Aux Closer: Move coop-close aux finalization to chain watcher

contractcourt/chain_arbitrator.go

@@ -230,6 +230,10 @@ type ChainArbitratorConfig struct {
 	// AuxResolver is an optional interface that can be used to modify the
 	// way contracts are resolved.
 	AuxResolver fn.Option[lnwallet.AuxContractResolver]
+
+	// AuxCloser is an optional interface that can be used to finalize
+	// cooperative channel closes.
+	AuxCloser fn.Option[AuxChanCloser]
 }
 
 // ChainArbitrator is a sub-system that oversees the on-chain resolution of all
@@ -1138,6 +1142,7 @@ func (c *ChainArbitrator) WatchNewChannel(newChan *channeldb.OpenChannel) error
 			extractStateNumHint: lnwallet.GetStateNumHint,
 			auxLeafStore:        c.cfg.AuxLeafStore,
 			auxResolver:         c.cfg.AuxResolver,
+			auxCloser:           c.cfg.AuxCloser,
 		},
 	)
 	if err != nil {
@@ -1315,6 +1320,7 @@ func (c *ChainArbitrator) loadOpenChannels() error {
 				extractStateNumHint: lnwallet.GetStateNumHint,
 				auxLeafStore:        c.cfg.AuxLeafStore,
 				auxResolver:         c.cfg.AuxResolver,
+				auxCloser:           c.cfg.AuxCloser,
 			},
 		)
 		if err != nil {

contractcourt/chain_watcher.go

@@ -25,6 +25,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnutils"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 const (
@@ -37,6 +38,77 @@ const (
 	maxCommitPointPollTimeout = 10 * time.Minute
 )
 
+// CloseOutput represents an output that should be included in the close
+// transaction.
+type CloseOutput struct {
+	// Amt is the amount of the output.
+	Amt btcutil.Amount
+
+	// DustLimit is the dust limit for the local node.
+	DustLimit btcutil.Amount
+
+	// PkScript is the script that should be used to pay to the output.
+	PkScript []byte
+
+	// ShutdownRecords is the set of custom records that may result in
+	// extra close outputs being added.
+	ShutdownRecords lnwire.CustomRecords
+}
+
+// AuxShutdownReq is used to request a set of extra custom records to include
+// in the shutdown message.
+type AuxShutdownReq struct {
+	// ChanPoint is the channel point of the channel that is being shut
+	// down.
+	ChanPoint wire.OutPoint
+
+	// ShortChanID is the short channel ID of the channel that is being
+	// closed.
+	ShortChanID lnwire.ShortChannelID
+
+	// Initiator is true if the local node is the initiator of the channel.
+	Initiator bool
+
+	// InternalKey is the internal key for the shutdown addr. This will
+	// only be set for taproot shutdown addrs.
+	InternalKey fn.Option[btcec.PublicKey]
+
+	// CommitBlob is the blob that was included in the last commitment.
+	CommitBlob fn.Option[tlv.Blob]
+
+	// FundingBlob is the blob that was included in the funding state.
+	FundingBlob fn.Option[tlv.Blob]
+}
+
+// AuxCloseDesc is used to describe the channel close that is being performed.
+type AuxCloseDesc struct {
+	AuxShutdownReq
+
+	// CloseFee is the closing fee to be paid for this state.
+	CloseFee btcutil.Amount
+
+	// CommitFee is the fee that was paid for the last commitment.
+	CommitFee btcutil.Amount
+
+	// LocalCloseOutput is the output that the local node should be paid
+	// to. This is None if the local party will not have an output on the
+	// co-op close transaction.
+	LocalCloseOutput fn.Option[CloseOutput]
+
+	// RemoteCloseOutput is the output that the remote node should be paid
+	// to. This will be None if the remote party will not have an output on
+	// the co-op close transaction.
+	RemoteCloseOutput fn.Option[CloseOutput]
+}
+
+// AuxChanCloser is used to allow an external caller to finalize a cooperative
+// channel close.
+type AuxChanCloser interface {
+	// FinalizeClose is called after the close transaction has been agreed
+	// upon and confirmed.
+	FinalizeClose(desc AuxCloseDesc, closeTx *wire.MsgTx) error
+}
+
 // LocalUnilateralCloseInfo encapsulates all the information we need to act on
 // a local force close that gets confirmed.
 type LocalUnilateralCloseInfo struct {
@@ -229,6 +301,9 @@ type chainWatcherConfig struct {
 
 	// auxResolver is used to supplement contract resolution.
 	auxResolver fn.Option[lnwallet.AuxContractResolver]
+
+	// auxCloser is used to finalize cooperative closes.
+	auxCloser fn.Option[AuxChanCloser]
 }
 
 // chainWatcher is a system that's assigned to every active channel. The duty