Merge pull request #2685 from tnull/2022-12-add-electrum-sync

[rust-lightning] / lightning / src / chain / 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::Header;
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::{AtomicUsize, Ordering};
use bitcoin::secp256k1::PublicKey;

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

#[cfg(any(feature = "_test_utils", test))]
pub(crate) use update_origin::UpdateOrigin;
#[cfg(not(any(feature = "_test_utils", test)))]
use update_origin::UpdateOrigin;

/// An opaque identifier describing a specific [`Persist`] method call.
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
pub struct MonitorUpdateId {
        pub(crate) 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.
///
/// 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`].
///
///    Once a full [`ChannelMonitor`] has been persisted, all pending updates for that channel can
///    be marked as complete via [`ChainMonitor::channel_monitor_updated`].
///
///    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
///  [`MonitorUpdateId`].
///
///  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: 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, 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. 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>>,
        /// 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: &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 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) {
                                if self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state).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 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) {
                                if self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state).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, funding_outpoint: &OutPoint, monitor_state: &MonitorHolder<ChannelSigner>
        ) -> Result<(), ()> 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::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);
                                },
                                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,
                                        };
                                        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.
        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`, allowing you to filter out balances from channels which are still open
        /// (and whose balance should likely be pulled from the [`ChannelDetails`]).
        ///
        /// 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 {
                                        // If there are still monitor updates pending, we cannot yet construct a
                                        // 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: &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)
                });
        }

        fn block_disconnected(&self, header: &Header, 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: &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)
                });
        }

        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)
                });
        }

        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: 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>,
{
        fn watch_channel(&self, funding_outpoint: OutPoint, monitor: ChannelMonitor<ChannelSigner>) -> Result<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 Err(());
                        },
                        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::Completed => {
                                log_info!(self.logger, "Persistence of new ChannelMonitor for channel {} completed", log_funding_info!(monitor));
                        },
                        ChannelMonitorUpdateStatus::UnrecoverableError => {
                                let err_str = "ChannelMonitor[Update] persistence failed unrecoverably. This indicates we cannot continue normal operation and must shut down.";
                                log_error!(self.logger, "{}", err_str);
                                panic!("{}", err_str);
                        },
                }
                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),
                        last_chain_persist_height: AtomicUsize::new(self.highest_chain_height.load(Ordering::Acquire)),
                });
                Ok(persist_res)
        }

        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();
                let ret = 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(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;
                                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);

                                let update_id = MonitorUpdateId::from_monitor_update(update);
                                let mut pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
                                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!(self.logger, "Failed to update ChannelMonitor for channel {}. Going ahead and persisting the entire ChannelMonitor", log_funding_info!(monitor));
                                        self.persister.update_persisted_channel(funding_txo, None, monitor, update_id)
                                } else {
                                        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::Completed => {
                                                log_debug!(self.logger, "Persistence of ChannelMonitorUpdate for channel {} completed", log_funding_info!(monitor));
                                        },
                                        ChannelMonitorUpdateStatus::UnrecoverableError => { /* we'll panic in a moment */ },
                                }
                                if update_res.is_err() {
                                        ChannelMonitorUpdateStatus::InProgress
                                } else {
                                        persist_res
                                }
                        }
                };
                if let ChannelMonitorUpdateStatus::UnrecoverableError = ret {
                        // Take the monitors lock for writing so that we poison it and any future
                        // operations going forward fail immediately.
                        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!(self.logger, "{}", err_str);
                        panic!("{}", err_str);
                }
                ret
        }

        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) {
                                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;
        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, 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)
                        ), false, APIError::MonitorUpdateInProgress, {});
                check_added_monitors!(nodes[0], 1);

                // 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]
        #[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);

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

                assert!(std::panic::catch_unwind(|| {
                        // Returning an UnrecoverableError should always panic immediately
                        connect_blocks(&nodes[0], 1);
                }).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());
        }
}