Set the content length automatically before calling wrap_file

flask/helpers.py

@@ -516,6 +516,7 @@ def send_file(filename_or_fp, mimetype=None, as_attachment=False,
         if file is None:
             file = open(filename, 'rb')
             mtime = os.path.getmtime(filename)
+        headers['Content-Length'] = os.path.getsize(filename)
         data = wrap_file(request.environ, file)
 
     rv = current_app.response_class(data, mimetype=mimetype, headers=headers,

flask/testsuite/basic.py

@@ -786,6 +786,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
 
     def test_static_files(self):
         app = flask.Flask(__name__)
+        app.testing = True
         rv = app.test_client().get('/static/index.html')
         self.assert_equal(rv.status_code, 200)
         self.assert_equal(rv.data.strip(), b'<h1>Hello World!</h1>')