Allow nodes to be avoided during pathfinding

Users may want to - for whatever reasons - prevent payments to be routed
over certain nodes. This change therefore allows to add `NodeId`s to a
list of banned nodes, which then will be avoided during path finding.

Author: tnull

lightning/src/routing/router.rs

@@ -1878,7 +1878,7 @@ mod tests {
 	use routing::router::{get_route, build_route_from_hops_internal, add_random_cltv_offset, default_node_features,
 		PaymentParameters, Route, RouteHint, RouteHintHop, RouteHop, RoutingFees,
 		DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA, MAX_PATH_LENGTH_ESTIMATE};
-	use routing::scoring::{ChannelUsage, Score};
+	use routing::scoring::{ChannelUsage, Score, ProbabilisticScorer, ProbabilisticScoringParameters};
 	use chain::transaction::OutPoint;
 	use chain::keysinterface::KeysInterface;
 	use ln::features::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
@@ -5713,6 +5713,33 @@ mod tests {
 			}
 		}
 	}
+
+	#[test]
+	fn avoids_banned_nodes() {
+		let (secp_ctx, network_graph, _, _, logger) = build_line_graph();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+
+		let keys_manager = test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+
+		let scorer_params = ProbabilisticScoringParameters::default();
+		let mut scorer = ProbabilisticScorer::new(scorer_params, Arc::clone(&network_graph), Arc::clone(&logger));
+
+		// First check we can get a route.
+		let payment_params = PaymentParameters::from_node_id(nodes[10]);
+		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes);
+		assert!(route.is_ok());
+
+		// Then check that we can't get a route if we ban an intermediate node.
+		scorer.add_banned(&NodeId::from_pubkey(&nodes[3]));
+		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes);
+		assert!(route.is_err());
+
+		// Finally make sure we can route again, when we remove the ban.
+		scorer.remove_banned(&NodeId::from_pubkey(&nodes[3]));
+		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes);
+		assert!(route.is_ok());
+	}
 }
 
 #[cfg(all(test, not(feature = "no-std")))]

lightning/src/routing/scoring.rs

@@ -306,7 +306,7 @@ where L::Target: Logger {
 ///
 /// Used to configure base, liquidity, and amount penalties, the sum of which comprises the channel
 /// penalty (i.e., the amount in msats willing to be paid to avoid routing through the channel).
-#[derive(Clone, Copy)]
+#[derive(Clone)]
 pub struct ProbabilisticScoringParameters {
 	/// A fixed penalty in msats to apply to each channel.
 	///
@@ -361,6 +361,11 @@ pub struct ProbabilisticScoringParameters {
 	///
 	/// Default value: 256 msat
 	pub amount_penalty_multiplier_msat: u64,
+
+	/// A list of nodes that won't be considered during path finding.
+	///
+	/// (C-not exported)
+	pub banned_nodes: HashSet<NodeId>,
 }
 
 /// Accounting for channel liquidity balance uncertainty.
@@ -451,6 +456,22 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> ProbabilisticScorerU
 		}
 		None
 	}
+
+	/// Marks the node with the given `node_id` as banned, i.e.,
+	/// it will be avoided during path finding.
+	pub fn add_banned(&mut self, node_id: &NodeId) {
+		self.params.banned_nodes.insert(*node_id);
+	}
+
+	/// Removes the node with the given `node_id` from the list of nodes to avoid.
+	pub fn remove_banned(&mut self, node_id: &NodeId) {
+		self.params.banned_nodes.remove(node_id);
+	}
+
+	/// Clears the list of nodes that are avoided during path finding.
+	pub fn clear_banned(&mut self) {
+		self.params.banned_nodes = HashSet::new();
+	}
 }
 
