lsps2: Refill consumed payment leases

Keep one usable lease ready after fixed or variable receive flows
consume cached parameters. Foreground callers share the refill lock
and reuse its result when it completes.

Co-Authored-By: HAL 9000

Author: tnull

src/liquidity/client/lsps2/mod.rs

@@ -274,6 +274,7 @@ where
 		if let Some((lease, total_fee_msat, lsp)) =
 			self.take_cached_fixed_lease(amount_msat).await?
 		{
+			self.schedule_fixed_lease_refill(amount_msat, connection_manager);
 			return Ok((lease, total_fee_msat, lsp, false));
 		}
 		let request_lock = self
@@ -285,9 +286,20 @@ where
 		if let Some((lease, total_fee_msat, lsp)) =
 			self.take_cached_fixed_lease(amount_msat).await?
 		{
+			self.schedule_fixed_lease_refill(amount_msat, connection_manager);
 			return Ok((lease, total_fee_msat, lsp, false));
 		}
 
+		let (negotiated_lease, min_total_fee_msat, cheapest_lsp) =
+			self.negotiate_fixed_lease(amount_msat, connection_manager).await?;
+		let lease = self.consume_lease(&negotiated_lease.id).await?;
+		self.schedule_fixed_lease_refill(amount_msat, connection_manager);
+		Ok((lease, min_total_fee_msat, cheapest_lsp, true))
+	}
+
+	async fn negotiate_fixed_lease(
+		self: &Arc<Self>, amount_msat: u64, connection_manager: &Arc<ConnectionManager<L>>,
+	) -> Result<(PaymentLease, u64, LspConfig), Error> {
 		let all_offers = self.gather_lsps2_offers(connection_manager).await?;
 		let (cheapest_lsp, min_total_fee_msat, min_opening_params) = all_offers
 			.into_iter()
@@ -343,14 +355,14 @@ where
 				Some(&cheapest_lsp.node_id),
 			)
 			.await?;
-		let lease = self.consume_lease(&negotiated_lease.id).await?;
-		Ok((lease, min_total_fee_msat, cheapest_lsp, true))
+		Ok((negotiated_lease, min_total_fee_msat, cheapest_lsp))
 	}
 
 	async fn acquire_variable_lease(
 		self: &Arc<Self>, connection_manager: &Arc<ConnectionManager<L>>,
 	) -> Result<(PaymentLease, u64, LspConfig, bool), Error> {
 		if let Some((lease, proportional_fee, lsp)) = self.take_cached_variable_lease().await? {
+			self.schedule_variable_lease_refill(connection_manager);
 			return Ok((lease, proportional_fee, lsp, false));
 		}
 		let request_lock = self
@@ -360,9 +372,20 @@ where
 			.request_lock(LeaseRequestKey::Variable);
 		let _request_guard = request_lock.lock().await;
 		if let Some((lease, proportional_fee, lsp)) = self.take_cached_variable_lease().await? {
+			self.schedule_variable_lease_refill(connection_manager);
 			return Ok((lease, proportional_fee, lsp, false));
 		}
 
