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Utility for syncing a set of chain listeners
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Add a utility for syncing a set of chain listeners to a common chain
tip. Required to use before creating an SpvClient when the chain
listener used with the client is actually a set of listeners each of
which may have had left off at a different block. This would occur when
the listeners had been persisted individually at different frequencies
(e.g., a ChainMonitor's individual ChannelMonitors).
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@jkczyz
jkczyz committed Feb 26, 2021
1 parent 8505382 commit 8bfdfdc
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351 changes: 351 additions & 0 deletions lightning-block-sync/src/init.rs
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use crate::{BlockSource, BlockSourceResult, Cache, ChainNotifier};
use crate::poll::{ChainPoller, Validate, ValidatedBlockHeader};

use bitcoin::blockdata::block::{Block, BlockHeader};
use bitcoin::hash_types::BlockHash;
use bitcoin::network::constants::Network;

use lightning::chain;

/// Performs a one-time sync of chain listeners using a single *trusted* block source, bringing each
/// listener's view of the chain from its paired block hash to `block_source`'s best chain tip.
///
/// Upon success, the returned header can be used to initialize [`SpvClient`]. In the case of
/// failure, each listener may be left at a different block hash than the one it was originally
/// paired with.
///
/// Useful during startup to bring the [`ChannelManager`] and each [`ChannelMonitor`] in sync before
/// switching to [`SpvClient`]. For example:
///
/// ```
/// use bitcoin::hash_types::BlockHash;
/// use bitcoin::network::constants::Network;
///
/// use lightning::chain;
/// use lightning::chain::Watch;
/// use lightning::chain::chainmonitor::ChainMonitor;
/// use lightning::chain::channelmonitor;
/// use lightning::chain::channelmonitor::ChannelMonitor;
/// use lightning::chain::chaininterface::BroadcasterInterface;
/// use lightning::chain::chaininterface::FeeEstimator;
/// use lightning::chain::keysinterface;
/// use lightning::chain::keysinterface::KeysInterface;
/// use lightning::ln::channelmanager::ChannelManager;
/// use lightning::ln::channelmanager::ChannelManagerReadArgs;
/// use lightning::util::config::UserConfig;
/// use lightning::util::logger::Logger;
/// use lightning::util::ser::ReadableArgs;
///
/// use lightning_block_sync::*;
///
/// use std::cell::RefCell;
/// use std::io::Cursor;
///
/// async fn init_sync<
/// B: BlockSource,
/// K: KeysInterface<Signer = S>,
/// S: keysinterface::Sign,
/// T: BroadcasterInterface,
/// F: FeeEstimator,
/// L: Logger,
/// C: chain::Filter,
/// P: channelmonitor::Persist<S>,
/// >(
/// block_source: &mut B,
/// chain_monitor: &ChainMonitor<S, &C, &T, &F, &L, &P>,
/// config: UserConfig,
/// keys_manager: &K,
/// tx_broadcaster: &T,
/// fee_estimator: &F,
/// logger: &L,
/// persister: &P,
/// ) {
/// // Read a serialized channel monitor paired with the block hash when it was persisted.
/// let serialized_monitor = "...";
/// let (monitor_block_hash, mut monitor) = <(BlockHash, ChannelMonitor<S>)>::read(
/// &mut Cursor::new(&serialized_monitor), keys_manager).unwrap();
///
/// // Read the channel manager paired with the block hash when it was persisted.
/// let serialized_manager = "...";
/// let (manager_block_hash, mut manager) = {
/// let read_args = ChannelManagerReadArgs::new(
/// keys_manager,
/// fee_estimator,
/// chain_monitor,
/// tx_broadcaster,
/// logger,
/// config,
/// vec![&mut monitor],
/// );
/// <(BlockHash, ChannelManager<S, &ChainMonitor<S, &C, &T, &F, &L, &P>, &T, &K, &F, &L>)>::read(
/// &mut Cursor::new(&serialized_manager), read_args).unwrap()
/// };
///
/// // Synchronize any channel monitors and the channel manager to be on the best block.
/// let mut cache = UnboundedCache::new();
/// let mut monitor_listener = (RefCell::new(monitor), &*tx_broadcaster, &*fee_estimator, &*logger);
/// let listeners = vec![
/// (monitor_block_hash, &mut monitor_listener as &mut dyn chain::Listen),
/// (manager_block_hash, &mut manager as &mut dyn chain::Listen),
/// ];
/// let chain_tip = init::synchronize_listeners(
/// block_source, Network::Bitcoin, &mut cache, listeners).await.unwrap();
///
/// // Allow the chain monitor to watch any channels.
/// let monitor = monitor_listener.0.into_inner();
/// chain_monitor.watch_channel(monitor.get_funding_txo().0, monitor);
///
/// // Create an SPV client to notify the chain monitor and channel manager of block events.
/// let chain_poller = poll::ChainPoller::new(block_source, Network::Bitcoin);
/// let mut chain_listener = (chain_monitor, &manager);
/// let spv_client = SpvClient::new(chain_tip, chain_poller, &mut cache, &chain_listener);
/// }
/// ```
///
/// [`SpvClient`]: ../struct.SpvClient.html
/// [`ChannelManager`]: ../../lightning/ln/channelmanager/struct.ChannelManager.html
/// [`ChannelMonitor`]: ../../lightning/chain/channelmonitor/struct.ChannelMonitor.html
pub async fn synchronize_listeners<B: BlockSource, C: Cache>(
block_source: &mut B,
network: Network,
header_cache: &mut C,
mut chain_listeners: Vec<(BlockHash, &mut dyn chain::Listen)>,
) -> BlockSourceResult<ValidatedBlockHeader> {
let (best_block_hash, best_block_height) = block_source.get_best_block().await?;
let best_header = block_source
.get_header(&best_block_hash, best_block_height).await?
.validate(best_block_hash)?;

