From 7ff251ca44680c131f1542aabb13bb9c2ee385dd Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Wed, 29 May 2024 19:57:40 +0200
Subject: [PATCH] lnwallet/chancloser: add new AuxChanCloser interface

---
 lnwallet/chancloser/aux_closer.go | 104 ++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 lnwallet/chancloser/aux_closer.go

diff --git a/lnwallet/chancloser/aux_closer.go b/lnwallet/chancloser/aux_closer.go
new file mode 100644
index 000000000..8b1c445ca
--- /dev/null
+++ b/lnwallet/chancloser/aux_closer.go
@@ -0,0 +1,104 @@
+package chancloser
+
+import (
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+// 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]
+}
+
+// AuxCloseOutputs is used to specify extra outputs that should be used when
+// constructing the co-op close transaction.
+type AuxCloseOutputs struct {
+	// ExtraCloseOutputs is a set of extra outputs that should be included
+	// in the close transaction.
+	ExtraCloseOutputs []lnwallet.CloseOutput
+
+	// CustomSort is a custom function that can be used to sort the
+	// transaction outputs. If this isn't set, then the default BIP-69
+	// sorting is used.
+	CustomSort lnwallet.CloseSortFunc
+}
+
+// AuxChanCloser is used to allow an external caller to modify the co-op close
+// transaction.
+type AuxChanCloser interface {
+	// ShutdownBlob returns the set of custom records that should be
+	// included in the shutdown message.
+	ShutdownBlob(req AuxShutdownReq) (fn.Option[lnwire.CustomRecords],
+		error)
+
+	// AuxCloseOutputs returns the set of custom outputs that should be used
+	// to construct the co-op close transaction.
+	AuxCloseOutputs(desc AuxCloseDesc) (fn.Option[AuxCloseOutputs], error)
+
+	// FinalizeClose is called after the close transaction has been agreed
+	// upon.
+	FinalizeClose(desc AuxCloseDesc, closeTx *wire.MsgTx) error
+}