chainmonitor.rs

// 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::blockdata::block::BlockHeader;
use bitcoin::hash_types::{Txid, BlockHash};

use crate::chain;
use crate::chain::{ChannelMonitorUpdateStatus, Filter, WatchedOutput};
use crate::chain::chaininterface::{BroadcasterInterface, FeeEstimator};
use crate::chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, Balance, MonitorEvent, TransactionOutputs, LATENCY_GRACE_PERIOD_BLOCKS};
use crate::chain::transaction::{OutPoint, TransactionData};
use crate::sign::WriteableEcdsaChannelSigner;
use crate::events;
use crate::events::{Event, EventHandler};
use crate::util::atomic_counter::AtomicCounter;
use crate::util::logger::Logger;
use crate::util::errors::APIError;
use crate::util::wakers::{Future, Notifier};
use crate::ln::channelmanager::ChannelDetails;

use crate::prelude::*;
use crate::sync::{RwLock, RwLockReadGuard, Mutex, MutexGuard};
use core::iter::FromIterator;
use core::ops::Deref;
use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use bitcoin::secp256k1::PublicKey;

#[derive(Clone, Copy, Hash, PartialEq, Eq)]
/// A specific update's ID stored in a `MonitorUpdateId`, separated out to make the contents
/// entirely opaque.
enum UpdateOrigin {
	/// An update that was generated by the `ChannelManager` (via our `chain::Watch`
	/// implementation). This corresponds to an actual [`ChannelMonitorUpdate::update_id`] field
	/// and [`ChannelMonitor::get_latest_update_id`].
	OffChain(u64),
	/// An update that was generated during blockchain processing. The ID here is specific to the
	/// generating [`ChainMonitor`] and does *not* correspond to any on-disk IDs.
	ChainSync(u64),
}

/// An opaque identifier describing a specific [`Persist`] method call.
#[derive(Clone, Copy, Hash, PartialEq, Eq)]
pub struct MonitorUpdateId {
	contents: UpdateOrigin,
}

impl MonitorUpdateId {
	pub(crate) fn from_monitor_update(update: &ChannelMonitorUpdate) -> Self {
		Self { contents: UpdateOrigin::OffChain(update.update_id) }
	}
	pub(crate) fn from_new_monitor<ChannelSigner: WriteableEcdsaChannelSigner>(monitor: &ChannelMonitor<ChannelSigner>) -> Self {
		Self { contents: UpdateOrigin::OffChain(monitor.get_latest_update_id()) }
	}
}

/// `Persist` defines behavior for persisting channel monitors: this could mean
/// writing once to disk, and/or uploading to one or more backup services.
///
/// Each method can return three possible values:
///  * If persistence (including any relevant `fsync()` calls) happens immediately, the
///    implementation should return [`ChannelMonitorUpdateStatus::Completed`], indicating normal
///    channel operation should continue.
///  * If persistence happens asynchronously, implementations should first ensure the
///    [`ChannelMonitor`] or [`ChannelMonitorUpdate`] are written durably to disk, and then return
///    [`ChannelMonitorUpdateStatus::InProgress`] while the update continues in the background.
///    Once the update completes, [`ChainMonitor::channel_monitor_updated`] should be called with
///    the corresponding [`MonitorUpdateId`].
///
///    Note that unlike the direct [`chain::Watch`] interface,
///    [`ChainMonitor::channel_monitor_updated`] must be called once for *each* update which occurs.
///
///  * If persistence fails for some reason, implementations should return
///    [`ChannelMonitorUpdateStatus::PermanentFailure`], in which case the channel will likely be
///    closed without broadcasting the latest state. See
///    [`ChannelMonitorUpdateStatus::PermanentFailure`] for more details.
///
/// Third-party watchtowers may be built as a part of an implementation of this trait, with the
/// advantage that you can control whether to resume channel operation depending on if an update
/// has been persisted to a watchtower. A utility for tracking and building signed justice
/// transactions is provided in the [`util::watchtower`] module. Otherwise, you may find the
/// following methods useful: [`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
/// [`util::watchtower`]: crate::util::watchtower
pub trait Persist<ChannelSigner: WriteableEcdsaChannelSigner> {
	/// 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.
	///
	/// The data can be stored any way you want, but the identifier provided by LDK is the
	/// channel's outpoint (and it is up to you to maintain a correct mapping between the outpoint
	/// and the stored channel data). Note that you **must** persist every new monitor to disk.
	///
	/// The `update_id` is used to identify this call to [`ChainMonitor::channel_monitor_updated`],
	/// if 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, channel_id: OutPoint, data: &ChannelMonitor<ChannelSigner>, update_id: MonitorUpdateId) -> 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, 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. 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 `update_id` is used to identify this call to [`ChainMonitor::channel_monitor_updated`],
	/// if 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, channel_id: OutPoint, update: Option<&ChannelMonitorUpdate>, data: &ChannelMonitor<ChannelSigner>, update_id: MonitorUpdateId) -> ChannelMonitorUpdateStatus;
}

