Test that the excess fees of many dust htlcs count towards the dust limit

Author: tankyleo

lightning/src/ln/functional_tests.rs

@@ -10518,28 +10518,37 @@ 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();
 	// Set the dust limit to the default value
 	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.
@@ -10561,14 +10570,13 @@ fn test_nondust_htlc_fees_are_dust() {
 
 	// 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;
+	let commitment_tx_per_htlc_cost = chan_utils::per_outbound_htlc_counterparty_commit_tx_fee_msat(EXCESS_FEERATE, &ChannelTypeFeatures::empty());
 	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.