Clarify rescan rules for block_connected somewhat

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

//! Traits and utility impls which allow other parts of rust-lightning to interact with the
//! blockchain.
//!
//! Includes traits for monitoring and receiving notifications of new blocks and block
//! disconnections, transaction broadcasting, and feerate information requests.

use bitcoin::blockdata::block::{Block, BlockHeader};
use bitcoin::blockdata::transaction::Transaction;
use bitcoin::blockdata::script::Script;
use bitcoin::blockdata::constants::genesis_block;
use bitcoin::util::hash::BitcoinHash;
use bitcoin_hashes::sha256d::Hash as Sha256dHash;
use bitcoin::network::constants::Network;

use util::logger::Logger;

use std::sync::{Mutex, MutexGuard, Arc};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::collections::HashSet;
use std::ops::Deref;
use std::marker::PhantomData;

/// Used to give chain error details upstream
pub enum ChainError {
        /// Client doesn't support UTXO lookup (but the chain hash matches our genesis block hash)
        NotSupported,
        /// Chain isn't the one watched
        NotWatched,
        /// Tx doesn't exist or is unconfirmed
        UnknownTx,
}

/// An interface to request notification of certain scripts as they appear the
/// chain.
///
/// Note that all of the functions implemented here *must* be reentrant-safe (obviously - they're
/// called from inside the library in response to ChainListener events, P2P events, or timer
/// events).
pub trait ChainWatchInterface: Sync + Send {
        /// Provides a txid/random-scriptPubKey-in-the-tx which much be watched for.
        fn install_watch_tx(&self, txid: &Sha256dHash, script_pub_key: &Script);

        /// Provides an outpoint which must be watched for, providing any transactions which spend the
        /// given outpoint.
        fn install_watch_outpoint(&self, outpoint: (Sha256dHash, u32), out_script: &Script);

        /// Indicates that a listener needs to see all transactions.
        fn watch_all_txn(&self);

        /// Gets the script and value in satoshis for a given unspent transaction output given a
        /// short_channel_id (aka unspent_tx_output_identier). For BTC/tBTC channels the top three
        /// bytes are the block height, the next 3 the transaction index within the block, and the
        /// final two the output within the transaction.
        fn get_chain_utxo(&self, genesis_hash: Sha256dHash, unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError>;

        /// Gets the list of transactions and transaction indices that the ChainWatchInterface is
        /// watching for.
        fn filter_block<'a>(&self, block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>);

        /// Returns a usize that changes when the ChainWatchInterface's watched data is modified.
        /// Users of `filter_block` should pre-save a copy of `reentered`'s return value and use it to
        /// determine whether they need to re-filter a given block.
        fn reentered(&self) -> usize;
}

/// An interface to send a transaction to the Bitcoin network.
pub trait BroadcasterInterface: Sync + Send {
        /// Sends a transaction out to (hopefully) be mined.
        fn broadcast_transaction(&self, tx: &Transaction);
}

/// A trait indicating a desire to listen for events from the chain
pub trait ChainListener: Sync + Send {
        /// Notifies a listener that a block was connected.
        ///
        /// The txn_matched array should be set to references to transactions which matched the
        /// relevant installed watch outpoints/txn, or the full set of transactions in the block.
        ///
        /// Note that if txn_matched includes only matched transactions, and a new
        /// transaction/outpoint is watched during a block_connected call, the block *must* be
        /// re-scanned with the new transaction/outpoints and block_connected should be called
        /// again with the same header and (at least) the new transactions.
        ///
        /// Note that if non-new transaction/outpoints are be registered during a call, a second call
        /// *must not* happen.
        ///
        /// This also means those counting confirmations using block_connected callbacks should watch
        /// for duplicate headers and not count them towards confirmations!
        fn block_connected(&self, header: &BlockHeader, height: u32, txn_matched: &[&Transaction], indexes_of_txn_matched: &[u32]);
        /// Notifies a listener that a block was disconnected.
        /// Unlike block_connected, this *must* never be called twice for the same disconnect event.
        /// Height must be the one of the block which was disconnected (not new height of the best chain)
        fn block_disconnected(&self, header: &BlockHeader, disconnected_height: u32);
}

