x6e, 0x6e,
+	0x65, 0x6c, 0x44, 0x61, 0x74, 0x61, 0x22, 0x9a, 0x07, 0x0a, 0x12, 0x51, 0x75, 0x65, 0x72, 0x79,
 	0x52, 0x6f, 0x75, 0x74, 0x65, 0x73, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x17, 0x0a,
 	0x07, 0x70, 0x75, 0x62, 0x5f, 0x6b, 0x65, 0x79, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x06,
 	0x70, 0x75, 0x62, 0x4b, 0x65, 0x79, 0x12, 0x10, 0x0a, 0x03, 0x61, 0x6d, 0x74, 0x18, 0x02, 0x20,

lnrpc/lightning.proto

@@ -1592,6 +1592,11 @@ message Channel {
     the channel's operation.
     */
     string memo = 36;
+
+    /*
+    Custom channel data that might be populated in custom channels.
+    */
+    bytes custom_channel_data = 37;
 }
 
 message ListChannelsRequest {
@@ -2709,6 +2714,11 @@ message PendingChannelsResponse {
         impacts the channel's operation.
         */
         string memo = 13;
+
+        /*
+        Custom channel data that might be populated in custom channels.
+        */
+        bytes custom_channel_data = 34;
     }
 
     message PendingOpenChannel {
@@ -2968,6 +2978,12 @@ message ChannelBalanceResponse {
 
     // Sum of channels pending remote balances.
     Amount pending_open_remote_balance = 8;
+
+    /*
+    Custom channel data that might be populated if there are custom channels
+    present.
+    */
+    bytes custom_channel_data = 9;
 }
 
 message QueryRoutesRequest {

lnrpc/lightning.swagger.json

@@ -3127,6 +3127,11 @@
         "memo": {
           "type": "string",
           "description": "An optional note-to-self to go along with the channel containing some\nuseful information. This is only ever stored locally and in no way\nimpacts the channel's operation."
+        },
+        "custom_channel_data": {
+          "type": "string",
+          "format": "byte",
+          "description": "Custom channel data that might be populated in custom channels."
         }
       }
     },
@@ -3849,6 +3854,11 @@
         "memo": {
           "type": "string",
           "description": "An optional note-to-self to go along with the channel containing some\nuseful information. This is only ever stored locally and in no way impacts\nthe channel's operation."
+        },
+        "custom_channel_data": {
+          "type": "string",
+          "format": "byte",
+          "description": "Custom channel data that might be populated in custom channels."
         }
       }
     },
@@ -4052,6 +4062,11 @@
         "pending_open_remote_balance": {
           "$ref": "#/definitions/lnrpcAmount",
           "description": "Sum of channels pending remote balances."
+        },
+        "custom_channel_data": {
+          "type": "string",
+          "format": "byte",
+          "description": "Custom channel data that might be populated if there are custom channels\npresent."
         }
       }
     },

lnrpc/routerrpc/router_backend.go

@@ -25,6 +25,7 @@ import (
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/subscribe"
 	"github.com/lightningnetwork/lnd/zpay32"
+	"google.golang.org/protobuf/proto"
 )
 
 const (
@@ -104,6 +105,10 @@ type RouterBackend struct {
 	// TODO(yy): remove this config after the new status code is fully
 	// deployed to the network(v0.20.0).
 	UseStatusInitiated bool
+
+	// ParseCustomChannelData is a function that can be used to parse custom
+	// channel data from the first hop of a route.
+	ParseCustomChannelData func(message proto.Message) error
 }
 
 // MissionControl defines the mission control dependencies of routerrpc.
@@ -596,8 +601,14 @@ func (r *RouterBackend) MarshallRoute(route *route.Route) (*lnrpc.Route, error)
 
 		resp.CustomChannelData = customData
 
-		// TODO(guggero): Feed the route into the custom data parser
-		// (part 3 of the mega PR series).
+		// Allow the aux data parser to parse the custom records into
+		// a human-readable JSON (if available).
+		if r.ParseCustomChannelData != nil {
+			err := r.ParseCustomChannelData(resp)
+			if err != nil {
+				return nil, err
+			}
+		}
 	}
 
 	incomingAmt := route.TotalAmount

lntest/harness_assertion.go

@@ -964,6 +964,11 @@ func (h *HarnessTest) AssertChannelBalanceResp(hn *node.HarnessNode,
 	expected *lnrpc.ChannelBalanceResponse) {
 
 	resp := hn.RPC.ChannelBalance()
+
+	// Ignore custom channel data of both expected and actual responses.
+	expected.CustomChannelData = nil
+	resp.CustomChannelData = nil
+
 	require.True(h, proto.Equal(expected, resp), "balance is incorrect "+
 		"got: %v, want: %v", resp, expected)
 }

lnwallet/aux_signer.go

@@ -0,0 +1,250 @@
+package lnwallet
+
+import (
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+// htlcCustomSigType is the TLV type that is used to encode the custom HTLC
+// signatures within the custom data for an existing HTLC.
+var htlcCustomSigType tlv.TlvType65543
+
+// AuxHtlcDescriptor is a struct that contains the information needed to sign or
+// verify an HTLC for custom channels.
+type AuxHtlcDescriptor struct {
+	// ChanID is the ChannelID of the LightningChannel that this
+	// paymentDescriptor belongs to. We track this here so we can
+	// reconstruct the Messages that this paymentDescriptor is built from.
+	ChanID lnwire.ChannelID
+
+	// RHash is the payment hash for this HTLC. The HTLC can be settled iff
+	// the preimage to this hash is presented.
+	RHash PaymentHash
+
+	// Timeout is the absolute timeout in blocks, after which this HTLC
+	// expires.
+	Timeout uint32
+
+	// Amount is the HTLC amount in milli-satoshis.
+	Amount lnwire.MilliSatoshi
+
+	// HtlcIndex is the index within the main update log for this HTLC.
+	// Entries within the log of type Add will have this field populated,
+	// as other entries will point to the entry via this counter.
+	//
+	// NOTE: This field will only be populated if EntryType is Add.
+	HtlcIndex uint64
+
+	// ParentIndex is the HTLC index of the entry that this update settles
+	// or times out.
+	//
+	// NOTE: This field will only be populated if EntryType is Fail or
+	// Settle.
+	ParentIndex uint64
+
+	// EntryType denotes the exact type of the paymentDescriptor. In the
+	// case of a Timeout, or Settle type, then the Parent field will point
+	// into the log to the HTLC being modified.
+	EntryType updateType
+
+	// CustomRecords also stores the set of optional custom records that
+	// may have been attached to a sent HTLC.
+	CustomRecords lnwire.CustomRecords
+
+	// addCommitHeight[Remote|Local] encodes the height of the commitment
+	// which included this HTLC on either the remote or local commitment
+	// chain. This value is used to determine when an HTLC is fully
+	// "locked-in".
+	addCommitHeightRemote uint64
+	addCommitHeightLocal  uint64
+
+	// removeCommitHeight[Remote|Local] encodes the height of the
+	// commitment which removed the parent pointer of this
+	// paymentDescriptor either due to a timeout or a settle. Once both
+	// these heights are below the tail of both chains, the log entries can
+	// safely be removed.
+	removeCommitHeightRemote uint64
+	removeCommitHeightLocal  uint64
+}
+
+// AddHeight returns the height at which the HTLC was added to the commitment
+// chain. The height is returned based on the chain the HTLC is being added to
+// (local or remote chain).
+func (a *AuxHtlcDescriptor) AddHeight(
+	whoseCommitChain lntypes.ChannelParty) uint64 {
+
+	if whoseCommitChain.IsRemote() {
+		return a.addCommitHeightRemote
+	}
+
+	return a.addCommitHeightLocal
+}
+
+// RemoveHeight returns the height at which the HTLC was removed from the
+// commitment chain. The height is returned based on the chain the HTLC is being
+// removed from (local or remote chain).
+func (a *AuxHtlcDescriptor) RemoveHeight(
+	whoseCommitChain lntypes.ChannelParty) uint64 {
+
+	if whoseCommitChain.IsRemote() {
+		return a.removeCommitHeightRemote
+	}
+
+	return a.removeCommitHeightLocal
+}
+
+// newAuxHtlcDescriptor creates a new AuxHtlcDescriptor from a payment
+// descriptor.
+func newAuxHtlcDescriptor(p *paymentDescriptor) AuxHtlcDescriptor {
+	return AuxHtlcDescriptor{
+		ChanID:                   p.ChanID,
+		RHash:                    p.RHash,
+		Timeout:                  p.Timeout,
+		Amount:                   p.Amount,
+		HtlcIndex:                p.HtlcIndex,
+		ParentIndex:              p.ParentIndex,
+		EntryType:                p.EntryType,
+		CustomRecords:            p.CustomRecords.Copy(),
+		addCommitHeightRemote:    p.addCommitHeightRemote,
+		addCommitHeightLocal:     p.addCommitHeightLocal,
+		removeCommitHeightRemote: p.removeCommitHeightRemote,
+		removeCommitHeightLocal:  p.removeCommitHeightLocal,
+	}
+}
+
+// BaseAuxJob is a struct that contains the common fields that are shared among
+// the aux sign/verify jobs.
+type BaseAuxJob struct {
+	// OutputIndex is the output index of the HTLC on the commitment
+	// transaction being signed.
+	//
+	// NOTE: If the output is dust from the PoV of the commitment chain,
+	// then this value will be -1.
+	OutputIndex int32
+
+	// KeyRing is the commitment key ring that contains the keys needed to
+	// generate the second level HTLC signatures.
+	KeyRing CommitmentKeyRing
+
+	// HTLC is the HTLC that is being signed or verified.
+	HTLC AuxHtlcDescriptor
+
+	// Incoming is a boolean that indicates if the HTLC is incoming or
+	// outgoing.
+	Incoming bool
+
+	// CommitBlob is the commitment transaction blob that contains the aux
+	// information for this channel.
+	CommitBlob fn.Option[tlv.Blob]
+
+	// HtlcLeaf is the aux tap leaf that corresponds to the HTLC being
+	// signed/verified.
+	HtlcLeaf input.AuxTapLeaf
+}
+
+// AuxSigJob is a struct that contains all the information needed to sign an
+// HTLC for custom channels.
+type AuxSigJob struct {
+	// SignDesc is the sign desc for this HTLC.
+	SignDesc input.SignDescriptor
+
+	BaseAuxJob
+
+	// Resp is a channel that will be used to send the result of the sign
+	// job. This channel MUST be buffered.
+	Resp chan AuxSigJobResp
+
+	// Cancel is a channel that is closed by the caller if they wish to
+	// abandon all pending sign jobs part of a single batch. This should
+	// never be closed by the validator.
+	Cancel <-chan struct{}
+}
+
+// NewAuxSigJob creates a new AuxSigJob.
+func NewAuxSigJob(sigJob SignJob, keyRing CommitmentKeyRing, incoming bool,
+	htlc AuxHtlcDescriptor, commitBlob fn.Option[tlv.Blob],
+	htlcLeaf input.AuxTapLeaf, cancelChan <-chan struct{}) AuxSigJob {
+
+	return AuxSigJob{
+		SignDesc: sigJob.SignDesc,
+		BaseAuxJob: BaseAuxJob{
+			OutputIndex: sigJob.OutputIndex,
+			KeyRing:     keyRing,
+			HTLC:        htlc,
+			Incoming:    incoming,
+			CommitBlob:  commitBlob,
+			HtlcLeaf:    htlcLeaf,
+		},
+		Resp:   make(chan AuxSigJobResp, 1),
+		Cancel: cancelChan,
+	}
+}
+
+// AuxSigJobResp is a struct that contains the result of a sign job.
+type AuxSigJobResp struct {
+	// SigBlob is the signature blob that was generated for the HTLC. This
+	// is an opaque TLV field that may contain the signature and other data.
+	SigBlob fn.Option[tlv.Blob]
+
+	// HtlcIndex is the index of the HTLC that was signed.
+	HtlcIndex uint64
+
+	// Err is the error that occurred when executing the specified
+	// signature job. In the case that no error occurred, this value will
+	// be nil.
+	Err error
+}
+
+// AuxVerifyJob is a struct that contains all the information needed to verify
+// an HTLC for custom channels.
+type AuxVerifyJob struct {
+	// SigBlob is the signature blob that was generated for the HTLC. This
+	// is an opaque TLV field that may contain the signature and other data.
+	SigBlob fn.Option[tlv.Blob]
+
+	BaseAuxJob
+}
+
+// NewAuxVerifyJob creates a new AuxVerifyJob.
+func NewAuxVerifyJob(sig fn.Option[tlv.Blob], keyRing CommitmentKeyRing,
+	incoming bool, htlc AuxHtlcDescriptor, commitBlob fn.Option[tlv.Blob],
+	htlcLeaf input.AuxTapLeaf) AuxVerifyJob {
+
+	return AuxVerifyJob{
+		SigBlob: sig,
+		BaseAuxJob: BaseAuxJob{
+			KeyRing:    keyRing,
+			HTLC:       htlc,
+			Incoming:   incoming,
+			CommitBlob: commitBlob,
+			HtlcLeaf:   htlcLeaf,
+		},
+	}
+}
+
+// AuxSigner is an interface that is used to sign and verify HTLCs for custom
+// channels. It is similar to the existing SigPool, but uses opaque blobs to
+// shuffle around signature information and other metadata.
+type AuxSigner interface {
+	// SubmitSecondLevelSigBatch takes a batch of aux sign jobs and
+	// processes them asynchronously.
+	SubmitSecondLevelSigBatch(chanState AuxChanState, commitTx *wire.MsgTx,
+		sigJob []AuxSigJob) error
+
+	// PackSigs takes a series of aux signatures and packs them into a
+	// single blob that can be sent alongside the CommitSig messages.
+	PackSigs([]fn.Option[tlv.Blob]) fn.Result[fn.Option[tlv.Blob]]
+
+	// UnpackSigs takes a packed blob of signatures and returns the
+	// original signatures for each HTLC, keyed by HTLC index.
+	UnpackSigs(fn.Option[tlv.Blob]) fn.Result[[]fn.Option[tlv.Blob]]
+
+	// VerifySecondLevelSigs attempts to synchronously verify a batch of aux
+	// sig jobs.
+	VerifySecondLevelSigs(chanState AuxChanState, commitTx *wire.MsgTx,
+		verifyJob []AuxVerifyJob) error
+}

lnwallet/chanfunding/canned_assembler.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
@@ -98,6 +99,26 @@ func (s *ShimIntent) FundingOutput() ([]byte, *wire.TxOut, error) {
 	)
 }
 
