Allow mode='rt' on open_resource() helper

flask/helpers.py

@@ -1055,6 +1055,8 @@ class _PackageBoundObject(object):
                          subfolders use forward slashes as separator.
         :param mode: resource file opening mode, default is 'rb'.
         """
+        if mode == 'rt':
+            mode = 'r'
         if mode not in ("r", "rb"):
             raise ValueError("Resources can only be opened for reading")
         return open(os.path.join(self.root_path, resource), mode)

tests/test_helpers.py

@@ -1014,6 +1014,7 @@ class TestSafeJoin(object):
                 print(flask.safe_join(*args))
 
 
+
 class TestHelpers(object):
     @pytest.mark.parametrize(
         "debug, expected_flag, expected_default_flag",
@@ -1060,3 +1061,27 @@ class TestHelpers(object):
             assert rv.status_code == 200
             assert rv.data == b"Hello"
             assert rv.mimetype == "text/html"
+
+    @pytest.mark.parametrize('mode', [
+        'r',
+        'rb',
+        'rt'
+    ])
+    def test_open_resource(self, mode):
+        app = flask.Flask(__name__)
+        with app.open_resource('static/index.html', mode) as f:
+            assert '<h1>Hello World!</h1>' in str(f.read())
+
+    @pytest.mark.parametrize('mode', [
+        'w',
+        'x',
+        'a',
+        'b',
+        't',
+        '+'
+    ])
+    def test_open_resource_exceptions(self, mode):
+        app = flask.Flask(__name__)
+        with pytest.raises(ValueError):
+            app.open_resource('static/index.html', mode)
+