/// An enum that represents the speed at which we want a transaction to confirm used for feerate
/// estimation.
pub enum ConfirmationTarget {
        /// We are happy with this transaction confirming slowly when feerate drops some.
        Background,
        /// We'd like this transaction to confirm without major delay, but 12-18 blocks is fine.
        Normal,
        /// We'd like this transaction to confirm in the next few blocks.
        HighPriority,
}

/// A trait which should be implemented to provide feerate information on a number of time
/// horizons.
///
/// Note that all of the functions implemented here *must* be reentrant-safe (obviously - they're
/// called from inside the library in response to ChainListener events, P2P events, or timer
/// events).
pub trait FeeEstimator: Sync + Send {
        /// Gets estimated satoshis of fee required per 1000 Weight-Units.
        ///
        /// Must be no smaller than 253 (ie 1 satoshi-per-byte rounded up to ensure later round-downs
        /// don't put us below 1 satoshi-per-byte).
        ///
        /// This translates to:
        ///  * satoshis-per-byte * 250
        ///  * ceil(satoshis-per-kbyte / 4)
        fn get_est_sat_per_1000_weight(&self, confirmation_target: ConfirmationTarget) -> u64;
}

/// Minimum relay fee as required by bitcoin network mempool policy.
pub const MIN_RELAY_FEE_SAT_PER_1000_WEIGHT: u64 = 4000;

/// Utility for tracking registered txn/outpoints and checking for matches
pub struct ChainWatchedUtil {
        watch_all: bool,

        // We are more conservative in matching during testing to ensure everything matches *exactly*,
        // even though during normal runtime we take more optimized match approaches...
        #[cfg(test)]
        watched_txn: HashSet<(Sha256dHash, Script)>,
        #[cfg(not(test))]
        watched_txn: HashSet<Script>,

        watched_outpoints: HashSet<(Sha256dHash, u32)>,
}

impl ChainWatchedUtil {
        /// Constructs an empty (watches nothing) ChainWatchedUtil
        pub fn new() -> Self {
                Self {
                        watch_all: false,
                        watched_txn: HashSet::new(),
                        watched_outpoints: HashSet::new(),
                }
        }

        /// Registers a tx for monitoring, returning true if it was a new tx and false if we'd already
        /// been watching for it.
        pub fn register_tx(&mut self, txid: &Sha256dHash, script_pub_key: &Script) -> bool {
                if self.watch_all { return false; }
                #[cfg(test)]
                {
                        self.watched_txn.insert((txid.clone(), script_pub_key.clone()))
                }
                #[cfg(not(test))]
                {
                        let _tx_unused = txid; // It's used in cfg(test), though
                        self.watched_txn.insert(script_pub_key.clone())
                }
        }

        /// Registers an outpoint for monitoring, returning true if it was a new outpoint and false if
        /// we'd already been watching for it
        pub fn register_outpoint(&mut self, outpoint: (Sha256dHash, u32), _script_pub_key: &Script) -> bool {
                if self.watch_all { return false; }
                self.watched_outpoints.insert(outpoint)
        }

        /// Sets us to match all transactions, returning true if this is a new setting and false if
        /// we'd already been set to match everything.
        pub fn watch_all(&mut self) -> bool {
                if self.watch_all { return false; }
                self.watch_all = true;
                true
        }

