Update `ChannelMonitorUpdateStatus` documentation with async support

[rust-lightning] / lightning / src / chain / mod.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Structs and traits which allow other parts of rust-lightning to interact with the blockchain.

use bitcoin::blockdata::block::{Block, BlockHeader};
use bitcoin::blockdata::constants::genesis_block;
use bitcoin::blockdata::script::Script;
use bitcoin::hash_types::{BlockHash, Txid};
use bitcoin::network::constants::Network;
use bitcoin::secp256k1::PublicKey;

use crate::chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, MonitorEvent};
use crate::sign::WriteableEcdsaChannelSigner;
use crate::chain::transaction::{OutPoint, TransactionData};

use crate::prelude::*;

pub mod chaininterface;
pub mod chainmonitor;
pub mod channelmonitor;
pub mod transaction;
pub(crate) mod onchaintx;
pub(crate) mod package;

/// The best known block as identified by its hash and height.
#[derive(Clone, Copy, PartialEq, Eq)]
pub struct BestBlock {
        block_hash: BlockHash,
        height: u32,
}

impl BestBlock {
        /// Constructs a `BestBlock` that represents the genesis block at height 0 of the given
        /// network.
        pub fn from_network(network: Network) -> Self {
                BestBlock {
                        block_hash: genesis_block(network).header.block_hash(),
                        height: 0,
                }
        }

        /// Returns a `BestBlock` as identified by the given block hash and height.
        pub fn new(block_hash: BlockHash, height: u32) -> Self {
                BestBlock { block_hash, height }
        }

        /// Returns the best block hash.
        pub fn block_hash(&self) -> BlockHash { self.block_hash }

        /// Returns the best block height.
        pub fn height(&self) -> u32 { self.height }
}


/// The `Listen` trait is used to notify 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. Clients
/// sourcing chain data using a block-oriented API should prefer this interface over [`Confirm`].
/// Such clients fetch the entire header chain whereas clients using [`Confirm`] only fetch headers
/// when needed.
///
/// By using [`Listen::filtered_block_connected`] this interface supports clients fetching the
/// entire header chain and only blocks with matching transaction data using BIP 157 filters or
/// other similar filtering.
pub trait Listen {
        /// Notifies the listener that a block was added at the given height, with the transaction data
        /// possibly filtered.
        fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32);

        /// 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 LDK when relevant 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-based transaction sync implementation may implement
/// [`Filter`] to subscribe to relevant transactions and unspent outputs it should monitor for
/// on-chain activity. Then, it needs to notify LDK via this interface upon observing any changes
/// with reference to the confirmation status of the monitored objects.
///
/// # Use
/// The intended use is as follows:
/// - Call [`transactions_confirmed`] to notify LDK whenever any of the registered transactions or
///   outputs are, respectively, confirmed or spent on chain.
/// - Call [`transaction_unconfirmed`] to notify LDK whenever any transaction returned by
///   [`get_relevant_txids`] is no longer confirmed in the block with the given block hash.
/// - Call [`best_block_updated`] to notify LDK whenever a new chain tip becomes available.
///
/// # Order
///
/// Clients must call these methods in chain order. Specifically:
/// - Transactions which are confirmed in a particular 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.
/// - All unconfirmed transactions must be given after the original confirmations and before *any*
///   reconfirmations, i.e., [`transactions_confirmed`] and [`transaction_unconfirmed`] calls should
///   never be interleaved, but always conduced *en bloc*.
/// - Any reconfirmed transactions need to be explicitly unconfirmed before they are reconfirmed
///   in regard to the new block.
///
/// 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 {
        /// Notifies LDK of transactions confirmed in a block with a given header and height.
        ///
        /// Must 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);
        /// Notifies LDK of a transaction that is no longer confirmed as result of a chain reorganization.
        ///
        /// Must be called for any transaction returned by [`get_relevant_txids`] if it has been
        /// reorganized out of the best chain or if it is no longer confirmed in the block with the
        /// given block hash. 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);
        /// Notifies LDK of an update to the best header connected at the given height.
        ///
        /// Must be called whenever a new chain tip becomes available. May be skipped for intermediary
        /// blocks.
        fn best_block_updated(&self, header: &BlockHeader, height: u32);
        /// Returns transactions that must be monitored for reorganization out of the chain along
        /// with the hash of the block as part of which it had been previously confirmed.
        ///
        /// Note that the returned `Option<BlockHash>` might be `None` for channels created with LDK
        /// 0.0.112 and prior, in which case you need to manually track previous confirmations.
        ///
        /// 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.
        ///
        /// Must be called to determine the subset of transactions that must 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 must be
        /// given to [`transaction_unconfirmed`].
        ///
        /// If any of the returned transactions are confirmed in a block other than the one with the
        /// given hash, they need to be unconfirmed and reconfirmed via [`transaction_unconfirmed`] and
        /// [`transactions_confirmed`], respectively.
        ///
        /// [`transactions_confirmed`]: Self::transactions_confirmed
        /// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
        fn get_relevant_txids(&self) -> Vec<(Txid, Option<BlockHash>)>;
}