struct MonitorHolder<ChannelSigner: WriteableEcdsaChannelSigner> {
	monitor: ChannelMonitor<ChannelSigner>,
	/// The full set of pending monitor updates for this Channel.
	///
	/// Note that this lock must be held during updates to prevent a race where we call
	/// update_persisted_channel, the user returns a
	/// [`ChannelMonitorUpdateStatus::InProgress`], and then calls channel_monitor_updated
	/// immediately, racing our insertion of the pending update into the contained Vec.
	///
	/// Beyond the synchronization of updates themselves, we cannot handle user events until after
	/// any chain updates have been stored on disk. Thus, we scan this list when returning updates
	/// to the ChannelManager, refusing to return any updates for a ChannelMonitor which is still
	/// being persisted fully to disk after a chain update.
	///
	/// This avoids the possibility of handling, e.g. an on-chain claim, generating a claim monitor
	/// event, resulting in the relevant ChannelManager generating a PaymentSent event and dropping
	/// the pending payment entry, and then reloading before the monitor is persisted, resulting in
	/// the ChannelManager re-adding the same payment entry, before the same block is replayed,
	/// resulting in a duplicate PaymentSent event.
	pending_monitor_updates: Mutex<Vec<MonitorUpdateId>>,
	/// When the user returns a PermanentFailure error from an update_persisted_channel call during
	/// block processing, we inform the ChannelManager that the channel should be closed
	/// asynchronously. In order to ensure no further changes happen before the ChannelManager has
	/// processed the closure event, we set this to true and return PermanentFailure for any other
	/// chain::Watch events.
	channel_perm_failed: AtomicBool,
	/// The last block height at which no [`UpdateOrigin::ChainSync`] monitor updates were present
	/// in `pending_monitor_updates`.
	/// If it's been more than [`LATENCY_GRACE_PERIOD_BLOCKS`] since we started waiting on a chain
	/// sync event, we let monitor events return to `ChannelManager` because we cannot hold them up
	/// forever or we'll end up with HTLC preimages waiting to feed back into an upstream channel
	/// forever, risking funds loss.
	last_chain_persist_height: AtomicUsize,
}

impl<ChannelSigner: WriteableEcdsaChannelSigner> MonitorHolder<ChannelSigner> {
	fn has_pending_offchain_updates(&self, pending_monitor_updates_lock: &MutexGuard<Vec<MonitorUpdateId>>) -> bool {
		pending_monitor_updates_lock.iter().any(|update_id|
			if let UpdateOrigin::OffChain(_) = update_id.contents { true } else { false })
	}
	fn has_pending_chainsync_updates(&self, pending_monitor_updates_lock: &MutexGuard<Vec<MonitorUpdateId>>) -> bool {
		pending_monitor_updates_lock.iter().any(|update_id|
			if let UpdateOrigin::ChainSync(_) = update_id.contents { true } else { false })
	}
}

/// 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: WriteableEcdsaChannelSigner> {
	lock: RwLockReadGuard<'a, HashMap<OutPoint, MonitorHolder<ChannelSigner>>>,
	funding_txo: OutPoint,
}

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

/// 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: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref>
	where C::Target: chain::Filter,
        T::Target: BroadcasterInterface,
        F::Target: FeeEstimator,
        L::Target: Logger,
        P::Target: Persist<ChannelSigner>,
{
	monitors: RwLock<HashMap<OutPoint, MonitorHolder<ChannelSigner>>>,
	/// When we generate a [`MonitorUpdateId`] for a chain-event monitor persistence, we need a
	/// unique ID, which we calculate by simply getting the next value from this counter. Note that
	/// the ID is never persisted so it's ok that they reset on restart.
	sync_persistence_id: AtomicCounter,
	chain_source: Option<C>,
	broadcaster: T,
	logger: L,
	fee_estimator: F,
	persister: P,
	/// "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, Vec<MonitorEvent>, Option<PublicKey>)>>,
	/// The best block height seen, used as a proxy for the passage of time.
	highest_chain_height: AtomicUsize,

	event_notifier: Notifier,
}

impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref> ChainMonitor<ChannelSigner, C, T, F, L, P>
where C::Target: chain::Filter,
	    T::Target: BroadcasterInterface,
	    F::Target: FeeEstimator,
	    L::Target: Logger,
	    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: &BlockHeader, best_height: Option<u32>, txdata: &TransactionData, process: FN)
	where
		FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs>
	{
		let funding_outpoints: HashSet<OutPoint> = HashSet::from_iter(self.monitors.read().unwrap().keys().cloned());
		for funding_outpoint in funding_outpoints.iter() {
			let monitor_lock = self.monitors.read().unwrap();
			if let Some(monitor_state) = monitor_lock.get(funding_outpoint) {
				self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state);
			}
		}

