Persist outbound channel info in inbound HTLCs

We need these fields to generate a correct PaymentForwarded event if we need to
claim this inbound HTLC backwards after restart and it's already been claimed
and removed on the outbound edge.

Author: valentinewallace

lightning/src/ln/channel.rs

@@ -308,6 +308,32 @@ impl InboundHTLCState {
 	}
 }
 
+/// Information about the outbound hop for a forwarded HTLC. Useful for generating an accurate
+/// [`Event::PaymentForwarded`] if we need to claim this HTLC post-restart.
+///
+/// [`Event::PaymentForwarded`]: crate::events::Event::PaymentForwarded
+#[derive(Debug, Copy, Clone)]
+pub(super) struct OutboundHop {
+	/// The amount forwarded outbound.
+	pub(super) amt_msat: u64,
+	/// The outbound channel this HTLC was forwarded over.
+	pub(super) channel_id: ChannelId,
+	/// The next-hop recipient of this HTLC.
+	pub(super) node_id: PublicKey,
+	/// The outbound channel's funding outpoint.
+	pub(super) funding_txo: OutPoint,
+	/// The outbound channel's user channel ID.
+	pub(super) user_channel_id: u128,
+}
+
+impl_writeable_tlv_based!(OutboundHop, {
+	(0, amt_msat, required),
+	(2, channel_id, required),
+	(4, node_id, required),
+	(6, funding_txo, required),
+	(8, user_channel_id, required),
+});
+
 /// A field of `InboundHTLCState::Committed` containing the HTLC's `update_add_htlc` message. If
 /// the HTLC is a forward and gets irrevocably committed to the outbound edge, we convert to
 /// `InboundUpdateAdd::Forwarded`, thus pruning the onion and not persisting it on every
@@ -328,11 +354,7 @@ enum InboundUpdateAdd {
 		phantom_shared_secret: Option<[u8; 32]>,
 		trampoline_shared_secret: Option<[u8; 32]>,
 		blinded_failure: Option<BlindedFailure>,
-		/// Useful for generating an accurate [`Event::PaymentForwarded`], if we need to claim this
-		/// HTLC post-restart.
-		///
-		/// [`Event::PaymentForwarded`]: crate::events::Event::PaymentForwarded
-		outbound_amt_msat: u64,
+		outbound_hop: OutboundHop,
 	},
 	/// This HTLC was received pre-LDK 0.3, before we started persisting the onion for inbound
 	/// committed HTLCs.
@@ -346,7 +368,7 @@ impl_writeable_tlv_based_enum_upgradable!(InboundUpdateAdd,
 	(2, Legacy) => {},
 	(4, Forwarded) => {
 		(0, incoming_packet_shared_secret, required),
-		(2, outbound_amt_msat, required),
+		(2, outbound_hop, required),
 		(4, phantom_shared_secret, option),
 		(6, trampoline_shared_secret, option),
 		(8, blinded_failure, option),
@@ -7948,15 +7970,15 @@ where
 						phantom_shared_secret,
 						trampoline_shared_secret,
 						blinded_failure,
-						outbound_amt_msat,
+						outbound_hop: OutboundHop { amt_msat, .. },
 					},
 			} => {
 				if htlc_resolution_in_holding_cell(htlc.htlc_id) {
 					return None;
 				}
 				// The reconstructed `HTLCPreviousHopData` is used to fail or claim the HTLC backwards
 				// post-restart, if it is missing in the outbound edge.
-				let hop_data = HTLCPreviousHopData {
+				let prev_hop_data = HTLCPreviousHopData {
 					prev_outbound_scid_alias,
 					user_channel_id: Some(user_channel_id),
 					htlc_id: htlc.htlc_id,
@@ -7969,7 +7991,7 @@ where
 					counterparty_node_id: Some(counterparty_node_id),
 					cltv_expiry: Some(htlc.cltv_expiry),
 				};
-				Some((htlc.payment_hash, hop_data, *outbound_amt_msat))
+				Some((htlc.payment_hash, prev_hop_data, *amt_msat))
 			},
 			_ => None,
 		})
@@ -8019,17 +8041,18 @@ where
 	/// This inbound HTLC was irrevocably forwarded to the outbound edge, so we no longer need to
 	/// persist its onion.
 	pub(super) fn prune_inbound_htlc_onion(
-		&mut self, htlc_id: u64, hop_data: &HTLCPreviousHopData, outbound_amt_msat: u64,
+		&mut self, htlc_id: u64, prev_hop_data: &HTLCPreviousHopData,
+		outbound_hop_data: OutboundHop,
 	) {
 		for htlc in self.context.pending_inbound_htlcs.iter_mut() {
 			if htlc.htlc_id == htlc_id {
 				if let InboundHTLCState::Committed { ref mut update_add_htlc } = htlc.state {
 					*update_add_htlc = InboundUpdateAdd::Forwarded {
-						incoming_packet_shared_secret: hop_data.incoming_packet_shared_secret,
-						phantom_shared_secret: hop_data.phantom_shared_secret,
-						trampoline_shared_secret: hop_data.trampoline_shared_secret,
-						blinded_failure: hop_data.blinded_failure,
-						outbound_amt_msat,
+						incoming_packet_shared_secret: prev_hop_data.incoming_packet_shared_secret,
+						phantom_shared_secret: prev_hop_data.phantom_shared_secret,
+						trampoline_shared_secret: prev_hop_data.trampoline_shared_secret,
+						blinded_failure: prev_hop_data.blinded_failure,
+						outbound_hop: outbound_hop_data,
 					};
 					return;
 				}

