Expose zero-fee commitment channel configuration

This setting was recently introduced in LDK-node, we wire it to the
different configuration interfaces of LDK-server.

Co-Authored-By: Codex

Author: tankyleo

contrib/ldk-server-config.toml

@@ -8,6 +8,7 @@ alias = "ldk_server"                          # Lightning node alias
 #pathfinding_scores_source_url = "https://rapidsync.lightningdevkit.org/scoring/scorer.bin"  # External pathfinding scores source (optional, defaults to this URL on mainnet; set to "" to disable)
 #rgs_server_url = "https://rapidsync.lightningdevkit.org/snapshot/v2/"  # Optional: RGS URL for rapid gossip sync
 #async_payments_role = "client"               # Optional async payments role: "client" or "server"
+#enable_zero_fee_commitments = false          # Enable zero-fee commitment channels (default: false)
 
 # Background probing service (optional)
 # CAUTION: Probes send real HTLCs and can lock outbound liquidity until they time out.

docs/configuration.md

@@ -52,13 +52,18 @@ on macOS).
 
 Core node settings: which Bitcoin network to use, Lightning peer listening and announcement
 addresses, the gRPC bind address, node alias, optional Rapid Gossip Sync / pathfinding
-scores URLs, and the async payments role.
+scores URLs, the async payments role, and zero-fee commitment channels.
 
 Set `async_payments_role = "client"` to ask peers to hold HTLCs where possible, allowing
 this node to go offline. Set `async_payments_role = "server"` to hold async payment HTLCs
 and onion messages for peers. The server role requires an announceable node configuration.
 Leave the field unset to disable async payments.
 
+Set `enable_zero_fee_commitments = true` to prefer zero-fee commitment channels,
+falling back to other channel types supported by the peer. Enabling this setting requires a chain
+source that supports Bitcoin Core's `submitpackage` RPC, and relays TRUC, P2A, and ephemeral
+dust. The default is `false`.
+
 ### `[probing]`
 
 Enables LDK Node's background probing service to train the payment scorer with current

ldk-server/src/main.rs

@@ -156,6 +156,8 @@ fn main() {
 	ldk_node_config.announcement_addresses = config_file.announcement_addrs;
 	ldk_node_config.network = config_file.network;
 	ldk_node_config.hrn_config = config_file.hrn_config;
+	ldk_node_config.anchor_channels_config.enable_zero_fee_commitments =
+		config_file.enable_zero_fee_commitments;
 
 	let mut builder = Builder::from_config(ldk_node_config);
 	builder.set_log_facade_logger();

ldk-server/src/util/config.rs

@@ -70,6 +70,7 @@ pub struct Config {
 	pub pathfinding_scores_source_url: Option<String>,
 	pub probing_config: Option<ProbingConfig>,
 	pub async_payments_role: Option<AsyncPaymentsRole>,
+	pub enable_zero_fee_commitments: bool,
 	pub metrics_enabled: bool,
 	pub poll_metrics_interval: Option<u64>,
 	pub metrics_username: Option<String>,
@@ -144,6 +145,7 @@ struct ConfigBuilder {
 	pathfinding_scores_source_url: Option<String>,
 	probing: Option<ProbingTomlConfig>,
 	async_payments_role: Option<String>,
+	enable_zero_fee_commitments: Option<bool>,
 	metrics_enabled: Option<bool>,
 	poll_metrics_interval: Option<u64>,
 	metrics_username: Option<String>,
@@ -167,6 +169,8 @@ impl ConfigBuilder {
 				node.pathfinding_scores_source_url.or(self.pathfinding_scores_source_url.clone());
 			self.async_payments_role =
 				node.async_payments_role.or(self.async_payments_role.clone());
+			self.enable_zero_fee_commitments =
+				node.enable_zero_fee_commitments.or(self.enable_zero_fee_commitments);
 			self.rgs_server_url = node.rgs_server_url.or(self.rgs_server_url.clone());
 		}
 
@@ -286,6 +290,10 @@ impl ConfigBuilder {
 			self.async_payments_role = Some(async_payments_role.clone());
 		}
 
+		if let Some(enable_zero_fee_commitments) = args.node_enable_zero_fee_commitments {
+			self.enable_zero_fee_commitments = Some(enable_zero_fee_commitments);
+		}
+
 		if args.has_probing_options() {
 			let probing = self.probing.get_or_insert_with(ProbingTomlConfig::default);
 			if let Some(probing_strategy) = &args.probing_strategy {
@@ -595,6 +603,7 @@ impl ConfigBuilder {
 			pathfinding_scores_source_url,
 			probing_config,
 			async_payments_role,
+			enable_zero_fee_commitments: self.enable_zero_fee_commitments.unwrap_or(false),
 			metrics_enabled,
 			poll_metrics_interval,
 			metrics_username,
@@ -633,6 +642,7 @@ struct NodeConfig {
 	alias: Option<String>,
 	pathfinding_scores_source_url: Option<String>,
 	async_payments_role: Option<String>,
+	enable_zero_fee_commitments: Option<bool>,
 	rgs_server_url: Option<String>,
 }
 
@@ -1110,6 +1120,13 @@ pub struct ArgsConfig {
 	)]
 	node_async_payments_role: Option<String>,
 
