Add AChainMonitor trait and use it in background processor

Add a new `AChainMonitor` trait following the same pattern as
`AChannelManager`. This trait provides associated types for all
generic parameters of `ChainMonitor` and a `get_cm()` method to
access the underlying `ChainMonitor`.

Update the background processor to use `AChainMonitor` trait bounds
instead of spelling out the full `ChainMonitor` generic parameters.
This simplifies the function signatures by removing 5-6 explicit
generic parameters (CF, T, F, P, ES) per function.

This is preparation for adding a flush method to the AChainMonitor
trait.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: joostjager

lightning-background-processor/src/lib.rs

@@ -30,9 +30,11 @@ mod fwd_batch;
 
 use fwd_batch::BatchDelay;
 
+#[cfg(not(c_bindings))]
 use lightning::chain;
+#[cfg(not(c_bindings))]
 use lightning::chain::chaininterface::{BroadcasterInterface, FeeEstimator};
-use lightning::chain::chainmonitor::{ChainMonitor, Persist};
+use lightning::chain::chainmonitor::AChainMonitor;
 #[cfg(feature = "std")]
 use lightning::events::EventHandler;
 #[cfg(feature = "std")]
@@ -50,9 +52,9 @@ use lightning::onion_message::messenger::AOnionMessenger;
 use lightning::routing::gossip::{NetworkGraph, P2PGossipSync};
 use lightning::routing::scoring::{ScoreUpdate, WriteableScore};
 use lightning::routing::utxo::UtxoLookup;
-use lightning::sign::{
-	ChangeDestinationSource, ChangeDestinationSourceSync, EntropySource, OutputSpender,
-};
+#[cfg(not(c_bindings))]
+use lightning::sign::EntropySource;
+use lightning::sign::{ChangeDestinationSource, ChangeDestinationSourceSync, OutputSpender};
 #[cfg(not(c_bindings))]
 use lightning::util::async_poll::MaybeSend;
 use lightning::util::logger::Logger;
@@ -118,6 +120,7 @@ use alloc::vec::Vec;
 ///
 /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
 /// [`ChannelManager::timer_tick_occurred`]: lightning::ln::channelmanager::ChannelManager::timer_tick_occurred
+/// [`ChainMonitor::rebroadcast_pending_claims`]: lightning::chain::chainmonitor::ChainMonitor::rebroadcast_pending_claims
 /// [`ChannelMonitor`]: lightning::chain::channelmonitor::ChannelMonitor
 /// [`Event`]: lightning::events::Event
 /// [`PeerManager::timer_tick_occurred`]: lightning::ln::peer_handler::PeerManager::timer_tick_occurred
@@ -923,16 +926,11 @@ use futures_util::{dummy_waker, Joiner, OptionalSelector, Selector, SelectorOutp
 pub async fn process_events_async<
 	'a,
 	UL: UtxoLookup,
-	CF: chain::Filter,
-	T: BroadcasterInterface,
-	F: FeeEstimator,
 	G: Deref<Target = NetworkGraph<L>>,
 	L: Logger,
-	P: Deref,
 	EventHandlerFuture: core::future::Future<Output = Result<(), ReplayEvent>>,
 	EventHandler: Fn(Event) -> EventHandlerFuture,
-	ES: EntropySource,
-	M: Deref<Target = ChainMonitor<<CM::Target as AChannelManager>::Signer, CF, T, F, L, P, ES>>,
+	M: Deref,
 	CM: Deref,
 	OM: Deref,
 	PGS: Deref<Target = P2PGossipSync<G, UL, L>>,
@@ -942,7 +940,17 @@ pub async fn process_events_async<
 	D: Deref,
 	O: OutputSpender,
 	K: KVStore,
-	OS: Deref<Target = OutputSweeper<T, D, F, CF, K, L, O>>,
+	OS: Deref<
+		Target = OutputSweeper<
+			<M::Target as AChainMonitor>::Broadcaster,
+			D,
+			<M::Target as AChainMonitor>::FeeEstimator,
+			<M::Target as AChainMonitor>::Filter,
+			K,
+			L,
+			O,
+		>,
+	>,
 	S: Deref<Target = SC>,
 	SC: for<'b> WriteableScore<'b>,
 	SleepFuture: core::future::Future<Output = bool> + core::marker::Unpin,
@@ -955,7 +963,7 @@ pub async fn process_events_async<
 	sleeper: Sleeper, mobile_interruptable_platform: bool, fetch_time: FetchTime,
 ) -> Result<(), lightning::io::Error>
 where
-	P::Target: Persist<<CM::Target as AChannelManager>::Signer>,
+	M::Target: AChainMonitor<Signer = <CM::Target as AChannelManager>::Signer, Logger = L>,
 	CM::Target: AChannelManager,
 	OM::Target: AOnionMessenger,
 	PM::Target: APeerManager,
@@ -1004,7 +1012,7 @@ where
 	log_trace!(logger, "Calling ChannelManager's timer_tick_occurred on startup");
 	channel_manager.get_cm().timer_tick_occurred();
 	log_trace!(logger, "Rebroadcasting monitor's pending claims on startup");
-	chain_monitor.rebroadcast_pending_claims();
+	chain_monitor.get_cm().rebroadcast_pending_claims();
 
