Track the last time we received new information about a channel

In the next commit we'll enable users to assign a penalty to
channels which we don't have any recent information for to better
enable probing diversity. In order to do so, we need to actually
track the last time we received new information for a channel,
which we do here.

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -901,6 +901,10 @@ struct ChannelLiquidity {
 	/// Time when the historical liquidity bounds were last modified as an offset against the unix
 	/// epoch.
 	offset_history_last_updated: Duration,
+
+	/// The last time when the liquidity bounds were updated with new payment information (i.e.
+	/// ignoring decays).
+	last_datapoint_time: Duration,
 }
 
 /// A snapshot of [`ChannelLiquidity`] in one direction assuming a certain channel capacity.
@@ -911,6 +915,7 @@ struct DirectedChannelLiquidity<L: Deref<Target = u64>, HT: Deref<Target = Histo
 	capacity_msat: u64,
 	last_updated: T,
 	offset_history_last_updated: T,
+	last_datapoint_time: T,
 }
 
 impl<G: Deref<Target = NetworkGraph<L>>, L: Deref> ProbabilisticScorer<G, L> where L::Target: Logger {
@@ -1153,6 +1158,7 @@ impl ChannelLiquidity {
 			liquidity_history: HistoricalLiquidityTracker::new(),
 			last_updated,
 			offset_history_last_updated: last_updated,
+			last_datapoint_time: last_updated,
 		}
 	}
 
@@ -1185,6 +1191,7 @@ impl ChannelLiquidity {
 			capacity_msat,
 			last_updated: &self.last_updated,
 			offset_history_last_updated: &self.offset_history_last_updated,
+			last_datapoint_time: &self.last_datapoint_time,
 		}
 	}
 
@@ -1208,6 +1215,7 @@ impl ChannelLiquidity {
 			capacity_msat,
 			last_updated: &mut self.last_updated,
 			offset_history_last_updated: &mut self.offset_history_last_updated,
+			last_datapoint_time: &mut self.last_datapoint_time,
 		}
 	}
 
@@ -1554,6 +1562,7 @@ DirectedChannelLiquidity<L, HT, T> {
 			*self.max_liquidity_offset_msat = 0;
 		}
 		*self.last_updated = duration_since_epoch;
+		*self.last_datapoint_time = duration_since_epoch;
 	}
 
 	/// Adjusts the upper bound of the channel liquidity balance in this direction.
@@ -1563,6 +1572,7 @@ DirectedChannelLiquidity<L, HT, T> {
 			*self.min_liquidity_offset_msat = 0;
 		}
 		*self.last_updated = duration_since_epoch;
+		*self.last_datapoint_time = duration_since_epoch;
 	}
 }
 
@@ -2394,6 +2404,7 @@ impl Writeable for ChannelLiquidity {
 			(5, self.liquidity_history.writeable_min_offset_history(), required),
 			(7, self.liquidity_history.writeable_max_offset_history(), required),
 			(9, self.offset_history_last_updated, required),
+			(11, self.last_datapoint_time, required),
 		});
 		Ok(())
 	}
@@ -2410,6 +2421,7 @@ impl Readable for ChannelLiquidity {
 		let mut max_liquidity_offset_history: Option<HistoricalBucketRangeTracker> = None;
 		let mut last_updated = Duration::from_secs(0);
 		let mut offset_history_last_updated = None;
+		let mut last_datapoint_time = None;
 		read_tlv_fields!(r, {
 			(0, min_liquidity_offset_msat, required),
 			(1, legacy_min_liq_offset_history, option),
@@ -2419,6 +2431,7 @@ impl Readable for ChannelLiquidity {
 			(5, min_liquidity_offset_history, option),
 			(7, max_liquidity_offset_history, option),
 			(9, offset_history_last_updated, option),
+			(11, last_datapoint_time, option),
 		});
 
 		if min_liquidity_offset_history.is_none() {
@@ -2443,6 +2456,7 @@ impl Readable for ChannelLiquidity {
 			),
 			last_updated,
 			offset_history_last_updated: offset_history_last_updated.unwrap_or(last_updated),
+			last_datapoint_time: last_datapoint_time.unwrap_or(last_updated),
 		})
 	}
 }
@@ -2616,19 +2630,20 @@ mod tests {
 		let logger = TestLogger::new();
 		let last_updated = Duration::ZERO;
 		let offset_history_last_updated = Duration::ZERO;
+		let last_datapoint_time = Duration::ZERO;
 		let network_graph = network_graph(&logger);
 		let decay_params = ProbabilisticScoringDecayParameters::default();
 		let mut scorer = ProbabilisticScorer::new(decay_params, &network_graph, &logger)
 			.with_channel(42,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100,
-					last_updated, offset_history_last_updated,
+					last_updated, offset_history_last_updated, last_datapoint_time,
 					liquidity_history: HistoricalLiquidityTracker::new(),
 				})
 			.with_channel(43,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100,
-					last_updated, offset_history_last_updated,
+					last_updated, offset_history_last_updated, last_datapoint_time,
 					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
@@ -2695,13 +2710,14 @@ mod tests {
 		let logger = TestLogger::new();
 		let last_updated = Duration::ZERO;
 		let offset_history_last_updated = Duration::ZERO;
+		let last_datapoint_time = Duration::ZERO;
 		let network_graph = network_graph(&logger);
 		let decay_params = ProbabilisticScoringDecayParameters::default();
 		let mut scorer = ProbabilisticScorer::new(decay_params, &network_graph, &logger)
 			.with_channel(42,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400,
-					last_updated, offset_history_last_updated,
+					last_updated, offset_history_last_updated, last_datapoint_time,
 					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
@@ -2755,13 +2771,14 @@ mod tests {
 		let logger = TestLogger::new();
 		let last_updated = Duration::ZERO;
 		let offset_history_last_updated = Duration::ZERO;
+		let last_datapoint_time = Duration::ZERO;
 		let network_graph = network_graph(&logger);
 		let decay_params = ProbabilisticScoringDecayParameters::default();
 		let mut scorer = ProbabilisticScorer::new(decay_params, &network_graph, &logger)
 			.with_channel(42,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400,
-					last_updated, offset_history_last_updated,
+					last_updated, offset_history_last_updated, last_datapoint_time,
 					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
@@ -2867,6 +2884,7 @@ mod tests {
 		let logger = TestLogger::new();
 		let last_updated = Duration::ZERO;
 		let offset_history_last_updated = Duration::ZERO;
+		let last_datapoint_time = Duration::ZERO;
 		let network_graph = network_graph(&logger);
 		let params = ProbabilisticScoringFeeParameters {
 			liquidity_penalty_multiplier_msat: 1_000,
@@ -2880,7 +2898,7 @@ mod tests {
 			.with_channel(42,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 40, max_liquidity_offset_msat: 40,
-					last_updated, offset_history_last_updated,
+					last_updated, offset_history_last_updated, last_datapoint_time,
 					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();