// Fetch the header for the block hash paired with each listener.
let mut chain_listeners_with_old_headers = Vec::new();
for (old_block_hash, chain_listener) in chain_listeners.drain(..) {
let old_header = match header_cache.look_up(&old_block_hash) {
Some(header) => *header,
None => block_source
.get_header(&old_block_hash, None).await?
.validate(old_block_hash)?
};
chain_listeners_with_old_headers.push((old_header, chain_listener))
}

// Find differences and disconnect blocks for each listener individually.
let mut chain_poller = ChainPoller::new(block_source, network);
let mut chain_listeners_at_height = Vec::new();
let mut most_common_ancestor = None;
let mut most_connected_blocks = Vec::new();
for (old_header, chain_listener) in chain_listeners_with_old_headers.drain(..) {
// Disconnect any stale blocks, but keep them in the cache for the next iteration.
let header_cache = &mut ReadOnlyCache(header_cache);
let (common_ancestor, connected_blocks) = {
let chain_listener = &DynamicChainListener(chain_listener);
let mut chain_notifier = ChainNotifier { header_cache, chain_listener };
let difference =
chain_notifier.find_difference(best_header, &old_header, &mut chain_poller).await?;
chain_notifier.disconnect_blocks(difference.disconnected_blocks);
(difference.common_ancestor, difference.connected_blocks)
};

// Keep track of the most common ancestor and all blocks connected across all listeners.
chain_listeners_at_height.push((common_ancestor.height, chain_listener));
if connected_blocks.len() > most_connected_blocks.len() {
most_common_ancestor = Some(common_ancestor);
most_connected_blocks = connected_blocks;
}
}

// Connect new blocks for all listeners at once to avoid re-fetching blocks.
if let Some(common_ancestor) = most_common_ancestor {
let chain_listener = &ChainListenerSet(chain_listeners_at_height);
let mut chain_notifier = ChainNotifier { header_cache, chain_listener };
chain_notifier.connect_blocks(common_ancestor, most_connected_blocks, &mut chain_poller)
.await.or_else(|(e, _)| Err(e))?;
}

Ok(best_header)
}

/// A wrapper to make a cache read-only.
///
/// Used to prevent losing headers that may be needed to disconnect blocks common to more than one
/// listener.
struct ReadOnlyCache<'a, C: Cache>(&'a mut C);

impl<'a, C: Cache> Cache for ReadOnlyCache<'a, C> {
fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader> {
self.0.look_up(block_hash)
}

fn block_connected(&mut self, _block_hash: BlockHash, _block_header: ValidatedBlockHeader) {
unreachable!()
}

fn block_disconnected(&mut self, _block_hash: &BlockHash) -> Option<ValidatedBlockHeader> {
None
}
}

/// Wrapper for supporting dynamically sized chain listeners.
struct DynamicChainListener<'a>(&'a mut dyn chain::Listen);

impl<'a> chain::Listen for DynamicChainListener<'a> {
fn block_connected(&self, _block: &Block, _height: u32) {
unreachable!()
}

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

/// A set of dynamically sized chain listeners, each paired with a starting block height.
struct ChainListenerSet<'a>(Vec<(u32, &'a mut dyn chain::Listen)>);

impl<'a> chain::Listen for ChainListenerSet<'a> {
fn block_connected(&self, block: &Block, height: u32) {
for (starting_height, chain_listener) in self.0.iter() {
if height > *starting_height {
chain_listener.block_connected(block, height);
}
}
}

fn block_disconnected(&self, _header: &BlockHeader, _height: u32) {
unreachable!()
}
}

#[cfg(test)]
mod tests {
use crate::test_utils::{Blockchain, MockChainListener};
use super::*;

use bitcoin::network::constants::Network;

