lightning 0.3.0-beta1

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Logic to connect off-chain channel management with on-chain transaction monitoring.
//!
//! [`ChainMonitor`] is an implementation of [`chain::Watch`] used both to process blocks and to
//! update [`ChannelMonitor`]s accordingly. If any on-chain events need further processing, it will
//! make those available as [`MonitorEvent`]s to be consumed.
//!
//! [`ChainMonitor`] is parameterized by an optional chain source, which must implement the
//! [`chain::Filter`] trait. This provides a mechanism to signal new relevant outputs back to light
//! clients, such that transactions spending those outputs are included in block data.
//!
//! [`ChainMonitor`] may be used directly to monitor channels locally or as a part of a distributed
//! setup to monitor channels remotely. In the latter case, a custom [`chain::Watch`] implementation
//! would be responsible for routing each update to a remote server and for retrieving monitor
//! events. The remote server would make use of [`ChainMonitor`] for block processing and for
//! servicing [`ChannelMonitor`] updates from the client.

use bitcoin::block::Header;
use bitcoin::hash_types::{BlockHash, Txid};

use bitcoin::secp256k1::PublicKey;

use crate::chain;
use crate::chain::chaininterface::{BroadcasterInterface, FeeEstimator};
#[cfg(peer_storage)]
use crate::chain::channelmonitor::write_chanmon_internal;
use crate::chain::channelmonitor::{
	Balance, ChannelMonitor, ChannelMonitorUpdate, MonitorEvent, TransactionOutputs,
	WithChannelMonitor,
};
use crate::chain::transaction::{OutPoint, TransactionData};
use crate::chain::{BlockLocator, ChannelMonitorUpdateStatus, WatchedOutput};
use crate::events::{self, Event, EventHandler, ReplayEvent};
use crate::ln::channel_state::ChannelDetails;
#[cfg(peer_storage)]
use crate::ln::msgs::PeerStorage;
use crate::ln::msgs::{BaseMessageHandler, Init, MessageSendEvent, SendOnlyMessageHandler};
#[cfg(peer_storage)]
use crate::ln::our_peer_storage::{DecryptedOurPeerStorage, PeerStorageMonitorHolder};
use crate::ln::types::ChannelId;
use crate::prelude::*;
use crate::sign::ecdsa::EcdsaChannelSigner;
use crate::sign::{EntropySource, PeerStorageKey, SignerProvider};
use crate::sync::{Mutex, MutexGuard, RwLock, RwLockReadGuard};
use crate::types::features::{InitFeatures, NodeFeatures};
use crate::util::errors::APIError;
use crate::util::logger::{Logger, WithContext};
use crate::util::native_async::{FutureSpawner, MaybeSend, MaybeSync};
use crate::util::persist::{KVStore, MonitorName, MonitorUpdatingPersisterAsync};
#[cfg(peer_storage)]
use crate::util::ser::{VecWriter, Writeable};
use crate::util::wakers::{Future, Notifier};

use alloc::collections::VecDeque;
use alloc::sync::Arc;
#[cfg(peer_storage)]
use core::iter::Cycle;
use core::ops::Deref;
use core::sync::atomic::{AtomicUsize, Ordering};

/// A pending operation queued for later execution when `ChainMonitor` is in deferred mode.
enum PendingMonitorOp<ChannelSigner: EcdsaChannelSigner> {
	/// A new monitor to insert and persist.
	NewMonitor { channel_id: ChannelId, monitor: ChannelMonitor<ChannelSigner> },
	/// An update to apply and persist.
	Update { channel_id: ChannelId, update: ChannelMonitorUpdate },
}

/// `Persist` defines behavior for persisting channel monitors: this could mean
/// writing once to disk, and/or uploading to one or more backup services.
///
/// Persistence can happen in one of two ways - synchronously completing before the trait method
/// calls return or asynchronously in the background.
///
/// # For those implementing synchronous persistence
///
///  * If persistence completes fully (including any relevant `fsync()` calls), the implementation
///    should return [`ChannelMonitorUpdateStatus::Completed`], indicating normal channel operation
///    should continue.
///
///  * If persistence fails for some reason, implementations should consider returning
///    [`ChannelMonitorUpdateStatus::InProgress`] and retry all pending persistence operations in
///    the background with [`ChainMonitor::list_pending_monitor_updates`] and
///    [`ChainMonitor::get_monitor`].
///
///    Each pending update must be individually marked as complete by calling
///    [`ChainMonitor::channel_monitor_updated`] with the corresponding update ID. Note that
///    persisting a full [`ChannelMonitor`] covers all prior updates, but each update ID still
///    needs to be marked complete separately.
///
///    If at some point no further progress can be made towards persisting the pending updates, the
///    node should simply shut down.
///
///  * If the persistence has failed and cannot be retried further (e.g. because of an outage),
///    [`ChannelMonitorUpdateStatus::UnrecoverableError`] can be used, though this will result in
///    an immediate panic and future operations in LDK generally failing.
///
/// # For those implementing asynchronous persistence
///
///  All calls should generally spawn a background task and immediately return
///  [`ChannelMonitorUpdateStatus::InProgress`]. Once the update completes,
///  [`ChainMonitor::channel_monitor_updated`] should be called with the corresponding
///  [`ChannelMonitor::get_latest_update_id`] or [`ChannelMonitorUpdate::update_id`].
///
///  Note that unlike the direct [`chain::Watch`] interface,
///  [`ChainMonitor::channel_monitor_updated`] must be called once for *each* update which occurs.
///
///  If at some point no further progress can be made towards persisting a pending update, the node
///  should simply shut down. Until then, the background task should either loop indefinitely, or
///  persistence should be regularly retried with [`ChainMonitor::list_pending_monitor_updates`]
///  and [`ChainMonitor::get_monitor`] (note that if a full monitor is persisted all pending
///  monitor updates may be marked completed).
///
/// # Using remote watchtowers
///
/// Watchtowers may be updated as a part of an implementation of this trait, utilizing the async
/// update process described above while the watchtower is being updated. The following methods are
/// provided for bulding transactions for a watchtower:
/// [`ChannelMonitor::initial_counterparty_commitment_tx`],
/// [`ChannelMonitor::counterparty_commitment_txs_from_update`],
/// [`ChannelMonitor::sign_to_local_justice_tx`], [`TrustedCommitmentTransaction::revokeable_output_index`],
/// [`TrustedCommitmentTransaction::build_to_local_justice_tx`].
///
/// [`TrustedCommitmentTransaction::revokeable_output_index`]: crate::ln::chan_utils::TrustedCommitmentTransaction::revokeable_output_index
/// [`TrustedCommitmentTransaction::build_to_local_justice_tx`]: crate::ln::chan_utils::TrustedCommitmentTransaction::build_to_local_justice_tx
pub trait Persist<ChannelSigner: EcdsaChannelSigner> {
	/// Persist a new channel's data in response to a [`chain::Watch::watch_channel`] call. This is
	/// called by [`ChannelManager`] for new channels, or may be called directly, e.g. on startup,
	/// with the `monitor_name` returned by [`ChannelMonitor::persistence_key`].
	///
	/// The data can be stored any way you want, so long as `monitor_name` is used to maintain a
	/// correct mapping with the stored channel data (i.e., calls to `update_persisted_channel` with
	/// the same `monitor_name` must be applied to or overwrite this data). Note that you **must**
	/// persist every new monitor to disk.
	///
	/// The [`ChannelMonitor::get_latest_update_id`] uniquely links this call to [`ChainMonitor::channel_monitor_updated`].
	/// For [`Persist::persist_new_channel`], it is only necessary to call [`ChainMonitor::channel_monitor_updated`]
	/// when you return [`ChannelMonitorUpdateStatus::InProgress`].
	///
	/// See [`Writeable::write`] on [`ChannelMonitor`] for writing out a `ChannelMonitor`
	/// and [`ChannelMonitorUpdateStatus`] for requirements when returning errors.
	///
	/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
	/// [`Writeable::write`]: crate::util::ser::Writeable::write
	fn persist_new_channel(
		&self, monitor_name: MonitorName, monitor: &ChannelMonitor<ChannelSigner>,
	) -> ChannelMonitorUpdateStatus;

	/// Update one channel's data. The provided [`ChannelMonitor`] has already applied the given
	/// update.
	///
	/// Note that on every update, you **must** persist either the [`ChannelMonitorUpdate`] or the
	/// updated monitor itself to disk/backups. See the [`Persist`] trait documentation for more
	/// details.
	///
	/// During blockchain synchronization operations, and in some rare cases, this may be called with
	/// no [`ChannelMonitorUpdate`], in which case the full [`ChannelMonitor`] needs to be persisted.
	/// Note that after the full [`ChannelMonitor`] is persisted any previous
	/// [`ChannelMonitorUpdate`]s which were persisted should be discarded - they can no longer be
	/// applied to the persisted [`ChannelMonitor`] as they were already applied.
	///
	/// If an implementer chooses to persist the updates only, they need to make
	/// sure that all the updates are applied to the `ChannelMonitors` *before*
	/// the set of channel monitors is given to the `ChannelManager`
	/// deserialization routine. If there are any gaps in the persisted [`ChannelMonitorUpdate`]s,
	/// implementer can safely ignore [`ChannelMonitorUpdate`]s after the gap and load without them.
	/// See [`ChannelMonitor::update_monitor`] for
	/// applying a monitor update to a monitor. If full `ChannelMonitors` are
	/// persisted, then there is no need to persist individual updates.
	///
	/// Note that there could be a performance tradeoff between persisting complete
	/// channel monitors on every update vs. persisting only updates and applying
	/// them in batches. The size of each monitor grows `O(number of state updates)`
	/// whereas updates are small and `O(1)`.
	///
	/// The [`ChannelMonitorUpdate::update_id`] or [`ChannelMonitor::get_latest_update_id`] uniquely
	/// links this call to [`ChainMonitor::channel_monitor_updated`].
	/// For [`Persist::update_persisted_channel`], it is only necessary to call [`ChainMonitor::channel_monitor_updated`]
	/// when a [`ChannelMonitorUpdate`] is provided and when you return [`ChannelMonitorUpdateStatus::InProgress`].
	///
	/// See [`Writeable::write`] on [`ChannelMonitor`] for writing out a `ChannelMonitor`,
	/// [`Writeable::write`] on [`ChannelMonitorUpdate`] for writing out an update, and
	/// [`ChannelMonitorUpdateStatus`] for requirements when returning errors.
	///
	/// [`Writeable::write`]: crate::util::ser::Writeable::write
	fn update_persisted_channel(
		&self, monitor_name: MonitorName, monitor_update: Option<&ChannelMonitorUpdate>,
		monitor: &ChannelMonitor<ChannelSigner>,
	) -> 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.
	///
	/// Note that if a crash occurs during the archiving process, and its implementation is not
	/// atomic, a state may emerge with the archival operation only being partially complete. In
	/// that scenario, the monitor may still be loaded on startup pending successful completion of
	/// the archive process. Additionally, because the archive operation could be retried on
	/// restart, this method must in that case be idempotent, ensuring it can handle scenarios where
	/// the monitor already exists in the archive.
	fn archive_persisted_channel(&self, monitor_name: MonitorName);