		// do some followup cleanup if any funding outpoints were added in between iterations
		let monitor_states = self.monitors.write().unwrap();
		for (funding_outpoint, monitor_state) in monitor_states.iter() {
			if !funding_outpoints.contains(funding_outpoint) {
				self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state);
			}
		}

		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: &BlockHeader, best_height: Option<u32>, txdata: &TransactionData, process: FN, funding_outpoint: &OutPoint, monitor_state: &MonitorHolder<ChannelSigner>) where FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs> {
		let monitor = &monitor_state.monitor;
		let mut txn_outputs;
		{
			txn_outputs = process(monitor, txdata);
			let update_id = MonitorUpdateId {
				contents: UpdateOrigin::ChainSync(self.sync_persistence_id.get_increment()),
			};
			let mut pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
			if let Some(height) = best_height {
				if !monitor_state.has_pending_chainsync_updates(&pending_monitor_updates) {
					// If there are not ChainSync persists awaiting completion, go ahead and
					// set last_chain_persist_height here - we wouldn't want the first
					// InProgress to always immediately be considered "overly delayed".
					monitor_state.last_chain_persist_height.store(height as usize, Ordering::Release);
				}
			}

			log_trace!(self.logger, "Syncing Channel Monitor for channel {}", log_funding_info!(monitor));
			match self.persister.update_persisted_channel(*funding_outpoint, None, monitor, update_id) {
				ChannelMonitorUpdateStatus::Completed =>
					log_trace!(self.logger, "Finished syncing Channel Monitor for channel {}", log_funding_info!(monitor)),
				ChannelMonitorUpdateStatus::PermanentFailure => {
					monitor_state.channel_perm_failed.store(true, Ordering::Release);
					self.pending_monitor_events.lock().unwrap().push((*funding_outpoint, vec![MonitorEvent::UpdateFailed(*funding_outpoint)], monitor.get_counterparty_node_id()));
					self.event_notifier.notify();
				}
				ChannelMonitorUpdateStatus::InProgress => {
					log_debug!(self.logger, "Channel Monitor sync for channel {} in progress, holding events until completion!", log_funding_info!(monitor));
					pending_monitor_updates.push(update_id);
				}
			}
		}

		// 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,
					};
					chain_source.register_output(output)
				}
			}
		}
	}

	/// 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.
	pub fn new(chain_source: Option<C>, broadcaster: T, logger: L, feeest: F, persister: P) -> Self {
		Self {
			monitors: RwLock::new(HashMap::new()),
			sync_persistence_id: AtomicCounter::new(),
			chain_source,
			broadcaster,
			logger,
			fee_estimator: feeest,
			persister,
			pending_monitor_events: Mutex::new(Vec::new()),
			highest_chain_height: AtomicUsize::new(0),
			event_notifier: Notifier::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(|(funding_outpoint, _)| {
			for chan in ignored_channels {
				if chan.funding_txo.as_ref() == Some(funding_outpoint) {
					return false;
				}
			}
			true
		}) {
			ret.append(&mut monitor_state.monitor.get_claimable_balances());
		}
		ret
	}

	/// Gets the [`LockedChannelMonitor`] for a given funding outpoint, 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, funding_txo: OutPoint) -> Result<LockedChannelMonitor<'_, ChannelSigner>, ()> {
		let lock = self.monitors.read().unwrap();
		if lock.get(&funding_txo).is_some() {
			Ok(LockedChannelMonitor { lock, funding_txo })
		} else {
			Err(())
		}
	}

	/// Lists the funding outpoint 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<OutPoint> {
		self.monitors.read().unwrap().keys().map(|outpoint| *outpoint).collect()
	}

	#[cfg(not(c_bindings))]
	/// Lists the pending updates for each [`ChannelMonitor`] (by `OutPoint` being monitored).
	pub fn list_pending_monitor_updates(&self) -> HashMap<OutPoint, Vec<MonitorUpdateId>> {
		self.monitors.read().unwrap().iter().map(|(outpoint, holder)| {
			(*outpoint, holder.pending_monitor_updates.lock().unwrap().clone())
		}).collect()
	}

