Fix the CORSMethodMiddleware bug with subrouters

* Adds a test case for the repro given in issue #534
* Fixes the logic in CORSMethodMiddleware to handle matching routes
better

middleware.go

@@ -58,22 +58,17 @@ func CORSMethodMiddleware(r *Router) MiddlewareFunc {
 func getAllMethodsForRoute(r *Router, req *http.Request) ([]string, error) {
 	var allMethods []string
 
-	err := r.Walk(func(route *Route, _ *Router, _ []*Route) error {
-		for _, m := range route.matchers {
-			if _, ok := m.(*routeRegexp); ok {
-				if m.Match(req, &RouteMatch{}) {
-					methods, err := route.GetMethods()
-					if err != nil {
-						return err
-					}
-
-					allMethods = append(allMethods, methods...)
-				}
-				break
+	for _, route := range r.routes {
+		var match RouteMatch
+		if route.Match(req, &match) || match.MatchErr == ErrMethodMismatch {
+			methods, err := route.GetMethods()
+			if err != nil {
+				return nil, err
 			}
+
+			allMethods = append(allMethods, methods...)
 		}
-		return nil
-	})
+	}
 
-	return allMethods, err
+	return allMethods, nil
 }

middleware_test.go

@@ -478,6 +478,26 @@ func TestCORSMethodMiddleware(t *testing.T) {
 	}
 }
 
+func TestCORSMethodMiddlewareSubrouter(t *testing.T) {
+	router := NewRouter().StrictSlash(true)
+
+	subrouter := router.PathPrefix("/test").Subrouter()
+	subrouter.HandleFunc("/hello", stringHandler("a")).Methods(http.MethodGet, http.MethodOptions, http.MethodPost)
+	subrouter.HandleFunc("/hello/{name}", stringHandler("b")).Methods(http.MethodGet, http.MethodOptions)
+
+	subrouter.Use(CORSMethodMiddleware(subrouter))
+
+	rw := NewRecorder()
+	req := newRequest("GET", "/test/hello/asdf")
+	router.ServeHTTP(rw, req)
+
+	actualMethods := rw.Header().Get("Access-Control-Allow-Methods")
+	expectedMethods := "GET,OPTIONS"
+	if actualMethods != expectedMethods {
+		t.Fatalf("expected methods %q but got: %q", expectedMethods, actualMethods)
+	}
+}
+
 func TestMiddlewareOnMultiSubrouter(t *testing.T) {
 	first := "first"
 	second := "second"