From 846be8147fcf2a7a4802c1ae8e43483cdfc21333 Mon Sep 17 00:00:00 2001
From: Valentine Wallace <vwallace@protonmail.com>
Date: Mon, 4 Dec 2023 15:26:30 -0500
Subject: [PATCH] Adapt Channel::fail_htlc for failing with malformed OR
 update_fail_htlc.

Useful for failing blinded payments back with malformed, and will also be
useful in the future when we move onion decoding into
process_pending_htlc_forwards, after which Channel::fail_htlc will be used for
all malformed htlcs.
---
 lightning/src/ln/channel.rs | 43 +++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 44b09a861..a991c8eed 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -2543,6 +2543,29 @@ impl FailHTLCContents for msgs::OnionErrorPacket {
 		HTLCUpdateAwaitingACK::FailHTLC { htlc_id, err_packet: self }
 	}
 }
+impl FailHTLCContents for (u16, [u8; 32]) {
+	type Message = msgs::UpdateFailMalformedHTLC; // (failure_code, sha256_of_onion)
+	fn to_message(self, htlc_id: u64, channel_id: ChannelId) -> Self::Message {
+		msgs::UpdateFailMalformedHTLC {
+			htlc_id,
+			channel_id,
+			failure_code: self.0,
+			sha256_of_onion: self.1
+		}
+	}
+	fn to_inbound_htlc_state(self) -> InboundHTLCState {
+		InboundHTLCState::LocalRemoved(
+			InboundHTLCRemovalReason::FailMalformed((self.1, self.0))
+		)
+	}
+	fn to_htlc_update_awaiting_ack(self, htlc_id: u64) -> HTLCUpdateAwaitingACK {
+		HTLCUpdateAwaitingACK::FailMalformedHTLC {
+			htlc_id,
+			failure_code: self.0,
+			sha256_of_onion: self.1
+		}
+	}
+}
 
 trait FailHTLCMessageName {
 	fn name() -> &'static str;
@@ -2552,6 +2575,11 @@ impl FailHTLCMessageName for msgs::UpdateFailHTLC {
 		"update_fail_htlc"
 	}
 }
+impl FailHTLCMessageName for msgs::UpdateFailMalformedHTLC {
+	fn name() -> &'static str {
+		"update_fail_malformed_htlc"
+	}
+}
 
 impl<SP: Deref> Channel<SP> where
 	SP::Target: SignerProvider,
@@ -3598,8 +3626,19 @@ impl<SP: Deref> Channel<SP> where
 							}
 						}
 					},
-					&HTLCUpdateAwaitingACK::FailMalformedHTLC { .. } => {
-						todo!()
+					&HTLCUpdateAwaitingACK::FailMalformedHTLC { htlc_id, failure_code, sha256_of_onion } => {
+						match self.fail_htlc(htlc_id, (failure_code, sha256_of_onion), false, logger) {
+							Ok(update_fail_malformed_opt) => {
+								debug_assert!(update_fail_malformed_opt.is_some()); // See above comment
+								update_fail_count += 1;
+							},
+							Err(e) => {
+								if let ChannelError::Ignore(_) = e {}
+								else {
+									panic!("Got a non-IgnoreError action trying to fail holding cell HTLC");
+								}
+							}
+						}
 					},
 				}
 			}
-- 
2.39.5