Add and update high priority feerate in Channel

To find the maximum dust exposure as a multiplier of the current high
priority feerate, we keep an updated record of the feerate inside of
the channel.

Author: alecchendev

lightning/src/ln/channel.rs

@@ -601,6 +601,10 @@ pub(super) struct Channel<Signer: ChannelSigner> {
 	next_holder_htlc_id: u64,
 	next_counterparty_htlc_id: u64,
 	feerate_per_kw: u32,
+	/// We keep an updated high priority feerate in order to calculate the max dust
+	/// exposure limit if [`ChannelConfig::max_dust_htlc_exposure_multiplier_thousandths`]
+	/// is set.
+	high_priority_feerate_per_kw: Option<u32>,
 
 	/// The timestamp set on our latest `channel_update` message for this channel. It is updated
 	/// when the channel is updated in ways which may impact the `channel_update` message or when a
@@ -1018,6 +1022,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		debug_assert!(channel_type.is_subset(&channelmanager::provided_channel_type_features(&config)));
 
 		let feerate = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+		let high_priority_feerate = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority);
 
 		let value_to_self_msat = channel_value_satoshis * 1000 - push_msat;
 		let commitment_tx_fee = Self::commit_tx_fee_msat(feerate, MIN_AFFORDABLE_HTLC_COUNT, channel_type.requires_anchors_zero_fee_htlc_tx());
@@ -1114,6 +1119,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 			channel_creation_height: current_chain_height,
 
 			feerate_per_kw: feerate,
+			high_priority_feerate_per_kw: Some(high_priority_feerate),
 			counterparty_dust_limit_satoshis: 0,
 			holder_dust_limit_satoshis: MIN_CHAN_DUST_LIMIT_SATOSHIS,
 			counterparty_max_htlc_value_in_flight_msat: 0,
@@ -1470,6 +1476,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 			channel_creation_height: current_chain_height,
 
 			feerate_per_kw: msg.feerate_per_kw,
+			high_priority_feerate_per_kw: Some(fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority)),
 			channel_value_satoshis: msg.funding_satoshis,
 			counterparty_dust_limit_satoshis: msg.dust_limit_satoshis,
 			holder_dust_limit_satoshis: MIN_CHAN_DUST_LIMIT_SATOSHIS,
@@ -4962,6 +4969,11 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		self.config.options.max_dust_htlc_exposure_msat
 	}
 
+	/// Sets the channel's high priority feerate per kw.
+	pub fn update_high_priority_feerate(&mut self, high_priority_feerate_per_kw: u32) {
+		self.high_priority_feerate_per_kw = Some(high_priority_feerate_per_kw);
+	}
+
 	/// Returns the previous [`ChannelConfig`] applied to this channel, if any.
 	pub fn prev_config(&self) -> Option<ChannelConfig> {
 		self.prev_config.map(|prev_config| prev_config.0)
@@ -7046,6 +7058,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 		let mut holder_max_accepted_htlcs: Option<u16> = None;
 
 		let mut pending_monitor_updates = Some(Vec::new());
+		let mut high_priority_feerate_per_kw = None;
 
 		read_tlv_fields!(reader, {
 			(0, announcement_sigs, option),
@@ -7070,6 +7083,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 			(29, temporary_channel_id, option),
 			(31, channel_pending_event_emitted, option),
 			(33, pending_monitor_updates, vec_type),
+			(35, high_priority_feerate_per_kw, option),
 		});
 
 		let (channel_keys_id, holder_signer) = if let Some(channel_keys_id) = channel_keys_id {
@@ -7172,6 +7186,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 			next_counterparty_htlc_id,
 			update_time_counter,
 			feerate_per_kw,
+			high_priority_feerate_per_kw,
 
 			#[cfg(debug_assertions)]
 			holder_max_commitment_tx_output: Mutex::new((0, 0)),

lightning/src/ln/channelmanager.rs

@@ -4008,6 +4008,7 @@ where
 			let mut should_persist = self.process_background_events();
 
 			let new_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Normal);
+			let new_high_priority_feerate = self.fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority);
 
 			let mut handle_errors: Vec<(Result<(), _>, _)> = Vec::new();
 			let mut timed_out_mpp_htlcs = Vec::new();
@@ -4020,6 +4021,7 @@ where
 					let pending_msg_events = &mut peer_state.pending_msg_events;
 					let counterparty_node_id = *counterparty_node_id;
 					peer_state.channel_by_id.retain(|chan_id, chan| {
+						chan.update_high_priority_feerate(new_high_priority_feerate);
 						let chan_needs_persist = self.update_channel_fee(chan_id, chan, new_feerate);
 						if chan_needs_persist == NotifyOption::DoPersist { should_persist = NotifyOption::DoPersist; }