[3/5]: multi: add new AuxFundingController for custom external funding flows

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

@@ -35,6 +35,7 @@ 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"
@@ -44,6 +45,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/btcwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/rpcwallet"
 	"github.com/lightningnetwork/lnd/macaroons"
+	"github.com/lightningnetwork/lnd/protofsm"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/rpcperms"
 	"github.com/lightningnetwork/lnd/signal"
@@ -162,6 +164,16 @@ type AuxComponents struct {
 	// TrafficShaper is an optional traffic shaper that can be used to
 	// control the outgoing channel of a payment.
 	TrafficShaper fn.Option[routing.TlvTrafficShaper]
+
+	// MsgRouter is an optional message router that if set will be used in
+	// place of a new blank default message router.
+	MsgRouter fn.Option[protofsm.MsgRouter]
+
+	// AuxFundingController is an optional controller that can be used to
+	// modify the way we handle certain custom chanenl types. It's also
+	// able to automatically handle new custom protocol messages related to
+	// the funding process.
+	AuxFundingController fn.Option[funding.AuxFundingController]
 }
 
 // DefaultWalletImpl is the default implementation of our normal, btcwallet

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/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lnpeer"
@@ -82,9 +83,10 @@ var (
 // can provide that serve useful when processing a specific network
 // announcement.
 type optionalMsgFields struct {
-	capacity     *btcutil.Amount
-	channelPoint *wire.OutPoint
-	remoteAlias  *lnwire.ShortChannelID
+	capacity      *btcutil.Amount
+	channelPoint  *wire.OutPoint
+	remoteAlias   *lnwire.ShortChannelID
+	tapscriptRoot fn.Option[chainhash.Hash]
 }
 
 // apply applies the optional fields within the functional options.
@@ -115,6 +117,14 @@ func ChannelPoint(op wire.OutPoint) OptionalMsgField {
 	}
 }
 
+// TapscriptRoot is an optional field that lets the gossiper know of the root of
+// the tapscript tree for a custom channel.
+func TapscriptRoot(root fn.Option[chainhash.Hash]) OptionalMsgField {
+	return func(f *optionalMsgFields) {
+		f.tapscriptRoot = root
+	}
+}
+
 // RemoteAlias is an optional field that lets the gossiper know that a locally
 // sent channel update is actually an update for the peer that should replace
 // the ShortChannelID field with the remote's alias. This is only used for
@@ -2513,6 +2523,9 @@ 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",

funding/aux_funding.go

@@ -0,0 +1,82 @@
+package funding
+
+import (
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/protofsm"
+)
+
+// 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 {
+	// MsgEndpoint 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.
+	protofsm.MsgEndpoint
+
+	// 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 *channeldb.OpenChannel,
+		localKeyRing, remoteKeyRing lnwallet.CommitmentKeyRing,
+		initiator bool) (fn.Option[lnwallet.AuxFundingDesc], error)
+
+	// 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) (fn.Option[chainhash.Hash], error)
+
+	// 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 *channeldb.OpenChannel) 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
+}
+
+// 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.
+func descFromPendingChanID(controller fn.Option[AuxFundingController],
+	chanID PendingChanID, openChan *channeldb.OpenChannel,
+	localKeyRing, remoteKeyRing lnwallet.CommitmentKeyRing,
+	initiator bool) (fn.Option[lnwallet.AuxFundingDesc], error) {
+
+	var result fn.Option[lnwallet.AuxFundingDesc]
+	mapErr := fn.MapOptionZ(controller, func(c AuxFundingController) error {
+		var err error
+		result, err = c.DescFromPendingChanID(
+			chanID, openChan, localKeyRing, remoteKeyRing,
+			initiator,
+		)
+
+		return err
+	})
+
+	return result, mapErr
+}
+
+// deriveTapscriptRoot takes a pending channel ID and maybe returns a
+// tapscript root that should be used when creating any MuSig2 sessions for a
+// channel.
+func deriveTapscriptRoot(controller fn.Option[AuxFundingController],
+	chanID PendingChanID) (fn.Option[chainhash.Hash], error) {
+
+	var result fn.Option[chainhash.Hash]
+	mapErr := fn.MapOptionZ(controller, func(c AuxFundingController) error {
+		var err error
+		result, err = c.DeriveTapscriptRoot(chanID)
+		return err
+	})
+
+	return result, mapErr
+}