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/scoring.rs

@@ -300,6 +300,7 @@ where L::Target: Logger {
 	logger: L,
 	// TODO: Remove entries of closed channels.
 	channel_liquidities: HashMap<u64, ChannelLiquidity<T>>,
+	banned_nodes: HashSet<NodeId>,
 }
 
 /// Parameters for configuring [`ProbabilisticScorer`].
@@ -399,6 +400,7 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> ProbabilisticScorerU
 			network_graph,
 			logger,
 			channel_liquidities: HashMap::new(),
+			banned_nodes: HashSet::new(),
 		}
 	}
 
@@ -408,6 +410,22 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref, T: Time> ProbabilisticScorerU
 		self
 	}
 
+	/// 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.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.banned_nodes.remove(node_id);
+	}
+
+	/// Clears the list of nodes that are avoided during path finding.
+	pub fn clear_banned(&mut self) {
+		self.banned_nodes = HashSet::new();
+	}
+
 	/// Dump the contents of this scorer into the configured logger.
 	///
 	/// Note that this writes roughly one line per channel for which we have a liquidity estimate,
@@ -655,6 +673,10 @@ 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.banned_nodes.contains(source) || self.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();
@@ -1055,7 +1077,7 @@ 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(())
 	}
@@ -1070,13 +1092,14 @@ 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,
 			network_graph,
 			logger,
 			channel_liquidities,
+			banned_nodes: HashSet::new(),
 		})
 	}
 }