1 use crate::common::{ConfirmedTx, FilterQueue, SyncState};
2 use crate::error::{InternalError, TxSyncError};
4 use electrum_client::Client as ElectrumClient;
5 use electrum_client::ElectrumApi;
6 use electrum_client::GetMerkleRes;
8 use lightning::chain::WatchedOutput;
9 use lightning::chain::{Confirm, Filter};
10 use lightning::util::logger::Logger;
11 use lightning::{log_debug, log_error, log_trace};
13 use bitcoin::block::Header;
14 use bitcoin::hash_types::TxMerkleNode;
15 use bitcoin::hashes::sha256d::Hash as Sha256d;
16 use bitcoin::hashes::Hash;
17 use bitcoin::{BlockHash, Script, Transaction, Txid};
19 use std::collections::HashSet;
22 use std::time::Instant;
24 /// Synchronizes LDK with a given Electrum server.
26 /// Needs to be registered with a [`ChainMonitor`] via the [`Filter`] interface to be informed of
27 /// transactions and outputs to monitor for on-chain confirmation, unconfirmation, and
30 /// Note that registration via [`Filter`] needs to happen before any calls to
31 /// [`Watch::watch_channel`] to ensure we get notified of the items to monitor.
33 /// [`ChainMonitor`]: lightning::chain::chainmonitor::ChainMonitor
34 /// [`Watch::watch_channel`]: lightning::chain::Watch::watch_channel
35 /// [`Filter`]: lightning::chain::Filter
36 pub struct ElectrumSyncClient<L: Deref>
40 sync_state: Mutex<SyncState>,
41 queue: Mutex<FilterQueue>,
42 client: ElectrumClient,
46 impl<L: Deref> ElectrumSyncClient<L>
50 /// Returns a new [`ElectrumSyncClient`] object.
51 pub fn new(server_url: String, logger: L) -> Result<Self, TxSyncError> {
52 let client = ElectrumClient::new(&server_url).map_err(|e| {
53 log_error!(logger, "Failed to connect to electrum server '{}': {}", server_url, e);
57 Self::from_client(client, logger)
60 /// Returns a new [`ElectrumSyncClient`] object using the given Electrum client.
62 /// This is not exported to bindings users as the underlying client from BDK is not exported.
63 pub fn from_client(client: ElectrumClient, logger: L) -> Result<Self, TxSyncError> {
64 let sync_state = Mutex::new(SyncState::new());
65 let queue = Mutex::new(FilterQueue::new());
67 Ok(Self { sync_state, queue, client, logger })
70 /// Synchronizes the given `confirmables` via their [`Confirm`] interface implementations. This
71 /// method should be called regularly to keep LDK up-to-date with current chain data.
73 /// For example, instances of [`ChannelManager`] and [`ChainMonitor`] can be informed about the
74 /// newest on-chain activity related to the items previously registered via the [`Filter`]
77 /// [`Confirm`]: lightning::chain::Confirm
78 /// [`ChainMonitor`]: lightning::chain::chainmonitor::ChainMonitor
79 /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
80 /// [`Filter`]: lightning::chain::Filter
81 pub fn sync<C: Deref>(&self, confirmables: Vec<C>) -> Result<(), TxSyncError>
85 // This lock makes sure we're syncing once at a time.
86 let mut sync_state = self.sync_state.lock().unwrap();
88 log_trace!(self.logger, "Starting transaction sync.");
89 #[cfg(feature = "time")]
90 let start_time = Instant::now();
91 let mut num_confirmed = 0;
92 let mut num_unconfirmed = 0;
94 // Clear any header notifications we might have gotten to keep the queue count low.
95 while let Some(_) = self.client.block_headers_pop()? {}
97 let tip_notification = self.client.block_headers_subscribe()?;
98 let mut tip_header = tip_notification.header;
99 let mut tip_height = tip_notification.height as u32;
102 let pending_registrations = self.queue.lock().unwrap().process_queues(&mut sync_state);
103 let tip_is_new = Some(tip_header.block_hash()) != sync_state.last_sync_hash;
105 // We loop until any registered transactions have been processed at least once, or the
106 // tip hasn't been updated during the last iteration.
