Assert dust exposure exhaustion in the excess fees are dust test

The payments in this test previously failed for reasons other
than exhausting the dust exposure limit with excess fees. Upon payment
failures, we now check the logs to assert failures due to dust
exposure exhaustion.

lightning/src/ln/functional_tests.rs

@@ -10596,9 +10596,20 @@ fn test_max_dust_htlc_exposure() {
 }
 
 #[test]
-fn test_nondust_htlc_fees_are_dust() {
-	// Test that the transaction fees paid in nondust HTLCs count towards our dust limit
+fn test_nondust_htlc_excess_fees_are_dust() {
+	// Test that the excess transaction fees paid in nondust HTLCs count towards our dust limit
+	const DEFAULT_FEERATE: u32 = 253;
+	const HIGH_FEERATE: u32 = 275;
+	const EXCESS_FEERATE: u32 = HIGH_FEERATE - DEFAULT_FEERATE;
 	let chanmon_cfgs = create_chanmon_cfgs(3);
+	{
+		// Set the feerate of the channel funder above the `dust_exposure_limiting_feerate` of
+		// the fundee. This delta means that the fundee will add the mining fees of the commitment and
+		// htlc transactions in excess of its `dust_exposure_limiting_feerate` to its total dust htlc
+		// exposure.
+		let mut feerate_lock = chanmon_cfgs[1].fee_estimator.sat_per_kw.lock().unwrap();
+		*feerate_lock = HIGH_FEERATE;
+	}
 	let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
 
 	let mut config = test_default_channel_config();
@@ -10606,18 +10617,16 @@ fn test_nondust_htlc_fees_are_dust() {
 	config.channel_config.max_dust_htlc_exposure =
 		MaxDustHTLCExposure::FeeRateMultiplier(10_000);
 	// Make sure the HTLC limits don't get in the way
-	config.channel_handshake_limits.min_max_accepted_htlcs = 400;
-	config.channel_handshake_config.our_max_accepted_htlcs = 400;
+	config.channel_handshake_limits.min_max_accepted_htlcs = chan_utils::MAX_HTLCS;
+	config.channel_handshake_config.our_max_accepted_htlcs = chan_utils::MAX_HTLCS;
 	config.channel_handshake_config.our_htlc_minimum_msat = 1;
+	config.channel_handshake_config.max_inbound_htlc_value_in_flight_percent_of_channel = 100;
 
 	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[Some(config), Some(config), Some(config)]);
 	let nodes = create_network(3, &node_cfgs, &node_chanmgrs);
 
-	// Create a channel from 1 -> 0 but immediately push all of the funds towards 0
-	let chan_id_1 = create_announced_chan_between_nodes(&nodes, 1, 0).2;
-	while nodes[1].node.list_channels()[0].next_outbound_htlc_limit_msat > 0 {
-		send_payment(&nodes[1], &[&nodes[0]], nodes[1].node.list_channels()[0].next_outbound_htlc_limit_msat);
-	}
+	// Leave enough on the funder side to let it pay the mining fees for a commit tx with tons of htlcs
+	let chan_id_1 = create_announced_chan_between_nodes_with_value(&nodes, 1, 0, 1_000_000, 750_000_000).2;
 
 	// First get the channel one HTLC_VALUE HTLC away from the dust limit by sending dust HTLCs
 	// repeatedly until we run out of space.
@@ -10637,16 +10646,24 @@ fn test_nondust_htlc_fees_are_dust() {
 	assert_ne!(nodes[0].node.list_channels()[0].next_outbound_htlc_minimum_msat, 0,
 		"Make sure we are able to send once we clear one HTLC");
 
+	// Skip the router complaint when node 0 will attempt to pay node 1
+	let (route_0_1, payment_hash_0_1, _, payment_secret_0_1) = get_route_and_payment_hash!(nodes[0], nodes[1], dust_limit * 2);
+
+	assert_eq!(nodes[0].node.list_channels().len(), 1);
+	assert_eq!(nodes[1].node.list_channels().len(), 1);
+	assert_eq!(nodes[0].node.list_channels()[0].pending_inbound_htlcs.len(), 0);
+	assert_eq!(nodes[1].node.list_channels()[0].pending_outbound_htlcs.len(), 0);
+
 	// At this point we have somewhere between dust_limit and dust_limit * 2 left in our dust
 	// exposure limit, and we want to max that out using non-dust HTLCs.
 	let commitment_tx_per_htlc_cost =
-		htlc_success_tx_weight(&ChannelTypeFeatures::empty()) * 253;
+		htlc_success_tx_weight(&ChannelTypeFeatures::empty()) * EXCESS_FEERATE as u64;
 	let max_htlcs_remaining = dust_limit * 2 / commitment_tx_per_htlc_cost;
-	assert!(max_htlcs_remaining < 30,
+	assert!(max_htlcs_remaining < chan_utils::MAX_HTLCS.into(),
 		"We should be able to fill our dust limit without too many HTLCs");
 	for i in 0..max_htlcs_remaining + 1 {
 		assert_ne!(i, max_htlcs_remaining);
-		if nodes[0].node.list_channels()[0].next_outbound_htlc_limit_msat < dust_limit {
+		if nodes[0].node.list_channels()[0].next_outbound_htlc_limit_msat <= dust_limit {
 			// We found our limit, and it was less than max_htlcs_remaining!
 			// At this point we can only send dust HTLCs as any non-dust HTLCs will overuse our
 			// remaining dust exposure.
@@ -10655,6 +10672,57 @@ fn test_nondust_htlc_fees_are_dust() {
 		route_payment(&nodes[0], &[&nodes[1]], dust_limit * 2);
 	}
 
