Add archive_fully_resolved_monitors to ChainMonitor

fuzz/src/utils/test_persister.rs

@@ -17,4 +17,7 @@ impl chainmonitor::Persist<TestChannelSigner> for TestPersister {
 	fn update_persisted_channel(&self, _funding_txo: OutPoint, _update: Option<&channelmonitor::ChannelMonitorUpdate>, _data: &channelmonitor::ChannelMonitor<TestChannelSigner>, _update_id: MonitorUpdateId) -> chain::ChannelMonitorUpdateStatus {
 		self.update_ret.lock().unwrap().clone()
 	}
+
+	fn archive_persisted_channel(&self, _: OutPoint) {
+	}
 }

lightning/src/chain/chainmonitor.rs

@@ -194,6 +194,11 @@ pub trait Persist<ChannelSigner: WriteableEcdsaChannelSigner> {
 	///
 	/// [`Writeable::write`]: crate::util::ser::Writeable::write
 	fn update_persisted_channel(&self, channel_funding_outpoint: OutPoint, update: Option<&ChannelMonitorUpdate>, data: &ChannelMonitor<ChannelSigner>, update_id: MonitorUpdateId) -> ChannelMonitorUpdateStatus;
+	/// Prevents the channel monitor from being loaded on startup.
+	///
+	/// Archiving the data in a backup location (rather than deleting it fully) is useful for
+	/// hedging against data loss in case of unexpected failure.
+	fn archive_persisted_channel(&self, channel_funding_outpoint: OutPoint);
 }
 
 struct MonitorHolder<ChannelSigner: WriteableEcdsaChannelSigner> {
@@ -656,6 +661,41 @@ where C::Target: chain::Filter,
 			}
 		}
 	}
+
+	/// Archives fully resolved channel monitors by calling [`Persist::archive_persisted_channel`].
+	///
+	/// This is useful for pruning fully resolved monitors from the monitor set and primary
+	/// storage so they are not kept in memory and reloaded on restart.
+	///
+	/// Should be called occasionally (once every handful of blocks or on startup).
+	///
+	/// Depending on the implementation of [`Persist::archive_persisted_channel`] the monitor
+	/// data could be moved to an archive location or removed entirely.
+	pub fn archive_fully_resolved_channel_monitors(&self) {
+		let mut have_monitors_to_prune = false;
+		for (_, monitor_holder) in self.monitors.read().unwrap().iter() {
+			let logger = WithChannelMonitor::from(&self.logger, &monitor_holder.monitor);
+			if monitor_holder.monitor.is_fully_resolved(&logger) {
+				have_monitors_to_prune = true;
+			}
+		}
+		if have_monitors_to_prune {
+			let mut monitors = self.monitors.write().unwrap();
+			monitors.retain(|funding_txo, monitor_holder| {
+				let logger = WithChannelMonitor::from(&self.logger, &monitor_holder.monitor);
+				if monitor_holder.monitor.is_fully_resolved(&logger) {
+					log_info!(logger,
+						"Archiving fully resolved ChannelMonitor for funding txo {}",
+						funding_txo
+					);
+					self.persister.archive_persisted_channel(*funding_txo);
+					false
+				} else {
+					true
+				}
+			});
+		}
+	}
 }
 
 impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref>

lightning/src/chain/channelmonitor.rs

@@ -935,6 +935,9 @@ pub(crate) struct ChannelMonitorImpl<Signer: WriteableEcdsaChannelSigner> {
 	/// Ordering of tuple data: (their_per_commitment_point, feerate_per_kw, to_broadcaster_sats,
 	/// to_countersignatory_sats)
 	initial_counterparty_commitment_info: Option<(PublicKey, u32, u64, u64)>,
+
+	/// The first block height at which we had no remaining claimable balances.
+	balances_empty_height: Option<u32>,
 }
 