	#[cfg(c_bindings)]
	/// Lists the pending updates for each [`ChannelMonitor`] (by `OutPoint` being monitored).
	pub fn list_pending_monitor_updates(&self) -> Vec<(OutPoint, Vec<MonitorUpdateId>)> {
		self.monitors.read().unwrap().iter().map(|(outpoint, holder)| {
			(*outpoint, holder.pending_monitor_updates.lock().unwrap().clone())
		}).collect()
	}


	#[cfg(test)]
	pub fn remove_monitor(&self, funding_txo: &OutPoint) -> ChannelMonitor<ChannelSigner> {
		self.monitors.write().unwrap().remove(funding_txo).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 the
	///     `completed_update_id` that completed, and once all pending updates have completed the
	///     channel will be re-enabled.
	//      Note that we re-enable only after `UpdateOrigin::OffChain` updates complete, we don't
	//      care about `UpdateOrigin::ChainSync` updates for the channel state being updated. We
	//      only care about `UpdateOrigin::ChainSync` for returning `MonitorEvent`s.
	///
	/// Returns an [`APIError::APIMisuseError`] if `funding_txo` does not match any currently
	/// registered [`ChannelMonitor`]s.
	pub fn channel_monitor_updated(&self, funding_txo: OutPoint, completed_update_id: MonitorUpdateId) -> Result<(), APIError> {
		let monitors = self.monitors.read().unwrap();
		let monitor_data = if let Some(mon) = monitors.get(&funding_txo) { mon } else {
			return Err(APIError::APIMisuseError { err: format!("No ChannelMonitor matching funding outpoint {:?} found", funding_txo) });
		};
		let mut pending_monitor_updates = monitor_data.pending_monitor_updates.lock().unwrap();
		pending_monitor_updates.retain(|update_id| *update_id != completed_update_id);

		match completed_update_id {
			MonitorUpdateId { contents: UpdateOrigin::OffChain(_) } => {
				// Note that we only check for `UpdateOrigin::OffChain` failures here - if
				// we're being told that a `UpdateOrigin::OffChain` monitor update completed,
				// we only care about ensuring we don't tell the `ChannelManager` to restore
				// the channel to normal operation until all `UpdateOrigin::OffChain` updates
				// complete.
				// If there's some `UpdateOrigin::ChainSync` update still pending that's okay
				// - we can still update our channel state, just as long as we don't return
				// `MonitorEvent`s from the monitor back to the `ChannelManager` until they
				// complete.
				let monitor_is_pending_updates = monitor_data.has_pending_offchain_updates(&pending_monitor_updates);
				if monitor_is_pending_updates || monitor_data.channel_perm_failed.load(Ordering::Acquire) {
					// If there are still monitor updates pending (or an old monitor update
					// finished after a later one perm-failed), we cannot yet construct an
					// Completed event.
					return Ok(());
				}
				self.pending_monitor_events.lock().unwrap().push((funding_txo, vec![MonitorEvent::Completed {
					funding_txo,
					monitor_update_id: monitor_data.monitor.get_latest_update_id(),
				}], monitor_data.monitor.get_counterparty_node_id()));
			},
			MonitorUpdateId { contents: UpdateOrigin::ChainSync(_) } => {
				if !monitor_data.has_pending_chainsync_updates(&pending_monitor_updates) {
					monitor_data.last_chain_persist_height.store(self.highest_chain_height.load(Ordering::Acquire), Ordering::Release);
					// The next time release_pending_monitor_events is called, any events for this
					// ChannelMonitor will be returned.
				}
			},
		}
		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, funding_txo: OutPoint, monitor_update_id: u64) {
		let monitors = self.monitors.read().unwrap();
		let counterparty_node_id = monitors.get(&funding_txo).and_then(|m| m.monitor.get_counterparty_node_id());
		self.pending_monitor_events.lock().unwrap().push((funding_txo, vec![MonitorEvent::Completed {
			funding_txo,
			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| 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, 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 funding_txo in mons_to_process {
			let mut ev;
			super::channelmonitor::process_events_body!(
				self.monitors.read().unwrap().get(&funding_txo).map(|m| &m.monitor), ev, handler(ev).await);
		}
	}

