From 5b7b6ab9b06902e533f1c3fcdf24121a02332a7c Mon Sep 17 00:00:00 2001
From: carla <kirkcohenc@gmail.com>
Date: Thu, 22 Apr 2021 19:39:37 +0200
Subject: [PATCH] multi: send channel update for failed interceptor packets

---
 htlcswitch/interceptable_switch.go           | 11 ++++++++++-
 lntest/itest/lnd_forward_interceptor_test.go |  9 +++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/htlcswitch/interceptable_switch.go b/htlcswitch/interceptable_switch.go
index 834ca2b2..f6d0d2ef 100644
--- a/htlcswitch/interceptable_switch.go
+++ b/htlcswitch/interceptable_switch.go
@@ -139,7 +139,16 @@ func (f *interceptedForward) Resume() error {
 
 // Fail forward a failed packet to the switch.
 func (f *interceptedForward) Fail() error {
-	reason, err := f.packet.obfuscator.EncryptFirstHop(lnwire.NewTemporaryChannelFailure(nil))
+	update, err := f.htlcSwitch.cfg.FetchLastChannelUpdate(
+		f.packet.incomingChanID,
+	)
+	if err != nil {
+		return err
+	}
+
+	reason, err := f.packet.obfuscator.EncryptFirstHop(
+		lnwire.NewTemporaryChannelFailure(update),
+	)
 	if err != nil {
 		return fmt.Errorf("failed to encrypt failure reason %v", err)
 	}
diff --git a/lntest/itest/lnd_forward_interceptor_test.go b/lntest/itest/lnd_forward_interceptor_test.go
index 4dbc29af..46fdadf3 100644
--- a/lntest/itest/lnd_forward_interceptor_test.go
+++ b/lntest/itest/lnd_forward_interceptor_test.go
@@ -128,6 +128,15 @@ func testForwardInterceptor(net *lntest.NetworkHarness, t *harnessTest) {
 				require.Equal(t.t, lnrpc.HTLCAttempt_FAILED,
 					attempt.Status, "expected payment to fail")
 
+				// Assert that we get a temporary channel
+				// failure which has a channel update.
+				require.NotNil(t.t, attempt.Failure)
+				require.NotNil(t.t, attempt.Failure.ChannelUpdate)
+
+				require.Equal(t.t,
+					lnrpc.Failure_TEMPORARY_CHANNEL_FAILURE,
+					attempt.Failure.Code)
+
 			// For settle and resume we make sure the payment is successful.
 			case routerrpc.ResolveHoldForwardAction_SETTLE:
 				fallthrough