bugfix/subrouter custom methodNotAllowed handler returning 404 (#509)

mux_test.go

@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"net/url"
 	"reflect"
@@ -2729,6 +2730,63 @@ func TestMethodNotAllowed(t *testing.T) {
 	}
 }
 
+type customMethodNotAllowedHandler struct {
+	msg string
+}
+
+func (h customMethodNotAllowedHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusMethodNotAllowed)
+	fmt.Fprint(w, h.msg)
+}
+
+func TestSubrouterCustomMethodNotAllowed(t *testing.T) {
+	handler := func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusOK) }
+
+	router := NewRouter()
+	router.HandleFunc("/test", handler).Methods(http.MethodGet)
+	router.MethodNotAllowedHandler = customMethodNotAllowedHandler{msg: "custom router handler"}
+
+	subrouter := router.PathPrefix("/sub").Subrouter()
+	subrouter.HandleFunc("/test", handler).Methods(http.MethodGet)
+	subrouter.MethodNotAllowedHandler = customMethodNotAllowedHandler{msg: "custom sub router handler"}
+
+	testCases := map[string]struct {
+		path   string
+		expMsg string
+	}{
+		"router method not allowed": {
+			path:   "/test",
+			expMsg: "custom router handler",
+		},
+		"subrouter method not allowed": {
+			path:   "/sub/test",
+			expMsg: "custom sub router handler",
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(tt *testing.T) {
+			w := NewRecorder()
+			req := newRequest(http.MethodPut, tc.path)
+
+			router.ServeHTTP(w, req)
+
+			if w.Code != 405 {
+				tt.Errorf("Expected status code 405 (got %d)", w.Code)
+			}
+
+			b, err := ioutil.ReadAll(w.Body)
+			if err != nil {
+				tt.Errorf("failed to read body: %v", err)
+			}
+
+			if string(b) != tc.expMsg {
+				tt.Errorf("expected msg %q, got %q", tc.expMsg, string(b))
+			}
+		})
+	}
+}
+
 func TestSubrouterNotFound(t *testing.T) {
 	handler := func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusOK) }
 	router := NewRouter()

route.go

@@ -74,7 +74,7 @@ func (r *Route) Match(req *http.Request, match *RouteMatch) bool {
 		return false
 	}
 
-	if match.MatchErr == ErrMethodMismatch {
+	if match.MatchErr == ErrMethodMismatch && r.handler != nil {
 		// We found a route which matches request method, clear MatchErr
 		match.MatchErr = nil
 		// Then override the mis-matched handler