Fix BOLT11 DuplicatePayment triggering on-chain fallback in unified payments

Error::DuplicatePayment is now terminal in UnifiedPayment::send, preventing
a duplicate Lightning payment from falling back to an on-chain payment.

Author: elnafateh

src/payment/unified.rs

@@ -287,9 +287,22 @@ impl UnifiedPayment {
 
 					let payment_result = if let Ok(hrn) = HumanReadableName::from_encoded(uri_str) {
 						let hrn = maybe_wrap(hrn.clone());
-						self.bolt12_payment.send_using_amount_inner(&offer, amount_msat.unwrap_or(0), None, None, route_parameters, Some(hrn))
+						self.bolt12_payment.send_using_amount_inner(
+							&offer,
+							amount_msat.unwrap_or(0),
+							None,
+							None,
+							route_parameters,
+							Some(hrn),
+						)
 					} else if let Some(amount_msat) = amount_msat {
-						self.bolt12_payment.send_using_amount(&offer, amount_msat, None, None, route_parameters)
+						self.bolt12_payment.send_using_amount(
+							&offer,
+							amount_msat,
+							None,
+							None,
+							route_parameters,
+						)
 					} else {
 						self.bolt12_payment.send(&offer, None, None, route_parameters)
 					}
@@ -304,14 +317,19 @@ impl UnifiedPayment {
 				},
 				PaymentMethod::LightningBolt11(invoice) => {
 					let invoice = maybe_wrap(invoice.clone());
-					let payment_result = self.bolt11_invoice.send(&invoice, route_parameters)
-						.map_err(|e| {
+					let payment_result = self.bolt11_invoice.send(&invoice, route_parameters);
+
+					match payment_result {
+						Ok(payment_id) => {
+							return Ok(UnifiedPaymentResult::Bolt11 { payment_id });
+						},
+						Err(Error::DuplicatePayment) => {
+							log_error!(self.logger, "Failed to send BOLT11 invoice: DuplicatePayment. This is part of a unified payment. Aborting to avoid duplicate payment.");
+							return Err(Error::DuplicatePayment);
+						},
+						Err(e) => {
 							log_error!(self.logger, "Failed to send BOLT11 invoice: {:?}. This is part of a unified payment. Falling back to the on-chain transaction.", e);
-							e
-						});
-
-					if let Ok(payment_id) = payment_result {
-						return Ok(UnifiedPaymentResult::Bolt11 { payment_id });
+						},
 					}
 				},
 				PaymentMethod::OnChain(address) => {

tests/integration_tests_rust.rs

@@ -2912,6 +2912,84 @@ async fn unified_send_receive_bip21_uri() {
 	assert_eq!(node_b.list_balances().total_lightning_balance_sats, 200_000);
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn unified_send_bolt11_duplicate_payment_no_onchain_fallback() {
+	// Regression test for https://github.com/lightningdevkit/ldk-node/issues/1033
+	//
+	// Sending a unified BIP21 payment that resolves to BOLT11 should return
+	// Error::DuplicatePayment on retry, not fall back to the on-chain method.
+
+	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();
+	let chain_source = random_chain_source(&bitcoind, &electrsd);
+
+	let (node_a, node_b) = setup_two_nodes(&chain_source, false, false);
+
+	let address_a = node_a.onchain_payment().new_address().unwrap();
+	let premined_sats = 5_000_000;
+
+	premine_and_distribute_funds(
+		&bitcoind.client,
+		&electrsd.client,
+		vec![address_a],
+		Amount::from_sat(premined_sats),
+	)
+	.await;
+
+	node_a.sync_wallets().unwrap();
+	open_channel(&node_a, &node_b, 4_000_000, true, &electrsd).await;
+	generate_blocks_and_wait(&bitcoind.client, &electrsd.client, 6).await;
+
+	node_a.sync_wallets().unwrap();
+	node_b.sync_wallets().unwrap();
+
+	expect_channel_ready_event!(node_a, node_b.node_id());
+	expect_channel_ready_event!(node_b, node_a.node_id());
+
+	// Sleep until we broadcast a node announcement.
+	while node_b.status().latest_node_announcement_broadcast_timestamp.is_none() {
+		tokio::time::sleep(std::time::Duration::from_millis(10)).await;
+	}
+	tokio::time::sleep(std::time::Duration::from_secs(1)).await;
+
+	let expected_amount_sats = 100_000;
+	let expiry_sec = 4_000;
+
+	// Receive a unified payment on node_b — this will produce a URI with BOLT12 offer + BOLT11 invoice.
+	let uri_str = node_b.unified_payment().receive(expected_amount_sats, "asdf", expiry_sec).unwrap();
+
+	// Strip the BOLT12 offer so the URI resolves to BOLT11 only (no BOLT12, no on-chain fallback).
+	let uri_str_bolt11_only = uri_str.split("&lno=").next().unwrap();
+
+	// First send: should succeed via BOLT11.
+	let first_result = node_a.unified_payment().send(uri_str_bolt11_only, None, None).await;
+	let first_payment_id = match first_result {
+		Ok(UnifiedPaymentResult::Bolt11 { payment_id }) => payment_id,
+		Ok(other) => panic!("Expected Bolt11 result on first send, got: {:?}", other),
+		Err(e) => panic!("Expected Bolt11 result on first send, got error: {:?}", e),
+	};
+	expect_payment_successful_event!(node_a, Some(first_payment_id), None);
+
+	// Second send with the same URI: should return DuplicatePayment, NOT fall back to on-chain.
+	let second_result = node_a.unified_payment().send(uri_str_bolt11_only, None, None).await;
+	match second_result {
+		Err(NodeError::DuplicatePayment) => {
+			// Expected — this is the fix for #1033.
+		},
+		Ok(UnifiedPaymentResult::Onchain { txid }) => {
+			panic!(
+				"Regression: Duplicate BOLT11 payment fell back to on-chain. txid={}. See #1033",
+				txid
+			);
+		},
+		Ok(other) => {
+			panic!("Expected DuplicatePayment error on retry, got: {:?}", other);
+		},
+		Err(other) => {
+			panic!("Expected DuplicatePayment error on retry, got: {:?}", other);
+		},
+	}
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 async fn lsps2_client_service_integration() {
 	do_lsps2_client_service_integration(true).await;