107 if !sync_state.pending_sync && !pending_registrations && !tip_is_new {
111 // Update the known tip to the newest one.
113 // First check for any unconfirmed transactions and act on it immediately.
114 match self.get_unconfirmed_transactions(&confirmables) {
115 Ok(unconfirmed_txs) => {
116 // Double-check the tip hash. If it changed, a reorg happened since
117 // we started syncing and we need to restart last-minute.
118 match self.check_update_tip(&mut tip_header, &mut tip_height) {
120 num_unconfirmed += unconfirmed_txs.len();
121 sync_state.sync_unconfirmed_transactions(
127 log_debug!(self.logger,
128 "Encountered inconsistency during transaction sync, restarting.");
129 sync_state.pending_sync = true;
133 // (Semi-)permanent failure, retry later.
134 log_error!(self.logger,
135 "Failed during transaction sync, aborting. Synced so far: {} confirmed, {} unconfirmed.",
139 sync_state.pending_sync = true;
140 return Err(TxSyncError::from(err));
145 // (Semi-)permanent failure, retry later.
146 log_error!(self.logger,
147 "Failed during transaction sync, aborting. Synced so far: {} confirmed, {} unconfirmed.",
151 sync_state.pending_sync = true;
152 return Err(TxSyncError::from(err));
156 // Update the best block.
157 for c in &confirmables {
158 c.best_block_updated(&tip_header, tip_height);
161 // Prune any sufficiently confirmed output spends
162 sync_state.prune_output_spends(tip_height);
165 match self.get_confirmed_transactions(&sync_state) {
166 Ok(confirmed_txs) => {
167 // Double-check the tip hash. If it changed, a reorg happened since
168 // we started syncing and we need to restart last-minute.
169 match self.check_update_tip(&mut tip_header, &mut tip_height) {
171 num_confirmed += confirmed_txs.len();
173 .sync_confirmed_transactions(&confirmables, confirmed_txs);
176 log_debug!(self.logger,
177 "Encountered inconsistency during transaction sync, restarting.");
178 sync_state.pending_sync = true;
182 // (Semi-)permanent failure, retry later.
183 log_error!(self.logger,
184 "Failed during transaction sync, aborting. Synced so far: {} confirmed, {} unconfirmed.",
188 sync_state.pending_sync = true;
189 return Err(TxSyncError::from(err));
193 Err(InternalError::Inconsistency) => {
194 // Immediately restart syncing when we encounter any inconsistencies.
197 "Encountered inconsistency during transaction sync, restarting."
199 sync_state.pending_sync = true;
203 // (Semi-)permanent failure, retry later.
204 log_error!(self.logger,
205 "Failed during transaction sync, aborting. Synced so far: {} confirmed, {} unconfirmed.",
209 sync_state.pending_sync = true;
210 return Err(TxSyncError::from(err));
213 sync_state.last_sync_hash = Some(tip_header.block_hash());
214 sync_state.pending_sync = false;
217 #[cfg(feature = "time")]
220 "Finished transaction sync at tip {} in {}ms: {} confirmed, {} unconfirmed.",
221 tip_header.block_hash(),
222 start_time.elapsed().as_millis(),
226 #[cfg(not(feature = "time"))]
229 "Finished transaction sync at tip {}: {} confirmed, {} unconfirmed.",
230 tip_header.block_hash(),
238 &self, cur_tip_header: &mut Header, cur_tip_height: &mut u32,
239 ) -> Result<bool, InternalError> {
240 let check_notification = self.client.block_headers_subscribe()?;
241 let check_tip_hash = check_notification.header.block_hash();
243 // Restart if either the tip changed or we got some divergent tip
244 // change notification since we started. In the latter case we
245 // make sure we clear the queue before continuing.
