+/// [`Access`]: trait.Access.html
+#[derive(Clone)]
+pub enum AccessError {
+ /// The requested chain is unknown.
+ UnknownChain,
+
+ /// The requested transaction doesn't exist or hasn't confirmed.
+ UnknownTx,
+}
+
+/// The `Access` trait defines behavior for accessing chain data and state, such as blocks and
+/// UTXOs.
+pub trait Access: Send + Sync {
+ /// Returns the transaction output of a funding transaction encoded by [`short_channel_id`].
+ /// Returns an error if `genesis_hash` is for a different chain or if such a transaction output
+ /// is unknown.
+ ///
+ /// [`short_channel_id`]: https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md#definition-of-short_channel_id
+ fn get_utxo(&self, genesis_hash: &BlockHash, short_channel_id: u64) -> Result<TxOut, AccessError>;
+}
+
+/// The `Listen` trait is used to be notified of when blocks have been connected or disconnected
+/// from the chain.
+///
+/// Useful when needing to replay chain data upon startup or as new chain events occur.
+pub trait Listen {
+ /// Notifies the listener that a block was added at the given height.
+ fn block_connected(&self, block: &Block, height: u32);
+
+ /// Notifies the listener that a block was removed at the given height.
+ fn block_disconnected(&self, header: &BlockHeader, height: u32);
+}
+
+/// 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/struct.ChannelMonitor.html
+/// [`ChannelMonitorUpdateErr`]: channelmonitor/enum.ChannelMonitorUpdateErr.html
+/// [`PermanentFailure`]: channelmonitor/enum.ChannelMonitorUpdateErr.html#variant.PermanentFailure
+pub trait Watch<ChannelSigner: Sign>: Send + Sync {
+ /// 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/struct.ChannelMonitor.html#method.get_outputs_to_watch
+ /// [`block_connected`]: channelmonitor/struct.ChannelMonitor.html#method.block_connected
+ /// [`block_disconnected`]: channelmonitor/struct.ChannelMonitor.html#method.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/struct.ChannelMonitor.html#method.update_monitor
+ /// [`ChannelMonitorUpdateErr`]: channelmonitor/enum.ChannelMonitorUpdateErr.html
+ 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>;