//! A lightweight client for keeping in sync with chain activity.
//!
+//! Defines an [`SpvClient`] utility for polling one or more block sources for the best chain tip.
+//! It is used to notify listeners of blocks connected or disconnected since the last poll. Useful
+//! for keeping a Lightning node in sync with the chain.
+//!
//! Defines a [`BlockSource`] trait, which is an asynchronous interface for retrieving block headers
//! and data.
//!
//! Both features support either blocking I/O using `std::net::TcpStream` or, with feature `tokio`,
//! non-blocking I/O using `tokio::net::TcpStream` from inside a Tokio runtime.
//!
+//! [`SpvClient`]: struct.SpvClient.html
//! [`BlockSource`]: trait.BlockSource.html
#[cfg(any(feature = "rest-client", feature = "rpc-client"))]
#[cfg(any(feature = "rest-client", feature = "rpc-client"))]
mod utils;
-use crate::poll::{Poll, ValidatedBlockHeader};
+use crate::poll::{ChainTip, Poll, ValidatedBlockHeader};
use bitcoin::blockdata::block::{Block, BlockHeader};
use bitcoin::hash_types::BlockHash;
/// error.
fn get_block<'a>(&'a mut self, header_hash: &'a BlockHash) -> AsyncBlockSourceResult<'a, Block>;
- // TODO: Phrase in terms of `Poll` once added.
- /// Returns the hash of the best block and, optionally, its height. When polling a block source,
- /// the height is passed to `get_header` to allow for a more efficient lookup.
+ /// Returns the hash of the best block and, optionally, its height.
+ ///
+ /// When polling a block source, [`Poll`] implementations may pass the height to [`get_header`]
+ /// to allow for a more efficient lookup.
+ ///
+ /// [`Poll`]: poll/trait.Poll.html
+ /// [`get_header`]: #tymethod.get_header
fn get_best_block<'a>(&'a mut self) -> AsyncBlockSourceResult<(BlockHash, Option<u32>)>;
}
pub chainwork: Uint256,
}
+/// A lightweight client for keeping a listener in sync with the chain, allowing for Simplified
+/// Payment Verification (SPV).
+///
+/// The client is parameterized by a chain poller which is responsible for polling one or more block
+/// sources for the best chain tip. During this process it detects any chain forks, determines which
+/// constitutes the best chain, and updates the listener accordingly with any blocks that were
+/// connected or disconnected since the last poll.
+///
+/// Block headers for the best chain are maintained in the parameterized cache, allowing for a
+/// custom cache eviction policy. This offers flexibility to those sensitive to resource usage.
+/// Hence, there is a trade-off between a lower memory footprint and potentially increased network
+/// I/O as headers are re-fetched during fork detection.
+pub struct SpvClient<P: Poll, C: Cache, L: ChainListener> {
+ chain_tip: ValidatedBlockHeader,
+ chain_poller: P,
+ chain_notifier: ChainNotifier<C>,
+ chain_listener: L,
+}
+
/// Adaptor used for notifying when blocks have been connected or disconnected from the chain.
///
/// Used when needing to replay chain data upon startup or as new chain events occur.
}
}
+impl<P: Poll, C: Cache, L: ChainListener> SpvClient<P, C, L> {
+ /// Creates a new SPV client using `chain_tip` as the best known chain tip.
+ ///
+ /// Subsequent calls to [`poll_best_tip`] will poll for the best chain tip using the given chain
+ /// poller, which may be configured with one or more block sources to query. At least one block
+ /// source must provide headers back from the best chain tip to its common ancestor with
+ /// `chain_tip`.
+ /// * `header_cache` is used to look up and store headers on the best chain
+ /// * `chain_listener` is notified of any blocks connected or disconnected
+ ///
+ /// [`poll_best_tip`]: struct.SpvClient.html#method.poll_best_tip
+ pub fn new(
+ chain_tip: ValidatedBlockHeader,
+ chain_poller: P,
+ header_cache: C,
+ chain_listener: L,
+ ) -> Self {
+ let chain_notifier = ChainNotifier { header_cache };
+ Self { chain_tip, chain_poller, chain_notifier, chain_listener }
+ }
+
+ /// Polls for the best tip and updates the chain listener with any connected or disconnected
+ /// blocks accordingly.
+ ///
+ /// Returns the best polled chain tip relative to the previous best known tip and whether any
+ /// blocks were indeed connected or disconnected.
+ pub async fn poll_best_tip(&mut self) -> BlockSourceResult<(ChainTip, bool)> {
+ let chain_tip = self.chain_poller.poll_chain_tip(self.chain_tip).await?;
+ let blocks_connected = match chain_tip {
+ ChainTip::Common => false,
+ ChainTip::Better(chain_tip) => {
+ debug_assert_ne!(chain_tip.block_hash, self.chain_tip.block_hash);
+ debug_assert!(chain_tip.chainwork > self.chain_tip.chainwork);
+ self.update_chain_tip(chain_tip).await
+ },
+ ChainTip::Worse(chain_tip) => {
+ debug_assert_ne!(chain_tip.block_hash, self.chain_tip.block_hash);
+ debug_assert!(chain_tip.chainwork <= self.chain_tip.chainwork);
+ false
+ },
+ };
+ Ok((chain_tip, blocks_connected))
+ }
+
+ /// Updates the chain tip, syncing the chain listener with any connected or disconnected
+ /// blocks. Returns whether there were any such blocks.