246 let mut restart_sync = check_tip_hash != cur_tip_header.block_hash();
247 while let Some(queued_notif) = self.client.block_headers_pop()? {
248 if queued_notif.header.block_hash() != check_tip_hash {
254 *cur_tip_header = check_notification.header;
255 *cur_tip_height = check_notification.height as u32;
262 fn get_confirmed_transactions(
263 &self, sync_state: &SyncState,
264 ) -> Result<Vec<ConfirmedTx>, InternalError> {
265 // First, check the confirmation status of registered transactions as well as the
266 // status of dependent transactions of registered outputs.
267 let mut confirmed_txs: Vec<ConfirmedTx> = Vec::new();
268 let mut watched_script_pubkeys = Vec::with_capacity(
269 sync_state.watched_transactions.len() + sync_state.watched_outputs.len(),
271 let mut watched_txs = Vec::with_capacity(sync_state.watched_transactions.len());
273 for txid in &sync_state.watched_transactions {
274 match self.client.transaction_get(&txid) {
276 watched_txs.push((txid, tx.clone()));
277 if let Some(tx_out) = tx.output.first() {
278 // We watch an arbitrary output of the transaction of interest in order to
279 // retrieve the associated script history, before narrowing down our search
280 // through `filter`ing by `txid` below.
281 watched_script_pubkeys.push(tx_out.script_pubkey.clone());
283 debug_assert!(false, "Failed due to retrieving invalid tx data.");
284 log_error!(self.logger, "Failed due to retrieving invalid tx data.");
285 return Err(InternalError::Failed);
288 Err(electrum_client::Error::Protocol(_)) => {
289 // We couldn't find the tx, do nothing.
292 log_error!(self.logger, "Failed to look up transaction {}: {}.", txid, e);
293 return Err(InternalError::Failed);
298 let num_tx_lookups = watched_script_pubkeys.len();
299 debug_assert_eq!(num_tx_lookups, watched_txs.len());
301 for output in sync_state.watched_outputs.values() {
302 watched_script_pubkeys.push(output.script_pubkey.clone());
305 let num_output_spend_lookups = watched_script_pubkeys.len() - num_tx_lookups;
306 debug_assert_eq!(num_output_spend_lookups, sync_state.watched_outputs.len());
308 match self.client.batch_script_get_history(watched_script_pubkeys.iter().map(|s| s.deref()))
311 let (tx_results, output_results) = results.split_at(num_tx_lookups);
312 debug_assert_eq!(num_output_spend_lookups, output_results.len());
314 for (i, script_history) in tx_results.iter().enumerate() {
315 let (txid, tx) = &watched_txs[i];
316 if confirmed_txs.iter().any(|ctx| ctx.txid == **txid) {
319 let mut filtered_history =
320 script_history.iter().filter(|h| h.tx_hash == **txid);
321 if let Some(history) = filtered_history.next() {
322 let prob_conf_height = history.height as u32;
323 let confirmed_tx = self.get_confirmed_tx(tx, prob_conf_height)?;
324 confirmed_txs.push(confirmed_tx);
326 debug_assert!(filtered_history.next().is_none());
329 for (watched_output, script_history) in
330 sync_state.watched_outputs.values().zip(output_results)
332 for possible_output_spend in script_history {
333 if possible_output_spend.height <= 0 {
337 let txid = possible_output_spend.tx_hash;
338 if confirmed_txs.iter().any(|ctx| ctx.txid == txid) {
342 match self.client.transaction_get(&txid) {
344 let mut is_spend = false;
345 for txin in &tx.input {
346 let watched_outpoint =
347 watched_output.outpoint.into_bitcoin_outpoint();
348 if txin.previous_output == watched_outpoint {
358 let prob_conf_height = possible_output_spend.height as u32;
359 let confirmed_tx = self.get_confirmed_tx(&tx, prob_conf_height)?;
360 confirmed_txs.push(confirmed_tx);
365 "Inconsistency: Tx {} was unconfirmed during syncing: {}",
369 return Err(InternalError::Inconsistency);
376 log_error!(self.logger, "Failed to look up script histories: {}.", e);
377 return Err(InternalError::Failed);
381 // Sort all confirmed transactions first by block height, then by in-block
382 // position, and finally feed them to the interface in order.