+		let (negotiated_lease, min_prop_fee_ppm_msat, cheapest_lsp) =
+			self.negotiate_variable_lease(connection_manager).await?;
+		let lease = self.consume_lease(&negotiated_lease.id).await?;
+		self.schedule_variable_lease_refill(connection_manager);
+		Ok((lease, min_prop_fee_ppm_msat, cheapest_lsp, true))
+	}
+
+	async fn negotiate_variable_lease(
+		self: &Arc<Self>, connection_manager: &Arc<ConnectionManager<L>>,
+	) -> Result<(PaymentLease, u64, LspConfig), Error> {
 		let all_offers = self.gather_lsps2_offers(connection_manager).await?;
 		let mut rejected_for_fee = false;
 		let (cheapest_lsp, min_prop_fee_ppm_msat, min_opening_params) = all_offers
@@ -404,8 +427,73 @@ where
 		let negotiated_lease = self
 			.lsps2_send_buy_request(None, min_opening_params, Some(&cheapest_lsp.node_id))
 			.await?;
-		let lease = self.consume_lease(&negotiated_lease.id).await?;
-		Ok((lease, min_prop_fee_ppm_msat, cheapest_lsp, true))
+		Ok((negotiated_lease, min_prop_fee_ppm_msat, cheapest_lsp))
+	}
+
+	fn schedule_fixed_lease_refill(
+		self: &Arc<Self>, amount_msat: u64, connection_manager: &Arc<ConnectionManager<L>>,
+	) {
+		let client = Arc::clone(self);
+		let connection_manager = Arc::clone(connection_manager);
+		tokio::spawn(async move {
+			if let Err(error) = client.cache_fixed_lease(amount_msat, &connection_manager).await {
+				log_warn!(client.logger, "Failed refilling LSPS2 payment lease: {}", error);
+			}
+		});
+	}
+
+	fn schedule_variable_lease_refill(
+		self: &Arc<Self>, connection_manager: &Arc<ConnectionManager<L>>,
+	) {
+		let client = Arc::clone(self);
+		let connection_manager = Arc::clone(connection_manager);
+		tokio::spawn(async move {
+			if let Err(error) = client.cache_variable_lease(&connection_manager).await {
+				log_warn!(client.logger, "Failed refilling LSPS2 payment lease: {}", error);
+			}
+		});
+	}
+
+	async fn cache_fixed_lease(
+		self: &Arc<Self>, amount_msat: u64, connection_manager: &Arc<ConnectionManager<L>>,
+	) -> Result<(), Error> {
+		let request_lock = self
+			.pending_lease_request_state
+			.lock()
+			.expect("lock")
+			.request_lock(LeaseRequestKey::Fixed(amount_msat));
+		let _request_guard = request_lock.lock().await;
+		if self
+			.lease_state
+			.lock()
+			.expect("lock")
+			.has_fixed_amount(amount_msat, self.config.lsps2_max_total_lsp_fee_limit_msat)
+		{
+			return Ok(());
+		}
+		self.negotiate_fixed_lease(amount_msat, connection_manager).await?;
+		Ok(())
+	}
+
+	async fn cache_variable_lease(
+		self: &Arc<Self>, connection_manager: &Arc<ConnectionManager<L>>,
+	) -> Result<(), Error> {
+		let request_lock = self
+			.pending_lease_request_state
+			.lock()
+			.expect("lock")
+			.request_lock(LeaseRequestKey::Variable);
+		let _request_guard = request_lock.lock().await;
+		if self
+			.lease_state
+			.lock()
+			.expect("lock")
+			.has_variable_amount(self.config.lsps2_max_total_lsp_fee_limit_msat)
+		{
+			return Ok(());
+		}
+		self.negotiate_variable_lease(connection_manager).await?;
+		Ok(())
 	}
 
 	async fn gather_lsps2_offers(

src/liquidity/client/lsps2/state.rs

@@ -406,6 +406,21 @@ impl LSPS2LeaseState {
 		self.leases.remove(&id).map(|lease| (lease, fee_msat))
 	}
 
+	pub(crate) fn has_fixed_amount(&self, amount_msat: u64, max_fee_msat: Option<u64>) -> bool {
+		self.leases
+			.values()
+			.filter(|lease| lease.payment_size_msat == Some(amount_msat))
+			.filter(|lease| is_lease_usable(lease))
+			.filter_map(|lease| {
+				compute_opening_fee(
+					amount_msat,
+					lease.params.min_fee_msat,
+					lease.params.proportional as u64,
+				)
+			})
+			.any(|fee_msat| max_fee_msat.map_or(true, |max| fee_msat <= max))
+	}
+
 	/// Selects and removes a variable-amount lease in one operation.
 	pub(crate) fn variable_amount(
 		&mut self, max_total_fee_msat: Option<u64>,
@@ -423,6 +438,14 @@ impl LSPS2LeaseState {
 		self.leases.remove(&id).map(|lease| (lease, proportional_fee))
 	}
 
+	pub(crate) fn has_variable_amount(&self, max_total_fee_msat: Option<u64>) -> bool {
+		self.leases
+			.values()
+			.filter(|lease| lease.payment_size_msat.is_none())
+			.filter(|lease| is_lease_usable(lease))
+			.any(|lease| max_total_fee_msat.map_or(true, |max| lease.params.min_fee_msat <= max))
+	}
+
 	pub(crate) fn prune(&mut self) {
 		self.leases.retain(|_, lease| is_lease_usable(lease));
 	}
@@ -572,6 +595,20 @@ mod tests {
 		assert_eq!(state.variable_amount(Some(50)).unwrap().0.id, variable.id);
 	}
 
+	#[test]
+	fn detects_cached_leases_for_refill() {
+		let valid_until = now_secs() + MIN_LEASE_REMAINING_SECS + 60;
+		let fixed = lease(2, 46, 100, Some(1_000), valid_until);
+		let variable = lease(3, 47, 50, None, valid_until);
+		let state = LSPS2LeaseState::from_leases(vec![fixed, variable]);
+
+		assert!(state.has_fixed_amount(1_000, Some(100)));
+		assert!(!state.has_fixed_amount(1_000, Some(99)));
+		assert!(!state.has_fixed_amount(2_000, None));
+		assert!(state.has_variable_amount(Some(50)));
+		assert!(!state.has_variable_amount(Some(49)));
+	}
+
 	fn cache_target(
 		id: LeaseCacheTargetId, absolute_expiry: Option<u64>, last_accessed: u64,
 	) -> LeaseCacheTarget {