Allow setting a ChannelConfig for LSPS2 JIT channels

When acting as an LSPS2 service, we'd previously always reuse the
node-wide configuration for the JIT channels we open towards clients,
while hard-coding their forwarding fees to zero.

Here, we add an optional channel_config field to LSPS2ServiceConfig
that allows configuring the JIT channels separately from regular
channels. If unset, we retain the previous behavior, i.e., zero
forwarding fees, as we're compensated via the channel opening fee.

This resolves the TODO to revisit the hard-coded zero-fee decision.

This change was developed with the assistance of AI tooling (Claude Code).

Author: IgnacioPorte

src/liquidity/service/lsps2.rs

@@ -22,6 +22,7 @@ use lightning_liquidity::lsps2::msgs::LSPS2RawOpeningFeeParams;
 use lightning_liquidity::lsps2::service::LSPS2ServiceConfig as LdkLSPS2ServiceConfig;
 use lightning_types::payment::PaymentHash;
 
+use crate::config::ChannelConfig;
 use crate::logger::{log_error, LdkLogger};
 use crate::types::{ChannelManager, KeysManager, LiquidityManager, PeerManager, Wallet};
 use crate::{total_anchor_channels_reserve_sats, Config};
@@ -106,6 +107,15 @@ pub struct LSPS2ServiceConfig {
 	///
 	/// [`Node::open_0reserve_channel`]: crate::Node::open_0reserve_channel
 	pub disable_client_reserve: bool,
+	/// The channel config we'll apply to the JIT channels we open to clients, allowing to
+	/// configure them separately from regular channels.
+	///
+	/// If set, the given config is used without modification. Note that this means any
+	/// forwarding fees configured here are charged in addition to the channel opening fee.
+	///
+	/// If set to `None`, we'll reuse the node-wide config, but override the forwarding fees
+	/// to be zero, as we're already compensated via the channel opening fee.
+	pub channel_config: Option<ChannelConfig>,
 }
 
 impl<L: Deref> LSPS2ServiceLiquiditySource<L>
@@ -487,11 +497,17 @@ where
 				debug_assert!(!config.channel_handshake_config.announce_for_forwarding);
 				debug_assert!(config.accept_forwards_to_priv_channels);
 
-				// We set the forwarding fee to 0 for now as we're getting paid by the channel fee.
-				//
-				// TODO: revisit this decision eventually.
-				config.channel_config.forwarding_fee_base_msat = 0;
-				config.channel_config.forwarding_fee_proportional_millionths = 0;
+				match service_config.channel_config {
+					Some(channel_config) => {
+						config.channel_config = channel_config.into();
+					},
+					None => {
+						// By default we set the forwarding fees to 0 as we're getting paid by the
+						// channel opening fee.
+						config.channel_config.forwarding_fee_base_msat = 0;
+						config.channel_config.forwarding_fee_proportional_millionths = 0;
+					},
+				}
 
 				let result = if service_config.disable_client_reserve {
 					self.channel_manager.create_channel_to_trusted_peer_0reserve(

tests/integration_tests_rust.rs

@@ -29,7 +29,9 @@ use common::{
 };
 use electrsd::corepc_node::{self, Node as BitcoinD};
 use electrsd::ElectrsD;
-use ldk_node::config::{AsyncPaymentsRole, EsploraSyncConfig, DEFAULT_FULL_SCAN_STOP_GAP};
+use ldk_node::config::{
+	AsyncPaymentsRole, ChannelConfig, EsploraSyncConfig, DEFAULT_FULL_SCAN_STOP_GAP,
+};
 use ldk_node::entropy::NodeEntropy;
 use ldk_node::liquidity::LSPS2ServiceConfig;
 use ldk_node::payment::{
@@ -2787,6 +2789,13 @@ async fn do_lsps2_client_service_integration(client_trusts_lsp: bool) {
 	// Setup three nodes: service, client, and payer
 	let channel_opening_fee_ppm = 10_000;
 	let channel_over_provisioning_ppm = 100_000;
+
+	let jit_channel_config = ChannelConfig {
+		forwarding_fee_proportional_millionths: 0,
+		forwarding_fee_base_msat: 0,
+		force_close_avoidance_max_fee_satoshis: 1337,
+		..Default::default()
+	};
 	let lsps2_service_config = LSPS2ServiceConfig {
 		require_token: None,
 		advertise_service: false,
@@ -2799,6 +2808,7 @@ async fn do_lsps2_client_service_integration(client_trusts_lsp: bool) {
 		max_client_to_self_delay: 1024,
 		client_trusts_lsp,
 		disable_client_reserve: false,
+		channel_config: Some(jit_channel_config),
 	};
 
 	let service_config = random_config(true);
@@ -2890,6 +2900,14 @@ async fn do_lsps2_client_service_integration(client_trusts_lsp: bool) {
 	let channel_value_sats = client_node.list_channels().first().unwrap().channel_value_sats;
 	assert_eq!(channel_value_sats, expected_channel_size_sat);
 
+	let jit_channel = service_node
+		.list_channels()
+		.into_iter()
+		.find(|c| c.counterparty.node_id == client_node.node_id())
+		.unwrap();
+	assert_eq!(jit_channel.config.force_close_avoidance_max_fee_satoshis, 1337);
+	assert_eq!(jit_channel.config.forwarding_fee_base_msat, 0);
+
 	println!("Generating regular invoice!");
 	let invoice_description =
 		Bolt11InvoiceDescription::Direct(Description::new(String::from("asdf")).unwrap()).into();
@@ -3118,6 +3136,7 @@ async fn lsps2_client_trusts_lsp() {
 		max_client_to_self_delay: 1024,
 		client_trusts_lsp: true,
 		disable_client_reserve: false,
+		channel_config: None,
 	};
 
 	let service_config = random_config(true);
@@ -3293,6 +3312,7 @@ async fn lsps2_lsp_trusts_client_but_client_does_not_claim() {
 		max_client_to_self_delay: 1024,
 		client_trusts_lsp: false,
 		disable_client_reserve: false,
+		channel_config: None,
 	};
 
 	let service_config = random_config(true);
@@ -4092,6 +4112,7 @@ async fn do_lsps2_multi_lsp_picks_cheapest(reverse_order: bool) {
 		max_client_to_self_delay: 1024,
 		client_trusts_lsp: true,
 		disable_client_reserve: false,
+		channel_config: None,
 	};
 	let cheap_node_config = random_config(true);
 	setup_builder!(cheap_builder, cheap_node_config.node_config);
@@ -4115,6 +4136,7 @@ async fn do_lsps2_multi_lsp_picks_cheapest(reverse_order: bool) {
 		max_client_to_self_delay: 1024,
 		client_trusts_lsp: true,
 		disable_client_reserve: false,
+		channel_config: None,
 	};
 	let expensive_node_config = random_config(true);
 	setup_builder!(expensive_builder, expensive_node_config.node_config);