+ /// Notifies the listener that a block was added at the given height.
+ fn block_connected(&self, block: &Block, height: u32) {
+ let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
+ self.filtered_block_connected(&block.header, &txdata, height);
+ }
+
+ /// Notifies the listener that a block was removed at the given height.
+ fn block_disconnected(&self, header: &BlockHeader, height: u32);
+}
+
+/// The `Confirm` trait is used to notify when 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 client may implement [`Filter`] by subscribing to activity
+/// related to registered transactions and outputs. Upon notification, it would pass along the
+/// matching transactions using this interface.
+///
+/// # Use
+///
+/// The intended use is as follows:
+/// - Call [`transactions_confirmed`] to process any on-chain activity of interest.
+/// - Call [`transaction_unconfirmed`] to process any transaction returned by [`get_relevant_txids`]
+/// that has been reorganized out of the chain.
+/// - Call [`best_block_updated`] whenever a new chain tip becomes available.
+///
+/// # Order
+///
+/// Clients must call these methods in chain order. Specifically:
+/// - Transactions confirmed in a 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.
+/// - Unconfirmed transactions must be given after the original confirmations and before any
+/// reconfirmation.
+///
+/// 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 {
+ /// Processes transactions confirmed in a block with a given header and height.
+ ///
+ /// Should 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);
+
+ /// Processes a transaction that is no longer confirmed as result of a chain reorganization.
+ ///
+ /// Should be called for any transaction returned by [`get_relevant_txids`] if it has been
+ /// reorganized out of the best chain. 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);
+
+ /// Processes an update to the best header connected at the given height.
+ ///
+ /// Should be called when a new header is available but may be skipped for intermediary blocks
+ /// if they become available at the same time.
+ fn best_block_updated(&self, header: &BlockHeader, height: u32);
+
+ /// Returns transactions that should be monitored for reorganization out of the chain.
+ ///
+ /// 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.
+ ///
+ /// May be called to determine the subset of transactions that must still 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 may need to be
+ /// given to [`transaction_unconfirmed`].
+ ///
+ /// [`transactions_confirmed`]: Self::transactions_confirmed
+ /// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
+ fn get_relevant_txids(&self) -> Vec<Txid>;
+}
+
+/// An error enum representing a failure to persist a channel monitor update.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum ChannelMonitorUpdateErr {
+ /// Used to indicate a temporary failure (eg connection to a watchtower or remote backup of
+ /// our state failed, but is expected to succeed at some point in the future).
+ ///
+ /// Such a failure will "freeze" a channel, preventing us from revoking old states or
+ /// submitting new commitment transactions to the counterparty. Once the update(s) that failed
+ /// have been successfully applied, a [`MonitorEvent::UpdateCompleted`] event should be returned
+ /// via [`Watch::release_pending_monitor_events`] which will then restore the channel to an
+ /// operational state.
+ ///
+ /// Note that a given ChannelManager will *never* re-generate a given ChannelMonitorUpdate. If
+ /// you return a TemporaryFailure you must ensure that it is written to disk safely before
+ /// writing out the latest ChannelManager state.
+ ///
+ /// Even when a channel has been "frozen" updates to the ChannelMonitor can continue to occur
+ /// (eg if an inbound HTLC which we forwarded was claimed upstream resulting in us attempting
+ /// to claim it on this channel) and those updates must be applied wherever they can be. At
+ /// least one such updated ChannelMonitor must be persisted otherwise PermanentFailure should
+ /// be returned to get things on-chain ASAP using only the in-memory copy. Obviously updates to
+ /// the channel which would invalidate previous ChannelMonitors are not made when a channel has
+ /// been "frozen".
+ ///
+ /// Note that even if updates made after TemporaryFailure succeed you must still provide a
+ /// [`MonitorEvent::UpdateCompleted`] to ensure you have the latest monitor and re-enable
+ /// normal channel operation. Note that this is normally generated through a call to
+ /// [`ChainMonitor::channel_monitor_updated`].
+ ///
+ /// Note that the update being processed here will not be replayed for you when you return a
+ /// [`MonitorEvent::UpdateCompleted`] event via [`Watch::release_pending_monitor_events`], so
+ /// you must store the update itself on your own local disk prior to returning a
+ /// TemporaryFailure. You may, of course, employ a journaling approach, storing only the
+ /// ChannelMonitorUpdate on disk without updating the monitor itself, replaying the journal at
+ /// reload-time.
+ ///
+ /// For deployments where a copy of ChannelMonitors and other local state are backed up in a
+ /// remote location (with local copies persisted immediately), it is anticipated that all
+ /// updates will return TemporaryFailure until the remote copies could be updated.
+ ///
+ /// [`ChainMonitor::channel_monitor_updated`]: chainmonitor::ChainMonitor::channel_monitor_updated
+ TemporaryFailure,
+ /// Used to indicate no further channel monitor updates will be allowed (eg we've moved on to a
+ /// different watchtower and cannot update with all watchtowers that were previously informed
+ /// of this channel).
+ ///
+ /// At reception of this error, ChannelManager will force-close the channel and return at
+ /// least a final ChannelMonitorUpdate::ChannelForceClosed which must be delivered to at
+ /// least one ChannelMonitor copy. Revocation secret MUST NOT be released and offchain channel
+ /// update must be rejected.
+ ///
+ /// This failure may also signal a failure to update the local persisted copy of one of
+ /// the channel monitor instance.
