text: # Copyright 2019 The TensorFlow Authors. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # ==============================================================================
  """Redirect from an empty path to the virtual application root.
  
  Sometimes, middleware transformations will make the path empty: for
  example, navigating to "/foo" (no trailing slash) when the path prefix
  is exactly "/foo". In such cases, relative links on the frontend would
  break. Instead of handling this special case in each relevant
  middleware, we install a top-level redirect handler from "" to "/".
  
  This middleware respects `SCRIPT_NAME` as described by the WSGI spec. If
  `SCRIPT_NAME` is set to "/foo", then an empty `PATH_INFO` corresponds to
  the actual path "/foo", and so will be redirected to "/foo/".
  """
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  
  class EmptyPathRedirectMiddleware(object):
    """WSGI middleware to redirect from "" to "/"."""
  
    def __init__(self, application):
      """Initializes this middleware.
  
      Args:
        application: The WSGI application to wrap (see PEP 3333).
      """
      self._application = application
  
    def __call__(self, environ, start_response):
      path = environ.get("PATH_INFO", "")
      if path:
        return self._application(environ, start_response)
      location = environ.get("SCRIPT_NAME", "") + "/"
      start_response("301 Moved Permanently", [("Location", location)])
      return []
  