Introduce test for underpaying blinded path with dummy hops

Author: shaavan

lightning/src/ln/blinded_payment_tests.rs

@@ -267,6 +267,98 @@ fn one_hop_blinded_path_with_dummy_hops() {
 	claim_payment_along_route(claim_args);
 }
 
+#[test]
+fn one_hop_blinded_path_with_dummy_hops_underpaid() {
+	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]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+	let chan_upd =
+		create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0).0.contents;
+
+	let amt_msat = 5000;
+	let (_, payment_hash, payment_secret) =
+		get_payment_preimage_hash(&nodes[1], Some(amt_msat), None);
+	let payee_tlvs = ReceiveTlvs {
+		payment_secret,
+		payment_constraints: PaymentConstraints {
+			max_cltv_expiry: u32::max_value(),
+			htlc_minimum_msat: chan_upd.htlc_minimum_msat,
+		},
+		payment_context: PaymentContext::Bolt12Refund(Bolt12RefundContext {}),
+	};
+	let receive_auth_key = chanmon_cfgs[1].keys_manager.get_receive_auth_key();
+	let dummy_tlvs = [DummyTlvs::default(); 2];
+
+	let mut secp_ctx = Secp256k1::new();
+	// Advertise a receive path that includes dummy-hop relay requirements.
+	let blinded_path = BlindedPaymentPath::new_with_dummy_hops(
+		&[],
+		nodes[1].node.get_our_node_id(),
+		&dummy_tlvs,
+		receive_auth_key,
+		payee_tlvs,
+		u64::MAX,
+		TEST_FINAL_CLTV as u16,
+		&chanmon_cfgs[1].keys_manager,
+		&secp_ctx,
+	)
+	.unwrap();
+	assert!(blinded_path.payinfo.fee_base_msat > 0);
+	assert!(blinded_path.payinfo.cltv_expiry_delta > TEST_FINAL_CLTV as u16);
+
+	let mut route_params = RouteParameters::from_payment_params_and_value(
+		PaymentParameters::blinded(vec![blinded_path]),
+		amt_msat,
+	);
+	if let Payee::Blinded { ref mut route_hints, .. } = route_params.payment_params.payee {
+		// Simulate a payer that funds only the recipient amount, not the dummy-hop fees.
+		route_hints[0].payinfo.fee_base_msat = 0;
+		route_hints[0].payinfo.fee_proportional_millionths = 0;
+	} else {
+		panic!();
+	}
+
+	nodes[0]
+		.node
+		.send_payment(
+			payment_hash,
+			RecipientOnionFields::spontaneous_empty(amt_msat),
+			PaymentId(payment_hash.0),
+			route_params,
+			Retry::Attempts(0),
+		)
+		.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 ev = remove_first_msg_event_to_node(&nodes[1].node.get_our_node_id(), &mut events);
+
+	let path = &[&nodes[1]];
+	let args = PassAlongPathArgs::new(&nodes[0], path, amt_msat, payment_hash, ev)
+		// The receiver rejects the HTLC while processing the hidden dummy hops.
+		.expect_failure(HTLCHandlingFailureType::Receive { payment_hash })
+		.with_payment_secret(payment_secret)
+		.with_dummy_tlvs(&dummy_tlvs);
+	do_pass_along_path(args);
+
+	let mut updates = get_htlc_update_msgs(&nodes[1], &nodes[0].node.get_our_node_id());
+	// Blinded receive failures are surfaced to the sender as malformed onion blinding errors.
+	nodes[0].node.handle_update_fail_malformed_htlc(
+		nodes[1].node.get_our_node_id(),
+		&updates.update_fail_malformed_htlcs[0],
+	);
+	do_commitment_signed_dance(&nodes[0], &nodes[1], &updates.commitment_signed, false, false);
+	expect_payment_failed_conditions(
+		&nodes[0],
+		payment_hash,
+		false,
+		PaymentFailedConditions::new()
+			.expected_htlc_error_data(LocalHTLCFailureReason::InvalidOnionBlinding, &[0; 32]),
+	);
+}
+
 #[test]
 #[rustfmt::skip]
 fn mpp_to_one_hop_blinded_path() {