+	assert_eq!(nodes[0].node.list_channels().len(), 1);
+	assert_eq!(nodes[1].node.list_channels().len(), 1);
+	assert_eq!(nodes[0].node.list_channels()[0].pending_inbound_htlcs.len(), 0);
+	assert_eq!(nodes[1].node.list_channels()[0].pending_outbound_htlcs.len(), 0);
+
+	// Send an additional non-dust htlc from 1 to 0, and check the complaint
+	let (route, payment_hash, _, payment_secret) = get_route_and_payment_hash!(nodes[1], nodes[0], dust_limit * 2);
+	nodes[1].node.send_payment_with_route(route, payment_hash,
+		RecipientOnionFields::secret_only(payment_secret), PaymentId(payment_hash.0)).unwrap();
+	check_added_monitors!(nodes[1], 1);
+	let mut events = nodes[1].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	let payment_event = SendEvent::from_event(events.remove(0));
+	nodes[0].node.handle_update_add_htlc(nodes[1].node.get_our_node_id(), &payment_event.msgs[0]);
+	commitment_signed_dance!(nodes[0], nodes[1], payment_event.commitment_msg, false);
+	expect_pending_htlcs_forwardable!(nodes[0]);
+	expect_htlc_handling_failed_destinations!(nodes[0].node.get_and_clear_pending_events(), &[HTLCDestination::FailedPayment { payment_hash }]);
+	nodes[0].logger.assert_log("lightning::ln::channel",
+		format!("Cannot accept value that would put our total dust exposure at {} over the limit {} on counterparty commitment tx",
+			2535000, 2530000), 1);
+	check_added_monitors!(nodes[0], 1);
+
+	// Clear the failed htlc
+	let updates = get_htlc_update_msgs!(nodes[0], nodes[1].node.get_our_node_id());
+	assert!(updates.update_add_htlcs.is_empty());
+	assert!(updates.update_fulfill_htlcs.is_empty());
+	assert_eq!(updates.update_fail_htlcs.len(), 1);
+	assert!(updates.update_fail_malformed_htlcs.is_empty());
+	assert!(updates.update_fee.is_none());
+	nodes[1].node.handle_update_fail_htlc(nodes[0].node.get_our_node_id(), &updates.update_fail_htlcs[0]);
+	commitment_signed_dance!(nodes[1], nodes[0], updates.commitment_signed, false);
+	expect_payment_failed!(nodes[1], payment_hash, false);
+
+	assert_eq!(nodes[0].node.list_channels().len(), 1);
+	assert_eq!(nodes[1].node.list_channels().len(), 1);
+	assert_eq!(nodes[0].node.list_channels()[0].pending_inbound_htlcs.len(), 0);
+	assert_eq!(nodes[1].node.list_channels()[0].pending_outbound_htlcs.len(), 0);
+
+	// Send an additional non-dust htlc from 0 to 1 using the pre-calculated route above, and check the immediate complaint
+	unwrap_send_err!(nodes[0], nodes[0].node.send_payment_with_route(route_0_1, payment_hash_0_1,
+			RecipientOnionFields::secret_only(payment_secret_0_1), PaymentId(payment_hash_0_1.0)
+		), true, APIError::ChannelUnavailable { .. }, {});
+	nodes[0].logger.assert_log("lightning::ln::outbound_payment",
+		format!("Failed to send along path due to error: Channel unavailable: Cannot send more than our next-HTLC maximum - {} msat", 2325000), 1);
+	assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
+
+	assert_eq!(nodes[0].node.list_channels().len(), 1);
+	assert_eq!(nodes[1].node.list_channels().len(), 1);
+	assert_eq!(nodes[0].node.list_channels()[0].pending_inbound_htlcs.len(), 0);
+	assert_eq!(nodes[1].node.list_channels()[0].pending_outbound_htlcs.len(), 0);
+
 	// At this point non-dust HTLCs are no longer accepted from node 0 -> 1, we also check that
 	// such HTLCs can't be routed over the same channel either.
 	create_announced_chan_between_nodes(&nodes, 2, 0);