gossip: Implement NetworkGraph::node_failed_permanent

The original method, `NetworkGraph::node_failed` was not yet
implemented. Since `Scorer` is responsible for handling non-permanent
node failures, we've changed the method name here to indicate we handle
just permanent failures by removing a node (and related channels) from
the graph local storage.

Author: dunxen

lightning/src/routing/gossip.rs

@@ -269,7 +269,7 @@ impl<L: Deref> EventHandler for NetworkGraph<L> where L::Target: Logger {
 					NetworkUpdate::NodeFailure { ref node_id, is_permanent } => {
 						let action = if is_permanent { "Removing" } else { "Disabling" };
 						log_debug!(self.logger, "{} node graph entry for {} due to a payment failure.", action, node_id);
-						self.node_failed(node_id, is_permanent);
+						if is_permanent { self.node_failed_permanent(node_id); }
 					},
 				}
 			}
@@ -1522,12 +1522,27 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
 		}
 	}
 
-	/// Marks a node in the graph as failed.
-	pub fn node_failed(&self, _node_id: &PublicKey, is_permanent: bool) {
-		if is_permanent {
-			// TODO: Wholly remove the node
-		} else {
-			// TODO: downgrade the node
+	/// Marks a node in the graph as permanently failed, effectively removing it and its channels
+	/// from local storage.
+	pub fn node_failed_permanent(&self, node_id: &PublicKey) {
+		let node_id = NodeId::from_pubkey(node_id);
+		let mut nodes = self.nodes.write().unwrap();
+		let mut channels = self.channels.write().unwrap();
+
+		let mut scids_to_remove = Vec::new();
+		for (scid, info) in channels.iter_mut() {
+			if info.node_one == node_id || info.node_two == node_id {
+				scids_to_remove.push(*scid);
+			}
+		}
+		nodes.remove(&node_id);
+
+		if !scids_to_remove.is_empty() {
+			// TODO: Use BTreeMap::retain when our MSRV is >= 1.53.
+			for scid in scids_to_remove {
+				let info = channels.remove(&scid).expect("We just accessed this scid, it should be present");
+				Self::remove_channel_in_nodes(&mut nodes, &info, scid);
+			}
 		}
 	}