+// TaprootInternalKey may return the internal key for a MuSig2 funding output,
+// but only if this is actually a MuSig2 channel.
+func (s *ShimIntent) TaprootInternalKey() fn.Option[*btcec.PublicKey] {
+	if !s.musig2 {
+		return fn.None[*btcec.PublicKey]()
+	}
+
+	// Similar to the existing p2wsh script, we'll always ensure the keys
+	// are sorted before use. Since we're only interested in the internal
+	// key, we don't need to take into account any tapscript root.
+	//
+	// We ignore the error here as this is only called after FundingOutput
+	// is called.
+	combinedKey, _, _, _ := musig2.AggregateKeys(
+		[]*btcec.PublicKey{s.localKey.PubKey, s.remoteKey}, true,
+	)
+
+	return fn.Some(combinedKey.PreTweakedKey)
+}
+
 // Cancel allows the caller to cancel a funding Intent at any time.  This will
 // return any resources such as coins back to the eligible pool to be used in
 // order channel fundings.

lnwallet/chanfunding/psbt_assembler.go

@@ -6,11 +6,14 @@ import (
 	"sync"
 
 	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/btcutil/psbt"
 	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
 )
@@ -162,6 +165,13 @@ func (i *PsbtIntent) BindKeys(localKey *keychain.KeyDescriptor,
 	i.State = PsbtOutputKnown
 }
 
+// BindTapscriptRoot takes an optional tapscript root and binds it to the
+// underlying funding intent. This only applies to musig2 channels, and will be
+// used to make the musig2 funding output.
+func (i *PsbtIntent) BindTapscriptRoot(root fn.Option[chainhash.Hash]) {
+	i.tapscriptRoot = root
+}
+
 // FundingParams returns the parameters that are necessary to start funding the
 // channel output this intent was created for. It returns the P2WSH funding
 // address, the exact funding amount and a PSBT packet that contains exactly one
@@ -208,7 +218,18 @@ func (i *PsbtIntent) FundingParams() (btcutil.Address, int64, *psbt.Packet,
 		}
 	}
 	packet.UnsignedTx.TxOut = append(packet.UnsignedTx.TxOut, out)
-	packet.Outputs = append(packet.Outputs, psbt.POutput{})
+
+	var pOut psbt.POutput
+
+	// If this is a MuSig2 channel, we also need to communicate the internal
+	// key to the caller. Otherwise, they cannot verify the construction of
+	// the P2TR output script.
+	pOut.TaprootInternalKey = fn.MapOptionZ(
+		i.TaprootInternalKey(), schnorr.SerializePubKey,
+	)
+
+	packet.Outputs = append(packet.Outputs, pOut)
+
 	return addr, out.Value, packet, nil
 }
 

lnwallet/channel.go

@@ -6,7 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"sort"
+	"slices"
 	"sync"
 
 	"github.com/btcsuite/btcd/blockchain"
@@ -760,6 +760,10 @@ type LightningChannel struct {
 	// signatures, of which there may be hundreds.
 	sigPool *SigPool
 
+	// auxSigner is a special signer used to obtain opaque signatures for
+	// custom channel variants.
+	auxSigner fn.Option[AuxSigner]
+
 	// Capacity is the total capacity of this channel.
 	Capacity btcutil.Amount
 
@@ -821,6 +825,7 @@ type channelOpts struct {
 	remoteNonce *musig2.Nonces
 
 	leafStore fn.Option[AuxLeafStore]
+	auxSigner fn.Option[AuxSigner]
 
 	skipNonceInit bool
 }
@@ -859,6 +864,13 @@ func WithLeafStore(store AuxLeafStore) ChannelOpt {
 	}
 }
 
+// WithAuxSigner is used to specify a custom aux signer for the channel.
+func WithAuxSigner(signer AuxSigner) ChannelOpt {
+	return func(o *channelOpts) {
+		o.auxSigner = fn.Some[AuxSigner](signer)
+	}
+}
+
 // defaultChannelOpts returns the set of default options for a new channel.
 func defaultChannelOpts() *channelOpts {
 	return &channelOpts{}
@@ -911,6 +923,7 @@ func NewLightningChannel(signer input.Signer,
 	lc := &LightningChannel{
 		Signer:        signer,
 		leafStore:     opts.leafStore,
+		auxSigner:     opts.auxSigner,
 		sigPool:       sigPool,
 		currentHeight: localCommit.CommitHeight,
 		commitChains:  commitChains,
@@ -2545,6 +2558,18 @@ type HtlcView struct {
 	FeePerKw chainfee.SatPerKWeight
 }
 
+// AuxOurUpdates returns the outgoing HTLCs as a read-only copy of
+// AuxHtlcDescriptors.
+func (v *HtlcView) AuxOurUpdates() []AuxHtlcDescriptor {
+	return fn.Map(newAuxHtlcDescriptor, v.OurUpdates)
+}
+
+// AuxTheirUpdates returns the incoming HTLCs as a read-only copy of
+// AuxHtlcDescriptors.
+func (v *HtlcView) AuxTheirUpdates() []AuxHtlcDescriptor {
+	return fn.Map(newAuxHtlcDescriptor, v.TheirUpdates)
+}
+
 // fetchHTLCView returns all the candidate HTLC updates which should be
 // considered for inclusion within a commitment based on the passed HTLC log
 // indexes.
@@ -3064,7 +3089,8 @@ func processFeeUpdate(feeUpdate *paymentDescriptor, nextHeight uint64,
 func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 	chanState *channeldb.OpenChannel, leaseExpiry uint32,
 	remoteCommitView *commitment,
-	leafStore fn.Option[AuxLeafStore]) ([]SignJob, chan struct{}, error) {
+	leafStore fn.Option[AuxLeafStore]) ([]SignJob, []AuxSigJob,
+	chan struct{}, error) {
 
 	var (
 		isRemoteInitiator = !chanState.IsInitiator
@@ -3084,6 +3110,7 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 	numSigs := len(remoteCommitView.incomingHTLCs) +
 		len(remoteCommitView.outgoingHTLCs)
 	sigBatch := make([]SignJob, 0, numSigs)
+	auxSigBatch := make([]AuxSigJob, 0, numSigs)
 
 	var err error
 	cancelChan := make(chan struct{})
@@ -3098,8 +3125,8 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 		},
 	).Unpack()
 	if err != nil {
-		return nil, nil, fmt.Errorf("unable to fetch aux leaves: %w",
-			err)
+		return nil, nil, nil, fmt.Errorf("unable to fetch aux leaves: "+
+			"%w", err)
 	}
 
 	// For each outgoing and incoming HTLC, if the HTLC isn't considered a
@@ -3148,12 +3175,9 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 			auxLeaf,
 		)
 		if err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 
-		// TODO(roasbeef): hook up signer interface here (later commit
-		// in this PR).
-
 		// Construct a full hash cache as we may be signing a segwit v1
 		// sighash.
 		txOut := remoteCommitView.txn.TxOut[htlc.remoteOutputIndex]
@@ -3185,6 +3209,11 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 		}
 
 		sigBatch = append(sigBatch, sigJob)
+
+		auxSigBatch = append(auxSigBatch, NewAuxSigJob(
+			sigJob, *keyRing, true, newAuxHtlcDescriptor(&htlc),
+			remoteCommitView.customBlob, auxLeaf, cancelChan,
+		))
 	}
 	for _, htlc := range remoteCommitView.outgoingHTLCs {
 		if HtlcIsDust(
@@ -3228,7 +3257,7 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 			auxLeaf,
 		)
 		if err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 
 		// Construct a full hash cache as we may be signing a segwit v1
@@ -3257,13 +3286,19 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 		// If this is a taproot channel, then we'll need to set the
 		// method type to ensure we generate a valid signature.
 		if chanType.IsTaproot() {
-			sigJob.SignDesc.SignMethod = input.TaprootScriptSpendSignMethod //nolint:lll
+			//nolint:lll
+			sigJob.SignDesc.SignMethod = input.TaprootScriptSpendSignMethod
 		}
 
 		sigBatch = append(sigBatch, sigJob)
+
+		auxSigBatch = append(auxSigBatch, NewAuxSigJob(
+			sigJob, *keyRing, false, newAuxHtlcDescriptor(&htlc),
+			remoteCommitView.customBlob, auxLeaf, cancelChan,
+		))
 	}
 
-	return sigBatch, cancelChan, nil
+	return sigBatch, auxSigBatch, cancelChan, nil
 }
 
 // createCommitDiff will create a commit diff given a new pending commitment
@@ -3272,7 +3307,8 @@ func genRemoteHtlcSigJobs(keyRing *CommitmentKeyRing,
 // new commitment to the remote party. The commit diff returned contains all
 // information necessary for retransmission.
 func (lc *LightningChannel) createCommitDiff(newCommit *commitment,
-	commitSig lnwire.Sig, htlcSigs []lnwire.Sig) *channeldb.CommitDiff {
+	commitSig lnwire.Sig, htlcSigs []lnwire.Sig,
+	auxSigs []fn.Option[tlv.Blob]) (*channeldb.CommitDiff, error) {
 
 	var (
 		logUpdates        []channeldb.LogUpdate
@@ -3341,21 +3377,71 @@ func (lc *LightningChannel) createCommitDiff(newCommit *commitment,
 	// disk.
 	diskCommit := newCommit.toDiskCommit(lntypes.Remote)
 
-	return &channeldb.CommitDiff{
-		Commitment: *diskCommit,
-		CommitSig: &lnwire.CommitSig{
+	// We prepare the commit sig message to be sent to the remote party.
+	commitSigMsg := &lnwire.CommitSig{
 		ChanID: lnwire.NewChanIDFromOutPoint(
 			lc.channelState.FundingOutpoint,
 		),
 		CommitSig: commitSig,
 		HtlcSigs:  htlcSigs,
+	}
+
+	// Encode and check the size of the custom records now.
+	auxCustomRecords, err := fn.MapOptionZ(
+		lc.auxSigner,
+		func(s AuxSigner) fn.Result[lnwire.CustomRecords] {
+			blobOption, err := s.PackSigs(auxSigs).Unpack()
+			if err != nil {
+				return fn.Err[lnwire.CustomRecords](err)
+			}
+
+			// We now serialize the commit sig message without the
+			// custom records to make sure we have space for them.
+			var buf bytes.Buffer
+			err = commitSigMsg.Encode(&buf, 0)
+			if err != nil {
+				return fn.Err[lnwire.CustomRecords](err)
+			}
+
+			// The number of available bytes is the max message size
+			// minus the size of the message without the custom
+			// records. We also subtract 8 bytes for encoding
+			// overhead of the custom records (just some safety
+			// padding).
+			available := lnwire.MaxMsgBody - buf.Len() - 8
+
+			blob := blobOption.UnwrapOr(nil)
+			if len(blob) > available {
+				err = fmt.Errorf("aux sigs size %d exceeds "+
+					"max allowed size of %d", len(blob),
+					available)
+
+				return fn.Err[lnwire.CustomRecords](err)
+			}
+
+			records, err := lnwire.ParseCustomRecords(blob)
+			if err != nil {
+				return fn.Err[lnwire.CustomRecords](err)
+			}
+
+			return fn.Ok(records)
 		},
+	).Unpack()
+	if err != nil {
+		return nil, fmt.Errorf("error packing aux sigs: %w", err)
+	}
+
+	commitSigMsg.CustomRecords = auxCustomRecords
+
+	return &channeldb.CommitDiff{
+		Commitment:        *diskCommit,
+		CommitSig:         commitSigMsg,
 		LogUpdates:        logUpdates,
 		OpenedCircuitKeys: openCircuitKeys,
 		ClosedCircuitKeys: closedCircuitKeys,
 		AddAcks:           ackAddRefs,
 		SettleFailAcks:    settleFailRefs,
-	}
+	}, nil
 }
 
 // getUnsignedAckedUpdates returns all remote log updates that we haven't
@@ -3748,6 +3834,10 @@ type CommitSigs struct {
 	// PartialSig is the musig2 partial signature for taproot commitment
 	// transactions.
 	PartialSig lnwire.OptPartialSigWithNonceTLV
+
+	// AuxSigBlob is the blob containing all the auxiliary signatures for
+	// this new commitment state.
+	AuxSigBlob tlv.Blob
 }
 
