+/// 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.
+///
+/// [`ChannelMonitor`]: channelmonitor::ChannelMonitor
+/// [`ChannelMonitorUpdateErr`]: channelmonitor::ChannelMonitorUpdateErr
+/// [`PermanentFailure`]: channelmonitor::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.
+ ///
+ /// [`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
+ /// [`ChannelMonitorUpdateErr`]: channelmonitor::ChannelMonitorUpdateErr
+ 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.
+ fn release_pending_monitor_events(&self) -> Vec<MonitorEvent>;
+}
+
+/// 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`]: channelmonitor::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.
+ ///
+ /// Optionally, when `output.block_hash` is set, should return any transaction spending the
+ /// output that is found in the corresponding block along with its index.
+ ///
+ /// This return value is useful for Electrum clients in order to supply in-block descendant
+ /// transactions which otherwise were not included. This is not necessary for other clients if
+ /// such descendant transactions were already included (e.g., when a BIP 157 client provides the
+ /// full block).
+ fn register_output(&self, output: WatchedOutput) -> Option<(usize, Transaction)>;
+}
+
+/// A transaction output watched by a [`ChannelMonitor`] for spends on-chain.
+///
+/// Used to convey to a [`Filter`] such an output with a given spending condition. Any transaction
+/// spending the output must be given to [`ChannelMonitor::block_connected`] either directly or via
+/// the return value of [`Filter::register_output`].
+///
+/// If `block_hash` is `Some`, this indicates the output was created in the corresponding block and
+/// may have been spent there. See [`Filter::register_output`] for details.
+///
+/// [`ChannelMonitor`]: channelmonitor::ChannelMonitor
+/// [`ChannelMonitor::block_connected`]: channelmonitor::ChannelMonitor::block_connected
+pub struct WatchedOutput {
+ /// First block where the transaction output may have been spent.
+ pub block_hash: Option<BlockHash>,
+
+ /// Outpoint identifying the transaction output.
+ pub outpoint: OutPoint,
+
+ /// Spending condition of the transaction output.
+ pub script_pubkey: Script,
+}
+
+impl<T: Listen> Listen for core::ops::Deref<Target = T> {
+ fn block_connected(&self, block: &Block, height: u32) {
+ (**self).block_connected(block, height);
+ }
+
+ fn block_disconnected(&self, header: &BlockHeader, height: u32) {
+ (**self).block_disconnected(header, height);
+ }
+}
+
+impl<T: core::ops::Deref, U: core::ops::Deref> Listen for (T, U)
+where
+ T::Target: Listen,
+ U::Target: Listen,
+{
+ fn block_connected(&self, block: &Block, height: u32) {
+ self.0.block_connected(block, height);
+ self.1.block_connected(block, height);
+ }
+
+ fn block_disconnected(&self, header: &BlockHeader, height: u32) {
+ self.0.block_disconnected(header, height);
+ self.1.block_disconnected(header, height);