 /// Transaction outputs to watch for on-chain spends.
@@ -1145,6 +1148,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Writeable for ChannelMonitorImpl<Signe
 			(15, self.counterparty_fulfilled_htlcs, required),
 			(17, self.initial_counterparty_commitment_info, option),
 			(19, self.channel_id, required),
+			(21, self.balances_empty_height, option),
 		});
 
 		Ok(())
@@ -1328,6 +1332,7 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 			best_block,
 			counterparty_node_id: Some(counterparty_node_id),
 			initial_counterparty_commitment_info: None,
+			balances_empty_height: None,
 		})
 	}
 
@@ -1856,6 +1861,52 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 		spendable_outputs
 	}
 
+	/// Checks if the monitor is fully resolved. Resolved monitor is one that has claimed all of
+	/// its outputs and balances (i.e. [`Self::get_claimable_balances`] returns an empty set).
+	///
+	/// This function returns true only if [`Self::get_claimable_balances`] has been empty for at least
+	/// 2016 blocks as an additional protection against any bugs resulting in spuriously empty balance sets.
+	pub fn is_fully_resolved<L: Logger>(&self, logger: &L) -> bool {
+		let mut is_all_funds_claimed = self.get_claimable_balances().is_empty();
+		let current_height = self.current_best_block().height;
+		let mut inner = self.inner.lock().unwrap();
+
+		if is_all_funds_claimed {
+			if !inner.funding_spend_seen {
+				debug_assert!(false, "We should see funding spend by the time a monitor clears out");
+				is_all_funds_claimed = false;
+			}
+		}
+
+		match (inner.balances_empty_height, is_all_funds_claimed) {
+			(Some(balances_empty_height), true) => {
+				// Claimed all funds, check if reached the blocks threshold.
+				const BLOCKS_THRESHOLD: u32 = 4032; // ~four weeks
+				return current_height >= balances_empty_height + BLOCKS_THRESHOLD;
+			},
+			(Some(_), false) => {
+				// previously assumed we claimed all funds, but we have new funds to claim.
+				// Should not happen in practice.
+				debug_assert!(false, "Thought we were done claiming funds, but claimable_balances now has entries");
+				log_error!(logger,
+					"WARNING: LDK thought it was done claiming all the available funds in the ChannelMonitor for channel {}, but later decided it had more to claim. This is potentially an important bug in LDK, please report it at https://github.com/lightningdevkit/rust-lightning/issues/new",
+					inner.get_funding_txo().0);
+				inner.balances_empty_height = None;
+				false
+			},
+			(None, true) => {
+				// Claimed all funds but `balances_empty_height` is None. It is set to the
+				// current block height.
+				inner.balances_empty_height = Some(current_height);
+				false
+			},
+			(None, false) => {
+				// Have funds to claim.
+				false
+			},
+		}
+	}
+
 	#[cfg(test)]
 	pub fn get_counterparty_payment_script(&self) -> ScriptBuf {
 		self.inner.lock().unwrap().counterparty_payment_script.clone()
@@ -4632,6 +4683,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 		let mut spendable_txids_confirmed = Some(Vec::new());
 		let mut counterparty_fulfilled_htlcs = Some(new_hash_map());
 		let mut initial_counterparty_commitment_info = None;
+		let mut balances_empty_height = None;
 		let mut channel_id = None;
 		read_tlv_fields!(reader, {
 			(1, funding_spend_confirmed, option),
@@ -4644,6 +4696,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			(15, counterparty_fulfilled_htlcs, option),
 			(17, initial_counterparty_commitment_info, option),
 			(19, channel_id, option),
+			(21, balances_empty_height, option),
 		});
 
 		// `HolderForceClosedWithInfo` replaced `HolderForceClosed` in v0.0.122. If we have both
@@ -4722,6 +4775,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			best_block,
 			counterparty_node_id,
 			initial_counterparty_commitment_info,
+			balances_empty_height,
 		})))
 	}
 }

lightning/src/ln/monitor_tests.rs

@@ -158,6 +158,60 @@ fn revoked_output_htlc_resolution_timing() {
 	expect_payment_failed!(nodes[1], payment_hash_1, false);
 }
 