+	#[arg(
+		long,
+		env = "LDK_SERVER_NODE_ENABLE_ZERO_FEE_COMMITMENTS",
+		help = "Whether to enable zero-fee commitment channels. Defaults to false."
+	)]
+	node_enable_zero_fee_commitments: Option<bool>,
+
 	#[arg(
 		long,
 		env = "LDK_SERVER_PROBING_STRATEGY",
@@ -1289,6 +1306,7 @@ mod tests {
 				alias = "LDK Server"
 				rgs_server_url = "https://rapidsync.lightningdevkit.org/snapshot/v2/"
 				async_payments_role = "client"
+				enable_zero_fee_commitments = true
 
 				[tls]
 				cert_path = "/path/to/tls.crt"
@@ -1348,6 +1366,7 @@ mod tests {
 			node_alias: Some(String::from("LDK Server CLI")),
 			pathfinding_scores_source_url: Some(String::from("https://example.com/")),
 			node_async_payments_role: Some(String::from("server")),
+			node_enable_zero_fee_commitments: Some(false),
 			probing_strategy: None,
 			probing_top_node_count: None,
 			probing_max_hops: None,
@@ -1383,6 +1402,7 @@ mod tests {
 			storage_dir_path: None,
 			pathfinding_scores_source_url: None,
 			node_async_payments_role: None,
+			node_enable_zero_fee_commitments: None,
 			probing_strategy: None,
 			probing_top_node_count: None,
 			probing_max_hops: None,
@@ -1497,6 +1517,7 @@ mod tests {
 			pathfinding_scores_source_url: None,
 			probing_config: None,
 			async_payments_role: Some(AsyncPaymentsRole::Client),
+			enable_zero_fee_commitments: true,
 			metrics_enabled: false,
 			poll_metrics_interval: None,
 			metrics_username: None,
@@ -1522,6 +1543,7 @@ mod tests {
 		assert_eq!(config.log_file_path, expected.log_file_path);
 		assert_eq!(config.pathfinding_scores_source_url, expected.pathfinding_scores_source_url);
 		assert!(matches!(config.async_payments_role, Some(AsyncPaymentsRole::Client)));
+		assert_eq!(config.enable_zero_fee_commitments, expected.enable_zero_fee_commitments);
 		assert_eq!(config.metrics_enabled, expected.metrics_enabled);
 		assert_eq!(config.tor_config, expected.tor_config);
 
@@ -1731,7 +1753,8 @@ mod tests {
 			"#;
 
 		fs::write(storage_path.join(config_file_name), toml_config).unwrap();
-		assert!(load_config(&args_config).is_ok());
+		let config = load_config(&args_config).unwrap();
+		assert!(!config.enable_zero_fee_commitments);
 	}
 
 	#[test]
@@ -1939,6 +1962,7 @@ mod tests {
 			pathfinding_scores_source_url: Some("https://example.com/".to_string()),
 			probing_config: None,
 			async_payments_role: Some(AsyncPaymentsRole::Server),
+			enable_zero_fee_commitments: false,
 			metrics_enabled: false,
 			poll_metrics_interval: None,
 			metrics_username: None,
@@ -1961,6 +1985,7 @@ mod tests {
 		assert!(config.lsps2_service_config.is_none());
 		assert_eq!(config.pathfinding_scores_source_url, expected.pathfinding_scores_source_url);
 		assert!(matches!(config.async_payments_role, Some(AsyncPaymentsRole::Server)));
+		assert_eq!(config.enable_zero_fee_commitments, expected.enable_zero_fee_commitments);
 		assert_eq!(config.metrics_enabled, expected.metrics_enabled);
 		assert_eq!(config.tor_config, expected.tor_config);
 		assert_eq!(config.log_max_size_bytes, expected.log_max_size_bytes);
@@ -2059,6 +2084,7 @@ mod tests {
 			pathfinding_scores_source_url: Some("https://example.com/".to_string()),
 			probing_config: None,
 			async_payments_role: Some(AsyncPaymentsRole::Server),
+			enable_zero_fee_commitments: false,
 			metrics_enabled: false,
 			poll_metrics_interval: None,
 			metrics_username: None,
@@ -2085,6 +2111,7 @@ mod tests {
 		assert_eq!(config.lsps2_service_config.is_some(), expected.lsps2_service_config.is_some());
 		assert_eq!(config.pathfinding_scores_source_url, expected.pathfinding_scores_source_url);
 		assert!(matches!(config.async_payments_role, Some(AsyncPaymentsRole::Server)));
+		assert_eq!(config.enable_zero_fee_commitments, expected.enable_zero_fee_commitments);
 		assert_eq!(config.metrics_enabled, expected.metrics_enabled);
 		assert_eq!(config.tor_config, expected.tor_config);
 	}
@@ -2490,6 +2517,20 @@ mod tests {
 		assert_eq!(args_config.probing_cooldown_secs, Some(1800));
 	}
 
+	#[test]
+	fn test_accepts_zero_fee_commitments_arg() {
+		for (value, expected) in [("true", true), ("false", false)] {
+			let args_config = ArgsConfig::try_parse_from([
+				"ldk-server",
+				"--node-enable-zero-fee-commitments",
+				value,
+			])
+			.unwrap();
+
+			assert_eq!(args_config.node_enable_zero_fee_commitments, Some(expected));
+		}
+	}
+
 	#[test]
 	fn test_probing_args_override_strategy_specific_file_options() {
 		let mut builder = ConfigBuilder {