	/// 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
			)
		}
	}
}

impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref>
chain::Listen for ChainMonitor<ChannelSigner, C, T, F, L, P>
where
	C::Target: chain::Filter,
	T::Target: BroadcasterInterface,
	F::Target: FeeEstimator,
	L::Target: Logger,
	P::Target: Persist<ChannelSigner>,
{
	fn filtered_block_connected(&self, header: &BlockHeader, 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)
		});
	}

	fn block_disconnected(&self, header: &BlockHeader, height: u32) {
		let monitor_states = self.monitors.read().unwrap();
		log_debug!(self.logger, "Latest block {} at height {} removed via block_disconnected", header.block_hash(), height);
		for monitor_state in monitor_states.values() {
			monitor_state.monitor.block_disconnected(
				header, height, &*self.broadcaster, &*self.fee_estimator, &*self.logger);
		}
	}
}

impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref>
chain::Confirm for ChainMonitor<ChannelSigner, C, T, F, L, P>
where
	C::Target: chain::Filter,
	T::Target: BroadcasterInterface,
	F::Target: FeeEstimator,
	L::Target: Logger,
	P::Target: Persist<ChannelSigner>,
{
	fn transactions_confirmed(&self, header: &BlockHeader, 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)
		});
	}

	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: &BlockHeader, 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)
		});
	}

	fn get_relevant_txids(&self) -> Vec<(Txid, 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();
		txids.dedup();
		txids
	}
}

impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref , T: Deref , F: Deref , L: Deref , P: Deref >
chain::Watch<ChannelSigner> for ChainMonitor<ChannelSigner, C, T, F, L, P>
where C::Target: chain::Filter,
	    T::Target: BroadcasterInterface,
	    F::Target: FeeEstimator,
	    L::Target: Logger,
	    P::Target: Persist<ChannelSigner>,
{
	/// Adds the monitor that watches the channel referred to by the given outpoint.
	///
	/// Calls back to [`chain::Filter`] with the funding transaction and outputs to watch.
	///
	/// Note that we persist the given `ChannelMonitor` while holding the `ChainMonitor`
	/// monitors lock.
	fn watch_channel(&self, funding_outpoint: OutPoint, monitor: ChannelMonitor<ChannelSigner>) -> ChannelMonitorUpdateStatus {
		let mut monitors = self.monitors.write().unwrap();
		let entry = match monitors.entry(funding_outpoint) {
			hash_map::Entry::Occupied(_) => {
				log_error!(self.logger, "Failed to add new channel data: channel monitor for given outpoint is already present");
				return ChannelMonitorUpdateStatus::PermanentFailure
			},
			hash_map::Entry::Vacant(e) => e,
		};
		log_trace!(self.logger, "Got new ChannelMonitor for channel {}", log_funding_info!(monitor));
		let update_id = MonitorUpdateId::from_new_monitor(&monitor);
		let mut pending_monitor_updates = Vec::new();
		let persist_res = self.persister.persist_new_channel(funding_outpoint, &monitor, update_id);
		match persist_res {
			ChannelMonitorUpdateStatus::InProgress => {
				log_info!(self.logger, "Persistence of new ChannelMonitor for channel {} in progress", log_funding_info!(monitor));
				pending_monitor_updates.push(update_id);
			},
			ChannelMonitorUpdateStatus::PermanentFailure => {
				log_error!(self.logger, "Persistence of new ChannelMonitor for channel {} failed", log_funding_info!(monitor));
				return persist_res;
			},
			ChannelMonitorUpdateStatus::Completed => {
				log_info!(self.logger, "Persistence of new ChannelMonitor for channel {} completed", log_funding_info!(monitor));
			}
		}
		if let Some(ref chain_source) = self.chain_source {
			monitor.load_outputs_to_watch(chain_source);
		}
		entry.insert(MonitorHolder {
			monitor,
			pending_monitor_updates: Mutex::new(pending_monitor_updates),
			channel_perm_failed: AtomicBool::new(false),
			last_chain_persist_height: AtomicUsize::new(self.highest_chain_height.load(Ordering::Acquire)),
		});
		persist_res
	}

