fn get_relevant_txids(&self) -> Vec<Txid>;
}
-/// An error enum representing a failure to persist a channel monitor update.
+/// An enum representing the status of a channel monitor update persistence.
#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum ChannelMonitorUpdateErr {
+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,
/// 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.
+ /// submitting new commitment transactions to the counterparty. Once the update(s) which failed
+ /// have been successfully applied, a [`MonitorEvent::Completed`] can be used to restore the
+ /// channel to an operational state.
+ ///
+ /// Note that a given [`ChannelManager`] will *never* re-generate a [`ChannelMonitorUpdate`].
+ /// If you return this error you must ensure that it is written to disk safely before writing
+ /// the latest [`ChannelManager`] state, or you should return [`PermanentFailure`] instead.
+ ///
+ /// 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 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.
+ /// updates will return [`InProgress`] 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).
+ /// [`PermanentFailure`]: ChannelMonitorUpdateStatus::PermanentFailure
+ /// [`InProgress`]: ChannelMonitorUpdateStatus::InProgress
+ /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
+ InProgress,
+ /// Used to indicate no further channel monitor updates will be allowed (likely a disk failure
+ /// or a remote copy of this [`ChannelMonitor`] is no longer reachable and thus not updatable).
///
- /// 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.
+ /// When this is returned, [`ChannelManager`] will force-close the channel but *not* broadcast
+ /// our current commitment transaction. This avoids a dangerous case where a local disk failure
+ /// (e.g. the Linux-default remounting of the disk as read-only) causes [`PermanentFailure`]s
+ /// for all monitor updates. If we were to broadcast our latest commitment transaction and then
+ /// restart, we could end up reading a previous [`ChannelMonitor`] and [`ChannelManager`],
+ /// revoking our now-broadcasted state before seeing it confirm and losing all our funds.
///
- /// This failure may also signal a failure to update the local persisted copy of one of
- /// the channel monitor instance.
+ /// Note that this is somewhat of a tradeoff - if the disk is really gone and we may have lost
+ /// the data permanently, we really should broadcast immediately. If the data can be recovered
+ /// with manual intervention, we'd rather close the channel, rejecting future updates to it,
+ /// and broadcast the latest state only if we have HTLCs to claim which are timing out (which
+ /// we do as long as blocks are connected).
///
- /// 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 order to broadcast the latest local commitment transaction, you'll need to call
+ /// [`ChannelMonitor::get_latest_holder_commitment_txn`] and broadcast the resulting
+ /// transactions once you've safely ensured no further channel updates can be generated by your
+ /// [`ChannelManager`].
+ ///
+ /// Note that at least one final [`ChannelMonitorUpdate`] may still be provided, which must
+ /// still be processed by a running [`ChannelMonitor`]. This final update will mark the
+ /// [`ChannelMonitor`] as finalized, ensuring no further updates (e.g. revocation of the latest
+ /// commitment transaction) are allowed.
+ ///
+ /// Note that even if you return a [`PermanentFailure`] due to unavailability of secondary
+ /// [`ChannelMonitor`] copies, you should still make an attempt to store the update where
+ /// possible to ensure you can claim HTLC outputs on the latest commitment transaction
+ /// broadcasted later.
///
/// 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`]: ChannelMonitorUpdateStatus::PermanentFailure
+ /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
PermanentFailure,
}
/// 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
+/// funds in the channel. See [`ChannelMonitorUpdateStatus`] for more details about how to handle
/// multiple instances.
///
-/// [`PermanentFailure`]: ChannelMonitorUpdateErr::PermanentFailure
+/// [`PermanentFailure`]: ChannelMonitorUpdateStatus::PermanentFailure
pub trait Watch<ChannelSigner: Sign> {
/// Watches a channel identified by `funding_txo` using `monitor`.
///
/// 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
+ /// Note: this interface MUST error with [`ChannelMonitorUpdateStatus::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>;
+ fn watch_channel(&self, funding_txo: OutPoint, monitor: ChannelMonitor<ChannelSigner>) -> ChannelMonitorUpdateStatus;
/// 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.
+ /// [`ChannelMonitorUpdateStatus`] for invariants around returning an error.
///
/// [`update_monitor`]: channelmonitor::ChannelMonitor::update_monitor
- fn update_channel(&self, funding_txo: OutPoint, update: ChannelMonitorUpdate) -> Result<(), ChannelMonitorUpdateErr>;
+ fn update_channel(&self, funding_txo: OutPoint, update: ChannelMonitorUpdate) -> ChannelMonitorUpdateStatus;
/// Returns any monitor events since the last call. Subsequent calls must only return new
/// events.
/// to disk.
///
/// For details on asynchronous [`ChannelMonitor`] updating and returning
- /// [`MonitorEvent::UpdateCompleted`] here, see [`ChannelMonitorUpdateErr::TemporaryFailure`].
+ /// [`MonitorEvent::Completed`] here, see [`ChannelMonitorUpdateStatus::InProgress`].
fn release_pending_monitor_events(&self) -> Vec<(OutPoint, Vec<MonitorEvent>, Option<PublicKey>)>;
}
/// 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`].
+/// invocation that has called the `Filter` must return [`InProgress`].
///
-/// [`TemporaryFailure`]: ChannelMonitorUpdateErr::TemporaryFailure
+/// [`InProgress`]: ChannelMonitorUpdateStatus::InProgress
/// [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 {
projects / rust-lightning / blobdiff