+ async fn update_chain_tip(&mut self, best_chain_tip: ValidatedBlockHeader) -> bool {
+ match self.chain_notifier.synchronize_listener(
+ best_chain_tip, &self.chain_tip, &mut self.chain_poller, &mut self.chain_listener).await
+ {
+ Ok(_) => {
+ self.chain_tip = best_chain_tip;
+ true
+ },
+ Err((_, Some(chain_tip))) if chain_tip.block_hash != self.chain_tip.block_hash => {
+ self.chain_tip = chain_tip;
+ true
+ },
+ Err(_) => false,
+ }
+ }
+}
+
/// Notifies [listeners] of blocks that have been connected or disconnected from the chain.
///
/// [listeners]: trait.ChainListener.html
}
}
+#[cfg(test)]
+mod spv_client_tests {
+ use crate::test_utils::{Blockchain, NullChainListener};
+ use super::*;
+
+ use bitcoin::network::constants::Network;
+
+ #[tokio::test]
+ async fn poll_from_chain_without_headers() {
+ let mut chain = Blockchain::default().with_height(3).without_headers();
+ let best_tip = chain.at_height(1);
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(best_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => {
+ assert_eq!(e.kind(), BlockSourceErrorKind::Persistent);
+ assert_eq!(e.into_inner().as_ref().to_string(), "header not found");
+ },
+ Ok(_) => panic!("Expected error"),
+ }
+ assert_eq!(client.chain_tip, best_tip);
+ }
+
+ #[tokio::test]
+ async fn poll_from_chain_with_common_tip() {
+ let mut chain = Blockchain::default().with_height(3);
+ let common_tip = chain.tip();
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(common_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => panic!("Unexpected error: {:?}", e),
+ Ok((chain_tip, blocks_connected)) => {
+ assert_eq!(chain_tip, ChainTip::Common);
+ assert!(!blocks_connected);
+ },
+ }
+ assert_eq!(client.chain_tip, common_tip);
+ }
+
+ #[tokio::test]
+ async fn poll_from_chain_with_better_tip() {
+ let mut chain = Blockchain::default().with_height(3);
+ let new_tip = chain.tip();
+ let old_tip = chain.at_height(1);
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(old_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => panic!("Unexpected error: {:?}", e),
+ Ok((chain_tip, blocks_connected)) => {
+ assert_eq!(chain_tip, ChainTip::Better(new_tip));
+ assert!(blocks_connected);
+ },
+ }
+ assert_eq!(client.chain_tip, new_tip);
+ }
+
+ #[tokio::test]
+ async fn poll_from_chain_with_better_tip_and_without_any_new_blocks() {
+ let mut chain = Blockchain::default().with_height(3).without_blocks(2..);
+ let new_tip = chain.tip();
+ let old_tip = chain.at_height(1);
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(old_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => panic!("Unexpected error: {:?}", e),
+ Ok((chain_tip, blocks_connected)) => {
+ assert_eq!(chain_tip, ChainTip::Better(new_tip));
+ assert!(!blocks_connected);
+ },
+ }
+ assert_eq!(client.chain_tip, old_tip);
+ }
+
+ #[tokio::test]
+ async fn poll_from_chain_with_better_tip_and_without_some_new_blocks() {
+ let mut chain = Blockchain::default().with_height(3).without_blocks(3..);
+ let new_tip = chain.tip();
+ let old_tip = chain.at_height(1);
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(old_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => panic!("Unexpected error: {:?}", e),
+ Ok((chain_tip, blocks_connected)) => {
+ assert_eq!(chain_tip, ChainTip::Better(new_tip));
+ assert!(blocks_connected);
+ },
+ }
+ assert_eq!(client.chain_tip, chain.at_height(2));
+ }
+
+ #[tokio::test]
+ async fn poll_from_chain_with_worse_tip() {
+ let mut chain = Blockchain::default().with_height(3);
+ let best_tip = chain.tip();
+ chain.disconnect_tip();
+ let worse_tip = chain.tip();
+
+ let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
+ let cache = UnboundedCache::new();
+ let mut client = SpvClient::new(best_tip, poller, cache, NullChainListener {});
+ match client.poll_best_tip().await {
+ Err(e) => panic!("Unexpected error: {:?}", e),
+ Ok((chain_tip, blocks_connected)) => {
+ assert_eq!(chain_tip, ChainTip::Worse(worse_tip));
+ assert!(!blocks_connected);
+ },
+ }
+ assert_eq!(client.chain_tip, best_tip);
+ }
+}
+
#[cfg(test)]
mod chain_notifier_tests {
use crate::test_utils::{Blockchain, MockChainListener};
projects / rust-lightning / commitdiff