 // NewCommitState wraps the various signatures needed to properly
@@ -3772,6 +3862,8 @@ type NewCommitState struct {
 // any). The HTLC signatures are sorted according to the BIP 69 order of the
 // HTLC's on the commitment transaction. Finally, the new set of pending HTLCs
 // for the remote party's commitment are also returned.
+//
+//nolint:funlen
 func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 	lc.Lock()
 	defer lc.Unlock()
@@ -3864,15 +3956,37 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 	if lc.channelState.ChanType.HasLeaseExpiration() {
 		leaseExpiry = lc.channelState.ThawHeight
 	}
-	sigBatch, cancelChan, err := genRemoteHtlcSigJobs(
+	sigBatch, auxSigBatch, cancelChan, err := genRemoteHtlcSigJobs(
 		keyRing, lc.channelState, leaseExpiry, newCommitView,
 		lc.leafStore,
 	)
 	if err != nil {
 		return nil, err
 	}
+
+	// We'll need to send over the signatures to the remote party in the
+	// order as they appear on the commitment transaction after BIP 69
+	// sorting.
+	slices.SortFunc(sigBatch, func(i, j SignJob) int {
+		return int(i.OutputIndex - j.OutputIndex)
+	})
+	slices.SortFunc(auxSigBatch, func(i, j AuxSigJob) int {
+		return int(i.OutputIndex - j.OutputIndex)
+	})
+
 	lc.sigPool.SubmitSignBatch(sigBatch)
 
+	err = fn.MapOptionZ(lc.auxSigner, func(a AuxSigner) error {
+		return a.SubmitSecondLevelSigBatch(
+			NewAuxChanState(lc.channelState), newCommitView.txn,
+			auxSigBatch,
+		)
+	})
+	if err != nil {
+		return nil, fmt.Errorf("error submitting second level sig "+
+			"batch: %w", err)
+	}
+
 	// While the jobs are being carried out, we'll Sign their version of
 	// the new commitment transaction while we're waiting for the rest of
 	// the HTLC signatures to be processed.
@@ -3910,17 +4024,12 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 		}
 	}
 
-	// We'll need to send over the signatures to the remote party in the
-	// order as they appear on the commitment transaction after BIP 69
-	// sorting.
-	sort.Slice(sigBatch, func(i, j int) bool {
-		return sigBatch[i].OutputIndex < sigBatch[j].OutputIndex
-	})
-
-	// With the jobs sorted, we'll now iterate through all the responses to
-	// gather each of the signatures in order.
+	// Iterate through all the responses to gather each of the signatures
+	// in the order they were submitted.
 	htlcSigs = make([]lnwire.Sig, 0, len(sigBatch))
-	for _, htlcSigJob := range sigBatch {
+	auxSigs := make([]fn.Option[tlv.Blob], 0, len(auxSigBatch))
+	for i := range sigBatch {
+		htlcSigJob := sigBatch[i]
 		jobResp := <-htlcSigJob.Resp
 
 		// If an error occurred, then we'll cancel any other active
@@ -3931,12 +4040,34 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 		}
 
 		htlcSigs = append(htlcSigs, jobResp.Sig)
+
+		if lc.auxSigner.IsNone() {
+			continue
+		}
+
+		auxHtlcSigJob := auxSigBatch[i]
+		auxJobResp := <-auxHtlcSigJob.Resp
+
+		// If an error occurred, then we'll cancel any other active
+		// jobs.
+		if auxJobResp.Err != nil {
+			close(cancelChan)
+			return nil, auxJobResp.Err
+		}
+
+		auxSigs = append(auxSigs, auxJobResp.SigBlob)
 	}
 
 	// As we're about to proposer a new commitment state for the remote
 	// party, we'll write this pending state to disk before we exit, so we
 	// can retransmit it if necessary.
-	commitDiff := lc.createCommitDiff(newCommitView, sig, htlcSigs)
+	commitDiff, err := lc.createCommitDiff(
+		newCommitView, sig, htlcSigs, auxSigs,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	err = lc.channelState.AppendRemoteCommitChain(commitDiff)
 	if err != nil {
 		return nil, err
@@ -3950,11 +4081,18 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 	// latest commitment update.
 	lc.commitChains.Remote.addCommitment(newCommitView)
 
+	auxSigBlob, err := commitDiff.CommitSig.CustomRecords.Serialize()
+	if err != nil {
+		return nil, fmt.Errorf("unable to serialize aux sig blob: %w",
+			err)
+	}
+
 	return &NewCommitState{
 		CommitSigs: &CommitSigs{
 			CommitSig:  sig,
 			HtlcSigs:   htlcSigs,
 			PartialSig: lnwire.MaybePartialSigWithNonce(partialSig),
+			AuxSigBlob: auxSigBlob,
 		},
 		PendingHTLCs: commitDiff.Commitment.Htlcs,
 	}, nil
@@ -3966,8 +4104,8 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 // each time. After we receive the channel reestablish message, we learn the
 // nonce we need to use for the remote party. As a result, we need to generate
 // the partial signature again with the new nonce.
-func (lc *LightningChannel) resignMusigCommit(commitTx *wire.MsgTx,
-) (lnwire.OptPartialSigWithNonceTLV, error) {
+func (lc *LightningChannel) resignMusigCommit(
+	commitTx *wire.MsgTx) (lnwire.OptPartialSigWithNonceTLV, error) {
 
 	remoteSession := lc.musigSessions.RemoteSession
 	musig, err := remoteSession.SignCommit(commitTx)
@@ -4172,6 +4310,15 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 			// If we signed this state, then we'll accumulate
 			// another update to send over.
 			case err == nil:
+				customRecords, err := lnwire.ParseCustomRecords(
+					newCommit.AuxSigBlob,
+				)
+				if err != nil {
+					sErr := fmt.Errorf("error parsing aux "+
+						"sigs: %w", err)
+					return nil, nil, nil, sErr
+				}
+
 				commitSig := &lnwire.CommitSig{
 					ChanID: lnwire.NewChanIDFromOutPoint(
 						lc.channelState.FundingOutpoint,
@@ -4179,6 +4326,7 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 					CommitSig:     newCommit.CommitSig,
 					HtlcSigs:      newCommit.HtlcSigs,
 					PartialSig:    newCommit.PartialSig,
+					CustomRecords: customRecords,
 				}
 
 				updates = append(updates, commitSig)
@@ -4396,6 +4544,7 @@ func (lc *LightningChannel) computeView(view *HtlcView,
 	// need this to determine which HTLCs are dust, and also the final fee
 	// rate.
 	view.FeePerKw = commitChain.tip().feePerKw
+	view.NextHeight = nextHeight
 
 	// We evaluate the view at this stage, meaning settled and failed HTLCs
 	// will remove their corresponding added HTLCs.  The resulting filtered
@@ -4471,7 +4620,8 @@ func (lc *LightningChannel) computeView(view *HtlcView,
 func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 	localCommitmentView *commitment, keyRing *CommitmentKeyRing,
 	htlcSigs []lnwire.Sig, leaseExpiry uint32,
-	leafStore fn.Option[AuxLeafStore]) ([]VerifyJob, error) {
+	leafStore fn.Option[AuxLeafStore], auxSigner fn.Option[AuxSigner],
+	sigBlob fn.Option[tlv.Blob]) ([]VerifyJob, []AuxVerifyJob, error) {
 
 	var (
 		isLocalInitiator = chanState.IsInitiator
@@ -4490,6 +4640,7 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 	numHtlcs := len(localCommitmentView.incomingHTLCs) +
 		len(localCommitmentView.outgoingHTLCs)
 	verifyJobs := make([]VerifyJob, 0, numHtlcs)
+	auxVerifyJobs := make([]AuxVerifyJob, 0, numHtlcs)
 
 	diskCommit := localCommitmentView.toDiskCommit(lntypes.Local)
 	auxResult, err := fn.MapOptionZ(
@@ -4501,7 +4652,20 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 		},
 	).Unpack()
 	if err != nil {
-		return nil, fmt.Errorf("unable to fetch aux leaves: %w", err)
+		return nil, nil, fmt.Errorf("unable to fetch aux leaves: %w",
+			err)
+	}
+
+	// If we have a sig blob, then we'll attempt to map that to individual
+	// blobs for each HTLC we might need a signature for.
+	auxHtlcSigs, err := fn.MapOptionZ(
+		auxSigner, func(a AuxSigner) fn.Result[[]fn.Option[tlv.Blob]] {
+			return a.UnpackSigs(sigBlob)
+		},
+	).Unpack()
+	if err != nil {
+		return nil, nil, fmt.Errorf("error unpacking aux sigs: %w",
+			err)
 	}
 
 	// We'll iterate through each output in the commitment transaction,
@@ -4514,6 +4678,9 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 			htlcIndex uint64
 			sigHash   func() ([]byte, error)
 			sig       input.Signature
+			htlc      *paymentDescriptor
+			incoming  bool
+			auxLeaf   input.AuxTapLeaf
 			err       error
 		)
 
@@ -4523,10 +4690,12 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 		// If this output index is found within the incoming HTLC
 		// index, then this means that we need to generate an HTLC
 		// success transaction in order to validate the signature.
+		//nolint:lll
 		case localCommitmentView.incomingHTLCIndex[outputIndex] != nil:
-			htlc := localCommitmentView.incomingHTLCIndex[outputIndex]
+			htlc = localCommitmentView.incomingHTLCIndex[outputIndex]
 
 			htlcIndex = htlc.HtlcIndex
+			incoming = true
 
 			sigHash = func() ([]byte, error) {
 				op := wire.OutPoint{
@@ -4592,7 +4761,7 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 
 			// Make sure there are more signatures left.
 			if i >= len(htlcSigs) {
-				return nil, fmt.Errorf("not enough HTLC " +
+				return nil, nil, fmt.Errorf("not enough HTLC " +
 					"signatures")
 			}
 
@@ -4608,15 +4777,16 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 			// is valid.
 			sig, err = htlcSigs[i].ToSignature()
 			if err != nil {
-				return nil, err
+				return nil, nil, err
 			}
 			htlc.sig = sig
 
 		// Otherwise, if this is an outgoing HTLC, then we'll need to
 		// generate a timeout transaction so we can verify the
 		// signature presented.
+		//nolint:lll
 		case localCommitmentView.outgoingHTLCIndex[outputIndex] != nil:
-			htlc := localCommitmentView.outgoingHTLCIndex[outputIndex]
+			htlc = localCommitmentView.outgoingHTLCIndex[outputIndex]
 
 			htlcIndex = htlc.HtlcIndex
 
@@ -4687,7 +4857,7 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 
 			// Make sure there are more signatures left.
 			if i >= len(htlcSigs) {
-				return nil, fmt.Errorf("not enough HTLC " +
+				return nil, nil, fmt.Errorf("not enough HTLC " +
 					"signatures")
 			}
 
@@ -4703,7 +4873,7 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 			// is valid.
 			sig, err = htlcSigs[i].ToSignature()
 			if err != nil {
-				return nil, err
+				return nil, nil, err
 			}
 
 			htlc.sig = sig
@@ -4719,17 +4889,40 @@ func genHtlcSigValidationJobs(chanState *channeldb.OpenChannel,
 			SigHash:   sigHash,
 		})
 
+		if len(auxHtlcSigs) > i {
+			auxSig := auxHtlcSigs[i]
+			auxVerifyJob := NewAuxVerifyJob(
+				auxSig, *keyRing, incoming,
+				newAuxHtlcDescriptor(htlc),
+				localCommitmentView.customBlob, auxLeaf,
+			)
+
+			if htlc.CustomRecords == nil {
+				htlc.CustomRecords = make(lnwire.CustomRecords)
+			}
+
+			// As this HTLC has a custom signature associated with
+			// it, store it in the custom records map so we can
+			// write to disk later.
+			sigType := htlcCustomSigType.TypeVal()
+			htlc.CustomRecords[uint64(sigType)] = auxSig.UnwrapOr(
+				nil,
+			)
+
+			auxVerifyJobs = append(auxVerifyJobs, auxVerifyJob)
+		}
+
 		i++
 	}
 
 	// If we received a number of HTLC signatures that doesn't match our
 	// commitment, we'll return an error now.
 	if len(htlcSigs) != i {
-		return nil, fmt.Errorf("number of htlc sig mismatch. "+
+		return nil, nil, fmt.Errorf("number of htlc sig mismatch. "+
 			"Expected %v sigs, got %v", i, len(htlcSigs))
 	}
 
-	return verifyJobs, nil
+	return verifyJobs, auxVerifyJobs, nil
 }
 
 // InvalidCommitSigError is a struct that implements the error interface to
@@ -4888,6 +5081,11 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSigs *CommitSigs) error {
 		localCommitmentView.ourBalance, localCommitmentView.theirBalance,
 		lnutils.SpewLogClosure(localCommitmentView.txn))
 
+	var auxSigBlob fn.Option[tlv.Blob]
+	if commitSigs.AuxSigBlob != nil {
+		auxSigBlob = fn.Some(commitSigs.AuxSigBlob)
+	}
+
 	// As an optimization, we'll generate a series of jobs for the worker
 	// pool to verify each of the HTLC signatures presented. Once
 	// generated, we'll submit these jobs to the worker pool.
@@ -4895,9 +5093,10 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSigs *CommitSigs) error {
 	if lc.channelState.ChanType.HasLeaseExpiration() {
 		leaseExpiry = lc.channelState.ThawHeight
 	}
-	verifyJobs, err := genHtlcSigValidationJobs(
+	verifyJobs, auxVerifyJobs, err := genHtlcSigValidationJobs(
 		lc.channelState, localCommitmentView, keyRing,
-		commitSigs.HtlcSigs, leaseExpiry, lc.leafStore,
+		commitSigs.HtlcSigs, leaseExpiry, lc.leafStore, lc.auxSigner,
+		auxSigBlob,
 	)
 	if err != nil {
 		return err
@@ -5050,6 +5249,18 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSigs *CommitSigs) error {
 		}
 	}
 