	/// Fetches the set of [`ChannelMonitorUpdate`]s, previously persisted with
	/// [`Self::update_persisted_channel`], which have completed.
	///
	/// Returning an update here is equivalent to calling
	/// [`ChainMonitor::channel_monitor_updated`]. Because of this, this method is defaulted and
	/// hidden in the docs.
	#[doc(hidden)]
	fn get_and_clear_completed_updates(&self) -> Vec<(ChannelId, u64)> {
		Vec::new()
	}
}

struct MonitorHolder<ChannelSigner: EcdsaChannelSigner> {
	monitor: ChannelMonitor<ChannelSigner>,
	/// The full set of pending monitor updates for this Channel.
	///
	/// Note that this lock must be held from [`ChannelMonitor::update_monitor`] through to
	/// [`Persist::update_persisted_channel`] to prevent a race where we call
	/// [`Persist::update_persisted_channel`], the user returns a
	/// [`ChannelMonitorUpdateStatus::InProgress`], and then calls
	/// [`ChainMonitor::channel_monitor_updated`] immediately, racing our insertion of the pending
	/// update into the contained Vec.
	///
	/// This also avoids a race where we update a [`ChannelMonitor`], then while connecting a block
	/// persist a full [`ChannelMonitor`] prior to persisting the [`ChannelMonitorUpdate`]. This
	/// could cause users to have a full [`ChannelMonitor`] on disk as well as a
	/// [`ChannelMonitorUpdate`] which was already applied. While this isn't an issue for the
	/// LDK-provided update-based [`Persist`], it is somewhat surprising for users so we avoid it.
	pending_monitor_updates: Mutex<Vec<u64>>,
}

impl<ChannelSigner: EcdsaChannelSigner> MonitorHolder<ChannelSigner> {
	fn has_pending_updates(&self, pending_monitor_updates_lock: &MutexGuard<Vec<u64>>) -> bool {
		!pending_monitor_updates_lock.is_empty()
	}
}

/// A read-only reference to a current ChannelMonitor.
///
/// Note that this holds a mutex in [`ChainMonitor`] and may block other events until it is
/// released.
pub struct LockedChannelMonitor<'a, ChannelSigner: EcdsaChannelSigner> {
	lock: RwLockReadGuard<'a, HashMap<ChannelId, MonitorHolder<ChannelSigner>>>,
	channel_id: ChannelId,
}

impl<ChannelSigner: EcdsaChannelSigner> Deref for LockedChannelMonitor<'_, ChannelSigner> {
	type Target = ChannelMonitor<ChannelSigner>;
	fn deref(&self) -> &ChannelMonitor<ChannelSigner> {
		&self.lock.get(&self.channel_id).expect("Checked at construction").monitor
	}
}

/// An unconstructable [`Persist`]er which is used under the hood when you call
/// [`ChainMonitor::new_async_beta`].
///
/// This is not exported to bindings users as async is not supported outside of Rust.
pub struct AsyncPersister<
	K: KVStore + MaybeSend + MaybeSync + 'static,
	S: FutureSpawner,
	L: Logger + MaybeSend + MaybeSync + 'static,
	ES: EntropySource + MaybeSend + MaybeSync + 'static,
	SP: SignerProvider + MaybeSend + MaybeSync + 'static,
	BI: BroadcasterInterface + MaybeSend + MaybeSync + 'static,
	FE: FeeEstimator + MaybeSend + MaybeSync + 'static,
> {
	persister: MonitorUpdatingPersisterAsync<K, S, L, ES, SP, BI, FE>,
	event_notifier: Arc<Notifier>,
}

impl<
		K: KVStore + MaybeSend + MaybeSync + 'static,
		S: FutureSpawner,
		L: Logger + MaybeSend + MaybeSync + 'static,
		ES: EntropySource + MaybeSend + MaybeSync + 'static,
		SP: SignerProvider + MaybeSend + MaybeSync + 'static,
		BI: BroadcasterInterface + MaybeSend + MaybeSync + 'static,
		FE: FeeEstimator + MaybeSend + MaybeSync + 'static,
	> Deref for AsyncPersister<K, S, L, ES, SP, BI, FE>
{
	type Target = Self;
	fn deref(&self) -> &Self {
		self
	}
}

impl<
		K: KVStore + MaybeSend + MaybeSync + 'static,
		S: FutureSpawner,
		L: Logger + MaybeSend + MaybeSync + 'static,
		ES: EntropySource + MaybeSend + MaybeSync + 'static,
		SP: SignerProvider + MaybeSend + MaybeSync + 'static,
		BI: BroadcasterInterface + MaybeSend + MaybeSync + 'static,
		FE: FeeEstimator + MaybeSend + MaybeSync + 'static,
	> Persist<SP::EcdsaSigner> for AsyncPersister<K, S, L, ES, SP, BI, FE>
where
	SP::EcdsaSigner: MaybeSend + 'static,
{
	fn persist_new_channel(
		&self, monitor_name: MonitorName, monitor: &ChannelMonitor<SP::EcdsaSigner>,
	) -> ChannelMonitorUpdateStatus {
		let notifier = Arc::clone(&self.event_notifier);
		self.persister.spawn_async_persist_new_channel(monitor_name, monitor, notifier);
		ChannelMonitorUpdateStatus::InProgress
	}

	fn update_persisted_channel(
		&self, monitor_name: MonitorName, monitor_update: Option<&ChannelMonitorUpdate>,
		monitor: &ChannelMonitor<SP::EcdsaSigner>,
	) -> ChannelMonitorUpdateStatus {
		let notifier = Arc::clone(&self.event_notifier);
		self.persister.spawn_async_update_channel(monitor_name, monitor_update, monitor, notifier);
		ChannelMonitorUpdateStatus::InProgress
	}

	fn archive_persisted_channel(&self, monitor_name: MonitorName) {
		self.persister.spawn_async_archive_persisted_channel(monitor_name);
	}

	fn get_and_clear_completed_updates(&self) -> Vec<(ChannelId, u64)> {
		self.persister.get_and_clear_completed_updates()
	}
}

/// An implementation of [`chain::Watch`] for monitoring channels.
///
/// Connected and disconnected blocks must be provided to `ChainMonitor` as documented by
/// [`chain::Watch`]. May be used in conjunction with [`ChannelManager`] to monitor channels locally
/// or used independently to monitor channels remotely. See the [module-level documentation] for
/// details.
///
/// Note that `ChainMonitor` should regularly trigger rebroadcasts/fee bumps of pending claims from
/// a force-closed channel. This is crucial in preventing certain classes of pinning attacks,
/// detecting substantial mempool feerate changes between blocks, and ensuring reliability if
/// broadcasting fails. We recommend invoking this every 30 seconds, or lower if running in an
/// environment with spotty connections, like on mobile.
///
/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
/// [module-level documentation]: crate::chain::chainmonitor
/// [`rebroadcast_pending_claims`]: Self::rebroadcast_pending_claims
pub struct ChainMonitor<
	ChannelSigner: EcdsaChannelSigner,
	C: chain::Filter,
	T: BroadcasterInterface,
	F: FeeEstimator,
	L: Logger,
	P: Deref,
	ES: EntropySource,
> where
	P::Target: Persist<ChannelSigner>,
{
	monitors: RwLock<HashMap<ChannelId, MonitorHolder<ChannelSigner>>>,
	chain_source: Option<C>,
	broadcaster: T,
	logger: L,
	fee_estimator: F,
	persister: P,
	_entropy_source: ES,
	/// "User-provided" (ie persistence-completion/-failed) [`MonitorEvent`]s. These came directly
	/// from the user and not from a [`ChannelMonitor`].
	pending_monitor_events: Mutex<Vec<(OutPoint, ChannelId, Vec<MonitorEvent>, PublicKey)>>,
	/// The best block height seen, used as a proxy for the passage of time.
	highest_chain_height: AtomicUsize,

	/// A [`Notifier`] used to wake up the background processor in case we have any [`Event`]s for
	/// it to give to users (or [`MonitorEvent`]s for `ChannelManager` to process).
	event_notifier: Arc<Notifier>,

	/// Messages to send to the peer. This is currently used to distribute PeerStorage to channel partners.
	pending_send_only_events: Mutex<Vec<MessageSendEvent>>,

	#[cfg(peer_storage)]
	our_peerstorage_encryption_key: PeerStorageKey,

	/// When `true`, [`chain::Watch`] operations are queued rather than executed immediately.
	deferred: bool,
	/// Queued monitor operations awaiting flush. Unused when `deferred` is `false`.
	pending_ops: Mutex<VecDeque<PendingMonitorOp<ChannelSigner>>>,
	/// Guards [`Self::flush`] so that concurrent calls are serialized.
	flush_lock: Mutex<()>,
}

impl<
		K: KVStore + MaybeSend + MaybeSync + 'static,
		S: FutureSpawner,
		SP: SignerProvider + MaybeSend + MaybeSync + 'static,
		C: chain::Filter,
		T: BroadcasterInterface + MaybeSend + MaybeSync + 'static,
		F: FeeEstimator + MaybeSend + MaybeSync + 'static,
		L: Logger + MaybeSend + MaybeSync + 'static,
		ES: EntropySource + MaybeSend + MaybeSync + 'static,
	> ChainMonitor<SP::EcdsaSigner, C, T, F, L, AsyncPersister<K, S, L, ES, SP, T, F>, ES>
where
	SP::EcdsaSigner: MaybeSend + 'static,
{
	/// Creates a new `ChainMonitor` used to watch on-chain activity pertaining to channels.
	///
	/// This behaves the same as [`ChainMonitor::new`] except that it relies on
	/// [`MonitorUpdatingPersisterAsync`] and thus allows persistence to be completed async.
	///
	/// Note that async monitor updating is considered beta, and bugs may be triggered by its use.
	///
	/// When `deferred` is `true`, [`chain::Watch::watch_channel`] and
	/// [`chain::Watch::update_channel`] calls are not executed immediately. Instead, they are
	/// queued internally and must be flushed by the caller via [`Self::flush`]. Use
	/// [`Self::pending_operation_count`] to check how many operations are queued, then call
	/// [`Self::flush`] to process them. This allows the caller to ensure that the
	/// [`ChannelManager`] is persisted before its associated monitors, avoiding the risk of
	/// force closures from a crash between monitor and channel manager persistence.
	///
	/// When `deferred` is `false`, monitor operations are executed inline as usual.
	///
	/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
	///
	/// This is not exported to bindings users as async is not supported outside of Rust.
	pub fn new_async_beta(
		chain_source: Option<C>, broadcaster: T, logger: L, feeest: F,
		persister: MonitorUpdatingPersisterAsync<K, S, L, ES, SP, T, F>, _entropy_source: ES,
		_our_peerstorage_encryption_key: PeerStorageKey, deferred: bool,
	) -> Self {
		let event_notifier = Arc::new(Notifier::new());
		Self {
			monitors: RwLock::new(new_hash_map()),
			chain_source,
			broadcaster,
			logger,
			fee_estimator: feeest,
			_entropy_source,
			pending_monitor_events: Mutex::new(Vec::new()),
			highest_chain_height: AtomicUsize::new(0),
			event_notifier: Arc::clone(&event_notifier),
			persister: AsyncPersister { persister, event_notifier },
			pending_send_only_events: Mutex::new(Vec::new()),
			#[cfg(peer_storage)]
			our_peerstorage_encryption_key: _our_peerstorage_encryption_key,
			deferred,
			pending_ops: Mutex::new(VecDeque::new()),
			flush_lock: Mutex::new(()),
		}
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	/// Dispatches to per-channel monitors, which are responsible for updating their on-chain view
	/// of a channel and reacting accordingly based on transactions in the given chain data. See
	/// [`ChannelMonitor::block_connected`] for details. Any HTLCs that were resolved on chain will
	/// be returned by [`chain::Watch::release_pending_monitor_events`].
	///
	/// Calls back to [`chain::Filter`] if any monitor indicated new outputs to watch. Subsequent
	/// calls must not exclude any transactions matching the new outputs nor any in-block
	/// descendants of such transactions. It is not necessary to re-fetch the block to obtain
	/// updated `txdata`.
	///
	/// Calls which represent a new blockchain tip height should set `best_height`.
	fn process_chain_data<FN>(
		&self, header: &Header, best_height: Option<u32>, txdata: &TransactionData, process: FN,
	) where
		FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs>,
	{
		let err_str = "ChannelMonitor[Update] persistence failed unrecoverably. This indicates we cannot continue normal operation and must shut down.";
		let channel_ids = hash_set_from_iter(self.monitors.read().unwrap().keys().cloned());
		let channel_count = channel_ids.len();
		for channel_id in channel_ids.iter() {
			let monitor_lock = self.monitors.read().unwrap();
			if let Some(monitor_state) = monitor_lock.get(channel_id) {
				let update_res = self.update_monitor_with_chain_data(
					header,
					best_height,
					txdata,
					&process,
					channel_id,
					&monitor_state,
					channel_count,
				);
				if update_res.is_err() {
					// Take the monitors lock for writing so that we poison it and any future
					// operations going forward fail immediately.
					core::mem::drop(monitor_lock);
					let _poison = self.monitors.write().unwrap();
					log_error!(self.logger, "{}", err_str);
					panic!("{}", err_str);
				}
			}
		}