+ ///
+ /// Note that even when you fail a holder commitment transaction update, you must store the
+ /// update to ensure you can claim from it in case of a duplicate copy of this ChannelMonitor
+ /// broadcasts it (e.g distributed channel-monitor deployment)
+ ///
+ /// In case of distributed watchtowers deployment, the new version must be written to disk, as
+ /// state may have been stored but rejected due to a block forcing a commitment broadcast. This
+ /// storage is used to claim outputs of rejected state confirmed onchain by another watchtower,
+ /// lagging behind on block processing.
+ PermanentFailure,
+}
+
+/// The `Watch` trait defines behavior for watching on-chain activity pertaining to channels as
+/// blocks are connected and disconnected.
+///
+/// Each channel is associated with a [`ChannelMonitor`]. Implementations of this trait are
+/// responsible for maintaining a set of monitors such that they can be updated accordingly as
+/// channel state changes and HTLCs are resolved. See method documentation for specific
+/// requirements.
+///
+/// Implementations **must** ensure that updates are successfully applied and persisted upon method
+/// completion. If an update fails with a [`PermanentFailure`], then it must immediately shut down
+/// without taking any further action such as persisting the current state.
+///
+/// If an implementation maintains multiple instances of a channel's monitor (e.g., by storing
+/// backup copies), then it must ensure that updates are applied across all instances. Otherwise, it
+/// could result in a revoked transaction being broadcast, allowing the counterparty to claim all
+/// funds in the channel. See [`ChannelMonitorUpdateErr`] for more details about how to handle
+/// multiple instances.
+///
+/// [`PermanentFailure`]: ChannelMonitorUpdateErr::PermanentFailure
+pub trait Watch<ChannelSigner: Sign> {
+ /// Watches a channel identified by `funding_txo` using `monitor`.
+ ///
+ /// Implementations are responsible for watching the chain for the funding transaction along
+ /// with any spends of outputs returned by [`get_outputs_to_watch`]. In practice, this means
+ /// calling [`block_connected`] and [`block_disconnected`] on the monitor.
+ ///
+ /// Note: this interface MUST error with `ChannelMonitorUpdateErr::PermanentFailure` if
+ /// the given `funding_txo` has previously been registered via `watch_channel`.
+ ///
+ /// [`get_outputs_to_watch`]: channelmonitor::ChannelMonitor::get_outputs_to_watch
+ /// [`block_connected`]: channelmonitor::ChannelMonitor::block_connected
+ /// [`block_disconnected`]: channelmonitor::ChannelMonitor::block_disconnected
+ fn watch_channel(&self, funding_txo: OutPoint, monitor: ChannelMonitor<ChannelSigner>) -> Result<(), ChannelMonitorUpdateErr>;
+
+ /// Updates a channel identified by `funding_txo` by applying `update` to its monitor.
+ ///
+ /// Implementations must call [`update_monitor`] with the given update. See
+ /// [`ChannelMonitorUpdateErr`] for invariants around returning an error.
+ ///
+ /// [`update_monitor`]: channelmonitor::ChannelMonitor::update_monitor
+ fn update_channel(&self, funding_txo: OutPoint, update: ChannelMonitorUpdate) -> Result<(), ChannelMonitorUpdateErr>;
+
+ /// Returns any monitor events since the last call. Subsequent calls must only return new
+ /// events.
+ ///
+ /// Note that after any block- or transaction-connection calls to a [`ChannelMonitor`], no
+ /// further events may be returned here until the [`ChannelMonitor`] has been fully persisted
+ /// to disk.
+ ///
+ /// For details on asynchronous [`ChannelMonitor`] updating and returning
+ /// [`MonitorEvent::UpdateCompleted`] here, see [`ChannelMonitorUpdateErr::TemporaryFailure`].
+ fn release_pending_monitor_events(&self) -> Vec<(OutPoint, Vec<MonitorEvent>, Option<PublicKey>)>;
+}
+
+/// The `Filter` trait defines behavior for indicating chain activity of interest pertaining to
+/// channels.
+///
+/// This is useful in order to have a [`Watch`] implementation convey to a chain source which
+/// transactions to be notified of. Notification may take the form of pre-filtering blocks or, in
+/// the case of [BIP 157]/[BIP 158], only fetching a block if the compact filter matches. If
+/// receiving full blocks from a chain source, any further filtering is unnecessary.
+///
+/// After an output has been registered, subsequent block retrievals from the chain source must not
+/// exclude any transactions matching the new criteria nor any in-block descendants of such
+/// transactions.
+///
+/// Note that use as part of a [`Watch`] implementation involves reentrancy. Therefore, the `Filter`
+/// should not block on I/O. Implementations should instead queue the newly monitored data to be
+/// processed later. Then, in order to block until the data has been processed, any [`Watch`]
+/// invocation that has called the `Filter` must return [`TemporaryFailure`].
+///
+/// [`TemporaryFailure`]: ChannelMonitorUpdateErr::TemporaryFailure
+/// [BIP 157]: https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki
+/// [BIP 158]: https://github.com/bitcoin/bips/blob/master/bip-0158.mediawiki
+pub trait Filter {
+ /// Registers interest in a transaction with `txid` and having an output with `script_pubkey` as
+ /// a spending condition.
+ fn register_tx(&self, txid: &Txid, script_pubkey: &Script);
+
+ /// Registers interest in spends of a transaction output.
+ ///
+ /// Note that this method might be called during processing of a new block. You therefore need
+ /// to ensure that also dependent output spents within an already connected block are correctly
+ /// handled, e.g., by re-scanning the block in question whenever new outputs have been
+ /// registered mid-processing.
+ fn register_output(&self, output: WatchedOutput);