 impl ProbabilisticScoringParameters {
@@ -461,6 +482,15 @@ impl ProbabilisticScoringParameters {
 			liquidity_penalty_multiplier_msat: 0,
 			liquidity_offset_half_life: Duration::from_secs(3600),
 			amount_penalty_multiplier_msat: 0,
+			banned_nodes: HashSet::new(),
+		}
+	}
+
+	/// Marks all nodes in the given list as banned, i.e.,
+	/// they will be avoided during path finding.
+	pub fn add_banned_from_list(&mut self, node_ids: Vec<NodeId>) {
+		for id in node_ids {
+			self.banned_nodes.insert(id);
 		}
 	}
 }
@@ -472,6 +502,7 @@ impl Default for ProbabilisticScoringParameters {
 			liquidity_penalty_multiplier_msat: 40_000,
 			liquidity_offset_half_life: Duration::from_secs(3600),
 			amount_penalty_multiplier_msat: 256,
+			banned_nodes: HashSet::new(),
 		}
 	}
 }
@@ -543,7 +574,7 @@ const AMOUNT_PENALTY_DIVISOR: u64 = 1 << 20;
 impl<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> DirectedChannelLiquidity<L, T, U> {
 	/// Returns a penalty for routing the given HTLC `amount_msat` through the channel in this
 	/// direction.
-	fn penalty_msat(&self, amount_msat: u64, params: ProbabilisticScoringParameters) -> u64 {
+	fn penalty_msat(&self, amount_msat: u64, params: &ProbabilisticScoringParameters) -> u64 {
 		let max_liquidity_msat = self.max_liquidity_msat();
 		let min_liquidity_msat = core::cmp::min(self.min_liquidity_msat(), max_liquidity_msat);
 		if amount_msat <= min_liquidity_msat {
@@ -580,7 +611,7 @@ impl<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> DirectedChannelLiqui
 	#[inline(always)]
 	fn combined_penalty_msat(
 		&self, amount_msat: u64, negative_log10_times_2048: u64,
-		params: ProbabilisticScoringParameters
+		params: &ProbabilisticScoringParameters
 	) -> u64 {
 		let liquidity_penalty_msat = {
 			// Upper bound the liquidity penalty to ensure some channel is selected.
@@ -672,6 +703,10 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> Score for Probabilis
 	fn channel_penalty_msat(
 		&self, short_channel_id: u64, source: &NodeId, target: &NodeId, usage: ChannelUsage
 	) -> u64 {
+		if self.params.banned_nodes.contains(source) || self.params.banned_nodes.contains(target) {
+			return u64::max_value();
+		}
+
 		if let EffectiveCapacity::ExactLiquidity { liquidity_msat } = usage.effective_capacity {
 			if usage.amount_msat > liquidity_msat {
 				return u64::max_value();
@@ -688,7 +723,7 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> Score for Probabilis
 			.get(&short_channel_id)
 			.unwrap_or(&ChannelLiquidity::new())
 			.as_directed(source, target, capacity_msat, liquidity_offset_half_life)
-			.penalty_msat(amount_msat, self.params)
+			.penalty_msat(amount_msat, &self.params)
 	}
 
 	fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
@@ -1072,7 +1107,7 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> Writeable for Probab
 	#[inline]
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 		write_tlv_fields!(w, {
-			(0, self.channel_liquidities, required)
+			(0, self.channel_liquidities, required),
 		});
 		Ok(())
 	}
@@ -1087,7 +1122,7 @@ ReadableArgs<(ProbabilisticScoringParameters, G, L)> for ProbabilisticScorerUsin
 		let (params, network_graph, logger) = args;
 		let mut channel_liquidities = HashMap::new();
 		read_tlv_fields!(r, {
-			(0, channel_liquidities, required)
+			(0, channel_liquidities, required),
 		});
 		Ok(Self {
 			params,
@@ -1862,7 +1897,7 @@ mod tests {
 			liquidity_offset_half_life: Duration::from_secs(10),
 			..ProbabilisticScoringParameters::zero_penalty()
 		};
-		let mut scorer = ProbabilisticScorer::new(params, &network_graph, &logger);
+		let mut scorer = ProbabilisticScorer::new(params.clone(), &network_graph, &logger);
 		let source = source_node_id();
 		let target = target_node_id();
 		let usage = ChannelUsage {
@@ -1898,7 +1933,7 @@ mod tests {
 			liquidity_offset_half_life: Duration::from_secs(10),
 			..ProbabilisticScoringParameters::zero_penalty()
 		};
-		let mut scorer = ProbabilisticScorer::new(params, &network_graph, &logger);
+		let mut scorer = ProbabilisticScorer::new(params.clone(), &network_graph, &logger);
 		let source = source_node_id();
 		let target = target_node_id();
 		let usage = ChannelUsage {
@@ -2086,7 +2121,7 @@ mod tests {
 		let logger = TestLogger::new();
 		let network_graph = network_graph(&logger);
 		let params = ProbabilisticScoringParameters::default();
-		let scorer = ProbabilisticScorer::new(params, &network_graph, &logger);
+		let scorer = ProbabilisticScorer::new(params.clone(), &network_graph, &logger);
 		let source = source_node_id();
 		let target = target_node_id();