/// An enum representing the status of a channel monitor update persistence.
///
/// Note that there is no error variant - any failure to persist a [`ChannelMonitor`] should be
/// retried indefinitely, the node shut down (as if we cannot update stored data we can't do much
/// of anything useful).
///
/// Note that channels should generally *not* be force-closed after a persistence failure.
/// Force-closing with the latest [`ChannelMonitorUpdate`] applied may result in a transaction
/// being broadcast which can only be spent by the latest [`ChannelMonitor`]! Thus, if the
/// latest [`ChannelMonitor`] is not durably persisted anywhere and exists only in memory, naively
/// calling [`ChannelManager::force_close_broadcasting_latest_txn`] *may result in loss of funds*!
///
/// [`ChannelManager::force_close_broadcasting_latest_txn`]: crate::ln::channelmanager::ChannelManager::force_close_broadcasting_latest_txn
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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,
        /// Indicates that the update will happen asynchronously in the background or that a transient
        /// failure occurred which is being retried in the background and will eventually complete.
        ///
        /// This will "freeze" a channel, preventing us from revoking old states or submitting a new
        /// commitment transaction to the counterparty. Once the update(s) which are `InProgress` have
        /// been completed, a [`MonitorEvent::Completed`] can be used to restore the channel to an
        /// operational state.
        ///
        /// 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 [`InProgress`] until the remote copies could be updated.
        ///
        /// Note that while fully asynchronous persistence of [`ChannelMonitor`] data is generally
        /// reliable, this feature is considered beta, and a handful of edge-cases remain. Until the
        /// remaining cases are fixed, in rare cases, *using this feature may lead to funds loss*.
        ///
        /// [`InProgress`]: ChannelMonitorUpdateStatus::InProgress
        InProgress,
}

/// 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 as channel state
/// changes. On each update, *all copies* of a [`ChannelMonitor`] must be updated and the update
/// persisted to disk to ensure that the latest [`ChannelMonitor`] state can be reloaded if the
/// application crashes.
///
/// See method documentation and [`ChannelMonitorUpdateStatus`] for specific requirements.
pub trait Watch<ChannelSigner: WriteableEcdsaChannelSigner> {
        /// 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.
        ///
        /// A return of `Err(())` indicates that the channel should immediately be force-closed without
        /// broadcasting the funding transaction.
        ///
        /// If the given `funding_txo` has previously been registered via `watch_channel`, `Err(())`
        /// must be returned.
        ///
        /// [`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<ChannelMonitorUpdateStatus, ()>;

        /// Updates a channel identified by `funding_txo` by applying `update` to its monitor.
        ///
        /// Implementations must call [`ChannelMonitor::update_monitor`] with the given update. This
        /// may fail (returning an `Err(())`), in which case this should return
        /// [`ChannelMonitorUpdateStatus::InProgress`] (and the update should never complete). This
        /// generally implies the channel has been closed (either by the funding outpoint being spent
        /// on-chain or the [`ChannelMonitor`] having decided to do so and broadcasted a transaction),
        /// and the [`ChannelManager`] state will be updated once it sees the funding spend on-chain.
        ///
        /// If persistence fails, this should return [`ChannelMonitorUpdateStatus::InProgress`] and
        /// the node should shut down immediately.
        ///
        /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
        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.
        ///
        /// 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::Completed`] here, see [`ChannelMonitorUpdateStatus::InProgress`].
        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 [`InProgress`].
///
/// [`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 {
        /// 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);
}

/// 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
/// [`Confirm::transactions_confirmed`].
///
/// 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
#[derive(Clone, PartialEq, Eq, Hash)]
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 filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
                (**self).filtered_block_connected(header, txdata, 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 filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
                self.0.filtered_block_connected(header, txdata, height);
                self.1.filtered_block_connected(header, txdata, height);
        }

        fn block_disconnected(&self, header: &BlockHeader, height: u32) {
                self.0.block_disconnected(header, height);
                self.1.block_disconnected(header, height);
        }
}

/// A unique identifier to track each pending output claim within a [`ChannelMonitor`].
///
/// This is not exported to bindings users as we just use [u8; 32] directly.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
pub struct ClaimId(pub [u8; 32]);