	/// Note that we persist the given `ChannelMonitor` update while holding the
	/// `ChainMonitor` monitors lock.
	fn update_channel(&self, funding_txo: OutPoint, update: &ChannelMonitorUpdate) -> ChannelMonitorUpdateStatus {
		// Update the monitor that watches the channel referred to by the given outpoint.
		let monitors = self.monitors.read().unwrap();
		match monitors.get(&funding_txo) {
			None => {
				log_error!(self.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(any(test, fuzzing))]
				panic!("ChannelManager generated a channel update for a channel that was not yet registered!");
				#[cfg(not(any(test, fuzzing)))]
				ChannelMonitorUpdateStatus::PermanentFailure
			},
			Some(monitor_state) => {
				let monitor = &monitor_state.monitor;
				log_trace!(self.logger, "Updating ChannelMonitor for channel {}", log_funding_info!(monitor));
				let update_res = monitor.update_monitor(update, &self.broadcaster, &*self.fee_estimator, &self.logger);
				if update_res.is_err() {
					log_error!(self.logger, "Failed to update ChannelMonitor for channel {}.", log_funding_info!(monitor));
				}
				// Even if updating the monitor returns an error, the monitor's state will
				// still be changed. So, persist the updated monitor despite the error.
				let update_id = MonitorUpdateId::from_monitor_update(update);
				let mut pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
				let persist_res = self.persister.update_persisted_channel(funding_txo, Some(update), monitor, update_id);
				match persist_res {
					ChannelMonitorUpdateStatus::InProgress => {
						pending_monitor_updates.push(update_id);
						log_debug!(self.logger, "Persistence of ChannelMonitorUpdate for channel {} in progress", log_funding_info!(monitor));
					},
					ChannelMonitorUpdateStatus::PermanentFailure => {
						monitor_state.channel_perm_failed.store(true, Ordering::Release);
						log_error!(self.logger, "Persistence of ChannelMonitorUpdate for channel {} failed", log_funding_info!(monitor));
					},
					ChannelMonitorUpdateStatus::Completed => {
						log_debug!(self.logger, "Persistence of ChannelMonitorUpdate for channel {} completed", log_funding_info!(monitor));
					},
				}
				if update_res.is_err() {
					ChannelMonitorUpdateStatus::PermanentFailure
				} else if monitor_state.channel_perm_failed.load(Ordering::Acquire) {
					ChannelMonitorUpdateStatus::PermanentFailure
				} else {
					persist_res
				}
			}
		}
	}

	fn release_pending_monitor_events(&self) -> Vec<(OutPoint, Vec<MonitorEvent>, Option<PublicKey>)> {
		let mut pending_monitor_events = self.pending_monitor_events.lock().unwrap().split_off(0);
		for monitor_state in self.monitors.read().unwrap().values() {
			let is_pending_monitor_update = monitor_state.has_pending_chainsync_updates(&monitor_state.pending_monitor_updates.lock().unwrap());
			if is_pending_monitor_update &&
					monitor_state.last_chain_persist_height.load(Ordering::Acquire) + LATENCY_GRACE_PERIOD_BLOCKS as usize
						> self.highest_chain_height.load(Ordering::Acquire)
			{
				log_info!(self.logger, "A Channel Monitor sync is still in progress, refusing to provide monitor events!");
			} else {
				if monitor_state.channel_perm_failed.load(Ordering::Acquire) {
					// If a `UpdateOrigin::ChainSync` persistence failed with `PermanantFailure`,
					// we don't really know if the latest `ChannelMonitor` state is on disk or not.
					// We're supposed to hold monitor updates until the latest state is on disk to
					// avoid duplicate events, but the user told us persistence is screw-y and may
					// not complete. We can't hold events forever because we may learn some payment
					// preimage, so instead we just log and hope the user complied with the
					// `PermanentFailure` requirements of having at least the local-disk copy
					// updated.
					log_info!(self.logger, "A Channel Monitor sync returned PermanentFailure. Returning monitor events but duplicate events may appear after reload!");
				}
				if is_pending_monitor_update {
					log_error!(self.logger, "A ChannelMonitor sync took longer than {} blocks to complete.", LATENCY_GRACE_PERIOD_BLOCKS);
					log_error!(self.logger, "   To avoid funds-loss, we are allowing monitor updates to be released.");
					log_error!(self.logger, "   This may cause duplicate payment events to be generated.");
				}
				let monitor_events = monitor_state.monitor.get_and_clear_pending_monitor_events();
				if monitor_events.len() > 0 {
					let monitor_outpoint = monitor_state.monitor.get_funding_txo().0;
					let counterparty_node_id = monitor_state.monitor.get_counterparty_node_id();
					pending_monitor_events.push((monitor_outpoint, monitor_events, counterparty_node_id));
				}
			}
		}
		pending_monitor_events
	}
}

impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref> events::EventsProvider for ChainMonitor<ChannelSigner, C, T, F, L, P>
	where C::Target: chain::Filter,
	      T::Target: BroadcasterInterface,
	      F::Target: FeeEstimator,
	      L::Target: Logger,
	      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() {
			monitor_state.monitor.process_pending_events(&handler);
		}
	}
}

