middleware.rst

.. slideconf::
   :theme: single-level

Understanding Middleware

Overview of Middleware

• Lightweight "plug-ins" for Django
• Allows modifying the Request or Response, or mutating the View parameters
• Defined as a sequence (tuple) of classes in settings

.. testcode::

  MIDDLEWARE_CLASSES = (
      'django.middleware.common.CommonMiddleware',
      'django.contrib.sessions.middleware.SessionMiddleware',
      'django.middleware.csrf.CsrfViewMiddleware',
      'django.contrib.auth.middleware.AuthenticationMiddleware',
      'django.contrib.messages.middleware.MessageMiddleware',
  )

Middleware Hooks

• Middleware classes have hooks for processing:
  • request
  • response
  • view
  • template_response
  • exception
• Individual middleware may implement some or all

Typical Uses

• Sessions
• Authentication
• CSRF Protection
• GZipping Content

Middleware Example

.. testcode::

   class LocaleMiddleware(object):

       def process_request(self, request):

           if 'locale' in request.cookies:
               request.locale = request.cookies.locale
           else:
               request.locale = None

       def process_response(self, request, response):

           if getattr(request, 'locale', False):
               response.cookies['locale'] = request.locale

Request Middleware

• On ingress, middleware is executed in order
• Request middleware returns None to continue processing
• Returning an HttpResponse short circuits additional middleware

Response Middleware

• On egress, middleware is executed in reverse order
• Response middleware is executed even if corresponding request middleware not executed

Writing Your Own

• Simple Python Classes
• Can implement all or part of the interface
• Middleware is long-lived
• The place for storing request-specific information is cunningly named request

WSGI Middleware

• WSGI also defines a middleware interface
• The two have similar functions, but are not the same