Add encoding parameter to open resource (#5526)

CHANGES.rst

@@ -3,7 +3,9 @@ Version 3.1.0
 
 -   Provide a configuration option to control automatic option
     responses. :pr:`5496`
-
+-   ``Flask.open_resource``/``open_instance_resource`` and
+    ``Blueprint.open_resource`` take an ``encoding`` parameter to use when
+    opening in text mode. It defaults to ``utf-8``. :issue:`5504`
 
 Version 3.0.3
 -------------

src/flask/app.py

@@ -320,9 +320,10 @@ class Flask(App):
             t.cast(str, self.static_folder), filename, max_age=max_age
         )
 
-    def open_resource(self, resource: str, mode: str = "rb") -> t.IO[t.AnyStr]:
-        """Open a resource file relative to :attr:`root_path` for
-        reading.
+    def open_resource(
+        self, resource: str, mode: str = "rb", encoding: str | None = None
+    ) -> t.IO[t.AnyStr]:
+        """Open a resource file relative to :attr:`root_path` for reading.
 
         For example, if the file ``schema.sql`` is next to the file
         ``app.py`` where the ``Flask`` app is defined, it can be opened
@@ -333,31 +334,46 @@ class Flask(App):
             with app.open_resource("schema.sql") as f:
                 conn.executescript(f.read())
 
-        :param resource: Path to the resource relative to
-            :attr:`root_path`.
-        :param mode: Open the file in this mode. Only reading is
-            supported, valid values are "r" (or "rt") and "rb".
-
-        Note this is a duplicate of the same method in the Flask
-        class.
+        :param resource: Path to the resource relative to :attr:`root_path`.
+        :param mode: Open the file in this mode. Only reading is supported,
+            valid values are ``"r"`` (or ``"rt"``) and ``"rb"``.
+        :param encoding: Open the file with this encoding when opening in text
+            mode. This is ignored when opening in binary mode.
 
+        .. versionchanged:: 3.1
+            Added the ``encoding`` parameter.
         """
         if mode not in {"r", "rt", "rb"}:
             raise ValueError("Resources can only be opened for reading.")
 
-        return open(os.path.join(self.root_path, resource), mode)
+        path = os.path.join(self.root_path, resource)
 
-    def open_instance_resource(self, resource: str, mode: str = "rb") -> t.IO[t.AnyStr]:
-        """Opens a resource from the application's instance folder
-        (:attr:`instance_path`).  Otherwise works like
-        :meth:`open_resource`.  Instance resources can also be opened for
-        writing.
+        if mode == "rb":
+            return open(path, mode)
 
-        :param resource: the name of the resource.  To access resources within
-                         subfolders use forward slashes as separator.
-        :param mode: resource file opening mode, default is 'rb'.
+        return open(path, mode, encoding=encoding)
+
+    def open_instance_resource(
+        self, resource: str, mode: str = "rb", encoding: str | None = "utf-8"
+    ) -> t.IO[t.AnyStr]:
+        """Open a resource file relative to the application's instance folder
+        :attr:`instance_path`. Unlike :meth:`open_resource`, files in the
+        instance folder can be opened for writing.
+
+        :param resource: Path to the resource relative to :attr:`instance_path`.
+        :param mode: Open the file in this mode.
+        :param encoding: Open the file with this encoding when opening in text
+            mode. This is ignored when opening in binary mode.
+
+        .. versionchanged:: 3.1
+            Added the ``encoding`` parameter.
         """
-        return open(os.path.join(self.instance_path, resource), mode)
+        path = os.path.join(self.instance_path, resource)
+
+        if "b" in mode:
+            return open(path, mode)
+
+        return open(path, mode, encoding=encoding)
 
     def create_jinja_environment(self) -> Environment:
         """Create the Jinja environment based on :attr:`jinja_options`

src/flask/blueprints.py

@@ -101,29 +101,28 @@ class Blueprint(SansioBlueprint):
             t.cast(str, self.static_folder), filename, max_age=max_age
         )
 
-    def open_resource(self, resource: str, mode: str = "rb") -> t.IO[t.AnyStr]:
-        """Open a resource file relative to :attr:`root_path` for
-        reading.
+    def open_resource(
+        self, resource: str, mode: str = "rb", encoding: str | None = "utf-8"
+    ) -> t.IO[t.AnyStr]:
+        """Open a resource file relative to :attr:`root_path` for reading. The
+        blueprint-relative equivalent of the app's :meth:`~.Flask.open_resource`
+        method.
 
-        For example, if the file ``schema.sql`` is next to the file
-        ``app.py`` where the ``Flask`` app is defined, it can be opened
-        with:
-
-        .. code-block:: python
-
-            with app.open_resource("schema.sql") as f:
-                conn.executescript(f.read())
-
-        :param resource: Path to the resource relative to
-            :attr:`root_path`.
-        :param mode: Open the file in this mode. Only reading is
-            supported, valid values are "r" (or "rt") and "rb".
-
-        Note this is a duplicate of the same method in the Flask
-        class.
+        :param resource: Path to the resource relative to :attr:`root_path`.
+        :param mode: Open the file in this mode. Only reading is supported,
+            valid values are ``"r"`` (or ``"rt"``) and ``"rb"``.
+        :param encoding: Open the file with this encoding when opening in text
+            mode. This is ignored when opening in binary mode.
 
+        .. versionchanged:: 3.1
+            Added the ``encoding`` parameter.
         """
         if mode not in {"r", "rt", "rb"}:
             raise ValueError("Resources can only be opened for reading.")
 
-        return open(os.path.join(self.root_path, resource), mode)
+        path = os.path.join(self.root_path, resource)
+
+        if mode == "rb":
+            return open(path, mode)
+
+        return open(path, mode, encoding=encoding)

tests/test_helpers.py

@@ -334,16 +334,27 @@ class TestHelpers:
             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", ("r", "rb", "rt"))
+def test_open_resource(mode):
+    app = flask.Flask(__name__)
 
-    @pytest.mark.parametrize("mode", ("w", "x", "a", "r+"))
-    def test_open_resource_exceptions(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())
 
-        with pytest.raises(ValueError):
-            app.open_resource("static/index.html", mode)
+
+@pytest.mark.parametrize("mode", ("w", "x", "a", "r+"))
+def test_open_resource_exceptions(mode):
+    app = flask.Flask(__name__)
+
+    with pytest.raises(ValueError):
+        app.open_resource("static/index.html", mode)
+
+
+@pytest.mark.parametrize("encoding", ("utf-8", "utf-16-le"))
+def test_open_resource_with_encoding(tmp_path, encoding):
+    app = flask.Flask(__name__, root_path=os.fspath(tmp_path))
+    (tmp_path / "test").write_text("test", encoding=encoding)
+
+    with app.open_resource("test", mode="rt", encoding=encoding) as f:
+        assert f.read() == "test"