tsweb: JSONHandler: supports HTTPError

Signed-off-by: Zijie Lu <zijie@tailscale.com>

tsweb/jsonhandler.go

@@ -102,26 +102,33 @@ func JSONHandler(fn interface{}) http.Handler {
 			panic("JSONHandler: number of input parameter should be 2 or 3")
 		}
 
+		var e reflect.Value
 		switch len(vs) {
 		case 1:
 			// todo support other error types
-			if vs[0].IsNil() {
+			if vs[0].IsZero() {
 				writeResponse(w, http.StatusOK, responseSuccess(nil))
-			} else {
+				return
-				err := vs[0].Interface().(error)
-				writeResponse(w, http.StatusBadRequest, responseError(err.Error()))
 			}
+			e = vs[0]
 		case 2:
-			if vs[1].IsNil() {
+			if vs[1].IsZero() {
-				if !vs[0].IsNil() {
+				if !vs[0].IsZero() {
 					writeResponse(w, http.StatusOK, responseSuccess(vs[0].Interface()))
 				}
-			} else {
+				return
-				err := vs[1].Interface().(error)
-				writeResponse(w, http.StatusBadRequest, responseError(err.Error()))
 			}
+			e = vs[1]
 		default:
 			panic("JSONHandler: number of return values should be 1 or 2")
 		}
+
+		if e.Type().AssignableTo(reflect.TypeOf(HTTPError{})) {
+			err := e.Interface().(HTTPError)
+			writeResponse(w, err.Code, responseError(err.Error()))
+		} else {
+			err := e.Interface().(error)
+			writeResponse(w, http.StatusBadRequest, responseError(err.Error()))
+		}
 	})
 }

tsweb/jsonhandler_test.go

@@ -59,6 +59,19 @@ func TestNewJSONHandler(t *testing.T) {
 		checkStatus(w, "success")
 	})
 
+	t.Run("2 1 HTTPError", func(t *testing.T) {
+		h := JSONHandler(func(w http.ResponseWriter, r *http.Request) HTTPError {
+			return Error(http.StatusForbidden, "forbidden", nil)
+		})
+
+		w := httptest.NewRecorder()
+		r := httptest.NewRequest("GET", "/", nil)
+		h.ServeHTTP(w, r)
+		if w.Code != http.StatusForbidden {
+			t.Fatalf("wrong code: %d %d", w.Code, http.StatusForbidden)
+		}
+	})
+
 	// 2 2
 	h22 := JSONHandler(func(w http.ResponseWriter, r *http.Request) (*Data, error) {
 		return &Data{Name: "tailscale"}, nil