From 70292253d1d124ec827dccbcad9e8629137f726f Mon Sep 17 00:00:00 2001
From: Keagan McClelland <keagan.mcclelland@gmail.com>
Date: Sun, 26 Nov 2023 12:43:21 -0800
Subject: [PATCH] htlcswitch: make link forward eligibility flush aware

---
 htlcswitch/link.go | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/htlcswitch/link.go b/htlcswitch/link.go
index def2e2f01..8ef618b02 100644
--- a/htlcswitch/link.go
+++ b/htlcswitch/link.go
@@ -538,10 +538,19 @@ func (l *channelLink) WaitForShutdown() {
 
 // EligibleToForward returns a bool indicating if the channel is able to
 // actively accept requests to forward HTLC's. We're able to forward HTLC's if
-// we know the remote party's next revocation point. Otherwise, we can't
-// initiate new channel state. We also require that the short channel ID not be
-// the all-zero source ID, meaning that the channel has had its ID finalized.
+// we are eligible to update AND the channel isn't currently flushing the
+// outgoing half of the channel.
 func (l *channelLink) EligibleToForward() bool {
+	return l.EligibleToUpdate() &&
+		!l.IsFlushing(Outgoing)
+}
+
+// EligibleToUpdate returns a bool indicating if the channel is able to update
+// channel state. We're able to update channel state if we know the remote
+// party's next revocation point. Otherwise, we can't initiate new channel
+// state. We also require that the short channel ID not be the all-zero source
+// ID, meaning that the channel has had its ID finalized.
+func (l *channelLink) EligibleToUpdate() bool {
 	return l.channel.RemoteNextRevocation() != nil &&
 		l.ShortChanID() != hop.Source &&
 		l.isReestablished()
@@ -2831,7 +2840,7 @@ func (l *channelLink) updateChannelFee(feePerKw chainfee.SatPerKWeight) error {
 
 	// We skip sending the UpdateFee message if the channel is not
 	// currently eligible to forward messages.
-	if !l.EligibleToForward() {
+	if !l.EligibleToUpdate() {
 		l.log.Debugf("skipping fee update for inactive channel")
 		return nil
 	}