		// Do another pass to handle any monitors added in between iterations.
		let monitor_states = self.monitors.write().unwrap();
		for (channel_id, monitor_state) in monitor_states.iter() {
			if !channel_ids.contains(channel_id) {
				let update_res = self.update_monitor_with_chain_data(
					header,
					best_height,
					txdata,
					&process,
					channel_id,
					&monitor_state,
					channel_count,
				);
				if update_res.is_err() {
					log_error!(self.logger, "{}", err_str);
					panic!("{}", err_str);
				}
			}
		}

		if let Some(height) = best_height {
			// If the best block height is being updated, update highest_chain_height under the
			// monitors write lock.
			let old_height = self.highest_chain_height.load(Ordering::Acquire);
			let new_height = height as usize;
			if new_height > old_height {
				self.highest_chain_height.store(new_height, Ordering::Release);
			}
		}
	}

	fn update_monitor_with_chain_data<FN>(
		&self, header: &Header, best_height: Option<u32>, txdata: &TransactionData, process: FN,
		channel_id: &ChannelId, monitor_state: &MonitorHolder<ChannelSigner>, channel_count: usize,
	) -> Result<(), ()>
	where
		FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs>,
	{
		let monitor = &monitor_state.monitor;
		let logger = WithChannelMonitor::from(&self.logger, &monitor, None);

		let mut txn_outputs = process(monitor, txdata);

		let get_partition_key = |channel_id: &ChannelId| {
			let channel_id_bytes = channel_id.0;
			let channel_id_u32 = u32::from_be_bytes([
				channel_id_bytes[0],
				channel_id_bytes[1],
				channel_id_bytes[2],
				channel_id_bytes[3],
			]);
			best_height.map(|height| channel_id_u32.wrapping_add(height))
		};

		let partition_factor = if channel_count < 15 {
			5
		} else {
			50 // ~ 8hours
		};

		let has_pending_claims = monitor_state.monitor.has_pending_claims();
		if has_pending_claims
			|| get_partition_key(channel_id).is_some_and(|key| key % partition_factor == 0)
		{
			log_trace!(logger, "Syncing Channel Monitor");
			// Even though we don't track monitor updates from chain-sync as pending, we still want
			// updates per-channel to be well-ordered so that users don't see a
			// `ChannelMonitorUpdate` after a channel persist for a channel with the same
			// `latest_update_id`.
			let _pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
			match self.persister.update_persisted_channel(monitor.persistence_key(), None, monitor)
			{
				ChannelMonitorUpdateStatus::Completed => {
					log_trace!(logger, "Finished syncing Channel Monitor for block-data")
				},
				ChannelMonitorUpdateStatus::InProgress => {
					log_trace!(
						logger,
						"Channel Monitor sync for channel {} in progress.",
						log_funding_info!(monitor)
					);
				},
				ChannelMonitorUpdateStatus::UnrecoverableError => {
					return Err(());
				},
			}
		}

		// Register any new outputs with the chain source for filtering, storing any dependent
		// transactions from within the block that previously had not been included in txdata.
		if let Some(ref chain_source) = self.chain_source {
			let block_hash = header.block_hash();
			for (txid, mut outputs) in txn_outputs.drain(..) {
				for (idx, output) in outputs.drain(..) {
					// Register any new outputs with the chain source for filtering
					let output = WatchedOutput {
						block_hash: Some(block_hash),
						outpoint: OutPoint { txid, index: idx as u16 },
						script_pubkey: output.script_pubkey,
					};
					log_trace!(
						logger,
						"Adding monitoring for spends of outpoint {} to the filter",
						output.outpoint
					);
					chain_source.register_output(output);
				}
			}
		}
		Ok(())
	}

	/// Creates a new `ChainMonitor` used to watch on-chain activity pertaining to channels.
	///
	/// When an optional chain source implementing [`chain::Filter`] is provided, the chain monitor
	/// will call back to it indicating transactions and outputs of interest. This allows clients to
	/// pre-filter blocks or only fetch blocks matching a compact filter. Otherwise, clients may
	/// always need to fetch full blocks absent another means for determining which blocks contain
	/// transactions relevant to the watched channels.
	///
	/// # Note
	/// `our_peerstorage_encryption_key` must be obtained from [`NodeSigner::get_peer_storage_key`].
	/// This key is used to encrypt peer storage backups.
	///
	/// **Important**: This key should not be set arbitrarily or changed after initialization. The same key
	/// is obtained by the [`ChannelManager`] through [`NodeSigner`] to decrypt peer backups.
	/// Using an inconsistent or incorrect key will result in the inability to decrypt previously encrypted backups.
	///
	/// When `deferred` is `true`, [`chain::Watch::watch_channel`] and
	/// [`chain::Watch::update_channel`] calls are not executed immediately. Instead, they are
	/// queued internally and must be flushed by the caller via [`Self::flush`]. Use
	/// [`Self::pending_operation_count`] to check how many operations are queued, then call
	/// [`Self::flush`] to process them. This allows the caller to ensure that the
	/// [`ChannelManager`] is persisted before its associated monitors, avoiding the risk of
	/// force closures from a crash between monitor and channel manager persistence.
	///
	/// When `deferred` is `false`, monitor operations are executed inline as usual.
	///
	/// [`NodeSigner`]: crate::sign::NodeSigner
	/// [`NodeSigner::get_peer_storage_key`]: crate::sign::NodeSigner::get_peer_storage_key
	/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
	pub fn new(
		chain_source: Option<C>, broadcaster: T, logger: L, feeest: F, persister: P,
		_entropy_source: ES, _our_peerstorage_encryption_key: PeerStorageKey, deferred: bool,
	) -> Self {
		Self {
			monitors: RwLock::new(new_hash_map()),
			chain_source,
			broadcaster,
			logger,
			fee_estimator: feeest,
			persister,
			_entropy_source,
			pending_monitor_events: Mutex::new(Vec::new()),
			highest_chain_height: AtomicUsize::new(0),
			event_notifier: Arc::new(Notifier::new()),
			pending_send_only_events: Mutex::new(Vec::new()),
			#[cfg(peer_storage)]
			our_peerstorage_encryption_key: _our_peerstorage_encryption_key,
			deferred,
			pending_ops: Mutex::new(VecDeque::new()),
			flush_lock: Mutex::new(()),
		}
	}

	/// Gets the balances in the contained [`ChannelMonitor`]s which are claimable on-chain or
	/// claims which are awaiting confirmation.
	///
	/// Includes the balances from each [`ChannelMonitor`] *except* those included in
	/// `ignored_channels`.
	///
	/// See [`ChannelMonitor::get_claimable_balances`] for more details on the exact criteria for
	/// inclusion in the return value.
	pub fn get_claimable_balances(&self, ignored_channels: &[&ChannelDetails]) -> Vec<Balance> {
		let mut ret = Vec::new();
		let monitor_states = self.monitors.read().unwrap();
		for (_, monitor_state) in monitor_states.iter().filter(|(channel_id, _)| {
			for chan in ignored_channels {
				if chan.channel_id == **channel_id {
					return false;
				}
			}
			true
		}) {
			ret.append(&mut monitor_state.monitor.get_claimable_balances());
		}
		ret
	}

	/// Gets the [`LockedChannelMonitor`] for a given channel ID, returning an `Err` if no
	/// such [`ChannelMonitor`] is currently being monitored for.
	///
	/// Note that the result holds a mutex over our monitor set, and should not be held
	/// indefinitely.
	pub fn get_monitor(
		&self, channel_id: ChannelId,
	) -> Result<LockedChannelMonitor<'_, ChannelSigner>, ()> {
		let lock = self.monitors.read().unwrap();
		if lock.get(&channel_id).is_some() {
			Ok(LockedChannelMonitor { lock, channel_id })
		} else {
			Err(())
		}
	}

	/// Lists the channel ID of each [`ChannelMonitor`] being monitored.
	///
	/// Note that [`ChannelMonitor`]s are not removed when a channel is closed as they are always
	/// monitoring for on-chain state resolutions.
	pub fn list_monitors(&self) -> Vec<ChannelId> {
		self.monitors.read().unwrap().keys().copied().collect()
	}

	#[cfg(not(c_bindings))]
	/// Lists the pending updates for each [`ChannelMonitor`] (by `ChannelId` being monitored).
	/// Each `Vec<u64>` contains `update_id`s from [`ChannelMonitor::get_latest_update_id`] for updates
	/// that have not yet been fully persisted. Note that if a full monitor is persisted all the pending
	/// monitor updates must be individually marked completed by calling [`ChainMonitor::channel_monitor_updated`].
	pub fn list_pending_monitor_updates(&self) -> HashMap<ChannelId, Vec<u64>> {
		hash_map_from_iter(self.monitors.read().unwrap().iter().map(|(channel_id, holder)| {
			(*channel_id, holder.pending_monitor_updates.lock().unwrap().clone())
		}))
	}