 	let mut last_freshness_call = sleeper(FRESHNESS_TIMER);
 	let mut last_onion_message_handler_call = sleeper(ONION_MESSAGE_HANDLER_TIMER);
@@ -1022,7 +1030,7 @@ where
 
 	loop {
 		channel_manager.get_cm().process_pending_events_async(async_event_handler).await;
-		chain_monitor.process_pending_events_async(async_event_handler).await;
+		chain_monitor.get_cm().process_pending_events_async(async_event_handler).await;
 		if let Some(om) = &onion_messenger {
 			om.get_om().process_pending_events_async(async_event_handler).await
 		}
@@ -1072,7 +1080,7 @@ where
 		let fut = Selector {
 			a: sleeper(sleep_delay),
 			b: channel_manager.get_cm().get_event_or_persistence_needed_future(),
-			c: chain_monitor.get_update_future(),
+			c: chain_monitor.get_cm().get_update_future(),
 			d: om_fut,
 			e: lm_fut,
 			f: gv_fut,
@@ -1164,7 +1172,7 @@ where
 		};
 		if archive_timer_elapsed {
 			log_trace!(logger, "Archiving stale ChannelMonitors.");
-			chain_monitor.archive_fully_resolved_channel_monitors();
+			chain_monitor.get_cm().archive_fully_resolved_channel_monitors();
 			have_archived = true;
 			log_trace!(logger, "Archived stale ChannelMonitors.");
 		}
@@ -1354,7 +1362,7 @@ where
 		match check_and_reset_sleeper(&mut last_rebroadcast_call, || sleeper(REBROADCAST_TIMER)) {
 			Some(false) => {
 				log_trace!(logger, "Rebroadcasting monitor's pending claims");
-				chain_monitor.rebroadcast_pending_claims();
+				chain_monitor.get_cm().rebroadcast_pending_claims();
 			},
 			Some(true) => break,
 			None => {},
@@ -1416,16 +1424,11 @@ fn check_and_reset_sleeper<
 /// synchronous background persistence.
 pub async fn process_events_async_with_kv_store_sync<
 	UL: UtxoLookup,
-	CF: chain::Filter,
-	T: BroadcasterInterface,
-	F: FeeEstimator,
 	G: Deref<Target = NetworkGraph<L>>,
 	L: Logger,
-	P: Deref,
 	EventHandlerFuture: core::future::Future<Output = Result<(), ReplayEvent>>,
 	EventHandler: Fn(Event) -> EventHandlerFuture,
-	ES: EntropySource,
-	M: Deref<Target = ChainMonitor<<CM::Target as AChannelManager>::Signer, CF, T, F, L, P, ES>>,
+	M: Deref,
 	CM: Deref,
 	OM: Deref,
 	PGS: Deref<Target = P2PGossipSync<G, UL, L>>,
@@ -1435,7 +1438,17 @@ pub async fn process_events_async_with_kv_store_sync<
 	D: Deref,
 	O: OutputSpender,
 	K: Deref,
-	OS: Deref<Target = OutputSweeperSync<T, D, F, CF, K, L, O>>,
+	OS: Deref<
+		Target = OutputSweeperSync<
+			<M::Target as AChainMonitor>::Broadcaster,
+			D,
+			<M::Target as AChainMonitor>::FeeEstimator,
+			<M::Target as AChainMonitor>::Filter,
+			K,
+			L,
+			O,
+		>,
+	>,
 	S: Deref<Target = SC>,
 	SC: for<'b> WriteableScore<'b>,
 	SleepFuture: core::future::Future<Output = bool> + core::marker::Unpin,
