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

//! 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::network::constants::Network;
use bitcoin::hash_types::{Txid, BlockHash};

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

/// Used to give chain error details upstream
#[derive(Clone)]
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: &Txid, 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: (Txid, 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: BlockHash, unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError>;

        /// Gets the list of transaction indices within a given block that the ChainWatchInterface is
        /// watching for.
        fn filter_block(&self, header: &BlockHeader, txdata: &[(usize, &Transaction)]) -> Vec<usize>;

        /// 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. Transactions may be filtered and are given
        /// paired with their position within the block.
        fn block_connected(&self, header: &BlockHeader, txdata: &[(usize, &Transaction)], height: 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) -> u32;
}

/// 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
#[cfg_attr(test, derive(PartialEq))]
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<(Txid, Script)>,
        #[cfg(not(test))]
        watched_txn: HashSet<Script>,

        watched_outpoints: HashSet<(Txid, 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: &Txid, 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: (Txid, 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.
///
/// (C-not exported) as we let clients handle any reference counting they need to do
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 when blocks are connected or disconnected.
///
/// 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 + 'a>
                where CL::Target: ChainListener + 'a {
        listeners: Mutex<Vec<CL>>,
        phantom: PhantomData<&'a ()>,
}

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

        /// Register the given listener to receive events.
        pub fn register_listener(&self, listener: CL) {
                let mut vec = self.listeners.lock().unwrap();
                vec.push(listener);
        }
        /// Unregister the given listener to no longer
        /// receive events.
        ///
        /// If the same listener is registered multiple times, unregistering
        /// will remove ALL occurrences of that listener. Comparison is done using
        /// the pointer returned by the Deref trait implementation.
        ///
        /// (C-not exported) because the equality check would always fail
        pub fn unregister_listener(&self, listener: CL) {
                let mut vec = self.listeners.lock().unwrap();
                // item is a ref to an abstract thing that dereferences to a ChainListener,
                // so dereference it twice to get the ChainListener itself
                vec.retain(|item | !ptr::eq(&(**item), &(*listener)));
        }

        /// Notify listeners that a block was connected.
        pub fn block_connected(&self, block: &Block, height: u32) {
                let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
                let listeners = self.listeners.lock().unwrap();
                for listener in listeners.iter() {
                        listener.block_connected(&block.header, &txdata, height);
                }
        }

        /// 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,
}

// We only expose PartialEq in test since its somewhat unclear exactly what it should do and we're
// only comparing a subset of fields (essentially just checking that the set of things we're
// watching is the same).
#[cfg(test)]
impl PartialEq for ChainWatchInterfaceUtil {
        fn eq(&self, o: &Self) -> bool {
                self.network == o.network &&
                *self.watched.lock().unwrap() == *o.watched.lock().unwrap()
        }
}

/// Register listener
impl ChainWatchInterface for ChainWatchInterfaceUtil {
        fn install_watch_tx(&self, txid: &Txid, 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: (Txid, 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: BlockHash, _unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError> {
                if genesis_hash != genesis_block(self.network).header.block_hash() {
                        return Err(ChainError::NotWatched);
                }
                Err(ChainError::NotSupported)
        }

        fn filter_block(&self, _header: &BlockHeader, txdata: &[(usize, &Transaction)]) -> Vec<usize> {
                let mut matched_index = Vec::new();
                let mut matched_txids = HashSet::new();
                {
                        let watched = self.watched.lock().unwrap();
                        for (index, transaction) in txdata.iter().enumerate() {
                                // A tx matches the filter if it either matches the filter directly (via
                                // does_match_tx_unguarded) or if it is a descendant of another matched
                                // transaction within the same block, which we check for in the loop.
                                let mut matched = self.does_match_tx_unguarded(transaction.1, &watched);
                                for input in transaction.1.input.iter() {
                                        if matched || matched_txids.contains(&input.previous_output.txid) {
                                                matched = true;
                                                break;
                                        }
                                }
                                if matched {
                                        matched_txids.insert(transaction.1.txid());
                                        matched_index.push(index);
                                }
                        }
                }
                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) -> ChainWatchInterfaceUtil {
                ChainWatchInterfaceUtil {
                        network,
                        watched: Mutex::new(ChainWatchedUtil::new()),
                        reentered: AtomicUsize::new(1),
                }
        }

        /// 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)
        }
}

#[cfg(test)]
mod tests {
        use bitcoin::blockdata::block::BlockHeader;
        use bitcoin::blockdata::transaction::Transaction;
        use super::{BlockNotifier, ChainListener};
        use std::ptr;

        struct TestChainListener(u8);

        impl ChainListener for TestChainListener {
                fn block_connected(&self, _header: &BlockHeader, _txdata: &[(usize, &Transaction)], _height: u32) {}
                fn block_disconnected(&self, _header: &BlockHeader, _disconnected_height: u32) {}
        }

        #[test]
        fn register_listener_test() {
                let block_notifier = BlockNotifier::new();
                assert_eq!(block_notifier.listeners.lock().unwrap().len(), 0);
                let listener = &TestChainListener(0);
                block_notifier.register_listener(listener as &ChainListener);
                let vec = block_notifier.listeners.lock().unwrap();
                assert_eq!(vec.len(), 1);
                let item = vec.first().unwrap();
                assert!(ptr::eq(&(**item), listener));
        }

        #[test]
        fn unregister_single_listener_test() {
                let block_notifier = BlockNotifier::new();
                let listener1 = &TestChainListener(1);
                let listener2 = &TestChainListener(2);
                block_notifier.register_listener(listener1 as &ChainListener);
                block_notifier.register_listener(listener2 as &ChainListener);
                let vec = block_notifier.listeners.lock().unwrap();
                assert_eq!(vec.len(), 2);
                drop(vec);
                block_notifier.unregister_listener(listener1);
                let vec = block_notifier.listeners.lock().unwrap();
                assert_eq!(vec.len(), 1);
                let item = vec.first().unwrap();
                assert!(ptr::eq(&(**item), listener2));
        }

        #[test]
        fn unregister_multiple_of_the_same_listeners_test() {
                let block_notifier = BlockNotifier::new();
                let listener1 = &TestChainListener(1);
                let listener2 = &TestChainListener(2);
                block_notifier.register_listener(listener1 as &ChainListener);
                block_notifier.register_listener(listener1 as &ChainListener);
                block_notifier.register_listener(listener2 as &ChainListener);
                let vec = block_notifier.listeners.lock().unwrap();
                assert_eq!(vec.len(), 3);
                drop(vec);
                block_notifier.unregister_listener(listener1);
                let vec = block_notifier.listeners.lock().unwrap();
                assert_eq!(vec.len(), 1);
                let item = vec.first().unwrap();
                assert!(ptr::eq(&(**item), listener2));
        }
}