	#[cfg(c_bindings)]
	/// Lists the pending updates for each [`ChannelMonitor`] (by `ChannelId` being monitored).
	/// Each `Vec<u64>` contains `update_id`s from [`ChannelMonitor::get_latest_update_id`] for updates
	/// that have not yet been fully persisted. Note that if a full monitor is persisted all the pending
	/// monitor updates must be individually marked completed by calling [`ChainMonitor::channel_monitor_updated`].
	pub fn list_pending_monitor_updates(&self) -> Vec<(ChannelId, Vec<u64>)> {
		let monitors = self.monitors.read().unwrap();
		monitors
			.iter()
			.map(|(channel_id, holder)| {
				(*channel_id, holder.pending_monitor_updates.lock().unwrap().clone())
			})
			.collect()
	}

	#[cfg(any(test, feature = "_test_utils"))]
	pub fn remove_monitor(&self, channel_id: &ChannelId) -> ChannelMonitor<ChannelSigner> {
		self.monitors.write().unwrap().remove(channel_id).unwrap().monitor
	}

	/// Indicates the persistence of a [`ChannelMonitor`] has completed after
	/// [`ChannelMonitorUpdateStatus::InProgress`] was returned from an update operation.
	///
	/// Thus, the anticipated use is, at a high level:
	///  1) This [`ChainMonitor`] calls [`Persist::update_persisted_channel`] which stores the
	///     update to disk and begins updating any remote (e.g. watchtower/backup) copies,
	///     returning [`ChannelMonitorUpdateStatus::InProgress`],
	///  2) once all remote copies are updated, you call this function with [`ChannelMonitor::get_latest_update_id`]
	///     or [`ChannelMonitorUpdate::update_id`] as the `completed_update_id`, and once all pending
	///     updates have completed the channel will be re-enabled.
	///
	/// It is only necessary to call [`ChainMonitor::channel_monitor_updated`] when you return [`ChannelMonitorUpdateStatus::InProgress`]
	/// from [`Persist`] and either:
	///   1. A new [`ChannelMonitor`] was added in [`Persist::persist_new_channel`], or
	///   2. A [`ChannelMonitorUpdate`] was provided as part of [`Persist::update_persisted_channel`].
	/// Note that we don't care about calls to [`Persist::update_persisted_channel`] where no
	/// [`ChannelMonitorUpdate`] was provided.
	///
	/// Returns an [`APIError::APIMisuseError`] if `channel_id` does not match any currently
	/// registered [`ChannelMonitor`]s.
	pub fn channel_monitor_updated(
		&self, channel_id: ChannelId, completed_update_id: u64,
	) -> Result<(), APIError> {
		let monitors = self.monitors.read().unwrap();
		let monitor_data = if let Some(mon) = monitors.get(&channel_id) {
			mon
		} else {
			return Err(APIError::APIMisuseError {
				err: format!("No ChannelMonitor matching channel ID {} found", channel_id),
			});
		};
		let mut pending_monitor_updates = monitor_data.pending_monitor_updates.lock().unwrap();
		pending_monitor_updates.retain(|update_id| *update_id != completed_update_id);

		// Note that we only check for pending non-chainsync monitor updates and we don't track monitor
		// updates resulting from chainsync in `pending_monitor_updates`.
		let monitor_is_pending_updates = monitor_data.has_pending_updates(&pending_monitor_updates);
		log_debug!(
			self.logger,
			"Completed off-chain monitor update {} for channel with channel ID {}, {}",
			completed_update_id,
			channel_id,
			if monitor_is_pending_updates {
				"still have pending off-chain updates"
			} else {
				"all off-chain updates complete, returning a MonitorEvent"
			}
		);
		if monitor_is_pending_updates {
			// If there are still monitor updates pending, we cannot yet construct a
			// Completed event.
			return Ok(());
		}
		let funding_txo = monitor_data.monitor.get_funding_txo();
		self.pending_monitor_events.lock().unwrap().push((
			funding_txo,
			channel_id,
			vec![MonitorEvent::Completed {
				funding_txo,
				channel_id,
				monitor_update_id: monitor_data.monitor.get_latest_update_id(),
			}],
			monitor_data.monitor.get_counterparty_node_id(),
		));

		self.event_notifier.notify();
		Ok(())
	}

	/// This wrapper avoids having to update some of our tests for now as they assume the direct
	/// chain::Watch API wherein we mark a monitor fully-updated by just calling
	/// channel_monitor_updated once with the highest ID.
	#[cfg(any(test, fuzzing))]
	pub fn force_channel_monitor_updated(&self, channel_id: ChannelId, monitor_update_id: u64) {
		let monitors = self.monitors.read().unwrap();
		let monitor = &monitors.get(&channel_id).unwrap().monitor;
		let counterparty_node_id = monitor.get_counterparty_node_id();
		let funding_txo = monitor.get_funding_txo();
		self.pending_monitor_events.lock().unwrap().push((
			funding_txo,
			channel_id,
			vec![MonitorEvent::Completed { funding_txo, channel_id, monitor_update_id }],
			counterparty_node_id,
		));
		self.event_notifier.notify();
	}

	#[cfg(any(test, feature = "_test_utils"))]
	pub fn get_and_clear_pending_events(&self) -> Vec<events::Event> {
		use crate::events::EventsProvider;
		let events = core::cell::RefCell::new(Vec::new());
		let event_handler = |event: events::Event| Ok(events.borrow_mut().push(event));
		self.process_pending_events(&event_handler);
		events.into_inner()
	}

	/// Processes any events asynchronously in the order they were generated since the last call
	/// using the given event handler.
	///
	/// See the trait-level documentation of [`EventsProvider`] for requirements.
	///
	/// [`EventsProvider`]: crate::events::EventsProvider
	pub async fn process_pending_events_async<
		Future: core::future::Future<Output = Result<(), ReplayEvent>>,
		H: Fn(Event) -> Future,
	>(
		&self, handler: H,
	) {
		// Sadly we can't hold the monitors read lock through an async call. Thus we have to do a
		// crazy dance to process a monitor's events then only remove them once we've done so.
		let mons_to_process = self.monitors.read().unwrap().keys().cloned().collect::<Vec<_>>();
		for channel_id in mons_to_process {
			let mut ev;
			match super::channelmonitor::process_events_body!(
				self.monitors.read().unwrap().get(&channel_id).map(|m| &m.monitor),
				self.logger,
				ev,
				handler(ev).await
			) {
				Ok(()) => {},
				Err(ReplayEvent()) => {
					self.event_notifier.notify();
				},
			}
		}
	}

	/// Gets a [`Future`] that completes when an event is available either via
	/// [`chain::Watch::release_pending_monitor_events`] or
	/// [`EventsProvider::process_pending_events`].
	///
	/// Note that callbacks registered on the [`Future`] MUST NOT call back into this
	/// [`ChainMonitor`] and should instead register actions to be taken later.
	///
	/// [`EventsProvider::process_pending_events`]: crate::events::EventsProvider::process_pending_events
	pub fn get_update_future(&self) -> Future {
		self.event_notifier.get_future()
	}

	/// Triggers rebroadcasts/fee-bumps of pending claims from a force-closed channel. This is
	/// crucial in preventing certain classes of pinning attacks, detecting substantial mempool
	/// feerate changes between blocks, and ensuring reliability if broadcasting fails. We recommend
	/// invoking this every 30 seconds, or lower if running in an environment with spotty
	/// connections, like on mobile.
	pub fn rebroadcast_pending_claims(&self) {
		let monitors = self.monitors.read().unwrap();
		for (_, monitor_holder) in &*monitors {
			monitor_holder.monitor.rebroadcast_pending_claims(
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			)
		}
	}

	/// Triggers rebroadcasts of pending claims from force-closed channels after a transaction
	/// signature generation failure.
	///
	/// `monitor_opt` can be used as a filter to only trigger them for a specific channel monitor.
	pub fn signer_unblocked(&self, monitor_opt: Option<ChannelId>) {
		let monitors = self.monitors.read().unwrap();
		if let Some(channel_id) = monitor_opt {
			if let Some(monitor_holder) = monitors.get(&channel_id) {
				monitor_holder.monitor.signer_unblocked(
					&self.broadcaster,
					&self.fee_estimator,
					&self.logger,
				)
			}
		} else {
			for (_, monitor_holder) in &*monitors {
				monitor_holder.monitor.signer_unblocked(
					&self.broadcaster,
					&self.fee_estimator,
					&self.logger,
				)
			}
		}
	}

	/// 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().values() {
			let logger = WithChannelMonitor::from(&self.logger, &monitor_holder.monitor, None);
			let (is_fully_resolved, needs_persistence) =
				monitor_holder.monitor.check_and_update_full_resolution_status(&logger);
			if is_fully_resolved {
				have_monitors_to_prune = true;
			}
			if needs_persistence {
				self.persister.update_persisted_channel(
					monitor_holder.monitor.persistence_key(),
					None,
					&monitor_holder.monitor,
				);
			}
		}
		if have_monitors_to_prune {
			let mut monitors = self.monitors.write().unwrap();
			monitors.retain(|_channel_id, monitor_holder| {
				let logger = WithChannelMonitor::from(&self.logger, &monitor_holder.monitor, None);
				let (is_fully_resolved, _) =
					monitor_holder.monitor.check_and_update_full_resolution_status(&logger);
				if is_fully_resolved {
					log_info!(logger, "Archiving fully resolved ChannelMonitor");
					self.persister
						.archive_persisted_channel(monitor_holder.monitor.persistence_key());
					false
				} else {
					true
				}
			});
		}
	}

	/// This function collects the counterparty node IDs from all monitors into a `HashSet`,
	/// ensuring unique IDs are returned.
	#[cfg(peer_storage)]
	fn all_counterparty_node_ids(&self) -> HashSet<PublicKey> {
		let mon = self.monitors.read().unwrap();
		mon.values().map(|monitor| monitor.monitor.get_counterparty_node_id()).collect()
	}

