Test that metrics label a request with an empty path as /

A request line such as GET http://pixa.example HTTP/1.1 leaves the
request's path empty; chi routes it as /, so its label is the / route's
pattern.

Model: opus-5-5

internal/middleware/middleware_internal_test.go

@@ -227,10 +227,12 @@ func TestMetricsRecordsServedRequest(t *testing.T) {
 // each request with the pattern of the route that answers it, never with its
 // path: two paths one route answers share that route's pattern, and requests
 // no route answers, a 404 or a 405, share "unmatched", among them requests for
-// the path the subrouter is mounted at, /v1 and /v1/. With a label per path,
+// the path the subrouter is mounted at, /v1 and /v1/. A request with an empty
-// any client could add series to the registry without limit. The middleware
+// path is answered by the / route, as chi routes it as /, and is labelled /.
-// registers with a registry of its own here, as another test in this package
+// With a label per path, any client could add series to the registry without
-// registers with Prometheus' default registry, which can be done only once.
+// limit. The middleware registers with a registry of its own here, as another
+// test in this package registers with Prometheus' default registry, which can
+// be done only once.
 func TestMetricsLabelsRequestsByRoute(t *testing.T) {
 	t.Parallel()
 
@@ -244,6 +246,9 @@ func TestMetricsLabelsRequestsByRoute(t *testing.T) {
 	// The image route is in a subrouter, as in pixa's router.
 	router := chi.NewRouter()
 	router.Use(mw.Metrics())
+	router.Get("/", func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
 	router.Route("/v1", func(r chi.Router) {
 		r.Get("/image/*", func(w http.ResponseWriter, _ *http.Request) {
 			w.WriteHeader(http.StatusOK)
@@ -258,15 +263,21 @@ func TestMetricsLabelsRequestsByRoute(t *testing.T) {
 		{http.MethodGet, "/v1"},
 		{http.MethodGet, "/v1/"},
 		{http.MethodPost, "/v1/image/a.example.com/one.jpg/1x1.png"},
+		// The request line GET http://pixa.example HTTP/1.1 leaves both
+		// r.URL.Path and r.URL.RawPath empty.
+		{http.MethodGet, "http://pixa.example"},
 	} {
-		router.ServeHTTP(httptest.NewRecorder(), httptest.NewRequestWithContext(
+		r := httptest.NewRequestWithContext(
-			t.Context(), req.method, req.path, nil))
+			t.Context(), req.method, req.path, nil)
+		t.Logf("%s %s: r.URL.Path %q, r.URL.RawPath %q",
+			req.method, req.path, r.URL.Path, r.URL.RawPath)
+		router.ServeHTTP(httptest.NewRecorder(), r)
 	}
 
 	got := requestCountsByHandler(t, registry)
 	t.Logf("requests counted by handler label: %v", got)
 
-	want := map[string]uint64{"/v1/image/*": 2, "unmatched": 5}
+	want := map[string]uint64{"/": 1, "/v1/image/*": 2, "unmatched": 5}
 	if !maps.Equal(got, want) {
 		t.Errorf("requests counted by handler label = %v, want %v", got, want)
 	}