+	// Now that we know all the normal sigs are valid, we'll also verify
+	// the aux jobs, if any exist.
+	err = fn.MapOptionZ(lc.auxSigner, func(a AuxSigner) error {
+		return a.VerifySecondLevelSigs(
+			NewAuxChanState(lc.channelState), localCommitTx,
+			auxVerifyJobs,
+		)
+	})
+	if err != nil {
+		return fmt.Errorf("unable to validate aux sigs: %w", err)
+	}
+
 	// The signature checks out, so we can now add the new commitment to
 	// our local commitment chain. For regular channels, we can just
 	// serialize the ECDSA sig. For taproot channels, we'll serialize the
@@ -5782,8 +5993,9 @@ func (lc *LightningChannel) ReceiveHTLC(htlc *lnwire.UpdateAddHTLC) (uint64,
 	defer lc.Unlock()
 
 	if htlc.ID != lc.updateLogs.Remote.htlcCounter {
-		return 0, fmt.Errorf("ID %d on HTLC add does not match expected next "+
-			"ID %d", htlc.ID, lc.updateLogs.Remote.htlcCounter)
+		return 0, fmt.Errorf("ID %d on HTLC add does not match "+
+			"expected next ID %d", htlc.ID,
+			lc.updateLogs.Remote.htlcCounter)
 	}
 
 	pd := &paymentDescriptor{

lnwallet/channel_test.go

@@ -27,6 +27,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -702,6 +703,68 @@ func testCommitHTLCSigTieBreak(t *testing.T, restart bool) {
 	require.NoError(t, err, "unable to receive bob's commitment")
 }
 
+// TestCommitHTLCSigCustomRecordSize asserts that custom records produced for
+// a commitment_signed message are properly limited in size.
+func TestCommitHTLCSigCustomRecordSize(t *testing.T) {
+	aliceChannel, bobChannel, err := CreateTestChannels(
+		t, channeldb.SimpleTaprootFeatureBit|
+			channeldb.TapscriptRootBit,
+	)
+	require.NoError(t, err, "unable to create test channels")
+
+	const (
+		htlcAmt  = lnwire.MilliSatoshi(20000000)
+		numHtlcs = 2
+	)
+
+	largeRecords := lnwire.CustomRecords{
+		lnwire.MinCustomRecordsTlvType: bytes.Repeat([]byte{0}, 65_500),
+	}
+	largeBlob, err := largeRecords.Serialize()
+	require.NoError(t, err)
+
+	aliceChannel.auxSigner.WhenSome(func(a AuxSigner) {
+		mockSigner, ok := a.(*MockAuxSigner)
+		require.True(t, ok, "expected MockAuxSigner")
+
+		// Replace the default PackSigs implementation to return a
+		// large custom records blob.
+		mockSigner.ExpectedCalls = fn.Filter(func(c *mock.Call) bool {
+			return c.Method != "PackSigs"
+		}, mockSigner.ExpectedCalls)
+		mockSigner.On("PackSigs", mock.Anything).
+			Return(fn.Ok(fn.Some(largeBlob)))
+	})
+
+	// Add HTLCs with identical payment hashes and amounts, but descending
+	// CLTV values. We will expect the signatures to appear in the reverse
+	// order that the HTLCs are added due to the commitment sorting.
+	for i := 0; i < numHtlcs; i++ {
+		var (
+			preimage lntypes.Preimage
+			hash     = preimage.Hash()
+		)
+
+		htlc := &lnwire.UpdateAddHTLC{
+			ID:          uint64(i),
+			PaymentHash: hash,
+			Amount:      htlcAmt,
+			Expiry:      uint32(numHtlcs - i),
+		}
+
+		if _, err := aliceChannel.AddHTLC(htlc, nil); err != nil {
+			t.Fatalf("alice unable to add htlc: %v", err)
+		}
+		if _, err := bobChannel.ReceiveHTLC(htlc); err != nil {
+			t.Fatalf("bob unable to receive htlc: %v", err)
+		}
+	}
+
+	// We expect an error because of the large custom records blob.
+	_, err = aliceChannel.SignNextCommitment()
+	require.ErrorContains(t, err, "exceeds max allowed size")
+}
+
 // TestCooperativeChannelClosure checks that the coop close process finishes
 // with an agreement from both parties, and that the final balances of the
 // close tx check out.
@@ -3046,6 +3109,10 @@ func restartChannel(channelOld *LightningChannel) (*LightningChannel, error) {
 	return channelNew, nil
 }
 
+// testChanSyncOweCommitment tests that if Bob restarts (and then Alice) before
+// he receives Alice's CommitSig message, then Alice concludes that she needs
+// to re-send the CommitDiff. After the diff has been sent, both nodes should
+// resynchronize and be able to complete the dangling commit.
 func testChanSyncOweCommitment(t *testing.T, chanType channeldb.ChannelType) {
 	// Create a test channel which will be used for the duration of this
 	// unittest. The channel will be funded evenly with Alice having 5 BTC,
@@ -3210,8 +3277,10 @@ func testChanSyncOweCommitment(t *testing.T, chanType channeldb.ChannelType) {
 				len(commitSigMsg.HtlcSigs))
 		}
 		for i, htlcSig := range commitSigMsg.HtlcSigs {
-			if !bytes.Equal(htlcSig.RawBytes(),
-				aliceNewCommit.HtlcSigs[i].RawBytes()) {
+			if !bytes.Equal(
+				htlcSig.RawBytes(),
+				aliceNewCommit.HtlcSigs[i].RawBytes(),
+			) {
 
 				t.Fatalf("htlc sig msgs don't match: "+
 					"expected %v got %v",
@@ -3389,6 +3458,100 @@ func TestChanSyncOweCommitment(t *testing.T) {
 	}
 }
 
+type testSigBlob struct {
+	BlobInt tlv.RecordT[tlv.TlvType65634, uint16]
+}
+
+// TestChanSyncOweCommitmentAuxSigner tests that when one party owes a
+// signature after a channel reest, if an aux signer is present, then the
+// signature message sent includes the additional aux sigs as extra data.
+func TestChanSyncOweCommitmentAuxSigner(t *testing.T) {
+	t.Parallel()
+
+	// Create a test channel which will be used for the duration of this
+	// unittest. The channel will be funded evenly with Alice having 5 BTC,
+	// and Bob having 5 BTC.
+	chanType := channeldb.SingleFunderTweaklessBit |
+		channeldb.AnchorOutputsBit | channeldb.SimpleTaprootFeatureBit |
+		channeldb.TapscriptRootBit
+
+	aliceChannel, bobChannel, err := CreateTestChannels(t, chanType)
+	require.NoError(t, err, "unable to create test channels")
+
+	// We'll now manually attach an aux signer to Alice's channel.
+	auxSigner := &MockAuxSigner{}
+	aliceChannel.auxSigner = fn.Some[AuxSigner](auxSigner)
+
+	var fakeOnionBlob [lnwire.OnionPacketSize]byte
+	copy(
+		fakeOnionBlob[:],
+		bytes.Repeat([]byte{0x05}, lnwire.OnionPacketSize),
+	)
+
+	// To kick things off, we'll have Alice send a single HTLC to Bob.
+	htlcAmt := lnwire.NewMSatFromSatoshis(20000)
+	var bobPreimage [32]byte
+	copy(bobPreimage[:], bytes.Repeat([]byte{0}, 32))
+	rHash := sha256.Sum256(bobPreimage[:])
+	h := &lnwire.UpdateAddHTLC{
+		PaymentHash: rHash,
+		Amount:      htlcAmt,
+		Expiry:      uint32(10),
+		OnionBlob:   fakeOnionBlob,
+	}
+
+	_, err = aliceChannel.AddHTLC(h, nil)
+	require.NoError(t, err, "unable to recv bob's htlc: %v", err)
+
+	// We'll set up the mock to expect calls to PackSigs and also
+	// SubmitSubmitSecondLevelSigBatch.
+	var sigBlobBuf bytes.Buffer
+	sigBlob := testSigBlob{
+		BlobInt: tlv.NewPrimitiveRecord[tlv.TlvType65634, uint16](5),
+	}
+	tlvStream, err := tlv.NewStream(sigBlob.BlobInt.Record())
+	require.NoError(t, err, "unable to create tlv stream")
+	require.NoError(t, tlvStream.Encode(&sigBlobBuf))
+
+	auxSigner.On(
+		"SubmitSecondLevelSigBatch", mock.Anything, mock.Anything,
+		mock.Anything,
+	).Return(nil).Twice()
+	auxSigner.On(
+		"PackSigs", mock.Anything,
+	).Return(
+		fn.Ok(fn.Some(sigBlobBuf.Bytes())), nil,
+	)
+
+	_, err = aliceChannel.SignNextCommitment()
+	require.NoError(t, err, "unable to sign commitment")
+
+	_, err = aliceChannel.GenMusigNonces()
+	require.NoError(t, err, "unable to generate musig nonces")
+
+	// Next we'll simulate a restart, by having Bob send over a chan sync
+	// message to Alice.
+	bobSyncMsg, err := bobChannel.channelState.ChanSyncMsg()
+	require.NoError(t, err, "unable to produce chan sync msg")
+
+	aliceMsgsToSend, _, _, err := aliceChannel.ProcessChanSyncMsg(
+		bobSyncMsg,
+	)
+	require.NoError(t, err)
+	require.Len(t, aliceMsgsToSend, 2)
+
+	// The first message should be an update add HTLC.
+	require.IsType(t, &lnwire.UpdateAddHTLC{}, aliceMsgsToSend[0])
+
+	// The second should be a commit sig message.
+	sigMsg, ok := aliceMsgsToSend[1].(*lnwire.CommitSig)
+	require.True(t, ok)
+	require.True(t, sigMsg.PartialSig.IsSome())
+
+	// The signature should have the CustomRecords field set.
+	require.NotEmpty(t, sigMsg.CustomRecords)
+}
+
 func testChanSyncOweCommitmentPendingRemote(t *testing.T,
 	chanType channeldb.ChannelType) {
 
@@ -3398,7 +3561,10 @@ func testChanSyncOweCommitmentPendingRemote(t *testing.T,
 	require.NoError(t, err, "unable to create test channels")
 
 	var fakeOnionBlob [lnwire.OnionPacketSize]byte
-	copy(fakeOnionBlob[:], bytes.Repeat([]byte{0x05}, lnwire.OnionPacketSize))
+	copy(
+		fakeOnionBlob[:],
+		bytes.Repeat([]byte{0x05}, lnwire.OnionPacketSize),
+	)
 
 	// We'll start off the scenario where Bob send two htlcs to Alice in a
 	// single state update.
@@ -3437,7 +3603,9 @@ func testChanSyncOweCommitmentPendingRemote(t *testing.T,
 
 	// Next, Alice settles the HTLCs from Bob in distinct state updates.
 	for i := 0; i < numHtlcs; i++ {
-		err = aliceChannel.SettleHTLC(preimages[i], uint64(i), nil, nil, nil)
+		err = aliceChannel.SettleHTLC(
+			preimages[i], uint64(i), nil, nil, nil,
+		)
 		if err != nil {
 			t.Fatalf("unable to settle htlc: %v", err)
 		}
@@ -3727,7 +3895,7 @@ func testChanSyncOweRevocation(t *testing.T, chanType channeldb.ChannelType) {
 }
 
 // TestChanSyncOweRevocation tests that if Bob restarts (and then Alice) before
-// he receiver's Alice's RevokeAndAck message, then Alice concludes that she
+// he received Alice's RevokeAndAck message, then Alice concludes that she
 // needs to re-send the RevokeAndAck. After the revocation has been sent, both
 // nodes should be able to successfully complete another state transition.
 func TestChanSyncOweRevocation(t *testing.T) {

lnwallet/config.go

@@ -67,4 +67,8 @@ type Config struct {
 	// AuxLeafStore is an optional store that can be used to store auxiliary
 	// leaves for certain custom channel types.
 	AuxLeafStore fn.Option[AuxLeafStore]
+
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[AuxSigner]
 }

lnwallet/mock.go

@@ -21,6 +21,7 @@ import (
 	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/mock"
 )
 
 var (
@@ -441,3 +442,54 @@ func (*MockAuxLeafStore) ApplyHtlcView(
 
 	return fn.Ok(fn.None[tlv.Blob]())
 }
+
+// MockAuxSigner is a mock implementation of the AuxSigner interface.
+type MockAuxSigner struct {
+	mock.Mock
+}
+
+// SubmitSecondLevelSigBatch takes a batch of aux sign jobs and
+// processes them asynchronously.
+func (a *MockAuxSigner) SubmitSecondLevelSigBatch(chanState AuxChanState,
+	tx *wire.MsgTx, jobs []AuxSigJob) error {
+
+	args := a.Called(chanState, tx, jobs)
+
+	// While we return, we'll also send back an instant response for the
+	// set of jobs.
+	for _, sigJob := range jobs {
+		sigJob.Resp <- AuxSigJobResp{}
+	}
+
+	return args.Error(0)
+}
+
+// PackSigs takes a series of aux signatures and packs them into a
+// single blob that can be sent alongside the CommitSig messages.
+func (a *MockAuxSigner) PackSigs(
+	sigs []fn.Option[tlv.Blob]) fn.Result[fn.Option[tlv.Blob]] {
+
+	args := a.Called(sigs)
+
+	return args.Get(0).(fn.Result[fn.Option[tlv.Blob]])
+}
+
+// UnpackSigs takes a packed blob of signatures and returns the
+// original signatures for each HTLC, keyed by HTLC index.
+func (a *MockAuxSigner) UnpackSigs(
+	sigs fn.Option[tlv.Blob]) fn.Result[[]fn.Option[tlv.Blob]] {
+
+	args := a.Called(sigs)
+
+	return args.Get(0).(fn.Result[[]fn.Option[tlv.Blob]])
+}
+
+// VerifySecondLevelSigs attempts to synchronously verify a batch of aux
+// sig jobs.
+func (a *MockAuxSigner) VerifySecondLevelSigs(chanState AuxChanState,
+	tx *wire.MsgTx, jobs []AuxVerifyJob) error {
+
+	args := a.Called(chanState, tx, jobs)
+
+	return args.Error(0)
+}

lnwallet/reservation.go

@@ -11,6 +11,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -25,7 +26,7 @@ type CommitmentType int
 const (
 	// CommitmentTypeLegacy is the legacy commitment format with a tweaked
 	// to_remote key.
-	CommitmentTypeLegacy = iota
+	CommitmentTypeLegacy CommitmentType = iota
 
