Add source and target nodes to routing::Score

Expand routing::Score::channel_penalty_msat to include the source and
target node ids of the channel. This allows scorers to avoid certain
nodes altogether if desired.

Author: jkczyz

lightning/src/routing/mod.rs

@@ -13,10 +13,13 @@ pub mod network_graph;
 pub mod router;
 pub mod scorer;
 
+use routing::network_graph::NodeId;
+
 /// An interface used to score payment channels for path finding.
 ///
 ///	Scoring is in terms of fees willing to be paid in order to avoid routing through a channel.
 pub trait Score {
-	/// Returns the fee in msats willing to be paid to avoid routing through the given channel.
-	fn channel_penalty_msat(&self, short_channel_id: u64) -> u64;
+	/// Returns the fee in msats willing to be paid to avoid routing through the given channel
+	/// in the direction from `source` to `target`.
+	fn channel_penalty_msat(&self, short_channel_id: u64, source: &NodeId, target: &NodeId) -> u64;
 }

lightning/src/routing/router.rs

@@ -748,7 +748,7 @@ where L::Target: Logger {
 							}
 
 							let path_penalty_msat = $next_hops_path_penalty_msat
-								.checked_add(scorer.channel_penalty_msat($chan_id.clone()))
+								.checked_add(scorer.channel_penalty_msat($chan_id.clone(), &$src_node_id, &$dest_node_id))
 								.unwrap_or_else(|| u64::max_value());
 							let new_graph_node = RouteGraphNode {
 								node_id: $src_node_id,
@@ -973,15 +973,17 @@ where L::Target: Logger {
 						_ => aggregate_next_hops_fee_msat.checked_add(999).unwrap_or(u64::max_value())
 					}) { Some( val / 1000 ) } else { break; }; // converting from msat or breaking if max ~ infinity
 
+					let src_node_id = NodeId::from_pubkey(&hop.src_node_id);
+					let dest_node_id = NodeId::from_pubkey(&prev_hop_id);
 					aggregate_next_hops_path_penalty_msat = aggregate_next_hops_path_penalty_msat
-						.checked_add(scorer.channel_penalty_msat(hop.short_channel_id))
+						.checked_add(scorer.channel_penalty_msat(hop.short_channel_id, &src_node_id, &dest_node_id))
 						.unwrap_or_else(|| u64::max_value());
 
 					// We assume that the recipient only included route hints for routes which had
 					// sufficient value to route `final_value_msat`. Note that in the case of "0-value"
 					// invoices where the invoice does not specify value this may not be the case, but
 					// better to include the hints than not.
-					if !add_entry!(hop.short_channel_id, NodeId::from_pubkey(&hop.src_node_id), NodeId::from_pubkey(&prev_hop_id), directional_info, reqd_channel_cap, &empty_channel_features, aggregate_next_hops_fee_msat, path_value_msat, aggregate_next_hops_path_htlc_minimum_msat, aggregate_next_hops_path_penalty_msat) {
+					if !add_entry!(hop.short_channel_id, src_node_id, dest_node_id, directional_info, reqd_channel_cap, &empty_channel_features, aggregate_next_hops_fee_msat, path_value_msat, aggregate_next_hops_path_htlc_minimum_msat, aggregate_next_hops_path_penalty_msat) {
 						// 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
@@ -1322,7 +1324,8 @@ where L::Target: Logger {
 
 #[cfg(test)]
 mod tests {
-	use routing::network_graph::{NetworkGraph, NetGraphMsgHandler};
+	use routing;
+	use routing::network_graph::{NetworkGraph, NetGraphMsgHandler, NodeId};
 	use routing::router::{get_route, Route, RouteHint, RouteHintHop, RouteHop, RoutingFees};
 	use routing::scorer::Scorer;
 	use chain::transaction::OutPoint;
@@ -4377,6 +4380,68 @@ mod tests {
 		assert_eq!(path, vec![2, 4, 7, 10]);
 	}
 
+	struct BadChannelScorer {
+		short_channel_id: u64,
+	}
+
+	impl routing::Score for BadChannelScorer {
+		fn channel_penalty_msat(&self, short_channel_id: u64, _source: &NodeId, _target: &NodeId) -> u64 {
+			if short_channel_id == self.short_channel_id { u64::max_value() } else { 0 }
+		}
+	}
+
+	struct BadNodeScorer {
+		node_id: NodeId,
+	}
+
+	impl routing::Score for BadNodeScorer {
+		fn channel_penalty_msat(&self, _short_channel_id: u64, _source: &NodeId, target: &NodeId) -> u64 {
+			if *target == self.node_id { u64::max_value() } else { 0 }
+		}
+	}
+
+	#[test]
+	fn avoids_routing_through_bad_channels_and_nodes() {
+		let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+
+		// A path to nodes[6] exists when no penalties are applied to any channel.
+		let scorer = Scorer::new(0);
+		let route = get_route(
+			&our_id, &net_graph_msg_handler.network_graph, &nodes[6], None, None,
+			&last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger), &scorer
+		).unwrap();
+		let path = route.paths[0].iter().map(|hop| hop.short_channel_id).collect::<Vec<_>>();
+
+		assert_eq!(route.get_total_fees(), 100);
+		assert_eq!(route.get_total_amount(), 100);
+		assert_eq!(path, vec![2, 4, 6, 11, 8]);
+
+		// A different path to nodes[6] exists if channel 6 cannot be routed over.
+		let scorer = BadChannelScorer { short_channel_id: 6 };
+		let route = get_route(
+			&our_id, &net_graph_msg_handler.network_graph, &nodes[6], None, None,
+			&last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger), &scorer
+		).unwrap();
+		let path = route.paths[0].iter().map(|hop| hop.short_channel_id).collect::<Vec<_>>();
+
+		assert_eq!(route.get_total_fees(), 300);
+		assert_eq!(route.get_total_amount(), 100);
+		assert_eq!(path, vec![2, 4, 7, 10]);
+
+		// A path to nodes[6] does not exist if nodes[2] cannot be routed through.
+		let scorer = BadNodeScorer { node_id: NodeId::from_pubkey(&nodes[2]) };
+		match get_route(
+			&our_id, &net_graph_msg_handler.network_graph, &nodes[6], None, None,
+			&last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger), &scorer
+		) {
+			Err(LightningError { err, .. } ) => {
+				assert_eq!(err, "Failed to find a path to the given destination");
+			},
+			Ok(_) => panic!("Expected error"),
+		}
+	}
+
 	#[test]
 	fn total_fees_single_path() {
 		let route = Route {

lightning/src/routing/scorer.rs

@@ -44,6 +44,8 @@
 
 use routing;
 
+use routing::network_graph::NodeId;
+
 /// [`routing::Score`] implementation that provides reasonable default behavior.
 ///
 /// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
@@ -71,5 +73,9 @@ impl Default for Scorer {
 }
 
 impl routing::Score for Scorer {
-	fn channel_penalty_msat(&self, _short_channel_id: u64) -> u64 { self.base_penalty_msat }
+	fn channel_penalty_msat(
+		&self, _short_channel_id: u64, _source: &NodeId, _target: &NodeId
+	) -> u64 {
+		self.base_penalty_msat
+	}
 }