feat: add default rest_service_address

Make `rest_service_address` optional in the config file, defaulting to
`127.0.0.1:3536` when not specified. This reduces required config for
most users who don't need a custom REST address.

Closes: #160

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vincenzopalazzo

ldk-server/ldk-server.config

@@ -5,8 +5,9 @@
   // The Bitcoin network to use.
   "network": "regtest",
 
-  // The address on which LDK Server will accept incoming requests.
-  "rest_service_address": "127.0.0.1:3002",
+  // (Optional) The address on which LDK Server will accept incoming requests.
+  // Defaults to 127.0.0.1:3536 if not specified.
+  // "rest_service_address": "127.0.0.1:3536",
 
   // The path where the underlying LDK and BDK persist their data.
   "storage_dir_path": "/tmp/ldk-server/",

ldk-server/src/util/config.rs

@@ -57,18 +57,25 @@ impl TryFrom<JsonConfig> for Config {
 	}
 }
 
+const DEFAULT_REST_SERVICE_ADDRESS: &str = "127.0.0.1:3536";
+
 /// Configuration loaded from a JSON file.
 #[derive(Deserialize, Serialize)]
 pub struct JsonConfig {
 	listening_address: String,
 	network: Network,
+	#[serde(default = "default_rest_service_address")]
 	rest_service_address: String,
 	storage_dir_path: String,
 	bitcoind_rpc_address: String,
 	bitcoind_rpc_user: String,
 	bitcoind_rpc_password: String,
 }
 
+fn default_rest_service_address() -> String {
+	DEFAULT_REST_SERVICE_ADDRESS.to_string()
+}
+
 /// Loads the configuration from a JSON file at the given path.
 pub fn load_config<P: AsRef<Path>>(config_path: P) -> io::Result<Config> {
 	let file_contents = fs::read_to_string(config_path.as_ref()).map_err(|e| {
@@ -133,4 +140,34 @@ mod tests {
 			}
 		)
 	}
+
+	#[test]
+	fn test_default_rest_service_address() {
+		let storage_path = std::env::temp_dir();
+		let config_file_name = "config_no_rest_addr.json";
+
+		let json_config = r#"{
+			"listening_address": "localhost:3001",
+			"network": "regtest",
+			"storage_dir_path": "/tmp",
+			"bitcoind_rpc_address":"127.0.0.1:8332",
+			"bitcoind_rpc_user": "bitcoind-testuser",
+			"bitcoind_rpc_password": "bitcoind-testpassword"
+			}"#;
+
+		fs::write(storage_path.join(config_file_name), json_config).unwrap();
+
+		assert_eq!(
+			load_config(storage_path.join(config_file_name)).unwrap(),
+			Config {
+				listening_addr: SocketAddress::from_str("localhost:3001").unwrap(),
+				network: Network::Regtest,
+				rest_service_addr: SocketAddr::from_str("127.0.0.1:3536").unwrap(),
+				storage_dir_path: "/tmp".to_string(),
+				bitcoind_rpc_addr: SocketAddr::from_str("127.0.0.1:8332").unwrap(),
+				bitcoind_rpc_user: "bitcoind-testuser".to_string(),
+				bitcoind_rpc_password: "bitcoind-testpassword".to_string(),
+			}
+		)
+	}
 }