Abide by route hint max_htlc in pathfinding

Author: valentinewallace

lightning/src/routing/gossip.rs

@@ -1033,6 +1033,11 @@ pub enum EffectiveCapacity {
 	/// A capacity sufficient to route any payment, typically used for private channels provided by
 	/// an invoice.
 	Infinite,
+	/// The maximum HTLC amount as provided by an invoice route hint.
+	HintMaxHTLC {
+		/// The maximum HTLC amount denominated in millisatoshi.
+		amount_msat: u64,
+	},
 	/// A capacity that is unknown possibly because either the chain state is unavailable to know
 	/// the total capacity or the `htlc_maximum_msat` was not advertised on the gossip network.
 	Unknown,
@@ -1049,6 +1054,7 @@ impl EffectiveCapacity {
 			EffectiveCapacity::ExactLiquidity { liquidity_msat } => *liquidity_msat,
 			EffectiveCapacity::AdvertisedMaxHTLC { amount_msat } => *amount_msat,
 			EffectiveCapacity::Total { capacity_msat, .. } => *capacity_msat,
+			EffectiveCapacity::HintMaxHTLC { amount_msat } => *amount_msat,
 			EffectiveCapacity::Infinite => u64::max_value(),
 			EffectiveCapacity::Unknown => UNKNOWN_CHANNEL_CAPACITY_MSAT,
 		}

lightning/src/routing/router.rs

@@ -951,7 +951,10 @@ impl<'a> CandidateRouteHop<'a> {
 				liquidity_msat: details.next_outbound_htlc_limit_msat,
 			},
 			CandidateRouteHop::PublicHop { info, .. } => info.effective_capacity(),
-			CandidateRouteHop::PrivateHop { .. } => EffectiveCapacity::Infinite,
+			CandidateRouteHop::PrivateHop { hint: RouteHintHop { htlc_maximum_msat: Some(max), .. }} =>
+				EffectiveCapacity::HintMaxHTLC { amount_msat: *max },
+			CandidateRouteHop::PrivateHop { hint: RouteHintHop { htlc_maximum_msat: None, .. }} =>
+				EffectiveCapacity::Infinite,
 		}
 	}
 }
@@ -965,6 +968,9 @@ fn max_htlc_from_capacity(capacity: EffectiveCapacity, max_channel_saturation_po
 		EffectiveCapacity::Unknown => EffectiveCapacity::Unknown.as_msat(),
 		EffectiveCapacity::AdvertisedMaxHTLC { amount_msat } =>
 			amount_msat.checked_shr(saturation_shift).unwrap_or(0),
+		// Treat htlc_maximum_msat from a route hint as an exact liquidity amount, since the invoice is
+		// expected to have been generated from up-to-date capacity information.
+		EffectiveCapacity::HintMaxHTLC { amount_msat } => amount_msat,
 		EffectiveCapacity::Total { capacity_msat, htlc_maximum_msat } =>
 			cmp::min(capacity_msat.checked_shr(saturation_shift).unwrap_or(0), htlc_maximum_msat),
 	}
@@ -1835,8 +1841,8 @@ where L::Target: Logger {
 
 					if !add_entry!(candidate, source, target, aggregate_next_hops_fee_msat,
 								path_value_msat, aggregate_next_hops_path_htlc_minimum_msat,
-								aggregate_next_hops_path_penalty_msat,
-								aggregate_next_hops_cltv_delta, aggregate_next_hops_path_length) {
+								aggregate_next_hops_path_penalty_msat, aggregate_next_hops_cltv_delta,
+								aggregate_next_hops_path_length) {
 						// If this hop was not used then there is no use checking the preceding
 						// hops in the RouteHint. We can break by just searching for a direct
 						// channel between last checked hop and first_hop_targets.
@@ -1863,14 +1869,15 @@ where L::Target: Logger {
 						.saturating_add(1);
 