	#[cfg(peer_storage)]
	fn send_peer_storage(&self, their_node_id: PublicKey) {
		let mut monitors_list: Vec<PeerStorageMonitorHolder> = Vec::new();
		let random_bytes = self._entropy_source.get_secure_random_bytes();

		const MAX_PEER_STORAGE_SIZE: usize = 65531;
		const USIZE_LEN: usize = core::mem::size_of::<usize>();
		let mut random_bytes_cycle_iter = random_bytes.iter().cycle();

		let mut current_size = 0;
		let monitors_lock = self.monitors.read().unwrap();
		let mut channel_ids = monitors_lock.keys().copied().collect();

		fn next_random_id(
			channel_ids: &mut Vec<ChannelId>,
			random_bytes_cycle_iter: &mut Cycle<core::slice::Iter<u8>>,
		) -> Option<ChannelId> {
			if channel_ids.is_empty() {
				return None;
			}
			let random_idx = {
				let mut usize_bytes = [0u8; USIZE_LEN];
				usize_bytes.iter_mut().for_each(|b| {
					*b = *random_bytes_cycle_iter.next().expect("A cycle never ends")
				});
				// Take one more to introduce a slight misalignment.
				random_bytes_cycle_iter.next().expect("A cycle never ends");
				usize::from_le_bytes(usize_bytes) % channel_ids.len()
			};
			Some(channel_ids.swap_remove(random_idx))
		}

		while let Some(channel_id) = next_random_id(&mut channel_ids, &mut random_bytes_cycle_iter)
		{
			let monitor_holder = if let Some(monitor_holder) = monitors_lock.get(&channel_id) {
				monitor_holder
			} else {
				debug_assert!(
					false,
					"Tried to access non-existing monitor, this should never happen"
				);
				break;
			};

			let mut serialized_channel = VecWriter(Vec::new());
			let min_seen_secret = monitor_holder.monitor.get_min_seen_secret();
			let counterparty_node_id = monitor_holder.monitor.get_counterparty_node_id();
			{
				let inner_lock = monitor_holder.monitor.inner.lock().unwrap();

				write_chanmon_internal(&inner_lock, true, &mut serialized_channel)
					.expect("can not write Channel Monitor for peer storage message");
			}
			let peer_storage_monitor = PeerStorageMonitorHolder {
				channel_id,
				min_seen_secret,
				counterparty_node_id,
				monitor_bytes: serialized_channel.0,
			};

			let serialized_length = peer_storage_monitor.serialized_length();

			if current_size + serialized_length > MAX_PEER_STORAGE_SIZE {
				continue;
			} else {
				current_size += serialized_length;
				monitors_list.push(peer_storage_monitor);
			}
		}

		let serialised_channels = monitors_list.encode();
		let our_peer_storage = DecryptedOurPeerStorage::new(serialised_channels);
		let cipher = our_peer_storage.encrypt(&self.our_peerstorage_encryption_key, &random_bytes);

		log_debug!(self.logger, "Sending Peer Storage to {}", log_pubkey!(their_node_id));
		let send_peer_storage_event = MessageSendEvent::SendPeerStorage {
			node_id: their_node_id,
			msg: PeerStorage { data: cipher.into_vec() },
		};

		self.pending_send_only_events.lock().unwrap().push(send_peer_storage_event)
	}

	/// Loads a [`ChannelMonitor`] which already exists on disk after startup.
	///
	/// Using this over [`chain::Watch::watch_channel`] avoids re-persisting a [`ChannelMonitor`]
	/// that hasn't changed, slowing down startup.
	///
	/// Note that this method *can* be used if additional blocks were replayed against the
	/// [`ChannelMonitor`] or if a [`ChannelMonitorUpdate`] loaded from disk was replayed such that
	/// it will replayed on startup, and in general can only *not* be used if you directly accessed
	/// the [`ChannelMonitor`] and changed its state in some way that will not be replayed again on
	/// a restart. Such direct access should generally never occur for most LDK-based nodes.
	///
	/// For [`ChannelMonitor`]s which were last serialized by an LDK version prior to 0.1 this will
	/// fall back to calling [`chain::Watch::watch_channel`] and persisting the [`ChannelMonitor`].
	/// See the release notes for LDK 0.1 for more information on this requirement.
	///
	/// [`ChannelMonitor`]s which do not need to be persisted (i.e. were last written by LDK 0.1 or
	/// later) will be loaded without persistence and this method will return
	/// [`ChannelMonitorUpdateStatus::Completed`].
	pub fn load_existing_monitor(
		&self, channel_id: ChannelId, monitor: ChannelMonitor<ChannelSigner>,
	) -> Result<ChannelMonitorUpdateStatus, ()> {
		if !monitor.written_by_0_1_or_later() {
			return self.watch_channel_internal(channel_id, monitor);
		}

		let logger = WithChannelMonitor::from(&self.logger, &monitor, None);
		let mut monitors = self.monitors.write().unwrap();
		let entry = match monitors.entry(channel_id) {
			hash_map::Entry::Occupied(_) => {
				log_error!(logger, "Failed to add new channel data: channel monitor for given channel ID is already present");
				return Err(());
			},
			hash_map::Entry::Vacant(e) => e,
		};
		log_trace!(logger, "Loaded existing ChannelMonitor");
		if let Some(ref chain_source) = self.chain_source {
			monitor.load_outputs_to_watch(chain_source, &self.logger);
		}
		entry.insert(MonitorHolder { monitor, pending_monitor_updates: Mutex::new(Vec::new()) });

		Ok(ChannelMonitorUpdateStatus::Completed)
	}

	fn watch_channel_internal(
		&self, channel_id: ChannelId, monitor: ChannelMonitor<ChannelSigner>,
	) -> Result<ChannelMonitorUpdateStatus, ()> {
		let logger = WithChannelMonitor::from(&self.logger, &monitor, None);
		let mut monitors = self.monitors.write().unwrap();
		let entry = match monitors.entry(channel_id) {
			hash_map::Entry::Occupied(_) => {
				log_error!(logger, "Failed to add new channel data: channel monitor for given channel ID is already present");
				return Err(());
			},
			hash_map::Entry::Vacant(e) => e,
		};
		log_trace!(logger, "Got new ChannelMonitor");
		let update_id = monitor.get_latest_update_id();
		let mut pending_monitor_updates = Vec::new();
		let persist_res = self.persister.persist_new_channel(monitor.persistence_key(), &monitor);
		match persist_res {
			ChannelMonitorUpdateStatus::InProgress => {
				log_info!(logger, "Persistence of new ChannelMonitor in progress",);
				pending_monitor_updates.push(update_id);
			},
			ChannelMonitorUpdateStatus::Completed => {
				log_info!(logger, "Persistence of new ChannelMonitor completed",);
			},
			ChannelMonitorUpdateStatus::UnrecoverableError => {
				let err_str = "ChannelMonitor[Update] persistence failed unrecoverably. This indicates we cannot continue normal operation and must shut down.";
				log_error!(logger, "{}", err_str);
				panic!("{}", err_str);
			},
		}
		if let Some(ref chain_source) = self.chain_source {
			monitor.load_outputs_to_watch(chain_source, &self.logger);
		}
		entry.insert(MonitorHolder {
			monitor,
			pending_monitor_updates: Mutex::new(pending_monitor_updates),
		});
		Ok(persist_res)
	}

	fn update_channel_internal(
		&self, channel_id: ChannelId, update: &ChannelMonitorUpdate,
	) -> ChannelMonitorUpdateStatus {
		// `ChannelMonitorUpdate`'s `channel_id` is `None` prior to 0.0.121 and all channels in those
		// versions are V1-established. For 0.0.121+ the `channel_id` fields is always `Some`.
		debug_assert_eq!(update.channel_id.unwrap(), channel_id);
		// Update the monitor that watches the channel referred to by the given outpoint.
		let monitors = self.monitors.read().unwrap();
		match monitors.get(&channel_id) {
			None => {
				let logger = WithContext::from(&self.logger, None, Some(channel_id), None);
				log_error!(logger, "Failed to update channel monitor: no such monitor registered");

				// We should never ever trigger this from within ChannelManager. Technically a
				// user could use this object with some proxying in between which makes this
				// possible, but in tests and fuzzing, this should be a panic.
				#[cfg(debug_assertions)]
				panic!("ChannelManager generated a channel update for a channel that was not yet registered!");
				#[cfg(not(debug_assertions))]
				ChannelMonitorUpdateStatus::InProgress
			},
			Some(monitor_state) => {
				let monitor = &monitor_state.monitor;
				let logger = WithChannelMonitor::from(&self.logger, &monitor, None);
				log_trace!(logger, "Updating ChannelMonitor to id {}", update.update_id,);

				// We hold a `pending_monitor_updates` lock through `update_monitor` to ensure we
				// have well-ordered updates from the users' point of view. See the
				// `pending_monitor_updates` docs for more.
				let mut pending_monitor_updates =
					monitor_state.pending_monitor_updates.lock().unwrap();
				let update_res = monitor.update_monitor(
					update,
					&self.broadcaster,
					&self.fee_estimator,
					&self.logger,
				);

				let update_id = update.update_id;
				let persist_res = if update_res.is_err() {
					// Even if updating the monitor returns an error, the monitor's state will
					// still be changed. Therefore, we should persist the updated monitor despite the error.
					// We don't want to persist a `monitor_update` which results in a failure to apply later
					// while reading `channel_monitor` with updates from storage. Instead, we should persist
					// the entire `channel_monitor` here.
					log_warn!(logger, "Failed to update ChannelMonitor. Going ahead and persisting the entire ChannelMonitor");
					self.persister.update_persisted_channel(
						monitor.persistence_key(),
						None,
						monitor,
					)
				} else {
					self.persister.update_persisted_channel(
						monitor.persistence_key(),
						Some(update),
						monitor,
					)
				};
				match persist_res {
					ChannelMonitorUpdateStatus::InProgress => {
						pending_monitor_updates.push(update_id);
						log_debug!(
							logger,
							"Persistence of ChannelMonitorUpdate id {:?} in progress",
							update_id,
						);
					},
					ChannelMonitorUpdateStatus::Completed => {
						log_debug!(
							logger,
							"Persistence of ChannelMonitorUpdate id {:?} completed",
							update_id,
						);
					},
					ChannelMonitorUpdateStatus::UnrecoverableError => {
						// Take the monitors lock for writing so that we poison it and any future
						// operations going forward fail immediately.
						core::mem::drop(pending_monitor_updates);
						core::mem::drop(monitors);
						let _poison = self.monitors.write().unwrap();
						let err_str = "ChannelMonitor[Update] persistence failed unrecoverably. This indicates we cannot continue normal operation and must shut down.";
						log_error!(logger, "{}", err_str);
						panic!("{}", err_str);
					},
				}

				// We may need to start monitoring for any alternative funding transactions.
				if let Some(ref chain_source) = self.chain_source {
					for (funding_outpoint, funding_script) in
						update.internal_renegotiated_funding_data()
					{
						log_trace!(
							logger,
							"Registering renegotiated funding outpoint {} with the filter to monitor confirmations and spends",
							funding_outpoint
						);
						chain_source.register_tx(&funding_outpoint.txid, &funding_script);
						chain_source.register_output(WatchedOutput {
							block_hash: None,
							outpoint: funding_outpoint,
							script_pubkey: funding_script,
						});
					}
				}

				debug_assert!(
					update_res.is_ok() || monitor.no_further_updates_allowed(),
					"update_monitor returned Err but channel is not post-close",
				);

				// We also check update_res.is_err() as a defensive measure: an
				// error should only occur on a post-close monitor (validated by
				// the debug_assert above), but we defer here regardless to avoid
				// returning Completed for a failed update.
				if (update_res.is_err() || monitor.no_further_updates_allowed())
					&& persist_res == ChannelMonitorUpdateStatus::Completed
				{
					// The channel is post-close (funding spend seen, lockdown, or
					// holder tx signed). Return InProgress so ChannelManager freezes
					// the channel until the force-close MonitorEvents are processed.
					// Push a Completed event into pending_monitor_events so it gets
					// picked up after the per-monitor events in the next
					// release_pending_monitor_events call.
					let funding_txo = monitor.get_funding_txo();
					let channel_id = monitor.channel_id();
					self.pending_monitor_events.lock().unwrap().push((
						funding_txo,
						channel_id,
						vec![MonitorEvent::Completed {
							funding_txo,
							channel_id,
							monitor_update_id: monitor.get_latest_update_id(),
						}],
						monitor.get_counterparty_node_id(),
					));
					log_debug!(
						logger,
						"Deferring completion of ChannelMonitorUpdate id {:?} (channel is post-close)",
						update_id,
					);
					ChannelMonitorUpdateStatus::InProgress
				} else {
					persist_res
				}
			},
		}
	}