#[cfg(test)]
mod tests {
	use crate::{check_added_monitors, check_closed_broadcast, check_closed_event};
	use crate::{expect_payment_claimed, expect_payment_path_successful, get_event_msg};
	use crate::{get_htlc_update_msgs, get_local_commitment_txn, get_revoke_commit_msgs, get_route_and_payment_hash, unwrap_send_err};
	use crate::chain::{ChannelMonitorUpdateStatus, Confirm, Watch};
	use crate::chain::channelmonitor::LATENCY_GRACE_PERIOD_BLOCKS;
	use crate::events::{Event, ClosureReason, MessageSendEvent, MessageSendEventsProvider};
	use crate::ln::channelmanager::{PaymentSendFailure, PaymentId, RecipientOnionFields};
	use crate::ln::functional_test_utils::*;
	use crate::ln::msgs::ChannelMessageHandler;
	use crate::util::errors::APIError;

	#[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);
		create_announced_chan_between_nodes(&nodes, 0, 1);

		// 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 (funding_txo, 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();
		// Should contain next_update when pending updates listed.
		#[cfg(not(c_bindings))]
		assert!(nodes[1].chain_monitor.chain_monitor.list_pending_monitor_updates().get(funding_txo)
			.unwrap().contains(&next_update));
		#[cfg(c_bindings)]
		assert!(nodes[1].chain_monitor.chain_monitor.list_pending_monitor_updates().iter()
			.find(|(txo, _)| txo == funding_txo).unwrap().1.contains(&next_update));
		nodes[1].chain_monitor.chain_monitor.channel_monitor_updated(*funding_txo, next_update.clone()).unwrap();
		// Should not contain the previously pending next_update when pending updates listed.
		#[cfg(not(c_bindings))]
		assert!(!nodes[1].chain_monitor.chain_monitor.list_pending_monitor_updates().get(funding_txo)
			.unwrap().contains(&next_update));
		#[cfg(c_bindings)]
		assert!(!nodes[1].chain_monitor.chain_monitor.list_pending_monitor_updates().iter()
			.find(|(txo, _)| txo == funding_txo).unwrap().1.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());
		nodes[1].chain_monitor.chain_monitor.channel_monitor_updated(*funding_txo, update_iter.next().unwrap().clone()).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 updates = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
		nodes[0].node.handle_update_fulfill_htlc(&nodes[1].node.get_our_node_id(), &updates.update_fulfill_htlcs[0]);
		expect_payment_sent(&nodes[0], payment_preimage_1, None, false, false);
		nodes[0].node.handle_commitment_signed(&nodes[1].node.get_our_node_id(), &updates.commitment_signed);
		check_added_monitors!(nodes[0], 1);
		let (as_first_raa, as_first_update) = get_revoke_commit_msgs!(nodes[0], nodes[1].node.get_our_node_id());

		nodes[1].node.handle_revoke_and_ack(&nodes[0].node.get_our_node_id(), &as_first_raa);
		check_added_monitors!(nodes[1], 1);
		let bs_second_updates = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
		nodes[1].node.handle_commitment_signed(&nodes[0].node.get_our_node_id(), &as_first_update);
		check_added_monitors!(nodes[1], 1);
		let bs_first_raa = get_event_msg!(nodes[1], MessageSendEvent::SendRevokeAndACK, nodes[0].node.get_our_node_id());

		nodes[0].node.handle_update_fulfill_htlc(&nodes[1].node.get_our_node_id(), &bs_second_updates.update_fulfill_htlcs[0]);
		expect_payment_sent(&nodes[0], payment_preimage_2, None, false, false);
		nodes[0].node.handle_commitment_signed(&nodes[1].node.get_our_node_id(), &bs_second_updates.commitment_signed);
		check_added_monitors!(nodes[0], 1);
		nodes[0].node.handle_revoke_and_ack(&nodes[1].node.get_our_node_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], nodes[1].node.get_our_node_id());

		nodes[1].node.handle_revoke_and_ack(&nodes[0].node.get_our_node_id(), &as_second_raa);
		check_added_monitors!(nodes[1], 1);
		nodes[1].node.handle_commitment_signed(&nodes[0].node.get_our_node_id(), &as_second_update);
		check_added_monitors!(nodes[1], 1);
		let bs_second_raa = get_event_msg!(nodes[1], MessageSendEvent::SendRevokeAndACK, nodes[0].node.get_our_node_id());

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

	fn do_chainsync_pauses_events(block_timeout: bool) {
		// When a chainsync monitor update occurs, any MonitorUpdates should be held before being
		// passed upstream to a `ChannelManager` via `Watch::release_pending_monitor_events`. This
		// tests that behavior, as well as some ways it might go wrong.
		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 = create_announced_chan_between_nodes(&nodes, 0, 1);

		// Get a route for later and rebalance the channel somewhat
		send_payment(&nodes[0], &[&nodes[1]], 10_000_000);
		let (route, second_payment_hash, _, second_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], 100_000);