#[tokio::test]
async fn sync_from_same_chain() {
let mut chain = Blockchain::default().with_height(4);

let mut listener_1 = MockChainListener::new()
.expect_block_connected(*chain.at_height(2))
.expect_block_connected(*chain.at_height(3))
.expect_block_connected(*chain.at_height(4));
let mut listener_2 = MockChainListener::new()
.expect_block_connected(*chain.at_height(3))
.expect_block_connected(*chain.at_height(4));
let mut listener_3 = MockChainListener::new()
.expect_block_connected(*chain.at_height(4));

let listeners = vec![
(chain.at_height(1).block_hash, &mut listener_1 as &mut dyn chain::Listen),
(chain.at_height(2).block_hash, &mut listener_2 as &mut dyn chain::Listen),
(chain.at_height(3).block_hash, &mut listener_3 as &mut dyn chain::Listen),
];
let mut cache = chain.header_cache(0..=4);
match synchronize_listeners(&mut chain, Network::Bitcoin, &mut cache, listeners).await {
Ok(header) => assert_eq!(header, chain.tip()),
Err(e) => panic!("Unexpected error: {:?}", e),
}
}

#[tokio::test]
async fn sync_from_different_chains() {
let mut main_chain = Blockchain::default().with_height(4);
let fork_chain_1 = main_chain.fork_at_height(1);
let fork_chain_2 = main_chain.fork_at_height(2);
let fork_chain_3 = main_chain.fork_at_height(3);

let mut listener_1 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_1.at_height(4))
.expect_block_disconnected(*fork_chain_1.at_height(3))
.expect_block_disconnected(*fork_chain_1.at_height(2))
.expect_block_connected(*main_chain.at_height(2))
.expect_block_connected(*main_chain.at_height(3))
.expect_block_connected(*main_chain.at_height(4));
let mut listener_2 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_2.at_height(4))
.expect_block_disconnected(*fork_chain_2.at_height(3))
.expect_block_connected(*main_chain.at_height(3))
.expect_block_connected(*main_chain.at_height(4));
let mut listener_3 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_3.at_height(4))
.expect_block_connected(*main_chain.at_height(4));

let listeners = vec![
(fork_chain_1.tip().block_hash, &mut listener_1 as &mut dyn chain::Listen),
(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn chain::Listen),
(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn chain::Listen),
];
let mut cache = fork_chain_1.header_cache(2..=4);
cache.extend(fork_chain_2.header_cache(3..=4));
cache.extend(fork_chain_3.header_cache(4..=4));
match synchronize_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
Ok(header) => assert_eq!(header, main_chain.tip()),
Err(e) => panic!("Unexpected error: {:?}", e),
}
}

#[tokio::test]
async fn sync_from_overlapping_chains() {
let mut main_chain = Blockchain::default().with_height(4);
let fork_chain_1 = main_chain.fork_at_height(1);
let fork_chain_2 = fork_chain_1.fork_at_height(2);
let fork_chain_3 = fork_chain_2.fork_at_height(3);

let mut listener_1 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_1.at_height(4))
.expect_block_disconnected(*fork_chain_1.at_height(3))
.expect_block_disconnected(*fork_chain_1.at_height(2))
.expect_block_connected(*main_chain.at_height(2))
.expect_block_connected(*main_chain.at_height(3))
.expect_block_connected(*main_chain.at_height(4));
let mut listener_2 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_2.at_height(4))
.expect_block_disconnected(*fork_chain_2.at_height(3))
.expect_block_disconnected(*fork_chain_2.at_height(2))
.expect_block_connected(*main_chain.at_height(2))
.expect_block_connected(*main_chain.at_height(3))
.expect_block_connected(*main_chain.at_height(4));
let mut listener_3 = MockChainListener::new()
.expect_block_disconnected(*fork_chain_3.at_height(4))
.expect_block_disconnected(*fork_chain_3.at_height(3))
.expect_block_disconnected(*fork_chain_3.at_height(2))
.expect_block_connected(*main_chain.at_height(2))
.expect_block_connected(*main_chain.at_height(3))
.expect_block_connected(*main_chain.at_height(4));

let listeners = vec![
(fork_chain_1.tip().block_hash, &mut listener_1 as &mut dyn chain::Listen),
(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn chain::Listen),
(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn chain::Listen),
];
let mut cache = fork_chain_1.header_cache(2..=4);
cache.extend(fork_chain_2.header_cache(3..=4));
cache.extend(fork_chain_3.header_cache(4..=4));
match synchronize_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
Ok(header) => assert_eq!(header, main_chain.tip()),
Err(e) => panic!("Unexpected error: {:?}", e),
}
}

#[tokio::test]
async fn cache_connected_and_keep_disconnected_blocks() {
let mut main_chain = Blockchain::default().with_height(2);
let fork_chain = main_chain.fork_at_height(1);
let new_tip = main_chain.tip();
let old_tip = fork_chain.tip();

let mut listener = MockChainListener::new()
.expect_block_disconnected(*old_tip)
.expect_block_connected(*new_tip);

let listeners = vec![(old_tip.block_hash, &mut listener as &mut dyn chain::Listen)];
let mut cache = fork_chain.header_cache(2..=2);
match synchronize_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
Ok(_) => {
assert!(cache.contains_key(&new_tip.block_hash));
assert!(cache.contains_key(&old_tip.block_hash));
},
Err(e) => panic!("Unexpected error: {:?}", e),
}
}
}

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