lightning/src/ln/channelmanager.rs

@@ -59,9 +59,9 @@ use crate::ln::chan_utils::selected_commitment_sat_per_1000_weight;
 use crate::ln::channel::QuiescentAction;
 use crate::ln::channel::{
 	self, hold_time_since, Channel, ChannelError, ChannelUpdateStatus, DisconnectResult,
-	FundedChannel, FundingTxSigned, InboundV1Channel, OutboundV1Channel, PendingV2Channel,
-	ReconnectionMsg, ShutdownResult, SpliceFundingFailed, StfuResponse, UpdateFulfillCommitFetch,
-	WithChannelContext,
+	FundedChannel, FundingTxSigned, InboundV1Channel, OutboundHop, OutboundV1Channel,
+	PendingV2Channel, ReconnectionMsg, ShutdownResult, SpliceFundingFailed, StfuResponse,
+	UpdateFulfillCommitFetch, WithChannelContext,
 };
 use crate::ln::channel_state::ChannelDetails;
 use crate::ln::funding::SpliceContribution;
@@ -1402,6 +1402,8 @@ enum PostMonitorUpdateChanResume {
 	Unblocked {
 		channel_id: ChannelId,
 		counterparty_node_id: PublicKey,
+		funding_txo: OutPoint,
+		user_channel_id: u128,
 		unbroadcasted_batch_funding_txid: Option<Txid>,
 		update_actions: Vec<MonitorUpdateCompletionAction>,
 		htlc_forwards: Option<PerSourcePendingForward>,
@@ -9582,8 +9584,8 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 	/// Handles actions which need to complete after a [`ChannelMonitorUpdate`] has been applied
 	/// which can happen after the per-peer state lock has been dropped.
 	fn post_monitor_update_unlock(
-		&self, channel_id: ChannelId, counterparty_node_id: PublicKey,
-		unbroadcasted_batch_funding_txid: Option<Txid>,
+		&self, channel_id: ChannelId, counterparty_node_id: PublicKey, funding_txo: OutPoint,
+		user_channel_id: u128, unbroadcasted_batch_funding_txid: Option<Txid>,
 		update_actions: Vec<MonitorUpdateCompletionAction>,
 		htlc_forwards: Option<PerSourcePendingForward>,
 		decode_update_add_htlcs: Option<(u64, Vec<msgs::UpdateAddHTLC>)>,
@@ -9660,7 +9662,13 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			};
 			self.fail_htlc_backwards_internal(&failure.0, &failure.1, &failure.2, receiver, None);
 		}
-		self.prune_persisted_inbound_htlc_onions(committed_outbound_htlc_sources);
+		self.prune_persisted_inbound_htlc_onions(
+			channel_id,
+			counterparty_node_id,
+			funding_txo,
+			user_channel_id,
+			committed_outbound_htlc_sources,
+		);
 	}
 
 	fn handle_monitor_update_completion_actions<
@@ -10129,6 +10137,8 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			PostMonitorUpdateChanResume::Unblocked {
 				channel_id: chan_id,
 				counterparty_node_id,
+				funding_txo: chan.funding_outpoint(),
+				user_channel_id: chan.context.get_user_id(),
 				unbroadcasted_batch_funding_txid,
 				update_actions,
 				htlc_forwards,
@@ -10144,7 +10154,9 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 	/// HTLC set on `ChannelManager` read. If an HTLC has been irrevocably forwarded to the outbound
 	/// edge, we no longer need to persist the inbound edge's onion and can prune it here.
 	fn prune_persisted_inbound_htlc_onions(
-		&self, committed_outbound_htlc_sources: Vec<(HTLCPreviousHopData, u64)>,
+		&self, outbound_channel_id: ChannelId, outbound_node_id: PublicKey,
+		outbound_funding_txo: OutPoint, outbound_user_channel_id: u128,
+		committed_outbound_htlc_sources: Vec<(HTLCPreviousHopData, u64)>,
 	) {
 		let per_peer_state = self.per_peer_state.read().unwrap();
 		for (source, outbound_amt_msat) in committed_outbound_htlc_sources {
@@ -10161,7 +10173,17 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			if let Some(chan) =
 				peer_state.channel_by_id.get_mut(&source.channel_id).and_then(|c| c.as_funded_mut())
 			{
-				chan.prune_inbound_htlc_onion(source.htlc_id, &source, outbound_amt_msat);
+				chan.prune_inbound_htlc_onion(
+					source.htlc_id,
+					&source,
+					OutboundHop {
+						amt_msat: outbound_amt_msat,
+						channel_id: outbound_channel_id,
+						node_id: outbound_node_id,
+						funding_txo: outbound_funding_txo,
+						user_channel_id: outbound_user_channel_id,
+					},
+				);
 			}
 		}
 	}
@@ -10217,6 +10239,8 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			PostMonitorUpdateChanResume::Unblocked {
 				channel_id,
 				counterparty_node_id,
+				funding_txo,
+				user_channel_id,
 				unbroadcasted_batch_funding_txid,
 				update_actions,
 				htlc_forwards,
@@ -10228,6 +10252,8 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 				self.post_monitor_update_unlock(
 					channel_id,
 					counterparty_node_id,
+					funding_txo,
+					user_channel_id,
 					unbroadcasted_batch_funding_txid,
 					update_actions,
 					htlc_forwards,