	/// Returns the number of pending monitor operations queued for later execution.
	///
	/// When the `ChainMonitor` is constructed with `deferred` set to `true`,
	/// [`chain::Watch::watch_channel`] and [`chain::Watch::update_channel`] calls are queued
	/// instead of being executed immediately. Call this method to determine how many operations
	/// are waiting, then pass the result to [`Self::flush`] to process them.
	pub fn pending_operation_count(&self) -> usize {
		self.pending_ops.lock().unwrap().len()
	}

	/// Flushes the first `count` pending monitor operations that were queued while the
	/// `ChainMonitor` operates in deferred mode. `count` must not exceed the number of
	/// pending operations returned by [`Self::pending_operation_count`].
	///
	/// A typical usage pattern is to call [`Self::pending_operation_count`], persist the
	/// [`ChannelManager`], then pass the count to this method to flush the queued operations.
	///
	/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
	pub fn flush(&self, count: usize, logger: &L) {
		let _guard = self.flush_lock.lock().unwrap();
		if count == 0 {
			return;
		}
		log_info!(logger, "Flushing up to {} monitor operations", count);
		for _ in 0..count {
			let mut queue = self.pending_ops.lock().unwrap();
			let op = match queue.pop_front() {
				Some(op) => op,
				None => {
					debug_assert!(false, "flush count exceeded queue length");
					log_error!(logger, "flush count exceeded queue length");
					return;
				},
			};

			let (channel_id, update_id, status) = match op {
				PendingMonitorOp::NewMonitor { channel_id, monitor } => {
					let logger = WithChannelMonitor::from(logger, &monitor, None);
					let update_id = monitor.get_latest_update_id();
					log_trace!(logger, "Flushing new monitor");
					// Hold `pending_ops` across the internal call so that
					// `watch_channel` (which checks `monitors` + `pending_ops`
					// atomically) cannot race with this insertion.
					match self.watch_channel_internal(channel_id, monitor) {
						Ok(status) => {
							drop(queue);
							(channel_id, update_id, status)
						},
						Err(()) => {
							// `watch_channel` checks both `pending_ops` and `monitors`
							// for duplicates before queueing, so this is unreachable.
							unreachable!();
						},
					}
				},
				PendingMonitorOp::Update { channel_id, update } => {
					let logger = WithContext::from(logger, None, Some(channel_id), None);
					log_trace!(logger, "Flushing monitor update {}", update.update_id);
					// Release `pending_ops` before the internal call so that
					// concurrent `update_channel` queuing is not blocked.
					drop(queue);
					let update_id = update.update_id;
					let status = self.update_channel_internal(channel_id, &update);
					(channel_id, update_id, status)
				},
			};

			match status {
				ChannelMonitorUpdateStatus::Completed => {
					let logger = WithContext::from(logger, None, Some(channel_id), None);
					if let Err(e) = self.channel_monitor_updated(channel_id, update_id) {
						debug_assert!(false, "channel_monitor_updated failed: {:?}", e);
						log_error!(logger, "channel_monitor_updated failed: {:?}", e);
					}
				},
				ChannelMonitorUpdateStatus::InProgress => {},
				ChannelMonitorUpdateStatus::UnrecoverableError => {
					// Neither watch_channel_internal nor update_channel_internal
					// return UnrecoverableError; they panic on that variant
					// before it can be returned.
					unreachable!();
				},
			}
		}

		// A flushed monitor update may have generated new events, so assume we have
		// some and wake the event processor.
		self.event_notifier.notify();
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> BaseMessageHandler for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent> {
		let mut pending_events = self.pending_send_only_events.lock().unwrap();
		core::mem::take(&mut *pending_events)
	}

	fn peer_disconnected(&self, _their_node_id: PublicKey) {}

	fn provided_node_features(&self) -> NodeFeatures {
		NodeFeatures::empty()
	}

	fn provided_init_features(&self, _their_node_id: PublicKey) -> InitFeatures {
		InitFeatures::empty()
	}

	fn peer_connected(
		&self, _their_node_id: PublicKey, _msg: &Init, _inbound: bool,
	) -> Result<(), ()> {
		Ok(())
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> SendOnlyMessageHandler for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> chain::Listen for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	fn filtered_block_connected(&self, header: &Header, txdata: &TransactionData, height: u32) {
		log_debug!(
			self.logger,
			"New best block {} at height {} provided via block_connected",
			header.block_hash(),
			height
		);
		self.process_chain_data(header, Some(height), &txdata, |monitor, txdata| {
			monitor.block_connected(
				header,
				txdata,
				height,
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			)
		});

		#[cfg(peer_storage)]
		// Send peer storage everytime a new block arrives.
		for node_id in self.all_counterparty_node_ids() {
			self.send_peer_storage(node_id);
		}

		// Assume we may have some new events and wake the event processor
		self.event_notifier.notify();
	}

	fn blocks_disconnected(&self, fork_point: BlockLocator) {
		let monitor_states = self.monitors.read().unwrap();
		log_debug!(
			self.logger,
			"Block(s) removed to height {} via blocks_disconnected. New best block is {}",
			fork_point.height,
			fork_point.block_hash,
		);
		for monitor_state in monitor_states.values() {
			monitor_state.monitor.blocks_disconnected(
				fork_point,
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			);
		}
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> chain::Confirm for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	fn transactions_confirmed(&self, header: &Header, txdata: &TransactionData, height: u32) {
		log_debug!(
			self.logger,
			"{} provided transactions confirmed at height {} in block {}",
			txdata.len(),
			height,
			header.block_hash()
		);
		self.process_chain_data(header, None, txdata, |monitor, txdata| {
			monitor.transactions_confirmed(
				header,
				txdata,
				height,
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			)
		});
		// Assume we may have some new events and wake the event processor
		self.event_notifier.notify();
	}

	fn transaction_unconfirmed(&self, txid: &Txid) {
		log_debug!(self.logger, "Transaction {} reorganized out of chain", txid);
		let monitor_states = self.monitors.read().unwrap();
		for monitor_state in monitor_states.values() {
			monitor_state.monitor.transaction_unconfirmed(
				txid,
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			);
		}
	}

	fn best_block_updated(&self, header: &Header, height: u32) {
		log_debug!(
			self.logger,
			"New best block {} at height {} provided via best_block_updated",
			header.block_hash(),
			height
		);
		self.process_chain_data(header, Some(height), &[], |monitor, txdata| {
			// While in practice there shouldn't be any recursive calls when given empty txdata,
			// it's still possible if a chain::Filter implementation returns a transaction.
			debug_assert!(txdata.is_empty());
			monitor.best_block_updated(
				header,
				height,
				&self.broadcaster,
				&self.fee_estimator,
				&self.logger,
			)
		});

		#[cfg(peer_storage)]
		// Send peer storage everytime a new block arrives.
		for node_id in self.all_counterparty_node_ids() {
			self.send_peer_storage(node_id);
		}

		// Assume we may have some new events and wake the event processor
		self.event_notifier.notify();
	}

	fn get_relevant_txids(&self) -> Vec<(Txid, u32, Option<BlockHash>)> {
		let mut txids = Vec::new();
		let monitor_states = self.monitors.read().unwrap();
		for monitor_state in monitor_states.values() {
			txids.append(&mut monitor_state.monitor.get_relevant_txids());
		}

		txids.sort_unstable_by(|a, b| a.0.cmp(&b.0).then(b.1.cmp(&a.1)));
		txids.dedup_by_key(|(txid, _, _)| *txid);
		txids
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> chain::Watch<ChannelSigner> for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	fn watch_channel(
		&self, channel_id: ChannelId, monitor: ChannelMonitor<ChannelSigner>,
	) -> Result<ChannelMonitorUpdateStatus, ()> {
		if !self.deferred {
			return self.watch_channel_internal(channel_id, monitor);
		}

		// Atomically check for duplicates in both the pending queue and the
		// flushed monitor set.
		let mut pending_ops = self.pending_ops.lock().unwrap();
		let monitors = self.monitors.read().unwrap();
		if monitors.contains_key(&channel_id) {
			return Err(());
		}
		let already_pending = pending_ops.iter().any(|op| match op {
			PendingMonitorOp::NewMonitor { channel_id: id, .. } => *id == channel_id,
			_ => false,
		});
		if already_pending {
			return Err(());
		}
		pending_ops.push_back(PendingMonitorOp::NewMonitor { channel_id, monitor });
		Ok(ChannelMonitorUpdateStatus::InProgress)
	}

	fn update_channel(
		&self, channel_id: ChannelId, update: &ChannelMonitorUpdate,
	) -> ChannelMonitorUpdateStatus {
		if !self.deferred {
			return self.update_channel_internal(channel_id, update);
		}

		let mut pending_ops = self.pending_ops.lock().unwrap();
		debug_assert!(
			{
				let monitors = self.monitors.read().unwrap();
				let in_monitors = monitors.contains_key(&channel_id);
				let in_pending = pending_ops.iter().any(|op| match op {
					PendingMonitorOp::NewMonitor { channel_id: id, .. } => *id == channel_id,
					_ => false,
				});
				in_monitors || in_pending
			},
			"ChannelManager generated a channel update for a channel that was not yet registered!"
		);
		pending_ops.push_back(PendingMonitorOp::Update { channel_id, update: update.clone() });
		ChannelMonitorUpdateStatus::InProgress
	}

	fn release_pending_monitor_events(
		&self,
	) -> Vec<(OutPoint, ChannelId, Vec<MonitorEvent>, PublicKey)> {
		for (channel_id, update_id) in self.persister.get_and_clear_completed_updates() {
			let _ = self.channel_monitor_updated(channel_id, update_id);
		}
		let monitors = self.monitors.read().unwrap();
		let mut pending_monitor_events = Vec::new();
		for monitor_state in monitors.values() {
			let monitor_events = monitor_state.monitor.get_and_clear_pending_monitor_events();
			if monitor_events.len() > 0 {
				let monitor_funding_txo = monitor_state.monitor.get_funding_txo();
				let monitor_channel_id = monitor_state.monitor.channel_id();
				let counterparty_node_id = monitor_state.monitor.get_counterparty_node_id();
				pending_monitor_events.push((
					monitor_funding_txo,
					monitor_channel_id,
					monitor_events,
					counterparty_node_id,
				));
			}
		}
		// Drain pending_monitor_events (which includes deferred post-close
		// completions) after per-monitor events so that force-close
		// MonitorEvents are processed by ChannelManager first.
		pending_monitor_events.extend(self.pending_monitor_events.lock().unwrap().split_off(0));
		pending_monitor_events
	}
}

impl<
		ChannelSigner: EcdsaChannelSigner,
		C: chain::Filter,
		T: BroadcasterInterface,
		F: FeeEstimator,
		L: Logger,
		P: Deref,
		ES: EntropySource,
	> events::EventsProvider for ChainMonitor<ChannelSigner, C, T, F, L, P, ES>
where
	P::Target: Persist<ChannelSigner>,
{
	/// Processes [`SpendableOutputs`] events produced from each [`ChannelMonitor`] upon maturity.
	///
	/// For channels featuring anchor outputs, this method will also process [`BumpTransaction`]
	/// events produced from each [`ChannelMonitor`] while there is a balance to claim onchain
	/// within each channel. As the confirmation of a commitment transaction may be critical to the
	/// safety of funds, we recommend invoking this every 30 seconds, or lower if running in an
	/// environment with spotty connections, like on mobile.
	///
	/// An [`EventHandler`] may safely call back to the provider, though this shouldn't be needed in
	/// order to handle these events.
	///
	/// [`SpendableOutputs`]: events::Event::SpendableOutputs
	/// [`BumpTransaction`]: events::Event::BumpTransaction
	fn process_pending_events<H: Deref>(&self, handler: H)
	where
		H::Target: EventHandler,
	{
		for monitor_state in self.monitors.read().unwrap().values() {
			match monitor_state.monitor.process_pending_events(&handler, &self.logger) {
				Ok(()) => {},
				Err(ReplayEvent()) => {
					self.event_notifier.notify();
				},
			}
		}
	}
}

