server: use a command line parser

This commit adds a command line parser to the server. The parser is
useful to avoid crashing when trying to run a simple --help command and
also in the future when we will add more configuration options.

It will be really cool if the config file is optional and the user can
configure the server using the command line by appending all the
options to `ldk-server --option1 value1 --option2 value2`.

     Running `target/debug/ldk-server --help`
thread 'main' panicked at ldk-server/src/main.rs:30:56:
Invalid configuration file.: Custom { kind: NotFound, error: "Failed to read config file '--help': No such file or directory (os error 2)" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
[1]    750067 IOT instruction (core dumped)  cargo run --bin ldk-server -- --help

Signed-off-by: Vincenzo Palazzo <[email protected]>

ldk-server/Cargo.toml

@@ -16,6 +16,7 @@ ldk-server-protos = { path = "../ldk-server-protos" }
 bytes = "1.4.0"
 hex = { package = "hex-conservative", version = "0.2.1", default-features = false }
 rusqlite = { version = "0.28.0", features = ["bundled"] }
+clap = { version = "4.0.5", default-features = false, features = ["derive", "std", "error-context", "suggestions", "help"] }
 
 [dev-dependencies]
 rand = "0.8.5"

ldk-server/src/args.rs

@@ -0,0 +1,7 @@
+use clap::Parser;
+
+#[derive(Parser, Debug)]
+pub struct Cli {
+	#[arg(short, long)]
+	pub config: Option<String>,
+}

ldk-server/src/main.rs

@@ -1,10 +1,12 @@
 mod api;
+mod args;
 mod io;
 mod service;
 mod util;
 
 use crate::service::NodeService;
 
+use clap::Parser;
 use ldk_node::{Builder, Event, LogLevel};
 
 use tokio::net::TcpListener;
@@ -18,16 +20,18 @@ use ldk_node::config::Config;
 use std::path::Path;
 use std::sync::Arc;
 
-fn main() {
-	let args: Vec<String> = std::env::args().collect();
+use args::Cli;
 
-	if args.len() < 2 {
-		eprintln!("Usage: {} config_path", args[0]);
-		std::process::exit(-1);
-	}
+fn main() {
+	let args = Cli::parse();
 
+	#[allow(deprecated)]
+	let config_file = args.config.unwrap_or_else(|| {
+		// FIXME: change this with a better default path
+		std::env::home_dir().unwrap().join("ldk-server.config").to_str().unwrap().to_string()
+	});
 	let mut ldk_node_config = Config::default();
-	let config_file = load_config(Path::new(&args[1])).expect("Invalid configuration file.");
+	let config_file = load_config(Path::new(&config_file)).expect("Invalid configuration file.");
 
 	ldk_node_config.log_level = LogLevel::Trace;
 	ldk_node_config.storage_dir_path = config_file.storage_dir_path;