+/// The `Confirm` trait is used to notify LDK when relevant transactions have been confirmed on
+/// chain or unconfirmed during a chain reorganization.
+///
+/// Clients sourcing chain data using a transaction-oriented API should prefer this interface over
+/// [`Listen`]. For instance, an Electrum-based transaction sync implementation may implement
+/// [`Filter`] to subscribe to relevant transactions and unspent outputs it should monitor for
+/// on-chain activity. Then, it needs to notify LDK via this interface upon observing any changes
+/// with reference to the confirmation status of the monitored objects.
+///
+/// # Use
+/// The intended use is as follows:
+/// - Call [`transactions_confirmed`] to notify LDK whenever any of the registered transactions or
+/// outputs are, respectively, confirmed or spent on chain.
+/// - Call [`transaction_unconfirmed`] to notify LDK whenever any transaction returned by
+/// [`get_relevant_txids`] is no longer confirmed in the block with the given block hash.
+/// - Call [`best_block_updated`] to notify LDK whenever a new chain tip becomes available.
+///
+/// # Order
+///
+/// Clients must call these methods in chain order. Specifically:
+/// - Transactions which are confirmed in a particular block must be given before transactions
+/// confirmed in a later block.
+/// - Dependent transactions within the same block must be given in topological order, possibly in
+/// separate calls.
+/// - All unconfirmed transactions must be given after the original confirmations and before *any*
+/// reconfirmations, i.e., [`transactions_confirmed`] and [`transaction_unconfirmed`] calls should
+/// never be interleaved, but always conduced *en bloc*.
+/// - Any reconfirmed transactions need to be explicitly unconfirmed before they are reconfirmed
+/// in regard to the new block.
+///
+/// See individual method documentation for further details.
+///
+/// [`transactions_confirmed`]: Self::transactions_confirmed
+/// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
+/// [`best_block_updated`]: Self::best_block_updated
+/// [`get_relevant_txids`]: Self::get_relevant_txids
+pub trait Confirm {
+ /// Notifies LDK of transactions confirmed in a block with a given header and height.
+ ///
+ /// Must be called for any transactions registered by [`Filter::register_tx`] or any
+ /// transactions spending an output registered by [`Filter::register_output`]. Such transactions
+ /// appearing in the same block do not need to be included in the same call; instead, multiple
+ /// calls with additional transactions may be made so long as they are made in [chain order].
+ ///
+ /// May be called before or after [`best_block_updated`] for the corresponding block. However,
+ /// in the event of a chain reorganization, it must not be called with a `header` that is no
+ /// longer in the chain as of the last call to [`best_block_updated`].
+ ///
+ /// [chain order]: Confirm#order
+ /// [`best_block_updated`]: Self::best_block_updated
+ fn transactions_confirmed(&self, header: &BlockHeader, txdata: &TransactionData, height: u32);
+ /// Notifies LDK of a transaction that is no longer confirmed as result of a chain reorganization.
+ ///
+ /// Must be called for any transaction returned by [`get_relevant_txids`] if it has been
+ /// reorganized out of the best chain or if it is no longer confirmed in the block with the
+ /// given block hash. Once called, the given transaction will not be returned
+ /// by [`get_relevant_txids`], unless it has been reconfirmed via [`transactions_confirmed`].
+ ///
+ /// [`get_relevant_txids`]: Self::get_relevant_txids
+ /// [`transactions_confirmed`]: Self::transactions_confirmed
+ fn transaction_unconfirmed(&self, txid: &Txid);
+ /// Notifies LDK of an update to the best header connected at the given height.
+ ///
+ /// Must be called whenever a new chain tip becomes available. May be skipped for intermediary
+ /// blocks.
+ fn best_block_updated(&self, header: &BlockHeader, height: u32);
+ /// Returns transactions that must be monitored for reorganization out of the chain along
+ /// with the hash of the block as part of which it had been previously confirmed.
+ ///
+ /// Note that the returned `Option<BlockHash>` might be `None` for channels created with LDK
+ /// 0.0.112 and prior, in which case you need to manually track previous confirmations.
+ ///
+ /// Will include any transactions passed to [`transactions_confirmed`] that have insufficient
+ /// confirmations to be safe from a chain reorganization. Will not include any transactions
+ /// passed to [`transaction_unconfirmed`], unless later reconfirmed.