 	// CommitmentTypeTweakless is a newer commitment format where the
 	// to_remote key is static.
@@ -100,6 +101,28 @@ func (c CommitmentType) String() string {
 	}
 }
 
+// ReservationState is a type that represents the current state of a channel
+// reservation within the funding workflow.
+type ReservationState int
+
+const (
+	// WaitingToSend is the state either the funder/fundee is in after
+	// creating a reservation, but hasn't sent a message yet.
+	WaitingToSend ReservationState = iota
+
+	// SentOpenChannel is the state the funder is in after sending the
+	// OpenChannel message.
+	SentOpenChannel
+
+	// SentAcceptChannel is the state the fundee is in after sending the
+	// AcceptChannel message.
+	SentAcceptChannel
+
+	// SentFundingCreated is the state the funder is in after sending the
+	// FundingCreated message.
+	SentFundingCreated
+)
+
 // ChannelContribution is the primary constituent of the funding workflow
 // within lnwallet. Each side first exchanges their respective contributions
 // along with channel specific parameters like the min fee/KB. Once
@@ -223,6 +246,8 @@ type ChannelReservation struct {
 	nextRevocationKeyLoc keychain.KeyLocator
 
 	musigSessions *MusigPairSession
+
+	state ReservationState
 }
 
 // NewChannelReservation creates a new channel reservation. This function is
@@ -459,6 +484,7 @@ func NewChannelReservation(capacity, localFundingAmt btcutil.Amount,
 		reservationID: id,
 		wallet:        wallet,
 		chanFunder:    req.ChanFunder,
+		state:         WaitingToSend,
 	}, nil
 }
 
@@ -470,6 +496,22 @@ func (r *ChannelReservation) AddAlias(scid lnwire.ShortChannelID) {
 	r.partialState.ShortChannelID = scid
 }
 
+// SetState sets the ReservationState.
+func (r *ChannelReservation) SetState(state ReservationState) {
+	r.Lock()
+	defer r.Unlock()
+
+	r.state = state
+}
+
+// State returns the current ReservationState.
+func (r *ChannelReservation) State() ReservationState {
+	r.RLock()
+	defer r.RUnlock()
+
+	return r.state
+}
+
 // SetNumConfsRequired sets the number of confirmations that are required for
 // the ultimate funding transaction before the channel can be considered open.
 // This is distinct from the main reservation workflow as it allows
@@ -610,12 +652,15 @@ func (r *ChannelReservation) IsCannedShim() bool {
 }
 
 // ProcessPsbt continues a previously paused funding flow that involves PSBT to
-// construct the funding transaction. This method can be called once the PSBT is
-// finalized and the signed transaction is available.
-func (r *ChannelReservation) ProcessPsbt() error {
+// construct the funding transaction. This method can be called once the PSBT
+// is finalized and the signed transaction is available.
+func (r *ChannelReservation) ProcessPsbt(
+	auxFundingDesc fn.Option[AuxFundingDesc]) error {
+
 	errChan := make(chan error, 1)
 
 	r.wallet.msgChan <- &continueContributionMsg{
+		auxFundingDesc:   auxFundingDesc,
 		pendingFundingID: r.reservationID,
 		err:              errChan,
 	}
@@ -717,8 +762,10 @@ func (r *ChannelReservation) CompleteReservation(fundingInputScripts []*input.Sc
 // available via the .OurSignatures() method. As this method should only be
 // called as a response to a single funder channel, only a commitment signature
 // will be populated.
-func (r *ChannelReservation) CompleteReservationSingle(fundingPoint *wire.OutPoint,
-	commitSig input.Signature) (*channeldb.OpenChannel, error) {
+func (r *ChannelReservation) CompleteReservationSingle(
+	fundingPoint *wire.OutPoint, commitSig input.Signature,
+	auxFundingDesc fn.Option[AuxFundingDesc]) (*channeldb.OpenChannel,
+	error) {
 
 	errChan := make(chan error, 1)
 	completeChan := make(chan *channeldb.OpenChannel, 1)
@@ -728,6 +775,7 @@ func (r *ChannelReservation) CompleteReservationSingle(fundingPoint *wire.OutPoi
 		fundingOutpoint:    fundingPoint,
 		theirCommitmentSig: commitSig,
 		completeChan:       completeChan,
+		auxFundingDesc:     auxFundingDesc,
 		err:                errChan,
 	}
 
@@ -813,6 +861,42 @@ func (r *ChannelReservation) Cancel() error {
 	return <-errChan
 }
 
+// ChanState the current open channel state.
+func (r *ChannelReservation) ChanState() *channeldb.OpenChannel {
+	r.RLock()
+	defer r.RUnlock()
+
+	return r.partialState
+}
+
+// CommitmentKeyRings returns the local+remote key ring used for the very first
+// commitment transaction both parties.
+//
+//nolint:lll
+func (r *ChannelReservation) CommitmentKeyRings() lntypes.Dual[CommitmentKeyRing] {
+	r.RLock()
+	defer r.RUnlock()
+
+	chanType := r.partialState.ChanType
+	ourChanCfg := r.ourContribution.ChannelConfig
+	theirChanCfg := r.theirContribution.ChannelConfig
+
+	localKeys := DeriveCommitmentKeys(
+		r.ourContribution.FirstCommitmentPoint, lntypes.Local, chanType,
+		ourChanCfg, theirChanCfg,
+	)
+
+	remoteKeys := DeriveCommitmentKeys(
+		r.theirContribution.FirstCommitmentPoint, lntypes.Remote,
+		chanType, ourChanCfg, theirChanCfg,
+	)
+
+	return lntypes.Dual[CommitmentKeyRing]{
+		Local:  *localKeys,
+		Remote: *remoteKeys,
+	}
+}
+
 // VerifyConstraints is a helper function that can be used to check the sanity
 // of various channel constraints.
 func VerifyConstraints(bounds *channeldb.ChannelStateBounds,

lnwallet/sigpool.go

@@ -45,17 +45,17 @@ type VerifyJob struct {
 	// party's update log.
 	HtlcIndex uint64
 
-	// Cancel is a channel that should be closed if the caller wishes to
+	// Cancel is a channel that is closed by the caller if they wish to
 	// cancel all pending verification jobs part of a single batch. This
-	// channel is to be closed in the case that a single signature in a
-	// batch has been returned as invalid, as there is no need to verify
-	// the remainder of the signatures.
-	Cancel chan struct{}
+	// channel is closed in the case that a single signature in a batch has
+	// been returned as invalid, as there is no need to verify the remainder
+	// of the signatures.
+	Cancel <-chan struct{}
 
 	// ErrResp is the channel that the result of the signature verification
 	// is to be sent over. In the see that the signature is valid, a nil
 	// error will be passed. Otherwise, a concrete error detailing the
-	// issue will be passed.
+	// issue will be passed. This channel MUST be buffered.
 	ErrResp chan *HtlcIndexErr
 }
 
@@ -86,12 +86,13 @@ type SignJob struct {
 	// transaction being signed.
 	OutputIndex int32
 
-	// Cancel is a channel that should be closed if the caller wishes to
-	// abandon all pending sign jobs part of a single batch.
-	Cancel chan struct{}
+	// Cancel is a channel that is closed by the caller if they wish to
+	// abandon all pending sign jobs part of a single batch. This should
+	// never be closed by the validator.
+	Cancel <-chan struct{}
 
 	// Resp is the channel that the response to this particular SignJob
-	// will be sent over.
+	// will be sent over. This channel MUST be buffered.
 	//
 	// TODO(roasbeef): actually need to allow caller to set, need to retain
 	// order mark commit sig as special

lnwallet/test/test_interface.go

@@ -34,6 +34,7 @@ import (
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/chainntnfs/btcdnotify"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
@@ -940,6 +941,7 @@ func testSingleFunderReservationWorkflow(miner *rpctest.Harness,
 	fundingPoint := aliceChanReservation.FundingOutpoint()
 	_, err = bobChanReservation.CompleteReservationSingle(
 		fundingPoint, aliceCommitSig,
+		fn.None[lnwallet.AuxFundingDesc](),
 	)
 	require.NoError(t, err, "bob unable to consume single reservation")
 

lnwallet/test_utils.go

@@ -1,6 +1,7 @@
 package lnwallet
 
 import (
+	"bytes"
 	"crypto/rand"
 	"encoding/binary"
 	"encoding/hex"
@@ -21,6 +22,8 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/shachain"
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -369,9 +372,13 @@ func CreateTestChannels(t *testing.T, chanType channeldb.ChannelType,
 
 	// TODO(roasbeef): make mock version of pre-image store
 
+	auxSigner := NewDefaultAuxSignerMock(t)
+
 	alicePool := NewSigPool(1, aliceSigner)
 	channelAlice, err := NewLightningChannel(
 		aliceSigner, aliceChannelState, alicePool,
+		WithLeafStore(&MockAuxLeafStore{}),
+		WithAuxSigner(auxSigner),
 	)
 	if err != nil {
 		return nil, nil, err
@@ -386,6 +393,8 @@ func CreateTestChannels(t *testing.T, chanType channeldb.ChannelType,
 	bobPool := NewSigPool(1, bobSigner)
 	channelBob, err := NewLightningChannel(
 		bobSigner, bobChannelState, bobPool,
+		WithLeafStore(&MockAuxLeafStore{}),
+		WithAuxSigner(auxSigner),
 	)
 	if err != nil {
 		return nil, nil, err
@@ -586,3 +595,38 @@ func ForceStateTransition(chanA, chanB *LightningChannel) error {
 
 	return nil
 }
+
+func NewDefaultAuxSignerMock(t *testing.T) *MockAuxSigner {
+	auxSigner := &MockAuxSigner{}
+
+	type testSigBlob struct {
+		BlobInt tlv.RecordT[tlv.TlvType65634, uint16]
+	}
+
+	var sigBlobBuf bytes.Buffer
+	sigBlob := testSigBlob{
+		BlobInt: tlv.NewPrimitiveRecord[tlv.TlvType65634, uint16](5),
+	}
+	tlvStream, err := tlv.NewStream(sigBlob.BlobInt.Record())
+	require.NoError(t, err, "unable to create tlv stream")
+	require.NoError(t, tlvStream.Encode(&sigBlobBuf))
+
+	auxSigner.On(
+		"SubmitSecondLevelSigBatch", mock.Anything, mock.Anything,
+		mock.Anything,
+	).Return(nil)
+	auxSigner.On(
+		"PackSigs", mock.Anything,
+	).Return(fn.Ok(fn.Some(sigBlobBuf.Bytes())))
+	auxSigner.On(
+		"UnpackSigs", mock.Anything,
+	).Return(fn.Ok([]fn.Option[tlv.Blob]{
+		fn.Some(sigBlobBuf.Bytes()),
+	}))
+	auxSigner.On(
+		"VerifySecondLevelSigs", mock.Anything, mock.Anything,
+		mock.Anything,
+	).Return(nil)
+
+	return auxSigner
+}

lnwallet/transactions_test.go

@@ -1018,9 +1018,12 @@ func createTestChannelsForVectors(tc *testContext, chanType channeldb.ChannelTyp
 		tc.remotePaymentBasepointSecret, remoteDummy1, remoteDummy2,
 	}, nil)
 
+	auxSigner := NewDefaultAuxSignerMock(t)
 	remotePool := NewSigPool(1, remoteSigner)
 	channelRemote, err := NewLightningChannel(
 		remoteSigner, remoteChannelState, remotePool,
+		WithLeafStore(&MockAuxLeafStore{}),
+		WithAuxSigner(auxSigner),
 	)
 	require.NoError(t, err)
 	require.NoError(t, remotePool.Start())
@@ -1028,6 +1031,8 @@ func createTestChannelsForVectors(tc *testContext, chanType channeldb.ChannelTyp
 	localPool := NewSigPool(1, localSigner)
 	channelLocal, err := NewLightningChannel(
 		localSigner, localChannelState, localPool,
+		WithLeafStore(&MockAuxLeafStore{}),
+		WithAuxSigner(auxSigner),
 	)
 	require.NoError(t, err)
 	require.NoError(t, localPool.Start())

lnwallet/wallet.go

@@ -32,6 +32,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chanvalidate"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/shachain"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 const (
@@ -90,6 +91,33 @@ func (p *PsbtFundingRequired) Error() string {
 	return ErrPsbtFundingRequired.Error()
 }
 
