Fail on unspecified run mode

src/main.rs

@@ -12,6 +12,7 @@ use std::str::FromStr;
 
 #[derive(PartialEq)]
 enum OperationMode {
+    None,
     Exporter,
     Validator,
 }
@@ -29,9 +30,9 @@ fn parse_nix_store_path(path: std::path::PathBuf) -> Result<(String, String), St
 #[tokio::main]
 async fn main() {
     let mut listen = String::from("[::]:9152");
-    let mut operationmode = OperationMode::Exporter;
+    let mut operationmode = OperationMode::None;
     let mut args = std::env::args();
-    args.next();
+    let name = args.next().unwrap();
     loop {
         let arg = if let Some(arg) = args.next() {
             arg
@@ -69,7 +70,10 @@ async fn main() {
     } else if operationmode == OperationMode::Validator {
         println!("Running NixOS Exporter in Validator mode");
         app = app.route("/metrics", get(check));
-    }
+    } else {
+        println!("Run mode not specified, do {} --help", name);
+        std::process::exit(1);
+    };
 
     let addr = SocketAddr::from_str(&listen).unwrap();
     println!("listening on http://{}", addr);