        /// Checks if a given transaction matches the current filter.
        pub fn does_match_tx(&self, tx: &Transaction) -> bool {
                if self.watch_all {
                        return true;
                }
                for out in tx.output.iter() {
                        #[cfg(test)]
                        for &(ref txid, ref script) in self.watched_txn.iter() {
                                if *script == out.script_pubkey {
                                        if tx.txid() == *txid {
                                                return true;
                                        }
                                }
                        }
                        #[cfg(not(test))]
                        for script in self.watched_txn.iter() {
                                if *script == out.script_pubkey {
                                        return true;
                                }
                        }
                }
                for input in tx.input.iter() {
                        for outpoint in self.watched_outpoints.iter() {
                                let &(outpoint_hash, outpoint_index) = outpoint;
                                if outpoint_hash == input.previous_output.txid && outpoint_index == input.previous_output.vout {
                                        return true;
                                }
                        }
                }
                false
        }
}

/// BlockNotifierArc is useful when you need a BlockNotifier that points to ChainListeners with
/// static lifetimes, e.g. when you're using lightning-net-tokio (since tokio::spawn requires
/// parameters with static lifetimes). Other times you can afford a reference, which is more
/// efficient, in which case BlockNotifierRef is a more appropriate type. Defining these type
/// aliases prevents issues such as overly long function definitions.
pub type BlockNotifierArc = Arc<BlockNotifier<'static, Arc<ChainListener>>>;

/// BlockNotifierRef is useful when you want a BlockNotifier that points to ChainListeners
/// with nonstatic lifetimes. This is useful for when static lifetimes are not needed. Nonstatic
/// lifetimes are more efficient but less flexible, and should be used by default unless static
/// lifetimes are required, e.g. when you're using lightning-net-tokio (since tokio::spawn
/// requires parameters with static lifetimes), in which case BlockNotifierArc is a more
/// appropriate type. Defining these type aliases for common usages prevents issues such as
/// overly long function definitions.
pub type BlockNotifierRef<'a> = BlockNotifier<'a, &'a ChainListener>;

/// Utility for notifying listeners about new blocks, and handling block rescans if new watch
/// data is registered.
///
/// Rather than using a plain BlockNotifier, it is preferable to use either a BlockNotifierArc
/// or a BlockNotifierRef for conciseness. See their documentation for more details, but essentially
/// you should default to using a BlockNotifierRef, and use a BlockNotifierArc instead when you
/// require ChainListeners with static lifetimes, such as when you're using lightning-net-tokio.
pub struct BlockNotifier<'a, CL: Deref<Target = ChainListener + 'a> + 'a> {
        listeners: Mutex<Vec<CL>>,
        chain_monitor: Arc<ChainWatchInterface>,
        phantom: PhantomData<&'a ()>,
}

impl<'a, CL: Deref<Target = ChainListener + 'a> + 'a> BlockNotifier<'a, CL> {
        /// Constructs a new BlockNotifier without any listeners.
        pub fn new(chain_monitor: Arc<ChainWatchInterface>) -> BlockNotifier<'a, CL> {
                BlockNotifier {
                        listeners: Mutex::new(Vec::new()),
                        chain_monitor,
                        phantom: PhantomData,
                }
        }

        /// Register the given listener to receive events.
        // TODO: unregister
        pub fn register_listener(&self, listener: CL) {
                let mut vec = self.listeners.lock().unwrap();
                vec.push(listener);
        }

        /// Notify listeners that a block was connected given a full, unfiltered block.
        ///
        /// Handles re-scanning the block and calling block_connected again if listeners register new
        /// watch data during the callbacks for you (see ChainListener::block_connected for more info).
        pub fn block_connected<'b>(&self, block: &'b Block, height: u32) {
                let mut reentered = true;
                while reentered {
                        let (matched, matched_index) = self.chain_monitor.filter_block(block);
                        reentered = self.block_connected_checked(&block.header, height, matched.as_slice(), matched_index.as_slice());
                }
        }

