404 on non-metrics endpoints on metrics server (#819)

rust/optics-base/src/metrics.rs

@@ -172,7 +172,9 @@ impl CoreMetrics {
                     port = port
                 );
                 tokio::spawn(async move {
-                    warp::serve(warp::path!("metrics").map(move || {
+                    warp::serve(
+                        warp::path!("metrics")
+                            .map(move || {
                                 warp::reply::with_header(
                                     self.gather().expect("failed to encode metrics"),
                                     "Content-Type",
@@ -181,7 +183,14 @@ impl CoreMetrics {
                                     // try text/plain to make web browsers happy.
                                     "text/plain; charset=utf-8",
                                 )
-                    }))
+                            })
+                            .or(warp::any().map(|| {
+                                warp::reply::with_status(
+                                    "go look at /metrics",
+                                    warp::http::StatusCode::NOT_FOUND,
+                                )
+                            })),
+                    )
                     .run(([0, 0, 0, 0], port))
                     .await;
                 })