 					// Searching for a direct channel between last checked hop and first_hop_targets
+					let hint_candidate_contribution_msat = cmp::min(path_value_msat,
+						candidate.effective_capacity().as_msat().saturating_sub(used_liquidity_msat));
 					if let Some(first_channels) = first_hop_targets.get(&NodeId::from_pubkey(&prev_hop_id)) {
 						for details in first_channels {
-							let candidate = CandidateRouteHop::FirstHop { details };
-							add_entry!(candidate, our_node_id, NodeId::from_pubkey(&prev_hop_id),
-								aggregate_next_hops_fee_msat, path_value_msat,
-								aggregate_next_hops_path_htlc_minimum_msat,
-								aggregate_next_hops_path_penalty_msat, aggregate_next_hops_cltv_delta,
-								aggregate_next_hops_path_length);
+							let first_hop_candidate = CandidateRouteHop::FirstHop { details };
+							add_entry!(first_hop_candidate, our_node_id, NodeId::from_pubkey(&prev_hop_id),
+								aggregate_next_hops_fee_msat, hint_candidate_contribution_msat,
+								aggregate_next_hops_path_htlc_minimum_msat, aggregate_next_hops_path_penalty_msat,
+								aggregate_next_hops_cltv_delta, aggregate_next_hops_path_length);
 						}
 					}
 
@@ -1905,10 +1912,11 @@ where L::Target: Logger {
 						// path.
 						if let Some(first_channels) = first_hop_targets.get(&NodeId::from_pubkey(&hop.src_node_id)) {
 							for details in first_channels {
-								let candidate = CandidateRouteHop::FirstHop { details };
-								add_entry!(candidate, our_node_id,
+								let first_hop_candidate = CandidateRouteHop::FirstHop { details };
+								add_entry!(first_hop_candidate, our_node_id,
 									NodeId::from_pubkey(&hop.src_node_id),
-									aggregate_next_hops_fee_msat, path_value_msat,
+									aggregate_next_hops_fee_msat,
+									hint_candidate_contribution_msat,
 									aggregate_next_hops_path_htlc_minimum_msat,
 									aggregate_next_hops_path_penalty_msat,
 									aggregate_next_hops_cltv_delta,
@@ -5906,6 +5914,119 @@ mod tests {
 		assert!(route.is_ok());
 	}
 
