Timestamp mempool evictions when observed

Locally inserted transactions can be newer than Bitcoin Core's latest
mempool timestamp. Reporting that stale timestamp for an eviction makes
BDK ignore it and leaves the transaction's inputs unavailable.

Use the later of the local observation time and Bitcoin Core's mempool
time. This makes local transactions evictable without regressing nodes
whose Bitcoin Core clock is ahead of the application clock.

Co-Authored-By: HAL 9000

Author: tnull

src/chain/bitcoind.rs

@@ -1302,18 +1302,18 @@ impl BitcoindClient {
 		&self, bdk_unconfirmed_txids: Vec<Txid>,
 	) -> Result<Vec<(Txid, u64)>, BitcoindClientError> {
 		match self {
-			BitcoindClient::Rpc { latest_mempool_timestamp, mempool_entries_cache, .. } => {
+			BitcoindClient::Rpc { mempool_entries_cache, latest_mempool_timestamp, .. } => {
 				Self::get_evicted_mempool_txids_and_timestamp_inner(
-					latest_mempool_timestamp,
 					mempool_entries_cache,
+					latest_mempool_timestamp,
 					bdk_unconfirmed_txids,
 				)
 				.await
 			},
-			BitcoindClient::Rest { latest_mempool_timestamp, mempool_entries_cache, .. } => {
+			BitcoindClient::Rest { mempool_entries_cache, latest_mempool_timestamp, .. } => {
 				Self::get_evicted_mempool_txids_and_timestamp_inner(
-					latest_mempool_timestamp,
 					mempool_entries_cache,
+					latest_mempool_timestamp,
 					bdk_unconfirmed_txids,
 				)
 				.await
@@ -1322,16 +1322,17 @@ impl BitcoindClient {
 	}
 
 	async fn get_evicted_mempool_txids_and_timestamp_inner(
-		latest_mempool_timestamp: &AtomicU64,
 		mempool_entries_cache: &tokio::sync::Mutex<HashMap<Txid, MempoolEntry>>,
-		bdk_unconfirmed_txids: Vec<Txid>,
+		latest_mempool_timestamp: &AtomicU64, bdk_unconfirmed_txids: Vec<Txid>,
 	) -> Result<Vec<(Txid, u64)>, BitcoindClientError> {
-		let latest_mempool_timestamp = latest_mempool_timestamp.load(Ordering::Relaxed);
 		let mempool_entries_cache = mempool_entries_cache.lock().await;
+		let observed_at =
+			SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
+		let evicted_at = observed_at.max(latest_mempool_timestamp.load(Ordering::Relaxed));
 		let evicted_txids = bdk_unconfirmed_txids
 			.into_iter()
 			.filter(|txid| !mempool_entries_cache.contains_key(txid))
-			.map(|txid| (txid, latest_mempool_timestamp))
+			.map(|txid| (txid, evicted_at))
 			.collect();
 		Ok(evicted_txids)
 	}
@@ -1616,8 +1617,10 @@ impl std::error::Error for BitcoindClientError {}
 
 #[cfg(test)]
 mod tests {
+	use std::collections::HashMap;
+	use std::sync::atomic::{AtomicU64, Ordering};
 	use std::sync::Mutex;
-	use std::time::Duration;
+	use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 	use bitcoin::hashes::Hash;
 	use bitcoin::{FeeRate, OutPoint, ScriptBuf, Transaction, TxIn, TxOut, Txid, Witness};
@@ -1628,7 +1631,7 @@ mod tests {
 	use serde_json::json;
 
 	use crate::chain::bitcoind::{
-		acquire_initial_wallet_sync_guard, FeeResponse, GetMempoolEntryResponse,
+		acquire_initial_wallet_sync_guard, BitcoindClient, FeeResponse, GetMempoolEntryResponse,
 		GetRawMempoolResponse, GetRawTransactionResponse, MempoolMinFeeResponse,
 	};
 	use crate::chain::{WalletSyncGuard, WalletSyncStatus};
@@ -1659,6 +1662,55 @@ mod tests {
 		acquired_guard.complete(Ok(()));
 	}
 
+	#[tokio::test]
+	async fn eviction_uses_absence_observation_time() {
+		let txid = Txid::all_zeros();
+		let mempool_entries = tokio::sync::Mutex::new(HashMap::new());
+		let latest_mempool_timestamp = AtomicU64::new(0);
+		let before = SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
+
+		let evicted = BitcoindClient::get_evicted_mempool_txids_and_timestamp_inner(
+			&mempool_entries,
+			&latest_mempool_timestamp,
+			vec![txid],
+		)
+		.await
+		.unwrap();
+
+		assert_eq!(evicted.len(), 1);
+		assert_eq!(evicted[0].0, txid);
+		assert!(evicted[0].1 >= before, "eviction timestamp must record when absence was observed");
+	}
+
+	#[tokio::test]
+	async fn eviction_preserves_newer_mempool_time() {
+		let txid = Txid::from_byte_array([1; 32]);
+		let client = BitcoindClient::new_rpc(
+			"127.0.0.1".to_string(),
+			18443,
+			"user".to_string(),
+			"password".to_string(),
+		);
+		let observed_at =
+			SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
+		let newer_mempool_time = observed_at.saturating_add(60);
+		match &client {
+			BitcoindClient::Rpc { latest_mempool_timestamp, .. } => {
+				latest_mempool_timestamp.store(newer_mempool_time, Ordering::Relaxed);
+			},
+			BitcoindClient::Rest { .. } => unreachable!(),
+		}
+
+		let evicted = client.get_evicted_mempool_txids_and_timestamp(vec![txid]).await.unwrap();
+
+		assert_eq!(evicted.len(), 1);
+		assert_eq!(evicted[0].0, txid);
+		assert_eq!(
+			evicted[0].1, newer_mempool_time,
+			"eviction timestamp must not precede Bitcoin Core's mempool time"
+		);
+	}
+
 	prop_compose! {
 		fn arbitrary_witness()(
 			witness_elements in vec(vec(any::<u8>(), 0..100), 0..20)