refactor hashmap to channelliquidities struct

Wrap the liquidities hash map into a struct so that decay and serialization functionality can be attached. This allows external data to be serialized into this struct and decayed to make it comparable and mergeable.

Author: joostjager

lightning/src/routing/scoring.rs

@@ -474,7 +474,63 @@ where L::Target: Logger {
 	decay_params: ProbabilisticScoringDecayParameters,
 	network_graph: G,
 	logger: L,
-	channel_liquidities: HashMap<u64, ChannelLiquidity>,
+	channel_liquidities: ChannelLiquidities,
+}
+/// ChannelLiquidities contains live and historical liquidity bounds for each channel.
+pub struct ChannelLiquidities(HashMap<u64, ChannelLiquidity>);
+
+impl ChannelLiquidities {
+	fn new() -> Self {
+		Self(new_hash_map())
+	}
+
+	fn time_passed(&mut self, duration_since_epoch: Duration, decay_params: ProbabilisticScoringDecayParameters) {
+		self.0.retain(|_scid, liquidity| {
+			liquidity.min_liquidity_offset_msat =
+				liquidity.decayed_offset(liquidity.min_liquidity_offset_msat, duration_since_epoch, decay_params);
+			liquidity.max_liquidity_offset_msat =
+				liquidity.decayed_offset(liquidity.max_liquidity_offset_msat, duration_since_epoch, decay_params);
+			liquidity.last_updated = duration_since_epoch;
+
+			// TODO: Call decay multiple times.
+			let elapsed_time =
+				duration_since_epoch.saturating_sub(liquidity.offset_history_last_updated);
+			if elapsed_time > decay_params.historical_no_updates_half_life {
+				let half_life = decay_params.historical_no_updates_half_life.as_secs_f64();
+				if half_life != 0.0 {
+					liquidity.liquidity_history.decay_buckets(elapsed_time.as_secs_f64() / half_life);
+					liquidity.offset_history_last_updated = duration_since_epoch;
+				}
+			}
+			liquidity.min_liquidity_offset_msat != 0 || liquidity.max_liquidity_offset_msat != 0 ||
+				liquidity.liquidity_history.has_datapoints()
+		});
+	}
+}
+
+impl Deref for ChannelLiquidities {
+	type Target = HashMap<u64, ChannelLiquidity>;
+	
+	fn deref(&self) -> &Self::Target {
+		&self.0
+	}
+}
+
+impl DerefMut for ChannelLiquidities {
+	fn deref_mut(&mut self) -> &mut Self::Target {
+		&mut self.0
+	}
+}
+
+impl Readable for ChannelLiquidities {
+	#[inline]
+	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+		let mut channel_liquidities = new_hash_map();
+		read_tlv_fields!(r, {
+			(0, channel_liquidities, required),
+		});
+		Ok(ChannelLiquidities(channel_liquidities))
+	}
 }
 
 /// Parameters for configuring [`ProbabilisticScorer`].
@@ -804,7 +860,7 @@ impl ProbabilisticScoringDecayParameters {
 /// first node in the ordering of the channel's counterparties. Thus, swapping the two liquidity
 /// offset fields gives the opposite direction.
 #[repr(C)] // Force the fields in memory to be in the order we specify
-struct ChannelLiquidity {
+pub struct ChannelLiquidity {
 	/// Lower channel liquidity bound in terms of an offset from zero.
 	min_liquidity_offset_msat: u64,
 
@@ -849,7 +905,7 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref> ProbabilisticScorer<G, L> whe
 			decay_params,
 			network_graph,
 			logger,
-			channel_liquidities: new_hash_map(),
+			channel_liquidities: ChannelLiquidities::new(),
 		}
 	}
 
@@ -1603,26 +1659,7 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref> ScoreUpdate for Probabilistic
 	}
 
 	fn time_passed(&mut self, duration_since_epoch: Duration) {
-		let decay_params = self.decay_params;
-		self.channel_liquidities.retain(|_scid, liquidity| {
-			liquidity.min_liquidity_offset_msat =
-				liquidity.decayed_offset(liquidity.min_liquidity_offset_msat, duration_since_epoch, decay_params);
-			liquidity.max_liquidity_offset_msat =
-				liquidity.decayed_offset(liquidity.max_liquidity_offset_msat, duration_since_epoch, decay_params);
-			liquidity.last_updated = duration_since_epoch;
-
-			let elapsed_time =
-				duration_since_epoch.saturating_sub(liquidity.offset_history_last_updated);
-			if elapsed_time > decay_params.historical_no_updates_half_life {
-				let half_life = decay_params.historical_no_updates_half_life.as_secs_f64();
-				if half_life != 0.0 {
-					liquidity.liquidity_history.decay_buckets(elapsed_time.as_secs_f64() / half_life);
-					liquidity.offset_history_last_updated = duration_since_epoch;
-				}
-			}
-			liquidity.min_liquidity_offset_msat != 0 || liquidity.max_liquidity_offset_msat != 0 ||
-				liquidity.liquidity_history.has_datapoints()
-		});
+		self.channel_liquidities.time_passed(duration_since_epoch, self.decay_params);
 	}
 }
 
@@ -2079,10 +2116,7 @@ ReadableArgs<(ProbabilisticScoringDecayParameters, G, L)> for ProbabilisticScore
 		r: &mut R, args: (ProbabilisticScoringDecayParameters, G, L)
 	) -> Result<Self, DecodeError> {
 		let (decay_params, network_graph, logger) = args;
-		let mut channel_liquidities = new_hash_map();
-		read_tlv_fields!(r, {
-			(0, channel_liquidities, required),
-		});
+		let channel_liquidities = ChannelLiquidities::read(r)?;
 		Ok(Self {
 			decay_params,
 			network_graph,