cache external pathfinding scores

Save external pathfinding scores in a cache so that they will be
available immediately after a node restart. Otherwise there might be a
time window where new scores need to be downloaded still and the node
operates on local data only.

src/builder.rs

@@ -16,10 +16,12 @@ use crate::event::EventQueue;
 use crate::fee_estimator::OnchainFeeEstimator;
 use crate::gossip::GossipSource;
 use crate::io::sqlite_store::SqliteStore;
-use crate::io::utils::{read_node_metrics, write_node_metrics};
+use crate::io::utils::{
+	read_external_pathfinding_scores_from_cache, read_node_metrics, write_node_metrics,
+};
 use crate::io::vss_store::VssStore;
 use crate::liquidity::LiquiditySource;
-use crate::logger::{log_error, log_info, LdkLogger, LogLevel, LogWriter, Logger};
+use crate::logger::{log_error, log_info, log_trace, LdkLogger, LogLevel, LogWriter, Logger};
 use crate::message_handler::NodeCustomMessageHandler;
 use crate::payment::store::PaymentStore;
 use crate::peer_store::PeerStore;
@@ -1002,6 +1004,21 @@ fn build_with_store_internal(
 
 	let scorer = Arc::new(Mutex::new(CombinedScorer::new(local_scorer)));
 
+	// Restore external pathfinding scores from cache if possible.
+	match read_external_pathfinding_scores_from_cache(Arc::clone(&kv_store), Arc::clone(&logger))
+	{
+		Ok(external_scores) => {
+			scorer.lock().unwrap().merge(external_scores, cur_time);
+			log_trace!(logger, "External scores from cache merged successfully");
+		}
+		Err(e) => {
+			if e.kind() != std::io::ErrorKind::NotFound {
+				log_error!(logger, "Error while reading external scores from cache: {}", e);
+				return Err(BuildError::ReadFailed);
+			}
+		},
+	}
+
 	let scoring_fee_params = ProbabilisticScoringFeeParameters::default();
 	let router = Arc::new(DefaultRouter::new(
 		Arc::clone(&network_graph),

src/io/utils.rs

@@ -23,7 +23,9 @@ use crate::{Error, EventQueue, NodeMetrics, PaymentDetails};
 use lightning::io::Cursor;
 use lightning::ln::msgs::DecodeError;
 use lightning::routing::gossip::NetworkGraph;
-use lightning::routing::scoring::{ProbabilisticScorer, ProbabilisticScoringDecayParameters};
+use lightning::routing::scoring::{
+	ChannelLiquidities, ProbabilisticScorer, ProbabilisticScoringDecayParameters,
+};
 use lightning::util::persist::{
 	KVSTORE_NAMESPACE_KEY_ALPHABET, KVSTORE_NAMESPACE_KEY_MAX_LEN, NETWORK_GRAPH_PERSISTENCE_KEY,
 	NETWORK_GRAPH_PERSISTENCE_PRIMARY_NAMESPACE, NETWORK_GRAPH_PERSISTENCE_SECONDARY_NAMESPACE,
@@ -52,6 +54,8 @@ use std::ops::Deref;
 use std::path::Path;
 use std::sync::Arc;
 
+pub const EXTERNAL_PATHFINDING_SCORES_CACHE_KEY: &str = "external_pathfinding_scores_cache";
+
 /// Generates a random [BIP 39] mnemonic.
 ///
 /// The result may be used to initialize the [`Node`] entropy, i.e., can be given to
@@ -166,6 +170,51 @@ where
 	})
 }
 
+/// Read previously persisted external pathfinding scores from the cache.
+pub(crate) fn read_external_pathfinding_scores_from_cache<L: Deref>(
+	kv_store: Arc<DynStore>, logger: L,
+) -> Result<ChannelLiquidities, std::io::Error>
+where
+	L::Target: LdkLogger,
+{
+	let mut reader = Cursor::new(kv_store.read(
+		SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+		SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+		EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+	)?);
+	ChannelLiquidities::read(&mut reader).map_err(|e| {
+		log_error!(logger, "Failed to deserialize scorer: {}", e);
+		std::io::Error::new(std::io::ErrorKind::InvalidData, "Failed to deserialize Scorer")
+	})
+}
+
+/// Persist external pathfinding scores to the cache.
+pub(crate) fn write_external_pathfinding_scores_to_cache<L: Deref>(
+	kv_store: Arc<DynStore>, data: &ChannelLiquidities, logger: L,
+) -> Result<(), Error>
+where
+	L::Target: LdkLogger,
+{
+	kv_store
+		.write(
+			SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+			SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+			EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			&data.encode(),
+		)
+		.map_err(|e| {
+			log_error!(
+				logger,
+				"Writing data to key {}/{}/{} failed due to: {}",
+				NODE_METRICS_PRIMARY_NAMESPACE,
+				NODE_METRICS_SECONDARY_NAMESPACE,
+				EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+				e
+			);
+			Error::PersistenceFailed
+		})
+}
+
 /// Read previously persisted events from the store.
 pub(crate) fn read_event_queue<L: Deref + Clone>(
 	kv_store: Arc<DynStore>, logger: L,

src/scoring.rs

@@ -4,10 +4,11 @@ use std::{
 	time::{Duration, SystemTime},
 };
 
-use crate::{logger::LdkLogger, NodeMetrics, Scorer};
+use crate::io::utils::write_external_pathfinding_scores_to_cache;
+use crate::logger::LdkLogger;
 use crate::{
-	write_node_metrics, DynStore, Logger, EXTERNAL_PATHFINDING_SCORES_SYNC_INTERVAL,
-	EXTERNAL_PATHFINDING_SCORES_SYNC_TIMEOUT_SECS,
+	write_node_metrics, DynStore, Logger, NodeMetrics, Scorer,
+	EXTERNAL_PATHFINDING_SCORES_SYNC_INTERVAL, EXTERNAL_PATHFINDING_SCORES_SYNC_TIMEOUT_SECS,
 };
 use lightning::{
 	log_error, log_info, log_trace, routing::scoring::ChannelLiquidities, util::ser::Readable,
@@ -78,15 +79,24 @@ async fn sync_external_scores(
 	let mut reader = Cursor::new(body.unwrap());
 	match ChannelLiquidities::read(&mut reader) {
 		Ok(liquidities) => {
+			if let Err(e) = write_external_pathfinding_scores_to_cache(
+				Arc::clone(&kv_store),
+				&liquidities,
+				logger,
+			) {
+				log_error!(logger, "Failed to persist external scores to cache: {}", e);
+			}
+
 			let duration_since_epoch =
 				SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap();
 			scorer.lock().unwrap().merge(liquidities, duration_since_epoch);
 			let mut locked_node_metrics = node_metrics.write().unwrap();
 			locked_node_metrics.latest_pathfinding_scores_sync_timestamp =
 				Some(duration_since_epoch.as_secs());
-			write_node_metrics(&*locked_node_metrics, kv_store, logger).unwrap_or_else(|e| {
-				log_error!(logger, "Persisting node metrics failed: {}", e);
-			});
+			write_node_metrics(&*locked_node_metrics, Arc::clone(&kv_store), logger)
+				.unwrap_or_else(|e| {
+					log_error!(logger, "Persisting node metrics failed: {}", e);
+				});
 			log_trace!(logger, "External scores merged successfully");
 		},
 		Err(e) => {