Trait lightning::chain::chainmonitor::Persist

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pub trait Persist<ChannelSigner: WriteableEcdsaChannelSigner> {
    // Required methods
    fn persist_new_channel(
        &self,
        channel_id: OutPoint,
        data: &ChannelMonitor<ChannelSigner>,
        update_id: MonitorUpdateId
    ) -> ChannelMonitorUpdateStatus;
    fn update_persisted_channel(
        &self,
        channel_id: OutPoint,
        update: Option<&ChannelMonitorUpdate>,
        data: &ChannelMonitor<ChannelSigner>,
        update_id: MonitorUpdateId
    ) -> ChannelMonitorUpdateStatus;
}

Expand description

Persist defines behavior for persisting channel monitors: this could mean writing once to disk, and/or uploading to one or more backup services.

Persistence can happen in one of two ways - synchronously completing before the trait method calls return or asynchronously in the background.

§For those implementing synchronous persistence

If persistence completes fully (including any relevant fsync() calls), the implementation should return ChannelMonitorUpdateStatus::Completed, indicating normal channel operation should continue.
If persistence fails for some reason, implementations should consider returning ChannelMonitorUpdateStatus::InProgress and retry all pending persistence operations in the background with ChainMonitor::list_pending_monitor_updates and ChainMonitor::get_monitor.

Once a full ChannelMonitor has been persisted, all pending updates for that channel can be marked as complete via ChainMonitor::channel_monitor_updated.

If at some point no further progress can be made towards persisting the pending updates, the node should simply shut down.
If the persistence has failed and cannot be retried further (e.g. because of an outage), ChannelMonitorUpdateStatus::UnrecoverableError can be used, though this will result in an immediate panic and future operations in LDK generally failing.

§For those implementing asynchronous persistence

All calls should generally spawn a background task and immediately return ChannelMonitorUpdateStatus::InProgress. Once the update completes, ChainMonitor::channel_monitor_updated should be called with the corresponding MonitorUpdateId.

Note that unlike the direct chain::Watch interface, ChainMonitor::channel_monitor_updated must be called once for each update which occurs.

If at some point no further progress can be made towards persisting a pending update, the node should simply shut down. Until then, the background task should either loop indefinitely, or persistence should be regularly retried with ChainMonitor::list_pending_monitor_updates and ChainMonitor::get_monitor (note that if a full monitor is persisted all pending monitor updates may be marked completed).

§Using remote watchtowers

Watchtowers may be updated as a part of an implementation of this trait, utilizing the async update process described above while the watchtower is being updated. The following methods are provided for bulding transactions for a watchtower: ChannelMonitor::initial_counterparty_commitment_tx, ChannelMonitor::counterparty_commitment_txs_from_update, ChannelMonitor::sign_to_local_justice_tx, TrustedCommitmentTransaction::revokeable_output_index, TrustedCommitmentTransaction::build_to_local_justice_tx.

Required Methods§

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fn persist_new_channel( &self, channel_id: OutPoint, data: &ChannelMonitor<ChannelSigner>, update_id: MonitorUpdateId ) -> ChannelMonitorUpdateStatus

Persist a new channel’s data in response to a chain::Watch::watch_channel call. This is called by ChannelManager for new channels, or may be called directly, e.g. on startup.

The data can be stored any way you want, but the identifier provided by LDK is the channel’s outpoint (and it is up to you to maintain a correct mapping between the outpoint and the stored channel data). Note that you must persist every new monitor to disk.

The update_id is used to identify this call to ChainMonitor::channel_monitor_updated, if you return ChannelMonitorUpdateStatus::InProgress.

See Writeable::write on ChannelMonitor for writing out a ChannelMonitor and ChannelMonitorUpdateStatus for requirements when returning errors.

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fn update_persisted_channel( &self, channel_id: OutPoint, update: Option<&ChannelMonitorUpdate>, data: &ChannelMonitor<ChannelSigner>, update_id: MonitorUpdateId ) -> ChannelMonitorUpdateStatus

Update one channel’s data. The provided ChannelMonitor has already applied the given update.

Note that on every update, you must persist either the ChannelMonitorUpdate or the updated monitor itself to disk/backups. See the Persist trait documentation for more details.

During blockchain synchronization operations, and in some rare cases, this may be called with no ChannelMonitorUpdate, in which case the full ChannelMonitor needs to be persisted. Note that after the full ChannelMonitor is persisted any previous ChannelMonitorUpdates which were persisted should be discarded - they can no longer be applied to the persisted ChannelMonitor as they were already applied.

If an implementer chooses to persist the updates only, they need to make sure that all the updates are applied to the ChannelMonitors before the set of channel monitors is given to the ChannelManager deserialization routine. See ChannelMonitor::update_monitor for applying a monitor update to a monitor. If full ChannelMonitors are persisted, then there is no need to persist individual updates.

Note that there could be a performance tradeoff between persisting complete channel monitors on every update vs. persisting only updates and applying them in batches. The size of each monitor grows O(number of state updates) whereas updates are small and O(1).

The update_id is used to identify this call to ChainMonitor::channel_monitor_updated, if you return ChannelMonitorUpdateStatus::InProgress.

See Writeable::write on ChannelMonitor for writing out a ChannelMonitor, Writeable::write on ChannelMonitorUpdate for writing out an update, and ChannelMonitorUpdateStatus for requirements when returning errors.

Implementors§

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impl<ChannelSigner: WriteableEcdsaChannelSigner, K: KVStore> Persist<ChannelSigner> for K