Expose the node's KV store to applications

src/io/mod.rs

@@ -19,6 +19,8 @@ pub(crate) mod utils;
 #[cfg(feature = "storage-vss")]
 pub mod vss_store;
 
+pub use crate::types::DynStoreRef;
+
 /// The event queue will be persisted under this key.
 pub(crate) const EVENT_QUEUE_PERSISTENCE_PRIMARY_NAMESPACE: &str = "";
 pub(crate) const EVENT_QUEUE_PERSISTENCE_SECONDARY_NAMESPACE: &str = "";

src/lib.rs

@@ -190,8 +190,8 @@ use probing::{run_prober, Prober};
 use runtime::Runtime;
 pub use tokio;
 use types::{
-	Broadcaster, BumpTransactionEventHandler, ChainMonitor, ChannelManager, DynStore, Graph,
-	KeysManager, OnionMessenger, PaymentStore, PeerManager, Router, Scorer, Sweeper, Wallet,
+	Broadcaster, BumpTransactionEventHandler, ChainMonitor, ChannelManager, DynStore, DynStoreRef,
+	Graph, KeysManager, OnionMessenger, PaymentStore, PeerManager, Router, Scorer, Sweeper, Wallet,
 };
 pub use types::{
 	ChannelCounterparty, ChannelDetails, CustomTlvRecord, PeerDetails, ReserveType, UserChannelId,
@@ -982,6 +982,19 @@ impl Node {
 		self.config.as_ref().clone()
 	}
 
+	/// Returns a handle to the [`KVStore`] the [`Node`] persists its state to.
+	///
+	/// This allows applications to persist their own data in the same store as the node, e.g., to
+	/// keep it in the same database and back it up together.
+	///
+	/// **Note:** Applications must only read and write namespaces of their own. Modifying or
+	/// removing any data written by the node itself may lead to loss of funds.
+	///
+	/// [`KVStore`]: lightning::util::persist::KVStore
+	pub fn kv_store(&self) -> DynStoreRef {
+		DynStoreRef(Arc::clone(&self.kv_store))
+	}
+
 	/// Returns the next event in the event queue, if currently available.
 	///
 	/// Will return `Some(..)` if an event is available and `None` otherwise.

src/types.rs

@@ -118,12 +118,16 @@ impl<'a> PaginatedKVStore for dyn DynStoreTrait + 'a {
 
 pub(crate) type DynStore = dyn DynStoreTrait;
 
+/// A handle to the store a [`Node`] persists its state to, as returned by [`Node::kv_store`].
+///
+/// [`Node`]: crate::Node
+/// [`Node::kv_store`]: crate::Node::kv_store
 // Newtype wrapper that implements `KVStore` for `Arc<DynStore>`. This is needed because `KVStore`
 // methods return `impl Future`, which is not object-safe. `DynStoreTrait` works around this by
 // returning `Pin<Box<dyn Future>>` instead, and this wrapper bridges the two by delegating
 // `KVStore` methods to the corresponding `DynStoreTrait::*_async` methods.
 #[derive(Clone)]
-pub(crate) struct DynStoreRef(pub(crate) Arc<DynStore>);
+pub struct DynStoreRef(pub(crate) Arc<DynStore>);
 
 impl KVStore for DynStoreRef {
 	fn read(

tests/integration_tests_rust.rs

@@ -562,6 +562,34 @@ async fn address_pool_is_reloaded_on_restart() {
 	expect_channel_ready_event!(node_b, node_a.node_id());
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn application_data_persists_in_node_kv_store() {
+	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();
+	let chain_source = random_chain_source(&bitcoind, &electrsd);
+	let mut config = random_config();
+	config.store_type = TestStoreType::Sqlite;
+
+	let (primary_namespace, secondary_namespace) = ("app", "data");
+	let node = setup_node(&chain_source, config.clone());
+	let kv_store = node.kv_store();
+	KVStore::write(&kv_store, primary_namespace, secondary_namespace, "key", vec![42; 32])
+		.await
+		.unwrap();
+	node.stop().unwrap();
+	drop(node);
+	drop(kv_store);
+
+	// Data written through the handle is persisted alongside the node's state and survives a
+	// restart.
+	let node = setup_node(&chain_source, config);
+	let kv_store = node.kv_store();
+	let data = KVStore::read(&kv_store, primary_namespace, secondary_namespace, "key").await;
+	assert_eq!(data.unwrap(), vec![42; 32]);
+	let keys = KVStore::list(&kv_store, primary_namespace, secondary_namespace).await.unwrap();
+	assert_eq!(keys, vec!["key".to_string()]);
+	node.stop().unwrap();
+}
+
 #[cfg(feature = "chain-bitcoind")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 async fn channel_full_cycle() {