Add a Metadata type into the ChannelScorer trait

This allows a user to pass the data they are tracking to the
trait's functions and update them whenever NetworkGraph makes
changes. By default, NetworkGraph has a placeholder type of u8.

Author: sourabhmarathe

lightning/src/routing/network_graph.rs

@@ -435,12 +435,15 @@ impl Readable for NodeInfo {
 /// objects can call into them to update the metadata and retrieve a minimum fee penalty when doing the
 /// route-finding algorithm.
 pub trait ChannelScorer {
+	/// Holds information about a given channel that is to be updated when the user wishes to update
+	/// the metadata they are tracking (eg metrics for reliability, uptime, floppiness, etc.)
+	type Metadata;
 	/// Returns penalty fee for a given channel ID based on user's channel metadata
-	fn calculate_minimum_fee_penalty(&self, _channel_id: u64) {}
+	fn calculate_minimum_fee_penalty(&self, _channel_id: u64) -> Option<u64> { None }
 	/// Optional: allows user to count PaymentSent events for channels
-	fn score_payment_success(&self, _route: Vec<Vec<RouteHop>>) {}
+	fn score_payment_success(&self, _route: Vec<Vec<RouteHop>>, _metadata: Vec<Self::Metadata>) {}
 	/// Optional: allows user to count PaymentFailed events for channels
-	fn score_payment_failure(&self, _route: Vec<Vec<RouteHop>>, _faulty_nodes: Vec<PublicKey>) {}
+	fn score_payment_failure(&self, _route: Vec<Vec<RouteHop>>, _faulty_nodes: Vec<PublicKey>, _metadata: Vec<Self::Metadata>) {}
 }
 
 /// Represents the network as nodes and channels between them
@@ -503,7 +506,12 @@ impl std::fmt::Display for NetworkGraph {
 	}
 }
 
-impl ChannelScorer for NetworkGraph {}
+/// By default, just do nothing when scoring channels. A user is free to extend these
+/// definitions to meet their needs.
+impl ChannelScorer for NetworkGraph {
+	/// The default type for Metadata is just a placeholder.
+	type Metadata = Option<u8>;
+}
 
 impl NetworkGraph {
 	/// Returns all known valid channels' short ids along with announced channel info.