383 confirmed_txs.sort_unstable_by(|tx1, tx2| {
384 tx1.block_height.cmp(&tx2.block_height).then_with(|| tx1.pos.cmp(&tx2.pos))
390 fn get_unconfirmed_transactions<C: Deref>(
391 &self, confirmables: &Vec<C>,
392 ) -> Result<Vec<Txid>, InternalError>
396 // Query the interface for relevant txids and check whether the relevant blocks are still
397 // in the best chain, mark them unconfirmed otherwise
398 let relevant_txids = confirmables
400 .flat_map(|c| c.get_relevant_txids())
401 .collect::<HashSet<(Txid, u32, Option<BlockHash>)>>();
403 let mut unconfirmed_txs = Vec::new();
405 for (txid, conf_height, block_hash_opt) in relevant_txids {
406 if let Some(block_hash) = block_hash_opt {
407 let block_header = self.client.block_header(conf_height as usize)?;
408 if block_header.block_hash() == block_hash {
409 // Skip if the tx is still confirmed in the block in question.
413 unconfirmed_txs.push(txid);
415 log_error!(self.logger,
416 "Untracked confirmation of funding transaction. Please ensure none of your channels had been created with LDK prior to version 0.0.113!");
417 panic!("Untracked confirmation of funding transaction. Please ensure none of your channels had been created with LDK prior to version 0.0.113!");
424 &self, tx: &Transaction, prob_conf_height: u32,
425 ) -> Result<ConfirmedTx, InternalError> {
426 let txid = tx.txid();
427 match self.client.transaction_get_merkle(&txid, prob_conf_height as usize) {
429 debug_assert_eq!(prob_conf_height, merkle_res.block_height as u32);
430 match self.client.block_header(prob_conf_height as usize) {
431 Ok(block_header) => {
432 let pos = merkle_res.pos;
433 if !self.validate_merkle_proof(
435 &block_header.merkle_root,
440 "Inconsistency: Block {} was unconfirmed during syncing.",
441 block_header.block_hash()
443 return Err(InternalError::Inconsistency);
445 let confirmed_tx = ConfirmedTx {
449 block_height: prob_conf_height,
457 "Failed to retrieve block header for height {}: {}.",
461 Err(InternalError::Failed)
468 "Inconsistency: Tx {} was unconfirmed during syncing: {}",
472 Err(InternalError::Inconsistency)
477 /// Returns a reference to the underlying Electrum client.
479 /// This is not exported to bindings users as the underlying client from BDK is not exported.
480 pub fn client(&self) -> &ElectrumClient {
484 fn validate_merkle_proof(
485 &self, txid: &Txid, merkle_root: &TxMerkleNode, merkle_res: GetMerkleRes,
486 ) -> Result<bool, InternalError> {
487 let mut index = merkle_res.pos;
488 let mut cur = txid.to_raw_hash();
489 for mut bytes in merkle_res.merkle {
491 // unwrap() safety: `bytes` has len 32 so `from_slice` can never fail.
492 let next_hash = Sha256d::from_slice(&bytes).unwrap();
493 let (left, right) = if index % 2 == 0 { (cur, next_hash) } else { (next_hash, cur) };
495 let data = [&left[..], &right[..]].concat();
496 cur = Sha256d::hash(&data);
500 Ok(cur == merkle_root.to_raw_hash())
504 impl<L: Deref> Filter for ElectrumSyncClient<L>
508 fn register_tx(&self, txid: &Txid, _script_pubkey: &Script) {
509 let mut locked_queue = self.queue.lock().unwrap();
510 locked_queue.transactions.insert(*txid);
513 fn register_output(&self, output: WatchedOutput) {
514 let mut locked_queue = self.queue.lock().unwrap();
515 locked_queue.outputs.insert(output.outpoint.into_bitcoin_outpoint(), output);