Add test coverage for failure of inconsistent MPP parts

When we receive multiple HTLCs which claim to be a part of the same
MPP but which are inconsistent for some reason, we should fail the
inconsistent HTLCs but keep the first HTLCs up until the first
inconsistency.

This works, but it turns out there was no test coverage, so we add
some here.

Author: TheBlueMatt

lightning/src/ln/functional_tests.rs

@@ -9435,12 +9435,7 @@ fn test_forwardable_regen() {
 	claim_payment(&nodes[0], &[&nodes[1], &nodes[2]], payment_preimage_2);
 }
 
-#[test]
-fn test_dup_htlc_second_fail_panic() {
-	// Previously, if we received two HTLCs back-to-back, where the second overran the expected
-	// value for the payment, we'd fail back both HTLCs after generating a `PaymentReceived` event.
-	// Then, if the user failed the second payment, they'd hit a "tried to fail an already failed
-	// HTLC" debug panic. This tests for this behavior, checking that only one HTLC is auto-failed.
+fn do_test_dup_htlc_second_rejected(test_for_second_fail_panic: bool) {
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
 	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
@@ -9452,7 +9447,7 @@ fn test_dup_htlc_second_fail_panic() {
 		.with_features(InvoiceFeatures::known());
 	let route = get_route!(nodes[0], payment_params, 10_000, TEST_FINAL_CLTV).unwrap();
 
-	let (_, our_payment_hash, our_payment_secret) = get_payment_preimage_hash!(&nodes[1]);
+	let (our_payment_preimage, our_payment_hash, our_payment_secret) = get_payment_preimage_hash!(&nodes[1]);
 
 	{
 		nodes[0].node.send_payment(&route, our_payment_hash, &Some(our_payment_secret)).unwrap();
@@ -9480,26 +9475,153 @@ fn test_dup_htlc_second_fail_panic() {
 		// the first HTLC delivered above.
 	}
 
-	// Now we go fail back the first HTLC from the user end.
 	expect_pending_htlcs_forwardable_ignore!(nodes[1]);
 	nodes[1].node.process_pending_htlc_forwards();
-	nodes[1].node.fail_htlc_backwards(&our_payment_hash);
 
-	expect_pending_htlcs_forwardable_ignore!(nodes[1]);
-	nodes[1].node.process_pending_htlc_forwards();
+	if test_for_second_fail_panic {
+		// Now we go fail back the first HTLC from the user end.
+		nodes[1].node.fail_htlc_backwards(&our_payment_hash);
 
-	check_added_monitors!(nodes[1], 1);
-	let fail_updates_1 = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
-	assert_eq!(fail_updates_1.update_fail_htlcs.len(), 2);
+		expect_pending_htlcs_forwardable_ignore!(nodes[1]);
+		nodes[1].node.process_pending_htlc_forwards();
+
+		check_added_monitors!(nodes[1], 1);
+		let fail_updates_1 = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
+		assert_eq!(fail_updates_1.update_fail_htlcs.len(), 2);
+
+		nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[0]);
+		nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[1]);
+		commitment_signed_dance!(nodes[0], nodes[1], fail_updates_1.commitment_signed, false);
+
+		let failure_events = nodes[0].node.get_and_clear_pending_events();
+		assert_eq!(failure_events.len(), 2);
+		if let Event::PaymentPathFailed { .. } = failure_events[0] {} else { panic!(); }
+		if let Event::PaymentPathFailed { .. } = failure_events[1] {} else { panic!(); }
+	} else {
+		// Let the second HTLC fail and claim the first
+		expect_pending_htlcs_forwardable_ignore!(nodes[1]);
+		nodes[1].node.process_pending_htlc_forwards();
+
+		check_added_monitors!(nodes[1], 1);
+		let fail_updates_1 = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
+		nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[0]);
+		commitment_signed_dance!(nodes[0], nodes[1], fail_updates_1.commitment_signed, false);
+
+		expect_payment_failed_conditions!(nodes[0], our_payment_hash, true, PaymentFailedConditions::new().mpp_parts_remain());
+
+		claim_payment(&nodes[0], &[&nodes[1]], our_payment_preimage);
+	}
+}
+
+#[test]
+fn test_dup_htlc_second_fail_panic() {
+	// Previously, if we received two HTLCs back-to-back, where the second overran the expected
+	// value for the payment, we'd fail back both HTLCs after generating a `PaymentReceived` event.
+	// Then, if the user failed the second payment, they'd hit a "tried to fail an already failed
+	// HTLC" debug panic. This tests for this behavior, checking that only one HTLC is auto-failed.
+	do_test_dup_htlc_second_rejected(true);
+}
+
+#[test]
+fn test_dup_htlc_second_rejected() {
+	// Test that if we receive a second HTLC for an MPP payment that overruns the payment amount we
+	// simply reject the second HTLC but are still able to claim the first HTLC.
+	do_test_dup_htlc_second_rejected(false);
+}
+
+#[test]
+fn test_inconsistent_mpp_params() {
+	// Test that if we recieve two HTLCs with different payment parameters we fail back the first
+	// such HTLC and allow the second to stay.
+	let chanmon_cfgs = create_chanmon_cfgs(4);
+	let node_cfgs = create_node_cfgs(4, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(4, &node_cfgs, &[None, None, None, None]);
+	let nodes = create_network(4, &node_cfgs, &node_chanmgrs);
+
+	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100_000, 0, InitFeatures::known(), InitFeatures::known());
+	create_announced_chan_between_nodes_with_value(&nodes, 0, 2, 100_000, 0, InitFeatures::known(), InitFeatures::known());
+	create_announced_chan_between_nodes_with_value(&nodes, 1, 3, 100_000, 0, InitFeatures::known(), InitFeatures::known());
+	create_announced_chan_between_nodes_with_value(&nodes, 2, 3, 100_000, 0, InitFeatures::known(), InitFeatures::known());
 