		// First route a payment that we will claim on chain and give the recipient the preimage.
		let (payment_preimage, payment_hash, _) = route_payment(&nodes[0], &[&nodes[1]], 1_000_000);
		nodes[1].node.claim_funds(payment_preimage);
		expect_payment_claimed!(nodes[1], payment_hash, 1_000_000);
		nodes[1].node.get_and_clear_pending_msg_events();
		check_added_monitors!(nodes[1], 1);
		let remote_txn = get_local_commitment_txn!(nodes[1], channel.2);
		assert_eq!(remote_txn.len(), 2);

		// Temp-fail the block connection which will hold the channel-closed event
		chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clear();
		chanmon_cfgs[0].persister.set_update_ret(ChannelMonitorUpdateStatus::InProgress);

		// Connect B's commitment transaction, but only to the ChainMonitor/ChannelMonitor. The
		// channel is now closed, but the ChannelManager doesn't know that yet.
		let new_header = create_dummy_header(nodes[0].best_block_info().0, 0);
		nodes[0].chain_monitor.chain_monitor.transactions_confirmed(&new_header,
			&[(0, &remote_txn[0]), (1, &remote_txn[1])], nodes[0].best_block_info().1 + 1);
		assert!(nodes[0].chain_monitor.release_pending_monitor_events().is_empty());
		nodes[0].chain_monitor.chain_monitor.best_block_updated(&new_header, nodes[0].best_block_info().1 + 1);
		assert!(nodes[0].chain_monitor.release_pending_monitor_events().is_empty());

		// If the ChannelManager tries to update the channel, however, the ChainMonitor will pass
		// the update through to the ChannelMonitor which will refuse it (as the channel is closed).
		chanmon_cfgs[0].persister.set_update_ret(ChannelMonitorUpdateStatus::Completed);
		unwrap_send_err!(nodes[0].node.send_payment_with_route(&route, second_payment_hash,
				RecipientOnionFields::secret_only(second_payment_secret), PaymentId(second_payment_hash.0)
			), true, APIError::ChannelUnavailable { ref err },
			assert!(err.contains("ChannelMonitor storage failure")));
		check_added_monitors!(nodes[0], 2); // After the failure we generate a close-channel monitor update
		check_closed_broadcast!(nodes[0], true);
		check_closed_event!(nodes[0], 1, ClosureReason::ProcessingError { err: "ChannelMonitor storage failure".to_string() },
			[nodes[1].node.get_our_node_id()], 100000);

		// However, as the ChainMonitor is still waiting for the original persistence to complete,
		// it won't yet release the MonitorEvents.
		assert!(nodes[0].chain_monitor.release_pending_monitor_events().is_empty());

		if block_timeout {
			// After three blocks, pending MontiorEvents should be released either way.
			let latest_header = create_dummy_header(nodes[0].best_block_info().0, 0);
			nodes[0].chain_monitor.chain_monitor.best_block_updated(&latest_header, nodes[0].best_block_info().1 + LATENCY_GRACE_PERIOD_BLOCKS);
		} else {
			let persistences = chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clone();
			for (funding_outpoint, update_ids) in persistences {
				for update_id in update_ids {
					nodes[0].chain_monitor.chain_monitor.channel_monitor_updated(funding_outpoint, update_id).unwrap();
				}
			}
		}

		expect_payment_sent(&nodes[0], payment_preimage, None, true, false);
	}

	#[test]
	fn chainsync_pauses_events() {
		do_chainsync_pauses_events(false);
		do_chainsync_pauses_events(true);
	}

	#[test]
	fn update_during_chainsync_fails_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);

		chanmon_cfgs[0].persister.chain_sync_monitor_persistences.lock().unwrap().clear();
		chanmon_cfgs[0].persister.set_update_ret(ChannelMonitorUpdateStatus::PermanentFailure);

		connect_blocks(&nodes[0], 1);
		// Before processing events, the ChannelManager will still think the Channel is open and
		// there won't be any ChannelMonitorUpdates
		assert_eq!(nodes[0].node.list_channels().len(), 1);
		check_added_monitors!(nodes[0], 0);
		// ... however once we get events once, the channel will close, creating a channel-closed
		// ChannelMonitorUpdate.
		check_closed_broadcast!(nodes[0], true);
		check_closed_event!(nodes[0], 1, ClosureReason::ProcessingError { err: "Failed to persist ChannelMonitor update during chain sync".to_string() },
			[nodes[1].node.get_our_node_id()], 100000);
		check_added_monitors!(nodes[0], 1);
	}
}