+ ///
+ /// Must be called to determine the subset of transactions that must be monitored for
+ /// reorganization. Will be idempotent between calls but may change as a result of calls to the
+ /// other interface methods. Thus, this is useful to determine which transactions must be
+ /// given to [`transaction_unconfirmed`].
+ ///
+ /// If any of the returned transactions are confirmed in a block other than the one with the
+ /// given hash, they need to be unconfirmed and reconfirmed via [`transaction_unconfirmed`] and
+ /// [`transactions_confirmed`], respectively.
+ ///
+ /// [`transactions_confirmed`]: Self::transactions_confirmed
+ /// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
+ fn get_relevant_txids(&self) -> Vec<(Txid, Option<BlockHash>)>;
+}
+
+/// An enum representing the status of a channel monitor update persistence.
+///
+/// These are generally used as the return value for an implementation of [`Persist`] which is used
+/// as the storage layer for a [`ChainMonitor`]. See the docs on [`Persist`] for a high-level
+/// explanation of how to handle different cases.
+///
+/// While `UnrecoverableError` is provided as a failure variant, it is not truly "handled" on the
+/// calling side, and generally results in an immediate panic. For those who prefer to avoid
+/// panics, `InProgress` can be used and you can retry the update operation in the background or
+/// shut down cleanly.
+///
+/// Note that channels should generally *not* be force-closed after a persistence failure.
+/// Force-closing with the latest [`ChannelMonitorUpdate`] applied may result in a transaction
+/// being broadcast which can only be spent by the latest [`ChannelMonitor`]! Thus, if the
+/// latest [`ChannelMonitor`] is not durably persisted anywhere and exists only in memory, naively
+/// calling [`ChannelManager::force_close_broadcasting_latest_txn`] *may result in loss of funds*!
+///
+/// [`Persist`]: chainmonitor::Persist
+/// [`ChainMonitor`]: chainmonitor::ChainMonitor
+/// [`ChannelManager::force_close_broadcasting_latest_txn`]: crate::ln::channelmanager::ChannelManager::force_close_broadcasting_latest_txn
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum ChannelMonitorUpdateStatus {
+ /// The update has been durably persisted and all copies of the relevant [`ChannelMonitor`]
+ /// have been updated.
+ ///
+ /// This includes performing any `fsync()` calls required to ensure the update is guaranteed to
+ /// be available on restart even if the application crashes.
+ Completed,
+ /// Indicates that the update will happen asynchronously in the background or that a transient
+ /// failure occurred which is being retried in the background and will eventually complete.
+ ///
+ /// This will "freeze" a channel, preventing us from revoking old states or submitting a new
+ /// commitment transaction to the counterparty. Once the update(s) which are `InProgress` have
+ /// been completed, a [`MonitorEvent::Completed`] can be used to restore the channel to an
+ /// operational state.
+ ///
+ /// Even when a channel has been "frozen", updates to the [`ChannelMonitor`] can continue to
+ /// occur (e.g. if an inbound HTLC which we forwarded was claimed upstream, resulting in us
+ /// attempting to claim it on this channel) and those updates must still be persisted.
+ ///
+ /// No updates to the channel will be made which could invalidate other [`ChannelMonitor`]s
+ /// until a [`MonitorEvent::Completed`] is provided, even if you return no error on a later
+ /// monitor update for the same channel.
+ ///
+ /// For deployments where a copy of [`ChannelMonitor`]s and other local state are backed up in
+ /// a remote location (with local copies persisted immediately), it is anticipated that all
+ /// updates will return [`InProgress`] until the remote copies could be updated.
+ ///
+ /// Note that while fully asynchronous persistence of [`ChannelMonitor`] data is generally
+ /// reliable, this feature is considered beta, and a handful of edge-cases remain. Until the
+ /// remaining cases are fixed, in rare cases, *using this feature may lead to funds loss*.
+ ///
+ /// [`InProgress`]: ChannelMonitorUpdateStatus::InProgress
+ InProgress,
+ /// Indicates that an update has failed and will not complete at any point in the future.
+ ///
+ /// Currently returning this variant will cause LDK to immediately panic to encourage immediate
+ /// shutdown. In the future this may be updated to disconnect peers and refuse to continue
+ /// normal operation without a panic.
+ ///
+ /// Applications which wish to perform an orderly shutdown after failure should consider
+ /// returning [`InProgress`] instead and simply shut down without ever marking the update
+ /// complete.
+ ///
+ /// [`InProgress`]: ChannelMonitorUpdateStatus::InProgress
+ UnrecoverableError,
+}
+