Rename manager HTLC forward maps to _legacy

We have an overarching goal of (mostly) getting rid of ChannelManager
persistence and rebuilding the ChannelManager's state from existing
ChannelMonitors, due to issues when the two structs are out-of-sync on restart.
The main issue that can arise is channel force closure.

Soon we'll be reconstructing these now-legacy maps from Channel data (that will
also be included in ChannelMonitors in future work), so rename them as part of
moving towards not needing to persist them in ChannelManager.

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -17200,7 +17200,11 @@ where
 
 		const MAX_ALLOC_SIZE: usize = 1024 * 64;
 		let forward_htlcs_count: u64 = Readable::read(reader)?;
-		let mut forward_htlcs = hash_map_with_capacity(cmp::min(forward_htlcs_count as usize, 128));
+		// This map is read but may no longer be used because we'll attempt to rebuild the set of HTLC
+		// forwards from the `Channel{Monitor}`s instead, as a step towards removing the requirement of
+		// regularly persisting the `ChannelManager`.
+		let mut forward_htlcs_legacy: HashMap<u64, Vec<HTLCForwardInfo>> =
+			hash_map_with_capacity(cmp::min(forward_htlcs_count as usize, 128));
 		for _ in 0..forward_htlcs_count {
 			let short_channel_id = Readable::read(reader)?;
 			let pending_forwards_count: u64 = Readable::read(reader)?;
@@ -17211,7 +17215,7 @@ where
 			for _ in 0..pending_forwards_count {
 				pending_forwards.push(Readable::read(reader)?);
 			}
-			forward_htlcs.insert(short_channel_id, pending_forwards);
+			forward_htlcs_legacy.insert(short_channel_id, pending_forwards);
 		}
 
 		let claimable_htlcs_count: u64 = Readable::read(reader)?;
@@ -17299,12 +17303,18 @@ where
 			};
 		}
 
+		// Some maps are read but may no longer be used because we attempt to rebuild the pending HTLC
+		// set from the `Channel{Monitor}`s instead, as a step towards removing the requirement of
+		// regularly persisting the `ChannelManager`.
+		let mut pending_intercepted_htlcs_legacy: Option<HashMap<InterceptId, PendingAddHTLCInfo>> =
+			Some(new_hash_map());
+		let mut decode_update_add_htlcs_legacy: Option<HashMap<u64, Vec<msgs::UpdateAddHTLC>>> =
+			None;
+
 		// pending_outbound_payments_no_retry is for compatibility with 0.0.101 clients.
 		let mut pending_outbound_payments_no_retry: Option<HashMap<PaymentId, HashSet<[u8; 32]>>> =
 			None;
 		let mut pending_outbound_payments = None;
-		let mut pending_intercepted_htlcs: Option<HashMap<InterceptId, PendingAddHTLCInfo>> =
-			Some(new_hash_map());
 		let mut received_network_pubkey: Option<PublicKey> = None;
 		let mut fake_scid_rand_bytes: Option<[u8; 32]> = None;
 		let mut probing_cookie_secret: Option<[u8; 32]> = None;
@@ -17322,13 +17332,12 @@ where
 		let mut in_flight_monitor_updates: Option<
 			HashMap<(PublicKey, ChannelId), Vec<ChannelMonitorUpdate>>,
 		> = None;
-		let mut decode_update_add_htlcs: Option<HashMap<u64, Vec<msgs::UpdateAddHTLC>>> = None;
 		let mut inbound_payment_id_secret = None;
 		let mut peer_storage_dir: Option<Vec<(PublicKey, Vec<u8>)>> = None;
 		let mut async_receive_offer_cache: AsyncReceiveOfferCache = AsyncReceiveOfferCache::new();
 		read_tlv_fields!(reader, {
 			(1, pending_outbound_payments_no_retry, option),
-			(2, pending_intercepted_htlcs, option),
+			(2, pending_intercepted_htlcs_legacy, option),
 			(3, pending_outbound_payments, option),
 			(4, pending_claiming_payments, option),
 			(5, received_network_pubkey, option),
@@ -17339,13 +17348,14 @@ where
 			(10, legacy_in_flight_monitor_updates, option),
 			(11, probing_cookie_secret, option),
 			(13, claimable_htlc_onion_fields, optional_vec),
-			(14, decode_update_add_htlcs, option),
+			(14, decode_update_add_htlcs_legacy, option),
 			(15, inbound_payment_id_secret, option),
 			(17, in_flight_monitor_updates, option),
 			(19, peer_storage_dir, optional_vec),
 			(21, async_receive_offer_cache, (default_value, async_receive_offer_cache)),
 		});
-		let mut decode_update_add_htlcs = decode_update_add_htlcs.unwrap_or_else(|| new_hash_map());
+		let mut decode_update_add_htlcs_legacy =
+			decode_update_add_htlcs_legacy.unwrap_or_else(|| new_hash_map());
 		let peer_storage_dir: Vec<(PublicKey, Vec<u8>)> = peer_storage_dir.unwrap_or_else(Vec::new);
 		if fake_scid_rand_bytes.is_none() {
 			fake_scid_rand_bytes = Some(args.entropy_source.get_secure_random_bytes());
@@ -17719,12 +17729,12 @@ where
 								// `pending_intercepted_htlcs`, we were apparently not persisted after
 								// the monitor was when forwarding the payment.
 								dedup_decode_update_add_htlcs(
-									&mut decode_update_add_htlcs,
+									&mut decode_update_add_htlcs_legacy,
 									&prev_hop_data,
 									"HTLC was forwarded to the closed channel",
 									&args.logger,
 								);
-								forward_htlcs.retain(|_, forwards| {
+								forward_htlcs_legacy.retain(|_, forwards| {
 									forwards.retain(|forward| {
 										if let HTLCForwardInfo::AddHTLC(htlc_info) = forward {
 											if pending_forward_matches_htlc(&htlc_info) {
@@ -17736,7 +17746,7 @@ where
 									});
 									!forwards.is_empty()
 								});
-								pending_intercepted_htlcs.as_mut().unwrap().retain(|intercepted_id, htlc_info| {
+								pending_intercepted_htlcs_legacy.as_mut().unwrap().retain(|intercepted_id, htlc_info| {
 									if pending_forward_matches_htlc(&htlc_info) {
 										log_info!(logger, "Removing pending intercepted HTLC with hash {} as it was forwarded to the closed channel {}",
 											&htlc.payment_hash, &monitor.channel_id());
@@ -18234,10 +18244,10 @@ where
 
 			inbound_payment_key: expanded_inbound_key,
 			pending_outbound_payments: pending_outbounds,
-			pending_intercepted_htlcs: Mutex::new(pending_intercepted_htlcs.unwrap()),
+			pending_intercepted_htlcs: Mutex::new(pending_intercepted_htlcs_legacy.unwrap()),
 
-			forward_htlcs: Mutex::new(forward_htlcs),
-			decode_update_add_htlcs: Mutex::new(decode_update_add_htlcs),
+			forward_htlcs: Mutex::new(forward_htlcs_legacy),
+			decode_update_add_htlcs: Mutex::new(decode_update_add_htlcs_legacy),
 			claimable_payments: Mutex::new(ClaimablePayments {
 				claimable_payments,
 				pending_claiming_payments: pending_claiming_payments.unwrap(),