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

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§

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