/// 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 super::ChainMonitor;
	use crate::chain::channelmonitor::{ChannelMonitorUpdate, ANTI_REORG_DELAY};
	use crate::chain::{ChannelMonitorUpdateStatus, Watch};
	use crate::events::{ClosureReason, Event};
	use crate::ln::functional_test_utils::*;
	use crate::ln::msgs::{BaseMessageHandler, ChannelMessageHandler, MessageSendEvent};
	use crate::ln::types::ChannelId;
	use crate::sign::NodeSigner;
	use crate::util::dyn_signer::DynSigner;
	use crate::util::test_channel_signer::TestChannelSigner;
	use crate::util::test_utils::{
		TestBroadcaster, TestChainSource, TestFeeEstimator, TestKeysInterface, TestLogger,
		TestPersister,
	};
	use crate::{expect_payment_path_successful, get_event_msg};
	use bitcoin::Network;

	const CHAINSYNC_MONITOR_PARTITION_FACTOR: u32 = 5;

	#[test]
	fn test_async_ooo_offchain_updates() {
		// Test that if we have multiple offchain updates being persisted and they complete
		// out-of-order, the ChainMonitor waits until all have completed before informing the
		// ChannelManager.
		let chanmon_cfgs = create_chanmon_cfgs(2);
		let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
		let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
		let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
		let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1).2;

		let node_a_id = nodes[0].node.get_our_node_id();
		let node_b_id = nodes[1].node.get_our_node_id();

		// Route two payments to be claimed at the same time.
		let (payment_preimage_1, payment_hash_1, ..) =
			route_payment(&nodes[0], &[&nodes[1]], 1_000_000);
		let (payment_preimage_2, payment_hash_2, ..) =
			route_payment(&nodes[0], &[&nodes[1]], 1_000_000);

		chanmon_cfgs[1].persister.offchain_monitor_updates.lock().unwrap().clear();
		chanmon_cfgs[1].persister.set_update_ret(ChannelMonitorUpdateStatus::InProgress);
		chanmon_cfgs[1].persister.set_update_ret(ChannelMonitorUpdateStatus::InProgress);

		nodes[1].node.claim_funds(payment_preimage_1);
		check_added_monitors(&nodes[1], 1);
		nodes[1].node.claim_funds(payment_preimage_2);
		check_added_monitors(&nodes[1], 1);

		let persistences =
			chanmon_cfgs[1].persister.offchain_monitor_updates.lock().unwrap().clone();
		assert_eq!(persistences.len(), 1);
		let (_, updates) = persistences.iter().next().unwrap();
		assert_eq!(updates.len(), 2);

		// Note that updates is a HashMap so the ordering here is actually random. This shouldn't
		// fail either way but if it fails intermittently it's depending on the ordering of updates.
		let mut update_iter = updates.iter();
		let next_update = update_iter.next().unwrap().clone();
		let node_b_mon = &nodes[1].chain_monitor.chain_monitor;

		// Should contain next_update when pending updates listed.
		let pending_updates = node_b_mon.list_pending_monitor_updates();
		#[cfg(not(c_bindings))]
		let pending_chan_updates = pending_updates.get(&channel_id).unwrap();
		#[cfg(c_bindings)]
		let pending_chan_updates =
			&pending_updates.iter().find(|(chan_id, _)| *chan_id == channel_id).unwrap().1;
		assert!(pending_chan_updates.contains(&next_update));

		node_b_mon.channel_monitor_updated(channel_id, next_update.clone()).unwrap();

		// Should not contain the previously pending next_update when pending updates listed.
		let pending_updates = node_b_mon.list_pending_monitor_updates();
		#[cfg(not(c_bindings))]
		let pending_chan_updates = pending_updates.get(&channel_id).unwrap();
		#[cfg(c_bindings)]
		let pending_chan_updates =
			&pending_updates.iter().find(|(chan_id, _)| *chan_id == channel_id).unwrap().1;
		assert!(!pending_chan_updates.contains(&next_update));

		assert!(nodes[1].chain_monitor.release_pending_monitor_events().is_empty());
		assert!(nodes[1].node.get_and_clear_pending_msg_events().is_empty());
		assert!(nodes[1].node.get_and_clear_pending_events().is_empty());

		let next_update = update_iter.next().unwrap().clone();
		node_b_mon.channel_monitor_updated(channel_id, next_update).unwrap();

		let claim_events = nodes[1].node.get_and_clear_pending_events();
		assert_eq!(claim_events.len(), 2);
		match claim_events[0] {
			Event::PaymentClaimed { ref payment_hash, amount_msat: 1_000_000, .. } => {
				assert_eq!(payment_hash_1, *payment_hash);
			},
			_ => panic!("Unexpected event"),
		}
		match claim_events[1] {
			Event::PaymentClaimed { ref payment_hash, amount_msat: 1_000_000, .. } => {
				assert_eq!(payment_hash_2, *payment_hash);
			},
			_ => panic!("Unexpected event"),
		}

		// Now manually walk the commitment signed dance - because we claimed two payments
		// back-to-back it doesn't fit into the neat walk commitment_signed_dance does.

		let mut updates = get_htlc_update_msgs(&nodes[1], &node_a_id);
		nodes[0].node.handle_update_fulfill_htlc(node_b_id, updates.update_fulfill_htlcs.remove(0));
		expect_payment_sent(&nodes[0], payment_preimage_1, None, false, false);
		nodes[0].node.handle_commitment_signed_batch_test(node_b_id, &updates.commitment_signed);
		check_added_monitors(&nodes[0], 1);
		let (as_first_raa, as_first_update) = get_revoke_commit_msgs(&nodes[0], &node_b_id);

		nodes[1].node.handle_revoke_and_ack(node_a_id, &as_first_raa);
		check_added_monitors(&nodes[1], 1);
		let mut bs_2nd_updates = get_htlc_update_msgs(&nodes[1], &node_a_id);
		nodes[1].node.handle_commitment_signed_batch_test(node_a_id, &as_first_update);
		check_added_monitors(&nodes[1], 1);
		let bs_first_raa = get_event_msg!(nodes[1], MessageSendEvent::SendRevokeAndACK, node_a_id);

		nodes[0]
			.node
			.handle_update_fulfill_htlc(node_b_id, bs_2nd_updates.update_fulfill_htlcs.remove(0));
		expect_payment_sent(&nodes[0], payment_preimage_2, None, false, false);
		nodes[0]
			.node
			.handle_commitment_signed_batch_test(node_b_id, &bs_2nd_updates.commitment_signed);
		check_added_monitors(&nodes[0], 1);
		nodes[0].node.handle_revoke_and_ack(node_b_id, &bs_first_raa);
		expect_payment_path_successful!(nodes[0]);
		check_added_monitors(&nodes[0], 1);
		let (as_second_raa, as_second_update) = get_revoke_commit_msgs(&nodes[0], &node_b_id);

		nodes[1].node.handle_revoke_and_ack(node_a_id, &as_second_raa);
		check_added_monitors(&nodes[1], 1);
		nodes[1].node.handle_commitment_signed_batch_test(node_a_id, &as_second_update);
		check_added_monitors(&nodes[1], 1);
		let bs_second_raa = get_event_msg!(nodes[1], MessageSendEvent::SendRevokeAndACK, node_a_id);

		nodes[0].node.handle_revoke_and_ack(node_b_id, &bs_second_raa);
		expect_payment_path_successful!(nodes[0]);
		check_added_monitors(&nodes[0], 1);
	}

	#[test]
	fn test_chainsync_triggers_distributed_monitor_persistence() {
		let chanmon_cfgs = create_chanmon_cfgs(3);
		let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
		let legacy_cfg = test_legacy_channel_config();
		let node_chanmgrs = create_node_chanmgrs(
			3,
			&node_cfgs,
			&[Some(legacy_cfg.clone()), Some(legacy_cfg.clone()), Some(legacy_cfg)],
		);
		let nodes = create_network(3, &node_cfgs, &node_chanmgrs);

		let node_a_id = nodes[0].node.get_our_node_id();
		let node_c_id = nodes[2].node.get_our_node_id();

		// Use FullBlockViaListen to avoid duplicate calls to process_chain_data and skips_blocks() in
		// case of other connect_styles.
		*nodes[0].connect_style.borrow_mut() = ConnectStyle::FullBlockViaListen;
		*nodes[1].connect_style.borrow_mut() = ConnectStyle::FullBlockViaListen;
		*nodes[2].connect_style.borrow_mut() = ConnectStyle::FullBlockViaListen;

		let _channel_1 = create_announced_chan_between_nodes(&nodes, 0, 1).2;
		let channel_2 =
			create_announced_chan_between_nodes_with_value(&nodes, 0, 2, 1_000_000, 0).2;

		chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clear();
		chanmon_cfgs[1].persister.chain_sync_monitor_persistences.lock().unwrap().clear();
		chanmon_cfgs[2].persister.chain_sync_monitor_persistences.lock().unwrap().clear();

		connect_blocks(&nodes[0], CHAINSYNC_MONITOR_PARTITION_FACTOR * 2);
		connect_blocks(&nodes[1], CHAINSYNC_MONITOR_PARTITION_FACTOR * 2);
		connect_blocks(&nodes[2], CHAINSYNC_MONITOR_PARTITION_FACTOR * 2);

		// Connecting [`DEFAULT_CHAINSYNC_PARTITION_FACTOR`] * 2 blocks should trigger only 2 writes
		// per monitor/channel.
		assert_eq!(
			2 * 2,
			chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);
		assert_eq!(
			2,
			chanmon_cfgs[1].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);
		assert_eq!(
			2,
			chanmon_cfgs[2].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);

