Allow disabling the scorer with an empty URL

Treat an explicitly empty pathfinding scores source as absent so users
can opt out of the mainnet default through config inputs.

This commit was prepared with OpenAI Codex.

Author: benthecarman

contrib/ldk-server-config.toml

@@ -5,7 +5,7 @@ listening_addresses = ["localhost:9735"]      # Lightning node listening address
 #announcement_addresses = ["54.3.7.81:9735"]  # Lightning node announcement addresses
 #grpc_service_address = "127.0.0.1:3536"      # LDK Server gRPC address (optional, defaults to 127.0.0.1:3536)
 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)
+#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"
 

ldk-server/src/util/config.rs

@@ -485,6 +485,7 @@ impl ConfigBuilder {
 		let lsps2_service_config = None;
 
 		let pathfinding_scores_source_url = match self.pathfinding_scores_source_url {
+			Some(url) if url.is_empty() => None,
 			Some(url) => Some(url),
 			None if network == Network::Bitcoin => {
 				Some(DEFAULT_PATHFINDING_SCORES_SOURCE_URL.to_string())
@@ -968,7 +969,7 @@ pub struct ArgsConfig {
 	#[arg(
 		long,
 		env = "LDK_SERVER_PATHFINDING_SCORES_SOURCE_URL",
-		help = "The external scores source that is merged into the local scoring system to improve routing. Defaults to https://rapidsync.lightningdevkit.org/scoring/scorer.bin on mainnet."
+		help = "The external scores source that is merged into the local scoring system to improve routing. Defaults to https://rapidsync.lightningdevkit.org/scoring/scorer.bin on mainnet. Set to an empty string to disable."
 	)]
 	pathfinding_scores_source_url: Option<String>,
 
@@ -1547,6 +1548,26 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn test_empty_pathfinding_scores_source_url_disables_source() {
+		let storage_path = std::env::temp_dir();
+		let config_file_name = "test_empty_pathfinding_scores_source_url.toml";
+		let toml_config = DEFAULT_CONFIG.replace(
+			"alias = \"LDK Server\"",
+			"alias = \"LDK Server\"\npathfinding_scores_source_url = \"\"",
+		);
+		fs::write(storage_path.join(config_file_name), toml_config).unwrap();
+
+		let mut args_config = empty_args_config();
+		args_config.config_file =
+			Some(storage_path.join(config_file_name).to_string_lossy().to_string());
+		args_config.node_network = Some(Network::Bitcoin);
+
+		let config = load_config(&args_config).unwrap();
+
+		assert_eq!(config.pathfinding_scores_source_url, None);
+	}
+
 	#[test]
 	fn test_config_missing_fields_in_file() {
 		let storage_path = std::env::temp_dir();