fixup! Implement tiered storage

Route the external pathfinding scores cache through
the ephemeral store, alongside the network graph and
scorer, as it is rebuildable cached data.

Add coverage for writing, reading, and removing the
cache through the ephemeral tier.

Author: enigbe

src/io/tier_store.rs

@@ -18,7 +18,7 @@ use lightning::util::persist::{
 use lightning::{io, log_error};
 use tokio::sync::Mutex as TokioMutex;
 
-use crate::io::utils::check_namespace_key_validity;
+use crate::io::utils::{check_namespace_key_validity, EXTERNAL_PATHFINDING_SCORES_CACHE_KEY};
 use crate::logger::{LdkLogger, Logger};
 use crate::types::DynStore;
 
@@ -605,6 +605,7 @@ fn is_ephemeral_cached_key(pn: &str, sn: &str, key: &str) -> bool {
 		(pn, sn, key),
 		(NETWORK_GRAPH_PERSISTENCE_PRIMARY_NAMESPACE, _, NETWORK_GRAPH_PERSISTENCE_KEY)
 			| (SCORER_PERSISTENCE_PRIMARY_NAMESPACE, _, SCORER_PERSISTENCE_KEY)
+			| (SCORER_PERSISTENCE_PRIMARY_NAMESPACE, _, EXTERNAL_PATHFINDING_SCORES_CACHE_KEY)
 	)
 }
 
@@ -621,7 +622,7 @@ mod tests {
 		CHANNEL_MANAGER_PERSISTENCE_SECONDARY_NAMESPACE,
 		CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
 		CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
-		NETWORK_GRAPH_PERSISTENCE_SECONDARY_NAMESPACE,
+		NETWORK_GRAPH_PERSISTENCE_SECONDARY_NAMESPACE, SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
 	};
 	use lightning_persister::fs_store::v2::FilesystemStoreV2;
 
@@ -779,6 +780,69 @@ mod tests {
 		assert_eq!(primary_read_cm.unwrap(), data);
 	}
 
+	#[tokio::test]
+	async fn external_pathfinding_scores_cache_routes_to_ephemeral_store() {
+		let base_dir = random_storage_path();
+		let log_path = base_dir.join("tier_store_test.log").to_string_lossy().into_owned();
+		let logger = Arc::new(Logger::new_fs_writer(log_path, Level::Trace).unwrap());
+
+		let _cleanup = CleanupDir(base_dir.clone());
+
+		let primary_store: Arc<DynStore> =
+			Arc::new(DynStoreWrapper(FilesystemStoreV2::new(base_dir.join("primary")).unwrap()));
+		let mut tier = setup_tier_store(Arc::clone(&primary_store), logger);
+
+		let ephemeral_store: Arc<DynStore> =
+			Arc::new(DynStoreWrapper(FilesystemStoreV2::new(base_dir.join("ephemeral")).unwrap()));
+		tier.set_ephemeral_store(Arc::clone(&ephemeral_store));
+
+		let data = vec![42u8; 32];
+		tier.write(
+			SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+			SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+			EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			data.clone(),
+		)
+		.await
+		.unwrap();
+
+		assert!(primary_store
+			.read(
+				SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+				SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+				EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			)
+			.await
+			.is_err());
+		assert_eq!(
+			tier.read(
+				SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+				SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+				EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			)
+			.await
+			.unwrap(),
+			data
+		);
+
+		tier.remove(
+			SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+			SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+			EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			false,
+		)
+		.await
+		.unwrap();
+		assert!(ephemeral_store
+			.read(
+				SCORER_PERSISTENCE_PRIMARY_NAMESPACE,
+				SCORER_PERSISTENCE_SECONDARY_NAMESPACE,
+				EXTERNAL_PATHFINDING_SCORES_CACHE_KEY,
+			)
+			.await
+			.is_err());
+	}
+
 	#[tokio::test]
 	async fn list_exposes_primary_and_routed_ephemeral_keys() {
 		let base_dir = random_storage_path();