		// Test that monitors with pending_claims are persisted on every block.
		// Now, close channel_2 i.e. b/w node-0 and node-2 to create pending_claim in node[0].
		let message = "Channel force-closed".to_owned();
		nodes[0]
			.node
			.force_close_broadcasting_latest_txn(&channel_2, &node_c_id, message.clone())
			.unwrap();
		let closure_reason =
			ClosureReason::HolderForceClosed { broadcasted_latest_txn: Some(true), message };
		check_closed_event(&nodes[0], 1, closure_reason, &[node_c_id], 1000000);
		check_closed_broadcast(&nodes[0], 1, true);
		let close_tx = nodes[0].tx_broadcaster.txn_broadcasted.lock().unwrap().split_off(0);
		assert_eq!(close_tx.len(), 1);

		mine_transaction(&nodes[2], &close_tx[0]);
		check_closed_broadcast(&nodes[2], 1, true);
		check_added_monitors(&nodes[2], 1);
		let closure_reason = ClosureReason::CommitmentTxConfirmed;
		check_closed_event(&nodes[2], 1, closure_reason, &[node_a_id], 1000000);

		chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clear();
		chanmon_cfgs[2].persister.chain_sync_monitor_persistences.lock().unwrap().clear();

		// For channel_2, there should be a monitor write for every block connection.
		// We connect [`DEFAULT_CHAINSYNC_MONITOR_PARTITION_FACTOR`] blocks since we don't know when
		// channel_1 monitor persistence will occur, with [`DEFAULT_CHAINSYNC_MONITOR_PARTITION_FACTOR`]
		// it will be persisted exactly once.
		connect_blocks(&nodes[0], CHAINSYNC_MONITOR_PARTITION_FACTOR);
		connect_blocks(&nodes[2], CHAINSYNC_MONITOR_PARTITION_FACTOR);

		// DEFAULT_CHAINSYNC_MONITOR_PARTITION_FACTOR writes for channel_2 due to pending_claim, 1 for
		// channel_1
		assert_eq!(
			(CHAINSYNC_MONITOR_PARTITION_FACTOR + 1) as usize,
			chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);
		// For node[2], there is no pending_claim
		assert_eq!(
			1,
			chanmon_cfgs[2].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);

		// Confirm claim for node[0] with ANTI_REORG_DELAY and reset monitor write counter.
		mine_transaction(&nodes[0], &close_tx[0]);
		connect_blocks(&nodes[0], ANTI_REORG_DELAY - 1);
		check_added_monitors(&nodes[0], 1);
		chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clear();

		// Again connect 1 full cycle of DEFAULT_CHAINSYNC_MONITOR_PARTITION_FACTOR blocks, it should only
		// result in 1 write per monitor/channel.
		connect_blocks(&nodes[0], CHAINSYNC_MONITOR_PARTITION_FACTOR);
		assert_eq!(
			2,
			chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().len()
		);
	}

	#[test]
	#[cfg(feature = "std")]
	fn update_during_chainsync_poisons_channel() {
		let chanmon_cfgs = create_chanmon_cfgs(2);
		let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
		let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
		let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
		create_announced_chan_between_nodes(&nodes, 0, 1);
		*nodes[0].connect_style.borrow_mut() = ConnectStyle::FullBlockViaListen;

		chanmon_cfgs[0].persister.set_update_ret(ChannelMonitorUpdateStatus::UnrecoverableError);

		assert!(std::panic::catch_unwind(|| {
			// Returning an UnrecoverableError should always panic immediately
			// Connecting [`DEFAULT_CHAINSYNC_PARTITION_FACTOR`] blocks so that we trigger some persistence
			// after accounting for block-height based partitioning/distribution.
			connect_blocks(&nodes[0], CHAINSYNC_MONITOR_PARTITION_FACTOR);
		})
		.is_err());
		assert!(std::panic::catch_unwind(|| {
			// ...and also poison our locks causing later use to panic as well
			core::mem::drop(nodes);
		})
		.is_err());
	}

	/// Concrete `ChainMonitor` type wired to the standard test utilities in deferred mode.
	type TestDeferredChainMonitor<'a> = ChainMonitor<
		TestChannelSigner,
		&'a TestChainSource,
		&'a TestBroadcaster,
		&'a TestFeeEstimator,
		&'a TestLogger,
		&'a TestPersister,
		&'a TestKeysInterface,
	>;

	/// Creates a minimal `ChannelMonitorUpdate` with no actual update steps.
	fn dummy_update(update_id: u64, channel_id: ChannelId) -> ChannelMonitorUpdate {
		ChannelMonitorUpdate { updates: vec![], update_id, channel_id: Some(channel_id) }
	}

	fn create_deferred_chain_monitor<'a>(
		chain_source: &'a TestChainSource, broadcaster: &'a TestBroadcaster,
		logger: &'a TestLogger, fee_est: &'a TestFeeEstimator, persister: &'a TestPersister,
		keys: &'a TestKeysInterface,
	) -> TestDeferredChainMonitor<'a> {
		ChainMonitor::new(
			Some(chain_source),
			broadcaster,
			logger,
			fee_est,
			persister,
			keys,
			keys.get_peer_storage_key(),
			true,
		)
	}

	/// Tests queueing and flushing of both `watch_channel` and `update_channel` operations
	/// when `ChainMonitor` is in deferred mode, verifying that operations flow through to
	/// `Persist` and that `channel_monitor_updated` is called on `Completed` status.
	#[test]
	fn test_queue_and_flush() {
		let broadcaster = TestBroadcaster::new(Network::Testnet);
		let fee_est = TestFeeEstimator::new(253);
		let logger = TestLogger::new();
		let persister = TestPersister::new();
		let chain_source = TestChainSource::new(Network::Testnet);
		let keys = TestKeysInterface::new(&[0; 32], Network::Testnet);
		let deferred = create_deferred_chain_monitor(
			&chain_source,
			&broadcaster,
			&logger,
			&fee_est,
			&persister,
			&keys,
		);

		// Queue starts empty.
		assert_eq!(deferred.pending_operation_count(), 0);

		// Queue a watch_channel, verifying InProgress status.
		let chan = ChannelId::from_bytes([1u8; 32]);
		let monitor = crate::chain::channelmonitor::dummy_monitor(chan, |keys| {
			TestChannelSigner::new(DynSigner::new(keys))
		});
		let status = Watch::watch_channel(&deferred, chan, monitor);
		assert_eq!(status, Ok(ChannelMonitorUpdateStatus::InProgress));
		assert_eq!(deferred.pending_operation_count(), 1);

		// Nothing persisted yet — operations are only queued.
		assert!(persister.new_channel_persistences.lock().unwrap().is_empty());

		// Queue two updates after the watch. Update IDs must be sequential (starting
		// from 1 since the initial monitor has update_id 0).
		assert_eq!(
			Watch::update_channel(&deferred, chan, &dummy_update(1, chan)),
			ChannelMonitorUpdateStatus::InProgress
		);
		assert_eq!(
			Watch::update_channel(&deferred, chan, &dummy_update(2, chan)),
			ChannelMonitorUpdateStatus::InProgress
		);
		assert_eq!(deferred.pending_operation_count(), 3);

		// Flush 2 of 3: persist_new_channel returns Completed (triggers
		// channel_monitor_updated), update_persisted_channel returns InProgress (does not).
		persister.set_update_ret(ChannelMonitorUpdateStatus::Completed);
		persister.set_update_ret(ChannelMonitorUpdateStatus::InProgress);
		deferred.flush(2, &&logger);

		assert_eq!(deferred.pending_operation_count(), 1);

		// persist_new_channel was called for the watch.
		assert_eq!(persister.new_channel_persistences.lock().unwrap().len(), 1);

		// Because persist_new_channel returned Completed, channel_monitor_updated was called,
		// so update_id 0 should no longer be pending.
		let pending = deferred.list_pending_monitor_updates();
		#[cfg(not(c_bindings))]
		let pending_for_chan = pending.get(&chan).unwrap();
		#[cfg(c_bindings)]
		let pending_for_chan = &pending.iter().find(|(chan_id, _)| *chan_id == chan).unwrap().1;
		assert!(!pending_for_chan.contains(&0));

		// update_persisted_channel was called for update_id 1, and because it returned
		// InProgress, update_id 1 remains pending.
		let monitor_name = deferred.get_monitor(chan).unwrap().persistence_key();
		assert!(persister
			.offchain_monitor_updates
			.lock()
			.unwrap()
			.get(&monitor_name)
			.unwrap()
			.contains(&1));
		assert!(pending_for_chan.contains(&1));

		// Flush remaining: update_persisted_channel returns Completed (default), triggers
		// channel_monitor_updated.
		deferred.flush(1, &&logger);
		assert_eq!(deferred.pending_operation_count(), 0);

		// update_persisted_channel was called for update_id 2.
		assert!(persister
			.offchain_monitor_updates
			.lock()
			.unwrap()
			.get(&monitor_name)
			.unwrap()
			.contains(&2));

		// update_id 1 is still pending from the InProgress earlier, but update_id 2 was
		// completed in this flush so it is no longer pending.
		let pending = deferred.list_pending_monitor_updates();
		#[cfg(not(c_bindings))]
		let pending_for_chan = pending.get(&chan).unwrap();
		#[cfg(c_bindings)]
		let pending_for_chan = &pending.iter().find(|(chan_id, _)| *chan_id == chan).unwrap().1;
		assert!(pending_for_chan.contains(&1));
		assert!(!pending_for_chan.contains(&2));

		// Flushing an empty queue is a no-op.
		let persist_count_before = persister.new_channel_persistences.lock().unwrap().len();
		deferred.flush(0, &&logger);
		assert_eq!(persister.new_channel_persistences.lock().unwrap().len(), persist_count_before);
	}

	/// Tests that `ChainMonitor` in deferred mode properly defers `watch_channel` and
	/// `update_channel` operations, verifying correctness through a complete channel open
	/// and payment flow. Operations are auto-flushed via the `TestChainMonitor`
	/// `release_pending_monitor_events` helper.
	#[test]
	fn test_deferred_monitor_payment() {
		let chanmon_cfgs = create_chanmon_cfgs(2);
		let node_cfgs = create_node_cfgs_deferred(2, &chanmon_cfgs);
		let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
		let nodes = create_network(2, &node_cfgs, &node_chanmgrs);

		let chain_monitor_a = &nodes[0].chain_monitor.chain_monitor;
		let chain_monitor_b = &nodes[1].chain_monitor.chain_monitor;

		create_announced_chan_between_nodes(&nodes, 0, 1);

		let (preimage, _hash, ..) = route_payment(&nodes[0], &[&nodes[1]], 10_000);
		claim_payment(&nodes[0], &[&nodes[1]], preimage);

		assert_eq!(chain_monitor_a.list_monitors().len(), 1);
		assert_eq!(chain_monitor_b.list_monitors().len(), 1);
		assert_eq!(chain_monitor_a.pending_operation_count(), 0);
		assert_eq!(chain_monitor_b.pending_operation_count(), 0);
	}
}