multi: use prev output fetcher where possible

watchtower/wtclient/backup_task.go

@@ -7,6 +7,7 @@ import (
 	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/btcutil/txsort"
+	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/input"
@@ -262,10 +263,14 @@ func (t *backupTask) craftSessionPayload(
 	// information. This will either be contain both the to-local and
 	// to-remote outputs, or only be the to-local output.
 	inputs := t.inputs()
-	for prevOutPoint, input := range inputs {
+	prevOutputFetcher := txscript.NewMultiPrevOutFetcher(nil)
+	for prevOutPoint, inp := range inputs {
+		prevOutputFetcher.AddPrevOut(
+			prevOutPoint, inp.SignDesc().Output,
+		)
 		justiceTxn.AddTxIn(&wire.TxIn{
 			PreviousOutPoint: prevOutPoint,
-			Sequence:         input.BlocksToMaturity(),
+			Sequence:         inp.BlocksToMaturity(),
 		})
 	}
 
@@ -284,7 +289,7 @@ func (t *backupTask) craftSessionPayload(
 	}
 
 	// Construct a sighash cache to improve signing performance.
-	hashCache := input.NewTxSigHashesV0Only(justiceTxn)
+	hashCache := txscript.NewTxSigHashes(justiceTxn, prevOutputFetcher)
 
 	// Since the transaction inputs could have been reordered as a result of
 	// the BIP69 sort, create an index mapping each prevout to it's new
@@ -303,7 +308,7 @@ func (t *backupTask) craftSessionPayload(
 
 		// Construct the full witness required to spend this input.
 		inputScript, err := inp.CraftInputScript(
-			signer, justiceTxn, hashCache, i,
+			signer, justiceTxn, hashCache, prevOutputFetcher, i,
 		)
 		if err != nil {
 			return hint, nil, err