Wait for replacement blocks after reorgs

The block helper only compared heights. Replacing invalidated blocks
with the same number of new blocks leaves the height unchanged, so it
could return while Electrum still exposed the old chain. Wallet syncs
then observed stale state and made reorg assertions timing-dependent.

Require Electrum's target-height hash to match bitcoind's replacement
block before returning.

Co-Authored-By: HAL 9000

Author: tnull

tests/common/mod.rs

@@ -753,7 +753,7 @@ pub(crate) async fn generate_blocks_and_wait<E: ElectrumApi>(
 	let address = bitcoind.new_address().expect("failed to get new address");
 	// TODO: expect this Result once the WouldBlock issue is resolved upstream.
 	let _block_hashes_res = bitcoind.generate_to_address(num, &address);
-	wait_for_block(electrs, cur_height as usize + num).await;
+	wait_for_block(bitcoind, electrs, cur_height as usize + num).await;
 	print!(" Done!");
 	println!("\n");
 }
@@ -773,27 +773,25 @@ pub(crate) fn invalidate_blocks(bitcoind: &BitcoindClient, num_blocks: usize) {
 	assert!(new_cur_height + num_blocks == cur_height);
 }
 
-pub(crate) async fn wait_for_block<E: ElectrumApi>(electrs: &E, min_height: usize) {
-	let mut header = match electrs.block_headers_subscribe() {
-		Ok(header) => header,
-		Err(_) => {
-			// While subscribing should succeed the first time around, we ran into some cases where
-			// it didn't. Since we can't proceed without subscribing, we try again after a delay
-			// and panic if it still fails.
-			tokio::time::sleep(Duration::from_secs(3)).await;
-			electrs.block_headers_subscribe().expect("failed to subscribe to block headers")
-		},
-	};
-	loop {
-		if header.height >= min_height {
-			break;
+pub(crate) async fn wait_for_block<E: ElectrumApi>(
+	bitcoind: &BitcoindClient, electrs: &E, min_height: usize,
+) {
+	let expected_block_hash = exponential_backoff_poll(|| {
+		let bitcoind_height =
+			bitcoind.get_blockchain_info().expect("failed to get blockchain info").blocks as usize;
+		if bitcoind_height < min_height {
+			return None;
 		}
-		header = exponential_backoff_poll(|| {
-			electrs.ping().expect("failed to ping electrs");
-			electrs.block_headers_pop().expect("failed to pop block header")
-		})
-		.await;
-	}
+		bitcoind.get_block_hash(min_height as u64).ok()?.block_hash().ok()
+	})
+	.await;
+	// A height-only wait can return the old header during a same-height reorg. Require the
+	// replacement hash so callers cannot sync against the stale chain by mistake.
+	exponential_backoff_poll(|| {
+		let header = electrs.block_header(min_height).ok()?;
+		(header.block_hash() == expected_block_hash).then_some(())
+	})
+	.await;
 }
 
 pub(crate) async fn wait_for_tx<E: ElectrumApi>(electrs: &E, txid: Txid) {

tests/integration_tests_rust.rs

@@ -807,7 +807,7 @@ async fn reorged_onchain_payment_returns_to_unconfirmed() {
 			.call("generateblock", &[json!(replacement_address.to_string()), json!([])])
 			.expect("failed to generate empty block");
 	}
-	wait_for_block(&electrsd.client, original_height as usize + 1).await;
+	wait_for_block(&bitcoind.client, &electrsd.client, original_height as usize + 1).await;
 
 	node_a.sync_wallets().unwrap();
 	node_b.sync_wallets().unwrap();
@@ -2056,7 +2056,7 @@ async fn splice_payment_reorged_to_unconfirmed() {
 			.call("generateblock", &[json!(replacement_address.to_string()), json!([])])
 			.expect("failed to generate empty block");
 	}
-	wait_for_block(&electrsd.client, original_height as usize + 1).await;
+	wait_for_block(&bitcoind.client, &electrsd.client, original_height as usize + 1).await;
 	node_b.sync_wallets().unwrap();
 
 	// The funding payment returns to `Unconfirmed` and stays `Pending`, exercising the