@@ -1448,7 +1461,7 @@ pub async fn process_events_async_with_kv_store_sync<
 	sleeper: Sleeper, mobile_interruptable_platform: bool, fetch_time: FetchTime,
 ) -> Result<(), lightning::io::Error>
 where
-	P::Target: Persist<<CM::Target as AChannelManager>::Signer>,
+	M::Target: AChainMonitor<Signer = <CM::Target as AChannelManager>::Signer, Logger = L>,
 	CM::Target: AChannelManager,
 	OM::Target: AOnionMessenger,
 	PM::Target: APeerManager,
@@ -1523,20 +1536,10 @@ impl BackgroundProcessor {
 	pub fn start<
 		'a,
 		UL: 'static + UtxoLookup,
-		CF: 'static + chain::Filter,
-		T: 'static + BroadcasterInterface,
-		F: 'static + FeeEstimator + Send,
 		G: 'static + Deref<Target = NetworkGraph<L>>,
 		L: 'static + Deref + Send,
-		P: 'static + Deref,
 		EH: 'static + EventHandler + Send,
-		ES: 'static + EntropySource + Send,
-		M: 'static
-			+ Deref<
-				Target = ChainMonitor<<CM::Target as AChannelManager>::Signer, CF, T, F, L, P, ES>,
-			>
-			+ Send
-			+ Sync,
+		M: 'static + Deref + Send + Sync,
 		CM: 'static + Deref + Send,
 		OM: 'static + Deref + Send,
 		PGS: 'static + Deref<Target = P2PGossipSync<G, UL, L>> + Send,
@@ -1548,15 +1551,27 @@ impl BackgroundProcessor {
 		D: 'static + Deref,
 		O: 'static + OutputSpender,
 		K: 'static + Deref + Send,
-		OS: 'static + Deref<Target = OutputSweeperSync<T, D, F, CF, K, L, O>> + Send,
+		OS: 'static
+			+ Deref<
+				Target = OutputSweeperSync<
+					<M::Target as AChainMonitor>::Broadcaster,
+					D,
+					<M::Target as AChainMonitor>::FeeEstimator,
+					<M::Target as AChainMonitor>::Filter,
+					K,
+					L,
+					O,
+				>,
+			>
+			+ Send,
 	>(
 		kv_store: K, event_handler: EH, chain_monitor: M, channel_manager: CM,
 		onion_messenger: Option<OM>, gossip_sync: GossipSync<PGS, RGS, G, UL, L>, peer_manager: PM,
 		liquidity_manager: Option<LM>, sweeper: Option<OS>, logger: L, scorer: Option<S>,
 	) -> Self
 	where
 		L::Target: 'static + Logger,
-		P::Target: 'static + Persist<<CM::Target as AChannelManager>::Signer>,
+		M::Target: AChainMonitor<Signer = <CM::Target as AChannelManager>::Signer, Logger = L>,
 		CM::Target: AChannelManager,
 		OM::Target: AOnionMessenger,
 		PM::Target: APeerManager,
@@ -1596,7 +1611,7 @@ impl BackgroundProcessor {
 			log_trace!(logger, "Calling ChannelManager's timer_tick_occurred on startup");
 			channel_manager.get_cm().timer_tick_occurred();
 			log_trace!(logger, "Rebroadcasting monitor's pending claims on startup");
-			chain_monitor.rebroadcast_pending_claims();
+			chain_monitor.get_cm().rebroadcast_pending_claims();
 
 			let mut last_freshness_call = Instant::now();
 			let mut last_onion_message_handler_call = Instant::now();
@@ -1615,7 +1630,7 @@ impl BackgroundProcessor {
 