        /// Notify listeners that a block was connected, given pre-filtered list of transactions in the
        /// block which matched the filter (probably using does_match_tx).
        ///
        /// Returns true if notified listeners registered additional watch data (implying that the
        /// block must be re-scanned and this function called again prior to further block_connected
        /// calls, see ChainListener::block_connected for more info).
        pub fn block_connected_checked(&self, header: &BlockHeader, height: u32, txn_matched: &[&Transaction], indexes_of_txn_matched: &[u32]) -> bool {
                let last_seen = self.chain_monitor.reentered();

                let listeners = self.listeners.lock().unwrap();
                for listener in listeners.iter() {
                        listener.block_connected(header, height, txn_matched, indexes_of_txn_matched);
                }
                return last_seen != self.chain_monitor.reentered();
        }

        /// Notify listeners that a block was disconnected.
        pub fn block_disconnected(&self, header: &BlockHeader, disconnected_height: u32) {
                let listeners = self.listeners.lock().unwrap();
                for listener in listeners.iter() {
                        listener.block_disconnected(&header, disconnected_height);
                }
        }
}

/// Utility to capture some common parts of ChainWatchInterface implementors.
///
/// Keeping a local copy of this in a ChainWatchInterface implementor is likely useful.
pub struct ChainWatchInterfaceUtil {
        network: Network,
        watched: Mutex<ChainWatchedUtil>,
        reentered: AtomicUsize,
        logger: Arc<Logger>,
}

/// Register listener
impl ChainWatchInterface for ChainWatchInterfaceUtil {
        fn install_watch_tx(&self, txid: &Sha256dHash, script_pub_key: &Script) {
                let mut watched = self.watched.lock().unwrap();
                if watched.register_tx(txid, script_pub_key) {
                        self.reentered.fetch_add(1, Ordering::Relaxed);
                }
        }

        fn install_watch_outpoint(&self, outpoint: (Sha256dHash, u32), out_script: &Script) {
                let mut watched = self.watched.lock().unwrap();
                if watched.register_outpoint(outpoint, out_script) {
                        self.reentered.fetch_add(1, Ordering::Relaxed);
                }
        }

        fn watch_all_txn(&self) {
                let mut watched = self.watched.lock().unwrap();
                if watched.watch_all() {
                        self.reentered.fetch_add(1, Ordering::Relaxed);
                }
        }

        fn get_chain_utxo(&self, genesis_hash: Sha256dHash, _unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError> {
                if genesis_hash != genesis_block(self.network).header.bitcoin_hash() {
                        return Err(ChainError::NotWatched);
                }
                Err(ChainError::NotSupported)
        }

        fn filter_block<'a>(&self, block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>) {
                let mut matched = Vec::new();
                let mut matched_index = Vec::new();
                {
                        let watched = self.watched.lock().unwrap();
                        for (index, transaction) in block.txdata.iter().enumerate() {
                                if self.does_match_tx_unguarded(transaction, &watched) {
                                        matched.push(transaction);
                                        matched_index.push(index as u32);
                                }
                        }
                }
                (matched, matched_index)
        }

        fn reentered(&self) -> usize {
                self.reentered.load(Ordering::Relaxed)
        }
}

impl ChainWatchInterfaceUtil {
        /// Creates a new ChainWatchInterfaceUtil for the given network
        pub fn new(network: Network, logger: Arc<Logger>) -> ChainWatchInterfaceUtil {
                ChainWatchInterfaceUtil {
                        network: network,
                        watched: Mutex::new(ChainWatchedUtil::new()),
                        reentered: AtomicUsize::new(1),
                        logger: logger,
                }
        }

        /// Checks if a given transaction matches the current filter.
        pub fn does_match_tx(&self, tx: &Transaction) -> bool {
                let watched = self.watched.lock().unwrap();
                self.does_match_tx_unguarded (tx, &watched)
        }

        fn does_match_tx_unguarded(&self, tx: &Transaction, watched: &MutexGuard<ChainWatchedUtil>) -> bool {
                watched.does_match_tx(tx)
        }
}