-	nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[0]);
-	nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[1]);
-	commitment_signed_dance!(nodes[0], nodes[1], fail_updates_1.commitment_signed, false);
+	let payment_params = PaymentParameters::from_node_id(nodes[3].node.get_our_node_id())
+		.with_features(InvoiceFeatures::known());
+	let mut route = get_route!(nodes[0], payment_params, 15_000_000, TEST_FINAL_CLTV).unwrap();
+	assert_eq!(route.paths.len(), 2);
+	route.paths.sort_by(|path_a, _| {
+		// Sort the path so that the path through nodes[1] comes first
+		if path_a[0].pubkey == nodes[1].node.get_our_node_id() {
+			core::cmp::Ordering::Less } else { core::cmp::Ordering::Greater }
+	});
+	let payment_params_opt = Some(payment_params);
+
+	let (our_payment_preimage, our_payment_hash, our_payment_secret) = get_payment_preimage_hash!(&nodes[3]);
+
+	let cur_height = nodes[0].best_block_info().1;
+	let payment_id = PaymentId([42; 32]);
+	{
+		nodes[0].node.send_payment_along_path(&route.paths[0], &payment_params_opt, &our_payment_hash, &Some(our_payment_secret), 15_000_000, cur_height, payment_id, &None).unwrap();
+		check_added_monitors!(nodes[0], 1);
+
+		let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		pass_along_path(&nodes[0], &[&nodes[1], &nodes[3]], 15_000_000, our_payment_hash, Some(our_payment_secret), events.pop().unwrap(), false, None);
+	}
+	assert!(nodes[3].node.get_and_clear_pending_events().is_empty());
+
+	{
+		nodes[0].node.send_payment_along_path(&route.paths[1], &payment_params_opt, &our_payment_hash, &Some(our_payment_secret), 14_000_000, cur_height, payment_id, &None).unwrap();
+		check_added_monitors!(nodes[0], 1);
+
+		let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		let payment_event = SendEvent::from_event(events.pop().unwrap());
+
+		nodes[2].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &payment_event.msgs[0]);
+		commitment_signed_dance!(nodes[2], nodes[0], payment_event.commitment_msg, false);
+
+		expect_pending_htlcs_forwardable!(nodes[2]);
+		check_added_monitors!(nodes[2], 1);
+
+		let mut events = nodes[2].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		let payment_event = SendEvent::from_event(events.pop().unwrap());
+
+		nodes[3].node.handle_update_add_htlc(&nodes[2].node.get_our_node_id(), &payment_event.msgs[0]);
+		check_added_monitors!(nodes[3], 0);
+		commitment_signed_dance!(nodes[3], nodes[2], payment_event.commitment_msg, true, true);
+
+		// At this point, nodes[3] should notice the two HTLCs don't contain the same total payment
+		// amount. It will assume the second is a privacy attack (no longer particularly relevant
+		// post-payment_secrets) and fail back the new HTLC.
+	}
+	expect_pending_htlcs_forwardable_ignore!(nodes[3]);
+	nodes[3].node.process_pending_htlc_forwards();
+	expect_pending_htlcs_forwardable_ignore!(nodes[3]);
+	nodes[3].node.process_pending_htlc_forwards();
+
+	check_added_monitors!(nodes[3], 1);
+
+	let fail_updates_1 = get_htlc_update_msgs!(nodes[3], nodes[2].node.get_our_node_id());
+	nodes[2].node.handle_update_fail_htlc(&nodes[3].node.get_our_node_id(), &fail_updates_1.update_fail_htlcs[0]);
+	commitment_signed_dance!(nodes[2], nodes[3], fail_updates_1.commitment_signed, false);
+
+	expect_pending_htlcs_forwardable!(nodes[2]);
+	check_added_monitors!(nodes[2], 1);
+
+	let fail_updates_2 = get_htlc_update_msgs!(nodes[2], nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_update_fail_htlc(&nodes[2].node.get_our_node_id(), &fail_updates_2.update_fail_htlcs[0]);
+	commitment_signed_dance!(nodes[0], nodes[2], fail_updates_2.commitment_signed, false);
+
+	expect_payment_failed_conditions!(nodes[0], our_payment_hash, true, PaymentFailedConditions::new().mpp_parts_remain());
+
+	nodes[0].node.send_payment_along_path(&route.paths[1], &payment_params_opt, &our_payment_hash, &Some(our_payment_secret), 15_000_000, cur_height, payment_id, &None).unwrap();
+	check_added_monitors!(nodes[0], 1);
+
+	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	pass_along_path(&nodes[0], &[&nodes[2], &nodes[3]], 15_000_000, our_payment_hash, Some(our_payment_secret), events.pop().unwrap(), true, None);
 
-	let failure_events = nodes[0].node.get_and_clear_pending_events();
-	assert_eq!(failure_events.len(), 2);
-	if let Event::PaymentPathFailed { .. } = failure_events[0] {} else { panic!(); }
-	if let Event::PaymentPathFailed { .. } = failure_events[1] {} else { panic!(); }
+	claim_payment_along_route(&nodes[0], &[&[&nodes[1], &nodes[3]], &[&nodes[2], &nodes[3]]], false, our_payment_preimage);
 }
 
 #[test]