 			loop {
 				channel_manager.get_cm().process_pending_events(&event_handler);
-				chain_monitor.process_pending_events(&event_handler);
+				chain_monitor.get_cm().process_pending_events(&event_handler);
 				if let Some(om) = &onion_messenger {
 					om.get_om().process_pending_events(&event_handler)
 				};
@@ -1648,7 +1663,7 @@ impl BackgroundProcessor {
 				let gv_fut = gossip_sync.validation_completion_future();
 				let always_futures = [
 					channel_manager.get_cm().get_event_or_persistence_needed_future(),
-					chain_monitor.get_update_future(),
+					chain_monitor.get_cm().get_update_future(),
 				];
 				let futures = always_futures.into_iter().chain(om_fut).chain(lm_fut).chain(gv_fut);
 				let sleeper = Sleeper::from_futures(futures);
@@ -1701,7 +1716,7 @@ impl BackgroundProcessor {
 				let archive_timer_elapsed = last_archive_call.elapsed() > archive_timer;
 				if archive_timer_elapsed {
 					log_trace!(logger, "Archiving stale ChannelMonitors.");
-					chain_monitor.archive_fully_resolved_channel_monitors();
+					chain_monitor.get_cm().archive_fully_resolved_channel_monitors();
 					have_archived = true;
 					last_archive_call = Instant::now();
 					log_trace!(logger, "Archived stale ChannelMonitors.");
@@ -1786,7 +1801,7 @@ impl BackgroundProcessor {
 				}
 				if last_rebroadcast_call.elapsed() > REBROADCAST_TIMER {
 					log_trace!(logger, "Rebroadcasting monitor's pending claims");
-					chain_monitor.rebroadcast_pending_claims();
+					chain_monitor.get_cm().rebroadcast_pending_claims();
 					last_rebroadcast_call = Instant::now();
 				}
 			}

lightning/src/chain/chainmonitor.rs

@@ -1488,6 +1488,66 @@ where
 	}
 }
 
+/// A trivial trait which describes any [`ChainMonitor`].
+///
+/// This is not exported to bindings users as general cover traits aren't useful in other
+/// languages.
+pub trait AChainMonitor {
+	/// A type implementing [`EcdsaChannelSigner`].
+	type Signer: EcdsaChannelSigner + Sized;
+	/// A type implementing [`chain::Filter`].
+	type Filter: chain::Filter;
+	/// A type implementing [`BroadcasterInterface`].
+	type Broadcaster: BroadcasterInterface;
+	/// A type implementing [`FeeEstimator`].
+	type FeeEstimator: FeeEstimator;
+	/// A type implementing [`Logger`].
+	type Logger: Logger;
+	/// A type that derefs to [`Persist`].
+	type Persister: Deref<Target = Self::PersisterTarget>;
+	/// The target of [`Self::Persister`].
+	type PersisterTarget: Persist<Self::Signer> + ?Sized;
+	/// A type implementing [`EntropySource`].
+	type EntropySource: EntropySource;
+	/// Returns a reference to the actual [`ChainMonitor`] object.
+	fn get_cm(
+		&self,
+	) -> &ChainMonitor<
+		Self::Signer,
+		Self::Filter,
+		Self::Broadcaster,
+		Self::FeeEstimator,
+		Self::Logger,
+		Self::Persister,
+		Self::EntropySource,
+	>;
+}
+
+impl<
+		ChannelSigner: EcdsaChannelSigner,
+		C: chain::Filter,
+		T: BroadcasterInterface,
+		F: FeeEstimator,
+		L: Logger,
+		P: Deref,
+		ES: EntropySource,
+	> AChainMonitor for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
+where
+	P::Target: Persist<ChannelSigner>,
+{
+	type Signer = ChannelSigner;
+	type Filter = C;
+	type Broadcaster = T;
+	type FeeEstimator = F;
+	type Logger = L;
+	type Persister = P;
+	type PersisterTarget = P::Target;
+	type EntropySource = ES;
+	fn get_cm(&self) -> &ChainMonitor<ChannelSigner, C, T, F, L, P, ES> {
+		self
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use crate::chain::channelmonitor::ANTI_REORG_DELAY;