+// AuxFundingDesc stores a series of attributes that may be used to modify the
+// way the channel funding occurs. This struct contains information that can
+// only be derived once both sides have received and sent their contributions
+// to the channel (keys, etc.).
+type AuxFundingDesc struct {
+	// CustomFundingBlob is a custom blob that'll be stored in the database
+	// within the OpenChannel struct. This should represent information
+	// static to the channel lifetime.
+	CustomFundingBlob tlv.Blob
+
+	// CustomLocalCommitBlob is a custom blob that'll be stored in the
+	// first commitment entry for the local party.
+	CustomLocalCommitBlob tlv.Blob
+
+	// CustomRemoteCommitBlob is a custom blob that'll be stored in the
+	// first commitment entry for the remote party.
+	CustomRemoteCommitBlob tlv.Blob
+
+	// LocalInitAuxLeaves is the set of aux leaves that'll be used for our
+	// very first commitment state.
+	LocalInitAuxLeaves CommitAuxLeaves
+
+	// RemoteInitAuxLeaves is the set of aux leaves that'll be used for the
+	// very first commitment state for the remote party.
+	RemoteInitAuxLeaves CommitAuxLeaves
+}
+
 // InitFundingReserveMsg is the first message sent to initiate the workflow
 // required to open a payment channel with a remote peer. The initial required
 // parameters are configurable across channels. These parameters are to be
@@ -211,9 +239,8 @@ type InitFundingReserveMsg struct {
 	// channel that will be useful to our future selves.
 	Memo []byte
 
-	// TapscriptRoot is the root of the tapscript tree that will be used to
-	// create the funding output. This is an optional field that should
-	// only be set for taproot channels.
+	// TapscriptRoot is an optional tapscript root that if provided, will
+	// be used to create the combined key for musig2 based channels.
 	TapscriptRoot fn.Option[chainhash.Hash]
 
 	// err is a channel in which all errors will be sent across. Will be
@@ -251,7 +278,6 @@ type fundingReserveCancelMsg struct {
 type addContributionMsg struct {
 	pendingFundingID uint64
 
-	// TODO(roasbeef): Should also carry SPV proofs in we're in SPV mode
 	contribution *ChannelContribution
 
 	// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
@@ -264,6 +290,10 @@ type addContributionMsg struct {
 type continueContributionMsg struct {
 	pendingFundingID uint64
 
+	// auxFundingDesc is an optional descriptor that contains information
+	// about the custom channel funding flow.
+	auxFundingDesc fn.Option[AuxFundingDesc]
+
 	// NOTE: In order to avoid deadlocks, this channel MUST be buffered.
 	err chan error
 }
@@ -319,6 +349,10 @@ type addCounterPartySigsMsg struct {
 type addSingleFunderSigsMsg struct {
 	pendingFundingID uint64
 
+	// auxFundingDesc is an optional descriptor that contains information
+	// about the custom channel funding flow.
+	auxFundingDesc fn.Option[AuxFundingDesc]
+
 	// fundingOutpoint is the outpoint of the completed funding
 	// transaction as assembled by the workflow initiator.
 	fundingOutpoint *wire.OutPoint
@@ -422,8 +456,6 @@ type LightningWallet struct {
 	quit chan struct{}
 
 	wg sync.WaitGroup
-
-	// TODO(roasbeef): handle wallet lock/unlock
 }
 
 // NewLightningWallet creates/opens and initializes a LightningWallet instance.
@@ -468,7 +500,6 @@ func (l *LightningWallet) Startup() error {
 	}
 
 	l.wg.Add(1)
-	// TODO(roasbeef): multiple request handlers?
 	go l.requestHandler()
 
 	return nil
@@ -1424,7 +1455,6 @@ func (l *LightningWallet) initOurContribution(reservation *ChannelReservation,
 // transaction via coin selection are freed allowing future reservations to
 // include them.
 func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMsg) {
-	// TODO(roasbeef): holding lock too long
 	l.limboMtx.Lock()
 	defer l.limboMtx.Unlock()
 
@@ -1449,11 +1479,6 @@ func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMs
 		)
 	}
 
-	// TODO(roasbeef): is it even worth it to keep track of unused keys?
-
-	// TODO(roasbeef): Is it possible to mark the unused change also as
-	// available?
-
 	delete(l.fundingLimbo, req.pendingFundingID)
 
 	pid := pendingReservation.pendingChanID
@@ -1473,7 +1498,8 @@ func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMs
 // createCommitOpts is a struct that holds the options for creating a new
 // commitment transaction.
 type createCommitOpts struct {
-	auxLeaves fn.Option[CommitAuxLeaves]
+	localAuxLeaves  fn.Option[CommitAuxLeaves]
+	remoteAuxLeaves fn.Option[CommitAuxLeaves]
 }
 
 // defaultCommitOpts returns a new createCommitOpts with default values.
@@ -1481,6 +1507,17 @@ func defaultCommitOpts() createCommitOpts {
 	return createCommitOpts{}
 }
 
+// WithAuxLeaves is a functional option that can be used to set the aux leaves
+// for a new commitment transaction.
+func WithAuxLeaves(localLeaves,
+	remoteLeaves fn.Option[CommitAuxLeaves]) CreateCommitOpt {
+
+	return func(o *createCommitOpts) {
+		o.localAuxLeaves = localLeaves
+		o.remoteAuxLeaves = remoteLeaves
+	}
+}
+
 // CreateCommitOpt is a functional option that can be used to modify the way a
 // new commitment transaction is created.
 type CreateCommitOpt func(*createCommitOpts)
@@ -1514,7 +1551,7 @@ func CreateCommitmentTxns(localBalance, remoteBalance btcutil.Amount,
 	ourCommitTx, err := CreateCommitTx(
 		chanType, fundingTxIn, localCommitmentKeys, ourChanCfg,
 		theirChanCfg, localBalance, remoteBalance, 0, initiator,
-		leaseExpiry, options.auxLeaves,
+		leaseExpiry, options.localAuxLeaves,
 	)
 	if err != nil {
 		return nil, nil, err
@@ -1528,7 +1565,7 @@ func CreateCommitmentTxns(localBalance, remoteBalance btcutil.Amount,
 	theirCommitTx, err := CreateCommitTx(
 		chanType, fundingTxIn, remoteCommitmentKeys, theirChanCfg,
 		ourChanCfg, remoteBalance, localBalance, 0, !initiator,
-		leaseExpiry, options.auxLeaves,
+		leaseExpiry, options.remoteAuxLeaves,
 	)
 	if err != nil {
 		return nil, nil, err
@@ -1621,16 +1658,24 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 		// and remote key which will be needed to calculate the multisig
 		// funding output in a next step.
 		pendingChanID := pendingReservation.pendingChanID
+
 		walletLog.Debugf("Advancing PSBT funding flow for "+
 			"pending_id(%x), binding keys local_key=%v, "+
 			"remote_key=%x", pendingChanID,
 			&ourContribution.MultiSigKey,
 			theirContribution.MultiSigKey.PubKey.SerializeCompressed())
+
 		fundingIntent.BindKeys(
 			&ourContribution.MultiSigKey,
 			theirContribution.MultiSigKey.PubKey,
 		)
 
+		// We might have a tapscript root, so we'll bind that now to
+		// ensure we make the proper funding output.
+		fundingIntent.BindTapscriptRoot(
+			pendingReservation.partialState.TapscriptRoot,
+		)
+
 		// Exit early because we can't continue the funding flow yet.
 		req.err <- &PsbtFundingRequired{
 			Intent: fundingIntent,
@@ -1703,8 +1748,8 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 // the commitment transaction for the remote party, and verify their incoming
 // partial signature.
 func genMusigSession(ourContribution, theirContribution *ChannelContribution,
-	signer input.MuSig2Signer,
-	fundingOutput *wire.TxOut) *MusigPairSession {
+	signer input.MuSig2Signer, fundingOutput *wire.TxOut,
+	tapscriptRoot fn.Option[chainhash.Hash]) *MusigPairSession {
 
 	return NewMusigPairSession(&MusigSessionCfg{
 		LocalKey:       ourContribution.MultiSigKey,
@@ -1713,6 +1758,7 @@ func genMusigSession(ourContribution, theirContribution *ChannelContribution,
 		RemoteNonce:    *theirContribution.LocalNonce,
 		Signer:         signer,
 		InputTxOut:     fundingOutput,
+		TapscriptTweak: tapscriptRoot,
 	})
 }
 
@@ -1762,6 +1808,7 @@ func (l *LightningWallet) signCommitTx(pendingReservation *ChannelReservation,
 			musigSessions := genMusigSession(
 				ourContribution, theirContribution,
 				l.Cfg.Signer, fundingOutput,
+				pendingReservation.partialState.TapscriptRoot,
 			)
 			pendingReservation.musigSessions = musigSessions
 		}
@@ -1797,6 +1844,26 @@ func (l *LightningWallet) handleChanPointReady(req *continueContributionMsg) {
 		return
 	}
 
+	chanState := pendingReservation.partialState
+
+	// If we have an aux funding desc, then we can use it to populate some
+	// of the optional, but opaque TLV blobs we'll carry for the channel.
+	chanState.CustomBlob = fn.MapOption(func(desc AuxFundingDesc) tlv.Blob {
+		return desc.CustomFundingBlob
+	})(req.auxFundingDesc)
+
+	chanState.LocalCommitment.CustomBlob = fn.MapOption(
+		func(desc AuxFundingDesc) tlv.Blob {
+			return desc.CustomLocalCommitBlob
+		},
+	)(req.auxFundingDesc)
+
+	chanState.RemoteCommitment.CustomBlob = fn.MapOption(
+		func(desc AuxFundingDesc) tlv.Blob {
+			return desc.CustomRemoteCommitBlob
+		},
+	)(req.auxFundingDesc)
+
 	ourContribution := pendingReservation.ourContribution
 	theirContribution := pendingReservation.theirContribution
 	chanPoint := pendingReservation.partialState.FundingOutpoint
@@ -1855,7 +1922,6 @@ func (l *LightningWallet) handleChanPointReady(req *continueContributionMsg) {
 	// Store their current commitment point. We'll need this after the
 	// first state transition in order to verify the authenticity of the
 	// revocation.
-	chanState := pendingReservation.partialState
 	chanState.RemoteCurrentRevocation = theirContribution.FirstCommitmentPoint
 
 	// Create the txin to our commitment transaction; required to construct
@@ -1871,6 +1937,18 @@ func (l *LightningWallet) handleChanPointReady(req *continueContributionMsg) {
 	if pendingReservation.partialState.ChanType.HasLeaseExpiration() {
 		leaseExpiry = pendingReservation.partialState.ThawHeight
 	}
+
+	localAuxLeaves := fn.MapOption(
+		func(desc AuxFundingDesc) CommitAuxLeaves {
+			return desc.LocalInitAuxLeaves
+		},
+	)(req.auxFundingDesc)
+	remoteAuxLeaves := fn.MapOption(
+		func(desc AuxFundingDesc) CommitAuxLeaves {
+			return desc.RemoteInitAuxLeaves
+		},
+	)(req.auxFundingDesc)
+
 	ourCommitTx, theirCommitTx, err := CreateCommitmentTxns(
 		localBalance, remoteBalance, ourContribution.ChannelConfig,
 		theirContribution.ChannelConfig,
@@ -1878,6 +1956,7 @@ func (l *LightningWallet) handleChanPointReady(req *continueContributionMsg) {
 		theirContribution.FirstCommitmentPoint, fundingTxIn,
 		pendingReservation.partialState.ChanType,
 		pendingReservation.partialState.IsInitiator, leaseExpiry,
+		WithAuxLeaves(localAuxLeaves, remoteAuxLeaves),
 	)
 	if err != nil {
 		req.err <- err
@@ -2138,6 +2217,7 @@ func (l *LightningWallet) verifyCommitSig(res *ChannelReservation,
 			res.musigSessions = genMusigSession(
 				res.ourContribution, res.theirContribution,
 				l.Cfg.Signer, fundingOutput,
+				res.partialState.TapscriptRoot,
 			)
 		}
 
@@ -2228,9 +2308,6 @@ func (l *LightningWallet) handleFundingCounterPartySigs(msg *addCounterPartySigs
 