+	#[test]
+	fn abide_by_route_hint_max_htlc() {
+		// Check that we abide by any htlc_maximum_msat provided in the route hints of the payment
+		// params in the final route.
+		let (secp_ctx, network_graph, _, _, logger) = build_graph();
+		let netgraph = network_graph.read_only();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+		let config = UserConfig::default();
+
+		let max_htlc_msat = 50_000;
+		let route_hint_1 = RouteHint(vec![RouteHintHop {
+			src_node_id: nodes[2],
+			short_channel_id: 42,
+			fees: RoutingFees {
+				base_msat: 100,
+				proportional_millionths: 0,
+			},
+			cltv_expiry_delta: 10,
+			htlc_minimum_msat: None,
+			htlc_maximum_msat: Some(max_htlc_msat),
+		}]);
+		let dest_node_id = ln_test_utils::pubkey(42);
+		let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
+			.with_route_hints(vec![route_hint_1.clone()]).unwrap()
+			.with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+
+		// Make sure we'll error if our route hints don't have enough liquidity according to their
+		// htlc_maximum_msat.
+		if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id,
+			&payment_params, &netgraph, None, max_htlc_msat + 1, Arc::clone(&logger), &scorer, &(),
+			&random_seed_bytes)
+		{
+			assert_eq!(err, "Failed to find a sufficient route to the given destination");
+		} else { panic!(); }
+
+		// Make sure we'll split an MPP payment across route hints if their htlc_maximum_msat warrants.
+		let mut route_hint_2 = route_hint_1.clone();
+		route_hint_2.0[0].short_channel_id = 43;
+		let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
+			.with_route_hints(vec![route_hint_1, route_hint_2]).unwrap()
+			.with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+		let route = get_route(&our_id, &payment_params, &netgraph, None, max_htlc_msat + 1,
+			Arc::clone(&logger), &scorer, &(), &random_seed_bytes).unwrap();
+		assert_eq!(route.paths.len(), 2);
+		assert!(route.paths[0].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert!(route.paths[1].hops.last().unwrap().fee_msat <= max_htlc_msat);
+	}
+
+	#[test]
+	fn direct_channel_to_hints_with_max_htlc() {
+		// Check that if we have a first hop channel peer that's connected to multiple provided route
+		// hints, that we properly split the payment between the route hints if needed.
+		let logger = Arc::new(ln_test_utils::TestLogger::new());
+		let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+		let config = UserConfig::default();
+
+		let our_node_id = ln_test_utils::pubkey(42);
+		let intermed_node_id = ln_test_utils::pubkey(43);
+		let first_hop = vec![get_channel_details(Some(42), intermed_node_id, InitFeatures::from_le_bytes(vec![0b11]), 10_000_000)];
+
+		let amt_msat = 900_000;
+		let max_htlc_msat = 500_000;
+		let route_hint_1 = RouteHint(vec![RouteHintHop {
+			src_node_id: intermed_node_id,
+			short_channel_id: 44,
+			fees: RoutingFees {
+				base_msat: 100,
+				proportional_millionths: 0,
+			},
+			cltv_expiry_delta: 10,
+			htlc_minimum_msat: None,
+			htlc_maximum_msat: Some(max_htlc_msat),
+		}]);
+		let mut route_hint_2 = route_hint_1.clone();
+		route_hint_2.0[0].short_channel_id = 45;
+		route_hint_2.0[0].htlc_maximum_msat = Some(max_htlc_msat);
+		let dest_node_id = ln_test_utils::pubkey(44);
+		let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
+			.with_route_hints(vec![route_hint_1, route_hint_2]).unwrap()
+			.with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+
+		let route = get_route(&our_node_id, &payment_params, &network_graph.read_only(),
+			Some(&first_hop.iter().collect::<Vec<_>>()), amt_msat, Arc::clone(&logger), &scorer, &(),
+			&random_seed_bytes).unwrap();
+		assert_eq!(route.paths.len(), 2);
+		assert!(route.paths[0].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert!(route.paths[1].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert_eq!(route.get_total_amount(), amt_msat);
+
+		// Re-run but with two first hop channels connected to the same route hint peers that must be
+		// split between.
+		let first_hops = vec![
+			get_channel_details(Some(42), intermed_node_id, InitFeatures::from_le_bytes(vec![0b11]), amt_msat - 10),
+			get_channel_details(Some(43), intermed_node_id, InitFeatures::from_le_bytes(vec![0b11]), amt_msat - 10),
+		];
+		let route = get_route(&our_node_id, &payment_params, &network_graph.read_only(),
+			Some(&first_hops.iter().collect::<Vec<_>>()), amt_msat, Arc::clone(&logger), &scorer, &(),
+			&random_seed_bytes).unwrap();
+		// TODO: `get_route` returns a suboptimal route here because first hop channels are not
+		// resorted on the fly when processing route hints.
+		assert_eq!(route.paths.len(), 3);
+		assert!(route.paths[0].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert!(route.paths[1].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert!(route.paths[2].hops.last().unwrap().fee_msat <= max_htlc_msat);
+		assert_eq!(route.get_total_amount(), amt_msat);
+	}
+
 	#[test]
 	fn blinded_route_ser() {
 		let blinded_path_1 = BlindedPath {

lightning/src/routing/scoring.rs

@@ -1243,8 +1243,10 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> Score for Probabilis
 
 		let mut anti_probing_penalty_msat = 0;
 		match usage.effective_capacity {
-			EffectiveCapacity::ExactLiquidity { liquidity_msat } => {
-				if usage.amount_msat > liquidity_msat {
+			EffectiveCapacity::ExactLiquidity { liquidity_msat: amount_msat } |
+				EffectiveCapacity::HintMaxHTLC { amount_msat } =>
+			{
+				if usage.amount_msat > amount_msat {
 					return u64::max_value();
 				} else {
 					return base_penalty_msat;