From 9c80088abda9a2ac34b79087376d72d98b6ae897 Mon Sep 17 00:00:00 2001
From: Jonathan Harvey-Buschel <j.s.harbus@gmail.com>
Date: Sun, 8 Sep 2024 17:00:13 -0400
Subject: [PATCH] lnwallet: sort sig jobs before submission

To make sure we attempt to read the results of the sig batches in the
same order they're processed, we sort them _before_ submitting them to
the batch processor.
Otherwise it might happen that we try to read on a result channel that
was never sent on because we aborted due to an error.
We also use slices.SortFunc now which doesn't use reflection and might
be slightly faster.
---
 lnwallet/channel.go | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/lnwallet/channel.go b/lnwallet/channel.go
index b344b543b..0bd1938a7 100644
--- a/lnwallet/channel.go
+++ b/lnwallet/channel.go
@@ -6,7 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"sort"
+	"slices"
 	"sync"
 
 	"github.com/btcsuite/btcd/blockchain"
@@ -3963,6 +3963,17 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 	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 {
@@ -4013,18 +4024,8 @@ 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
-	})
-	sort.Slice(auxSigBatch, func(i, j int) bool {
-		return auxSigBatch[i].OutputIndex < auxSigBatch[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))
 	auxSigs := make([]fn.Option[tlv.Blob], 0, len(auxSigBatch))
 	for i := range sigBatch {