 	// As we're about to broadcast the funding transaction, we'll take note
 	// of the current height for record keeping purposes.
-	//
-	// TODO(roasbeef): this info can also be piped into light client's
-	// basic fee estimation?
 	_, bestHeight, err := l.Cfg.ChainIO.GetBestBlock()
 	if err != nil {
 		msg.err <- err
@@ -2291,6 +2368,23 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 	defer pendingReservation.Unlock()
 
 	chanState := pendingReservation.partialState
+
+	// If we have an aux funding desc, then we can use it to populate some
+	// of the optional, but opaque TLV blobs we'll carry for the channel.
+	chanState.CustomBlob = fn.MapOption(func(desc AuxFundingDesc) tlv.Blob {
+		return desc.CustomFundingBlob
+	})(req.auxFundingDesc)
+	chanState.LocalCommitment.CustomBlob = fn.MapOption(
+		func(desc AuxFundingDesc) tlv.Blob {
+			return desc.CustomLocalCommitBlob
+		},
+	)(req.auxFundingDesc)
+	chanState.RemoteCommitment.CustomBlob = fn.MapOption(
+		func(desc AuxFundingDesc) tlv.Blob {
+			return desc.CustomRemoteCommitBlob
+		},
+	)(req.auxFundingDesc)
+
 	chanType := pendingReservation.partialState.ChanType
 	chanState.FundingOutpoint = *req.fundingOutpoint
 	fundingTxIn := wire.NewTxIn(req.fundingOutpoint, nil, nil)
@@ -2304,6 +2398,18 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 	if pendingReservation.partialState.ChanType.HasLeaseExpiration() {
 		leaseExpiry = pendingReservation.partialState.ThawHeight
 	}
+
+	localAuxLeaves := fn.MapOption(
+		func(desc AuxFundingDesc) CommitAuxLeaves {
+			return desc.LocalInitAuxLeaves
+		},
+	)(req.auxFundingDesc)
+	remoteAuxLeaves := fn.MapOption(
+		func(desc AuxFundingDesc) CommitAuxLeaves {
+			return desc.RemoteInitAuxLeaves
+		},
+	)(req.auxFundingDesc)
+
 	ourCommitTx, theirCommitTx, err := CreateCommitmentTxns(
 		localBalance, remoteBalance,
 		pendingReservation.ourContribution.ChannelConfig,
@@ -2312,6 +2418,7 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 		pendingReservation.theirContribution.FirstCommitmentPoint,
 		*fundingTxIn, chanType,
 		pendingReservation.partialState.IsInitiator, leaseExpiry,
+		WithAuxLeaves(localAuxLeaves, remoteAuxLeaves),
 	)
 	if err != nil {
 		req.err <- err
@@ -2500,6 +2607,9 @@ func (l *LightningWallet) ValidateChannel(channelState *channeldb.OpenChannel,
 	l.Cfg.AuxLeafStore.WhenSome(func(s AuxLeafStore) {
 		chanOpts = append(chanOpts, WithLeafStore(s))
 	})
+	l.Cfg.AuxSigner.WhenSome(func(s AuxSigner) {
+		chanOpts = append(chanOpts, WithAuxSigner(s))
+	})
 
 	// First, we'll obtain a fully signed commitment transaction so we can
 	// pass into it on the chanvalidate package for verification.

lnwire/commit_sig.go

@@ -45,6 +45,10 @@ type CommitSig struct {
 	// being signed for. In this case, the above Sig type MUST be blank.
 	PartialSig OptPartialSigWithNonceTLV
 
+	// CustomRecords maps TLV types to byte slices, storing arbitrary data
+	// intended for inclusion in the ExtraData field.
+	CustomRecords CustomRecords
+
 	// ExtraData is the set of data that was appended to this message to
 	// fill out the full maximum transport message size. These fields can
 	// be used to specify optional data such as custom TLV fields.
@@ -53,9 +57,7 @@ type CommitSig struct {
 
 // NewCommitSig creates a new empty CommitSig message.
 func NewCommitSig() *CommitSig {
-	return &CommitSig{
-		ExtraData: make([]byte, 0),
-	}
+	return &CommitSig{}
 }
 
 // A compile time check to ensure CommitSig implements the lnwire.Message
@@ -67,34 +69,37 @@ var _ Message = (*CommitSig)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (c *CommitSig) Decode(r io.Reader, pver uint32) error {
+	// msgExtraData is a temporary variable used to read the message extra
+	// data field from the reader.
+	var msgExtraData ExtraOpaqueData
+
 	err := ReadElements(r,
 		&c.ChanID,
 		&c.CommitSig,
 		&c.HtlcSigs,
+		&msgExtraData,
 	)
 	if err != nil {
 		return err
 	}
 
-	var tlvRecords ExtraOpaqueData
-	if err := ReadElements(r, &tlvRecords); err != nil {
-		return err
-	}
-
+	// Extract TLV records from the extra data field.
 	partialSig := c.PartialSig.Zero()
-	typeMap, err := tlvRecords.ExtractRecords(&partialSig)
+
+	customRecords, parsed, extraData, err := ParseAndExtractCustomRecords(
+		msgExtraData, &partialSig,
+	)
 	if err != nil {
 		return err
 	}
 
 	// Set the corresponding TLV types if they were included in the stream.
-	if val, ok := typeMap[c.PartialSig.TlvType()]; ok && val == nil {
+	if _, ok := parsed[partialSig.TlvType()]; ok {
 		c.PartialSig = tlv.SomeRecordT(partialSig)
 	}
 
-	if len(tlvRecords) != 0 {
-		c.ExtraData = tlvRecords
-	}
+	c.CustomRecords = customRecords
+	c.ExtraData = extraData
 
 	return nil
 }
@@ -108,7 +113,10 @@ func (c *CommitSig) Encode(w *bytes.Buffer, pver uint32) error {
 	c.PartialSig.WhenSome(func(sig PartialSigWithNonceTLV) {
 		recordProducers = append(recordProducers, &sig)
 	})
-	err := EncodeMessageExtraData(&c.ExtraData, recordProducers...)
+
+	extraData, err := MergeAndEncode(
+		recordProducers, c.ExtraData, c.CustomRecords,
+	)
 	if err != nil {
 		return err
 	}
@@ -125,7 +133,7 @@ func (c *CommitSig) Encode(w *bytes.Buffer, pver uint32) error {
 		return err
 	}
 
-	return WriteBytes(w, c.ExtraData)
+	return WriteBytes(w, extraData)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the

lnwire/commit_sig_test.go

@@ -0,0 +1,168 @@
+package lnwire
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/require"
+)
+
+// testCase is a test case for the CommitSig message.
+type commitSigTestCase struct {
+	// Msg is the message to be encoded and decoded.
+	Msg CommitSig
+
+	// ExpectEncodeError is a flag that indicates whether we expect the
+	// encoding of the message to fail.
+	ExpectEncodeError bool
+}
+
+// generateCommitSigTestCases generates a set of CommitSig message test cases.
+func generateCommitSigTestCases(t *testing.T) []commitSigTestCase {
+	// Firstly, we'll set basic values for the message fields.
+	//
+	// Generate random channel ID.
+	chanIDBytes, err := generateRandomBytes(32)
+	require.NoError(t, err)
+
+	var chanID ChannelID
+	copy(chanID[:], chanIDBytes)
+
+	// Generate random commit sig.
+	commitSigBytes, err := generateRandomBytes(64)
+	require.NoError(t, err)
+
+	sig, err := NewSigFromSchnorrRawSignature(commitSigBytes)
+	require.NoError(t, err)
+
+	sigScalar := new(btcec.ModNScalar)
+	sigScalar.SetByteSlice(sig.RawBytes())
+
+	var nonce [musig2.PubNonceSize]byte
+	copy(nonce[:], commitSigBytes)
+
+	sigWithNonce := NewPartialSigWithNonce(nonce, *sigScalar)
+	partialSig := MaybePartialSigWithNonce(sigWithNonce)
+
+	// Define custom records.
+	recordKey1 := uint64(MinCustomRecordsTlvType + 1)
+	recordValue1, err := generateRandomBytes(10)
+	require.NoError(t, err)
+
+	recordKey2 := uint64(MinCustomRecordsTlvType + 2)
+	recordValue2, err := generateRandomBytes(10)
+	require.NoError(t, err)
+
+	customRecords := CustomRecords{
+		recordKey1: recordValue1,
+		recordKey2: recordValue2,
+	}
+
+	// Construct an instance of extra data that contains records with TLV
+	// types below the minimum custom records threshold and that lack
+	// corresponding fields in the message struct. Content should persist in
+	// the extra data field after encoding and decoding.
+	var (
+		recordBytes45 = []byte("recordBytes45")
+		tlvRecord45   = tlv.NewPrimitiveRecord[tlv.TlvType45](
+			recordBytes45,
+		)
+
+		recordBytes55 = []byte("recordBytes55")
+		tlvRecord55   = tlv.NewPrimitiveRecord[tlv.TlvType55](
+			recordBytes55,
+		)
+	)
+
+	var extraData ExtraOpaqueData
+	err = extraData.PackRecords(
+		[]tlv.RecordProducer{&tlvRecord45, &tlvRecord55}...,
+	)
+	require.NoError(t, err)
+
+	invalidCustomRecords := CustomRecords{
+		MinCustomRecordsTlvType - 1: recordValue1,
+	}
+
+	return []commitSigTestCase{
+		{
+			Msg: CommitSig{
+				ChanID:        chanID,
+				CommitSig:     sig,
+				PartialSig:    partialSig,
+				CustomRecords: customRecords,
+				ExtraData:     extraData,
+			},
+		},
+		// Add a test case where the blinding point field is not
+		// populated.
+		{
+			Msg: CommitSig{
+				ChanID:        chanID,
+				CommitSig:     sig,
+				CustomRecords: customRecords,
+			},
+		},
+		// Add a test case where the custom records field is not
+		// populated.
+		{
+			Msg: CommitSig{
+				ChanID:     chanID,
+				CommitSig:  sig,
+				PartialSig: partialSig,
+			},
+		},
+		// Add a case where the custom records are invalid.
+		{
+			Msg: CommitSig{
+				ChanID:        chanID,
+				CommitSig:     sig,
+				PartialSig:    partialSig,
+				CustomRecords: invalidCustomRecords,
+			},
+			ExpectEncodeError: true,
+		},
+	}
+}
+
+// TestCommitSigEncodeDecode tests CommitSig message encoding and decoding for
+// all supported field values.
+func TestCommitSigEncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	// Generate test cases.
+	testCases := generateCommitSigTestCases(t)
+
+	// Execute test cases.
+	for tcIdx, tc := range testCases {
+		t.Run(fmt.Sprintf("testcase-%d", tcIdx), func(t *testing.T) {
+			// Encode test case message.
+			var buf bytes.Buffer
+			err := tc.Msg.Encode(&buf, 0)
+
+			// Check if we expect an encoding error.
+			if tc.ExpectEncodeError {
+				require.Error(t, err)
+				return
+			}
+
+			require.NoError(t, err)
+
+			// Decode the encoded message bytes message.
+			var actualMsg CommitSig
+			decodeReader := bytes.NewReader(buf.Bytes())
+			err = actualMsg.Decode(decodeReader, 0)
+			require.NoError(t, err)
+
+			// The signature type isn't serialized.
+			actualMsg.CommitSig.ForceSchnorr()
+
+			// Compare the two messages to ensure equality.
+			require.Equal(t, tc.Msg, actualMsg)
+		})
+	}
+}

lnwire/lnwire_test.go

@@ -965,6 +965,8 @@ func TestLightningWireProtocol(t *testing.T) {
 				}
 			}
 
+			req.CustomRecords = randCustomRecords(t, r)
+
 			// 50/50 chance to attach a partial sig.
 			if r.Int31()%2 == 0 {
 				req.PartialSig = somePartialSigWithNonce(t, r)

peer/brontide.go

@@ -376,6 +376,10 @@ type Config struct {
 	// leaves for certain custom channel types.
 	AuxLeafStore fn.Option[lnwallet.AuxLeafStore]
 
+	// AuxSigner is an optional signer that can be used to sign auxiliary
+	// leaves for certain custom channel types.
+	AuxSigner fn.Option[lnwallet.AuxSigner]
+
 	// PongBuf is a slice we'll reuse instead of allocating memory on the
 	// heap. Since only reads will occur and no writes, there is no need
 	// for any synchronization primitives. As a result, it's safe to share
@@ -952,6 +956,9 @@ func (p *Brontide) loadActiveChannels(chans []*channeldb.OpenChannel) (
 		p.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
 			chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
 		})
+		p.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
+			chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
+		})
 		lnChan, err := lnwallet.NewLightningChannel(
 			p.cfg.Signer, dbChan, p.cfg.SigPool, chanOpts...,
 		)
@@ -4164,6 +4171,9 @@ func (p *Brontide) addActiveChannel(c *lnpeer.NewChannel) error {
 	p.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
 		chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
 	})
+	p.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
+		chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
+	})
 
 	// If not already active, we'll add this channel to the set of active
 	// channels, so we can look it up later easily according to its channel

peer/test_utils.go

@@ -304,6 +304,8 @@ func createTestPeerWithChannel(t *testing.T, updateChan func(a,
 	alicePool := lnwallet.NewSigPool(1, aliceSigner)
 	channelAlice, err := lnwallet.NewLightningChannel(
 		aliceSigner, aliceChannelState, alicePool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(&lnwallet.MockAuxSigner{}),
 	)
 	if err != nil {
 		return nil, err
@@ -316,6 +318,8 @@ func createTestPeerWithChannel(t *testing.T, updateChan func(a,
 	bobPool := lnwallet.NewSigPool(1, bobSigner)
 	channelBob, err := lnwallet.NewLightningChannel(
 		bobSigner, bobChannelState, bobPool,
+		lnwallet.WithLeafStore(&lnwallet.MockAuxLeafStore{}),
+		lnwallet.WithAuxSigner(&lnwallet.MockAuxSigner{}),
 	)
 	if err != nil {
 		return nil, err

rpcserver.go

@@ -87,6 +87,7 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
 	"gopkg.in/macaroon-bakery.v2/bakery"
 )
 
@@ -579,6 +580,17 @@ func MainRPCServerPermissions() map[string][]bakery.Op {
 	}
 }
 
