Tweak documentation in `BestBlock` to be a bit more clear

[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::blockdata::transaction::{Transaction, TxOut};
use bitcoin::hash_types::{BlockHash, Txid};
use bitcoin::network::constants::Network;

use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateErr, MonitorEvent};
use chain::keysinterface::Sign;
use chain::transaction::{OutPoint, TransactionData};

use prelude::*;

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

/// The best known block as identified by its hash and height.
#[derive(Clone, Copy, PartialEq)]
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_genesis(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 }
}

/// An error when accessing the chain via [`Access`].
#[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 {
        /// 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 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.
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 `Confirm` trait is used to notify when 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 client may implement [`Filter`] by subscribing to activity
/// related to registered transactions and outputs. Upon notification, it would pass along the
/// matching transactions using this interface.
///
/// # Use
///
/// The intended use is as follows:
/// - Call [`transactions_confirmed`] to process any on-chain activity of interest.
/// - Call [`transaction_unconfirmed`] to process any transaction returned by [`get_relevant_txids`]
///   that has been reorganized out of the chain.
/// - Call [`best_block_updated`] whenever a new chain tip becomes available.
///
/// # Order
///
/// Clients must call these methods in chain order. Specifically:
/// - Transactions confirmed in a 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.
/// - Unconfirmed transactions must be given after the original confirmations and before any
///   reconfirmation.
///
/// 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 {
        /// Processes transactions confirmed in a block with a given header and height.
        ///
        /// Should 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);

        /// Processes a transaction that is no longer confirmed as result of a chain reorganization.
        ///
        /// Should be called for any transaction returned by [`get_relevant_txids`] if it has been
        /// reorganized out of the best chain. Once called, the given transaction should 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);

        /// Processes an update to the best header connected at the given height.
        ///
        /// Should be called when a new header is available but may be skipped for intermediary blocks
        /// if they become available at the same time.
        fn best_block_updated(&self, header: &BlockHeader, height: u32);

        /// Returns transactions that should be monitored for reorganization out of the chain.
        ///
        /// Should include any transactions passed to [`transactions_confirmed`] that have insufficient
        /// confirmations to be safe from a chain reorganization. Should not include any transactions
        /// passed to [`transaction_unconfirmed`] unless later reconfirmed.
        ///
        /// May be called to determine the subset of transactions that must still 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 may need to be
        /// given to [`transaction_unconfirmed`].
        ///
        /// [`transactions_confirmed`]: Self::transactions_confirmed
        /// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
        fn get_relevant_txids(&self) -> Vec<Txid>;
}

/// 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
#[derive(Clone, PartialEq, 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 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);
        }
}