Fix cmp::max execution in ChannelContext::get_dust_buffer_feerate

  The current `cmp::max` doesnt align with the function comment, ie its
  comparing 2530 and `feerate_plus_quarter` instead of `feerate_per_kw
  + 2530` and `feerate_plus_quarter` which is fixed in this commit

lightning/src/ln/channel.rs

@@ -2699,7 +2699,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider  {
 			feerate_per_kw = cmp::max(feerate_per_kw, feerate);
 		}
 		let feerate_plus_quarter = feerate_per_kw.checked_mul(1250).map(|v| v / 1000);
-		cmp::max(2530, feerate_plus_quarter.unwrap_or(u32::max_value()))
+		cmp::max(feerate_per_kw + 2530, feerate_plus_quarter.unwrap_or(u32::max_value()))
 	}
 
 	/// Get forwarding information for the counterparty.

lightning/src/ln/functional_tests.rs

@@ -9891,8 +9891,8 @@ fn do_test_max_dust_htlc_exposure(dust_outbound_balance: bool, exposure_breach_e
 		// Default test fee estimator rate is 253 sat/kw, so we set the multiplier to 5_000_000 / 253
 		// to get roughly the same initial value as the default setting when this test was
 		// originally written.
-		MaxDustHTLCExposure::FeeRateMultiplier(5_000_000 / 253)
-	} else { MaxDustHTLCExposure::FixedLimitMsat(5_000_000) }; // initial default setting value
+		MaxDustHTLCExposure::FeeRateMultiplier(6_000_000 / 253)
+	} else { MaxDustHTLCExposure::FixedLimitMsat(6_000_000) }; // initial default setting value
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
 	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[Some(config), None]);
 	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
@@ -9901,6 +9901,8 @@ fn do_test_max_dust_htlc_exposure(dust_outbound_balance: bool, exposure_breach_e
 	let mut open_channel = get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, nodes[1].node.get_our_node_id());
 	open_channel.common_fields.max_htlc_value_in_flight_msat = 50_000_000;
 	open_channel.common_fields.max_accepted_htlcs = 60;
+	// --
+
 	if on_holder_tx {
 		open_channel.common_fields.dust_limit_satoshis = 546;
 	}
@@ -9935,18 +9937,21 @@ fn do_test_max_dust_htlc_exposure(dust_outbound_balance: bool, exposure_breach_e
 	let (channel_ready, channel_id) = create_chan_between_nodes_with_value_confirm(&nodes[0], &nodes[1], &tx);
 	let (announcement, as_update, bs_update) = create_chan_between_nodes_with_value_b(&nodes[0], &nodes[1], &channel_ready);
 	update_nodes_with_chan_announce(&nodes, 0, 1, &announcement, &as_update, &bs_update);
+	//  Node A < - > Node B channel is now established
 
 	// Fetch a route in advance as we will be unable to once we're unable to send.
 	let (mut route, payment_hash, _, payment_secret) =
 		get_route_and_payment_hash!(nodes[0], nodes[1], 1000);
 
+
 	let (dust_buffer_feerate, max_dust_htlc_exposure_msat) = {
 		let per_peer_state = nodes[0].node.per_peer_state.read().unwrap();
 		let chan_lock = per_peer_state.get(&nodes[1].node.get_our_node_id()).unwrap().lock().unwrap();
 		let chan = chan_lock.channel_by_id.get(&channel_id).unwrap();
 		(chan.context().get_dust_buffer_feerate(None) as u64,
 		chan.context().get_max_dust_htlc_exposure_msat(&LowerBoundedFeeEstimator(nodes[0].fee_estimator)))
 	};
+
 	let dust_outbound_htlc_on_holder_tx_msat: u64 = (dust_buffer_feerate * htlc_timeout_tx_weight(&channel_type_features) / 1000 + open_channel.common_fields.dust_limit_satoshis - 1) * 1000;
 	let dust_outbound_htlc_on_holder_tx: u64 = max_dust_htlc_exposure_msat / dust_outbound_htlc_on_holder_tx_msat;
 
@@ -10032,7 +10037,7 @@ fn do_test_max_dust_htlc_exposure(dust_outbound_balance: bool, exposure_breach_e
 		// For the multiplier dust exposure limit, since it scales with feerate,
 		// we need to add a lot of HTLCs that will become dust at the new feerate
 		// to cross the threshold.
-		for _ in 0..20 {
+		for _ in 0..30 {
 			let (_, payment_hash, payment_secret) = get_payment_preimage_hash(&nodes[1], Some(1_000), None);
 			nodes[0].node.send_payment_with_route(&route, payment_hash,
 				RecipientOnionFields::secret_only(payment_secret), PaymentId(payment_hash.0)).unwrap();
@@ -10054,12 +10059,12 @@ fn do_test_max_dust_htlc_exposure(dust_outbound_balance: bool, exposure_breach_e
 fn do_test_max_dust_htlc_exposure_by_threshold_type(multiplier_dust_limit: bool) {
 	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtHTLCForward, true, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtHTLCForward, true, multiplier_dust_limit);
+	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtHTLCForward, false, multiplier_dust_limit);
+	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtHTLCForward, false, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtHTLCReception, true, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtHTLCReception, false, multiplier_dust_limit);
-	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtHTLCForward, false, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtHTLCReception, false, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtHTLCReception, true, multiplier_dust_limit);
-	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtHTLCForward, false, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtUpdateFeeOutbound, true, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(true, ExposureEvent::AtUpdateFeeOutbound, false, multiplier_dust_limit);
 	do_test_max_dust_htlc_exposure(false, ExposureEvent::AtUpdateFeeOutbound, false, multiplier_dust_limit);
@@ -10068,7 +10073,7 @@ fn do_test_max_dust_htlc_exposure_by_threshold_type(multiplier_dust_limit: bool)
 
 #[test]
 fn test_max_dust_htlc_exposure() {
-	do_test_max_dust_htlc_exposure_by_threshold_type(false);
+	do_test_max_dust_htlc_exposure_by_threshold_type(false); 
 	do_test_max_dust_htlc_exposure_by_threshold_type(true);
 }