+#[test]
+fn archive_fully_resolved_monitors() {
+	// Test we can archive fully resolved channel monitor.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let mut user_config = test_default_channel_config();
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[Some(user_config), Some(user_config)]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let (_, _, chan_id, funding_tx) =
+		create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 1_000_000);
+
+	nodes[0].node.close_channel(&chan_id, &nodes[1].node.get_our_node_id()).unwrap();
+	let node_0_shutdown = get_event_msg!(nodes[0], MessageSendEvent::SendShutdown, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_shutdown(&nodes[0].node.get_our_node_id(), &node_0_shutdown);
+	let node_1_shutdown = get_event_msg!(nodes[1], MessageSendEvent::SendShutdown, nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_shutdown(&nodes[1].node.get_our_node_id(), &node_1_shutdown);
+
+	let node_0_closing_signed = get_event_msg!(nodes[0], MessageSendEvent::SendClosingSigned, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_closing_signed(&nodes[0].node.get_our_node_id(), &node_0_closing_signed);
+	let node_1_closing_signed = get_event_msg!(nodes[1], MessageSendEvent::SendClosingSigned, nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_closing_signed(&nodes[1].node.get_our_node_id(), &node_1_closing_signed);
+	let (_, node_0_2nd_closing_signed) = get_closing_signed_broadcast!(nodes[0].node, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_closing_signed(&nodes[0].node.get_our_node_id(), &node_0_2nd_closing_signed.unwrap());
+	let (_, _) = get_closing_signed_broadcast!(nodes[1].node, nodes[0].node.get_our_node_id());
+
+	let shutdown_tx = nodes[0].tx_broadcaster.txn_broadcasted.lock().unwrap().split_off(0);
+
+	mine_transaction(&nodes[0], &shutdown_tx[0]);
+	mine_transaction(&nodes[1], &shutdown_tx[0]);
+
+	connect_blocks(&nodes[0], 6);
+	connect_blocks(&nodes[1], 6);
+
+	check_closed_event!(nodes[0], 1, ClosureReason::LocallyInitiatedCooperativeClosure, [nodes[1].node.get_our_node_id()], 1000000);
+	check_closed_event!(nodes[1], 1, ClosureReason::CounterpartyInitiatedCooperativeClosure, [nodes[0].node.get_our_node_id()], 1000000);
+
+	assert_eq!(nodes[0].chain_monitor.chain_monitor.list_monitors().len(), 1);
+	// First archive should set balances_empty_height to current block height
+	nodes[0].chain_monitor.chain_monitor.archive_fully_resolved_channel_monitors(); 
+	assert_eq!(nodes[0].chain_monitor.chain_monitor.list_monitors().len(), 1);
+	connect_blocks(&nodes[0], 4032);
+	// Second call after 4032 blocks, should archive the monitor
+	nodes[0].chain_monitor.chain_monitor.archive_fully_resolved_channel_monitors();
+	// Should have no monitors left
+	assert_eq!(nodes[0].chain_monitor.chain_monitor.list_monitors().len(), 0);
+	// Remove the corresponding outputs and transactions the chain source is
+	// watching. This is to make sure the `Drop` function assertions pass.
+	nodes.get_mut(0).unwrap().chain_source.remove_watched_txn_and_outputs(
+		OutPoint { txid: funding_tx.txid(), index: 0 },
+		funding_tx.output[0].script_pubkey.clone()
+	);
+}
+
 fn do_chanmon_claim_value_coop_close(anchors: bool) {
 	// Tests `get_claimable_balances` returns the correct values across a simple cooperative claim.
 	// Specifically, this tests that the channel non-HTLC balances show up in

lightning/src/util/persist.rs

@@ -56,6 +56,11 @@ pub const CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE: &str = "";
 /// The primary namespace under which [`ChannelMonitorUpdate`]s will be persisted.
 pub const CHANNEL_MONITOR_UPDATE_PERSISTENCE_PRIMARY_NAMESPACE: &str = "monitor_updates";
 