+// AuxDataParser is an interface that is used to parse auxiliary custom data
+// within RPC messages. This is used to transform binary blobs to human-readable
+// JSON representations.
+type AuxDataParser interface {
+	// InlineParseCustomData replaces any custom data binary blob in the
+	// given RPC message with its corresponding JSON formatted data. This
+	// transforms the binary (likely TLV encoded) data to a human-readable
+	// JSON representation (still as byte slice).
+	InlineParseCustomData(msg proto.Message) error
+}
+
 // rpcServer is a gRPC, RPC front end to the lnd daemon.
 // TODO(roasbeef): pagination support for the list-style calls
 type rpcServer struct {
@@ -731,6 +743,20 @@ func (r *rpcServer) addDeps(s *server, macService *macaroons.Service,
 		},
 		SetChannelAuto:     s.chanStatusMgr.RequestAuto,
 		UseStatusInitiated: subServerCgs.RouterRPC.UseStatusInitiated,
+		ParseCustomChannelData: func(msg proto.Message) error {
+			err = fn.MapOptionZ(
+				r.server.implCfg.AuxDataParser,
+				func(parser AuxDataParser) error {
+					return parser.InlineParseCustomData(msg)
+				},
+			)
+			if err != nil {
+				return fmt.Errorf("error parsing custom data: "+
+					"%w", err)
+			}
+
+			return nil
+		},
 	}
 
 	genInvoiceFeatures := func() *lnwire.FeatureVector {
@@ -3529,6 +3555,7 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 		unsettledRemoteBalance   lnwire.MilliSatoshi
 		pendingOpenLocalBalance  lnwire.MilliSatoshi
 		pendingOpenRemoteBalance lnwire.MilliSatoshi
+		customDataBuf            bytes.Buffer
 	)
 
 	openChannels, err := r.server.chanStateDB.FetchAllOpenChannels()
@@ -3536,6 +3563,12 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 		return nil, err
 	}
 
+	// Encode the number of open channels to the custom data buffer.
+	err = wire.WriteVarInt(&customDataBuf, 0, uint64(len(openChannels)))
+	if err != nil {
+		return nil, err
+	}
+
 	for _, channel := range openChannels {
 		c := channel.LocalCommitment
 		localBalance += c.LocalBalance
@@ -3549,6 +3582,13 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 				unsettledRemoteBalance += htlc.Amt
 			}
 		}
+
+		// Encode the custom data for this open channel.
+		openChanData := channel.LocalCommitment.CustomBlob.UnwrapOr(nil)
+		err = wire.WriteVarBytes(&customDataBuf, 0, openChanData)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	pendingChannels, err := r.server.chanStateDB.FetchPendingChannels()
@@ -3556,10 +3596,23 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 		return nil, err
 	}
 
+	// Encode the number of pending channels to the custom data buffer.
+	err = wire.WriteVarInt(&customDataBuf, 0, uint64(len(pendingChannels)))
+	if err != nil {
+		return nil, err
+	}
+
 	for _, channel := range pendingChannels {
 		c := channel.LocalCommitment
 		pendingOpenLocalBalance += c.LocalBalance
 		pendingOpenRemoteBalance += c.RemoteBalance
+
+		// Encode the custom data for this pending channel.
+		openChanData := channel.LocalCommitment.CustomBlob.UnwrapOr(nil)
+		err = wire.WriteVarBytes(&customDataBuf, 0, openChanData)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	rpcsLog.Debugf("[channelbalance] local_balance=%v remote_balance=%v "+
@@ -3569,7 +3622,7 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 		unsettledRemoteBalance, pendingOpenLocalBalance,
 		pendingOpenRemoteBalance)
 
-	return &lnrpc.ChannelBalanceResponse{
+	resp := &lnrpc.ChannelBalanceResponse{
 		LocalBalance: &lnrpc.Amount{
 			Sat:  uint64(localBalance.ToSatoshis()),
 			Msat: uint64(localBalance),
@@ -3594,11 +3647,24 @@ func (r *rpcServer) ChannelBalance(ctx context.Context,
 			Sat:  uint64(pendingOpenRemoteBalance.ToSatoshis()),
 			Msat: uint64(pendingOpenRemoteBalance),
 		},
+		CustomChannelData: customDataBuf.Bytes(),
 
 		// Deprecated fields.
 		Balance:            int64(localBalance.ToSatoshis()),
 		PendingOpenBalance: int64(pendingOpenLocalBalance.ToSatoshis()),
-	}, nil
+	}
+
+	err = fn.MapOptionZ(
+		r.server.implCfg.AuxDataParser,
+		func(parser AuxDataParser) error {
+			return parser.InlineParseCustomData(resp)
+		},
+	)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing custom data: %w", err)
+	}
+
+	return resp, nil
 }
 
 type (
@@ -3654,6 +3720,12 @@ func (r *rpcServer) fetchPendingOpenChannels() (pendingOpenChannels, error) {
 			pendingChan.BroadcastHeight()
 		fundingExpiryBlocks := int32(maxFundingHeight) - currentHeight
 
+		customChanBytes, err := encodeCustomChanData(pendingChan)
+		if err != nil {
+			return nil, fmt.Errorf("unable to encode open chan "+
+				"data: %w", err)
+		}
+
 		result[i] = &lnrpc.PendingChannelsResponse_PendingOpenChannel{
 			Channel: &lnrpc.PendingChannelsResponse_PendingChannel{
 				RemoteNodePub:        hex.EncodeToString(pub),
@@ -3667,6 +3739,7 @@ func (r *rpcServer) fetchPendingOpenChannels() (pendingOpenChannels, error) {
 				CommitmentType:       rpcCommitmentType(pendingChan.ChanType),
 				Private:              isPrivate(pendingChan),
 				Memo:                 string(pendingChan.Memo),
+				CustomChannelData:    customChanBytes,
 			},
 			CommitWeight:        commitWeight,
 			CommitFee:           int64(localCommitment.CommitFee),
@@ -4033,6 +4106,16 @@ func (r *rpcServer) PendingChannels(ctx context.Context,
 	resp.WaitingCloseChannels = waitingCloseChannels
 	resp.TotalLimboBalance += limbo
 
+	err = fn.MapOptionZ(
+		r.server.implCfg.AuxDataParser,
+		func(parser AuxDataParser) error {
+			return parser.InlineParseCustomData(resp)
+		},
+	)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing custom data: %w", err)
+	}
+
 	return resp, nil
 }
 
@@ -4347,6 +4430,16 @@ func (r *rpcServer) ListChannels(ctx context.Context,
 		resp.Channels = append(resp.Channels, channel)
 	}
 
+	err = fn.MapOptionZ(
+		r.server.implCfg.AuxDataParser,
+		func(parser AuxDataParser) error {
+			return parser.InlineParseCustomData(resp)
+		},
+	)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing custom data: %w", err)
+	}
+
 	return resp, nil
 }
 
@@ -4397,6 +4490,30 @@ func isPrivate(dbChannel *channeldb.OpenChannel) bool {
 	return dbChannel.ChannelFlags&lnwire.FFAnnounceChannel != 1
 }
 
+// encodeCustomChanData encodes the custom channel data for the open channel.
+// It encodes that data as a pair of var bytes blobs.
+func encodeCustomChanData(lnChan *channeldb.OpenChannel) ([]byte, error) {
+	customOpenChanData := lnChan.CustomBlob.UnwrapOr(nil)
+	customLocalCommitData := lnChan.LocalCommitment.CustomBlob.UnwrapOr(nil)
+
+	// We'll encode our custom channel data as two blobs. The first is a
+	// set of var bytes encoding of the open chan data, the second is an
+	// encoding of the local commitment data.
+	var customChanDataBuf bytes.Buffer
+	err := wire.WriteVarBytes(&customChanDataBuf, 0, customOpenChanData)
+	if err != nil {
+		return nil, fmt.Errorf("unable to encode open chan "+
+			"data: %w", err)
+	}
+	err = wire.WriteVarBytes(&customChanDataBuf, 0, customLocalCommitData)
+	if err != nil {
+		return nil, fmt.Errorf("unable to encode local commit "+
+			"data: %w", err)
+	}
+
+	return customChanDataBuf.Bytes(), nil
+}
+
 // createRPCOpenChannel creates an *lnrpc.Channel from the *channeldb.Channel.
 func createRPCOpenChannel(r *rpcServer, dbChannel *channeldb.OpenChannel,
 	isActive, peerAliasLookup bool) (*lnrpc.Channel, error) {
@@ -4451,6 +4568,14 @@ func createRPCOpenChannel(r *rpcServer, dbChannel *channeldb.OpenChannel,
 	// is returned and peerScidAlias will be an empty ShortChannelID.
 	peerScidAlias, _ := r.server.aliasMgr.GetPeerAlias(chanID)
 
+	// Finally we'll attempt to encode the custom channel data if any
+	// exists.
+	customChanBytes, err := encodeCustomChanData(dbChannel)
+	if err != nil {
+		return nil, fmt.Errorf("unable to encode open chan data: %w",
+			err)
+	}
+
 	channel := &lnrpc.Channel{
 		Active:                isActive,
 		Private:               isPrivate(dbChannel),
@@ -4483,6 +4608,7 @@ func createRPCOpenChannel(r *rpcServer, dbChannel *channeldb.OpenChannel,
 		ZeroConf:              dbChannel.IsZeroConf(),
 		ZeroConfConfirmedScid: dbChannel.ZeroConfRealScid().ToUint64(),
 		Memo:                  string(dbChannel.Memo),
+		CustomChannelData:     customChanBytes,
 		// TODO: remove the following deprecated fields
 		CsvDelay:             uint32(dbChannel.LocalChanCfg.CsvDelay),
 		LocalChanReserveSat:  int64(dbChannel.LocalChanCfg.ChanReserve),

rpcserver_test.go

@@ -1,14 +1,79 @@
 package lnd
 
 import (
+	"fmt"
 	"testing"
 
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/proto"
 )
 
 func TestGetAllPermissions(t *testing.T) {
 	perms := GetAllPermissions()
 
-	// Currently there are there are 16 entity:action pairs in use.
+	// Currently there are 16 entity:action pairs in use.
 	assert.Equal(t, len(perms), 16)
 }
+
+// mockDataParser is a mock implementation of the AuxDataParser interface.
+type mockDataParser struct {
+}
+
+// InlineParseCustomData replaces any custom data binary blob in the given RPC
+// message with its corresponding JSON formatted data. This transforms the
+// binary (likely TLV encoded) data to a human-readable JSON representation
+// (still as byte slice).
+func (m *mockDataParser) InlineParseCustomData(msg proto.Message) error {
+	switch m := msg.(type) {
+	case *lnrpc.ChannelBalanceResponse:
+		m.CustomChannelData = []byte(`{"foo": "bar"}`)
+
+		return nil
+
+	default:
+		return fmt.Errorf("mock only supports ChannelBalanceResponse")
+	}
+}
+
+func TestAuxDataParser(t *testing.T) {
+	// We create an empty channeldb, so we can fetch some channels.
+	cdb, err := channeldb.Open(t.TempDir())
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		require.NoError(t, cdb.Close())
+	})
+
+	r := &rpcServer{
+		server: &server{
+			chanStateDB: cdb.ChannelStateDB(),
+			implCfg: &ImplementationCfg{
+				AuxComponents: AuxComponents{
+					AuxDataParser: fn.Some[AuxDataParser](
+						&mockDataParser{},
+					),
+				},
+			},
+		},
+	}
+
+	// With the aux data parser in place, we should get a formatted JSON
+	// in the custom channel data field.
+	resp, err := r.ChannelBalance(nil, &lnrpc.ChannelBalanceRequest{})
+	require.NoError(t, err)
+	require.NotNil(t, resp)
+	require.Equal(t, []byte(`{"foo": "bar"}`), resp.CustomChannelData)
+
+	// If we don't supply the aux data parser, we should get the raw binary
+	// data. Which in this case is just two VarInt fields (1 byte each) that
+	// represent the value of 0 (zero active and zero pending channels).
+	r.server.implCfg.AuxComponents.AuxDataParser = fn.None[AuxDataParser]()
+
+	resp, err = r.ChannelBalance(nil, &lnrpc.ChannelBalanceRequest{})
+	require.NoError(t, err)
+	require.NotNil(t, resp)
+	require.Equal(t, []byte{0x00, 0x00}, resp.CustomChannelData)
+}

server.go

@@ -1287,6 +1287,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 			return &pc.Incoming
 		},
 		AuxLeafStore: implCfg.AuxLeafStore,
+		AuxSigner:    implCfg.AuxSigner,
 	}, dbs.ChanStateDB)
 
 	// Select the configuration and funding parameters for Bitcoin.
@@ -1534,6 +1535,8 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		DeleteAliasEdge:      deleteAliasEdge,
 		AliasManager:         s.aliasMgr,
 		IsSweeperOutpoint:    s.sweeper.IsSweeperOutpoint,
+		AuxFundingController: implCfg.AuxFundingController,
+		AuxSigner:            implCfg.AuxSigner,
 	})
 	if err != nil {
 		return nil, err
@@ -4089,6 +4092,7 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 		MaxFeeExposure:         thresholdMSats,
 		Quit:                   s.quit,
 		AuxLeafStore:           s.implCfg.AuxLeafStore,
+		AuxSigner:              s.implCfg.AuxSigner,
 		MsgRouter:              s.implCfg.MsgRouter,
 	}