+/// The primary namespace under which archived [`ChannelMonitor`]s will be persisted.
+pub const ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE: &str = "archived_monitors";
+/// The secondary namespace under which archived [`ChannelMonitor`]s will be persisted.
+pub const ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE: &str = "";
+
 /// The primary namespace under which the [`NetworkGraph`] will be persisted.
 pub const NETWORK_GRAPH_PERSISTENCE_PRIMARY_NAMESPACE: &str = "";
 /// The secondary namespace under which the [`NetworkGraph`] will be persisted.
@@ -212,6 +217,33 @@ impl<ChannelSigner: WriteableEcdsaChannelSigner, K: KVStore + ?Sized> Persist<Ch
 			Err(_) => chain::ChannelMonitorUpdateStatus::UnrecoverableError
 		}
 	}
+
+	fn archive_persisted_channel(&self, funding_txo: OutPoint) {
+		let monitor_name = MonitorName::from(funding_txo);
+		let monitor = match self.read(
+			CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+		) {
+			Ok(monitor) => monitor,
+			Err(_) => return
+		};
+		match self.write(
+			ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+			&monitor,
+		) {
+			Ok(()) => {}
+			Err(_e) => return
+		};
+		let _ = self.remove(
+			CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+			true,
+		);
+	}
 }
 
 /// Read previously persisted [`ChannelMonitor`]s from the store.
@@ -718,6 +750,29 @@ where
 			self.persist_new_channel(funding_txo, monitor, monitor_update_call_id)
 		}
 	}
+
+	fn archive_persisted_channel(&self, funding_txo: OutPoint) {
+		let monitor_name = MonitorName::from(funding_txo);
+		let monitor = match self.read_monitor(&monitor_name) {
+			Ok((_block_hash, monitor)) => monitor,
+			Err(_) => return
+		};
+		match self.kv_store.write(
+			ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			ARCHIVED_CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+			&monitor.encode()
+		) {
+			Ok(()) => {},
+			Err(_e) => return,
+		};
+		let _ = self.kv_store.remove(
+			CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+			true,
+		);
+	}
 }
 
 impl<K: Deref, L: Deref, ES: Deref, SP: Deref> MonitorUpdatingPersister<K, L, ES, SP>

lightning/src/util/test_utils.rs

@@ -504,6 +504,10 @@ impl<Signer: sign::ecdsa::WriteableEcdsaChannelSigner> chainmonitor::Persist<Sig
 		}
 		res
 	}
+
+	fn archive_persisted_channel(&self, funding_txo: OutPoint) {
+		<TestPersister as chainmonitor::Persist<TestChannelSigner>>::archive_persisted_channel(&self.persister, funding_txo);
+	}
 }
 
 pub struct TestPersister {
@@ -552,6 +556,18 @@ impl<Signer: sign::ecdsa::WriteableEcdsaChannelSigner> chainmonitor::Persist<Sig
 		}
 		ret
 	}
+
+	fn archive_persisted_channel(&self, funding_txo: OutPoint) { 
+		// remove the channel from the offchain_monitor_updates map
+		match self.offchain_monitor_updates.lock().unwrap().remove(&funding_txo) {
+			Some(_) => {},
+			None => {
+				// If the channel was not in the offchain_monitor_updates map, it should be in the
+				// chain_sync_monitor_persistences map.
+				assert!(self.chain_sync_monitor_persistences.lock().unwrap().remove(&funding_txo).is_some());
+			}
+		};
+	}
 }
 
 pub struct TestStore {
@@ -1363,6 +1379,10 @@ impl TestChainSource {
 			watched_outputs: Mutex::new(new_hash_set()),
 		}
 	}
+	pub fn remove_watched_txn_and_outputs(&self, outpoint: OutPoint, script_pubkey: ScriptBuf) {
+		self.watched_outputs.lock().unwrap().remove(&(outpoint, script_pubkey.clone())); 
+		self.watched_txn.lock().unwrap().remove(&(outpoint.txid, script_pubkey));
+	}
 }
 
 impl UtxoLookup for TestChainSource {