==========

Middleware

==========

.. module:: django.middleware

   :synopsis: Django's built-in middleware classes.

This document explains all middleware components that come with Django. For

information on how how to use them and how to write your own middleware, see

the :doc:`middleware usage guide </topics/http/middleware>`.

Available middleware

====================

Cache middleware

----------------

.. module:: django.middleware.cache

   :synopsis: Middleware for the site-wide cache.

.. class:: UpdateCacheMiddleware

.. class:: FetchFromCacheMiddleware

Enable the site-wide cache. If these are enabled, each Django-powered page will

be cached for as long as the :setting:`CACHE_MIDDLEWARE_SECONDS` setting

defines. See the :doc:`cache documentation </topics/cache>`.

"Common" middleware

-------------------

.. module:: django.middleware.common

   :synopsis: Middleware adding "common" conveniences for perfectionists.

.. class:: CommonMiddleware

Adds a few conveniences for perfectionists:

    * Forbids access to user agents in the :setting:`DISALLOWED_USER_AGENTS`

      setting, which should be a list of strings.

    * Performs URL rewriting based on the :setting:`APPEND_SLASH` and

      :setting:`PREPEND_WWW` settings.

      If :setting:`APPEND_SLASH` is ``True`` and the initial URL doesn't end

      with a slash, and it is not found in the URLconf, then a new URL is

      formed by appending a slash at the end. If this new URL is found in the

      URLconf, then Django redirects the request to this new URL. Otherwise,

      the initial URL is processed as usual.

      For example, ``foo.com/bar`` will be redirected to ``foo.com/bar/`` if

      you don't have a valid URL pattern for ``foo.com/bar`` but *do* have a

      valid pattern for ``foo.com/bar/``.

      .. versionchanged:: 1.0

         The behavior of :setting:`APPEND_SLASH` has changed slightly in this

         version. It didn't used to check whether the pattern was matched in

         the URLconf.

      If :setting:`PREPEND_WWW` is ``True``, URLs that lack a leading "www."

      will be redirected to the same URL with a leading "www."

      Both of these options are meant to normalize URLs. The philosophy is that

      each URL should exist in one, and only one, place. Technically a URL

      ``foo.com/bar`` is distinct from ``foo.com/bar/`` -- a search-engine

      indexer would treat them as separate URLs -- so it's best practice to

      normalize URLs.

    * Sends broken link notification emails to :setting:`MANAGERS` if

      :setting:`SEND_BROKEN_LINK_EMAILS` is set to ``True``.

    * Handles ETags based on the :setting:`USE_ETAGS` setting. If

      :setting:`USE_ETAGS` is set to ``True``, Django will calculate an ETag

      for each request by MD5-hashing the page content, and it'll take care of

      sending ``Not Modified`` responses, if appropriate.

View metadata middleware

------------------------

.. module:: django.middleware.doc

   :synopsis: Middleware to help your app self-document.

.. class:: XViewMiddleware

Sends custom ``X-View`` HTTP headers to HEAD requests that come from IP

addresses defined in the :setting:`INTERNAL_IPS` setting. This is used by

Django's :doc:`automatic documentation system </ref/contrib/admin/admindocs>`.

GZIP middleware

---------------

.. module:: django.middleware.gzip

   :synopsis: Middleware to serve gziped content for performance.

.. class:: GZipMiddleware

Compresses content for browsers that understand gzip compression (all modern

browsers).

It is suggested to place this first in the middleware list, so that the

compression of the response content is the last thing that happens. Will not

compress content bodies less than 200 bytes long, when the response code is

something other than 200, JavaScript files (for IE compatibility), or

responses that have the ``Content-Encoding`` header already specified.

Conditional GET middleware

--------------------------

.. module:: django.middleware.http

   :synopsis: Middleware handling advanced HTTP features.

.. class:: ConditionalGetMiddleware

Handles conditional GET operations. If the response has a ``ETag`` or

``Last-Modified`` header, and the request has ``If-None-Match`` or

``If-Modified-Since``, the response is replaced by an

:class:`~django.http.HttpNotModified`.

Also sets the ``Date`` and ``Content-Length`` response-headers.

Reverse proxy middleware

------------------------

.. class:: SetRemoteAddrFromForwardedFor

.. versionchanged:: 1.1

This middleware was removed in Django 1.1. See :ref:`the release notes

<removed-setremoteaddrfromforwardedfor-middleware>` for details.

Locale middleware

-----------------

.. module:: django.middleware.locale

   :synopsis: Middleware to enable language selection based on the request.

.. class:: LocaleMiddleware

Enables language selection based on data from the request. It customizes

content for each user. See the :doc:`internationalization documentation

</topics/i18n/index>`.

Message middleware

------------------

.. module:: django.contrib.messages.middleware

   :synopsis: Message middleware.

.. class:: MessageMiddleware

.. versionadded:: 1.2

   ``MessageMiddleware`` was added.

Enables cookie- and session-based message support. See the

:doc:`messages documentation </ref/contrib/messages>`.

Session middleware

------------------

.. module:: django.contrib.sessions.middleware

   :synopsis: Session middleware.

.. class:: SessionMiddleware

Enables session support. See the :doc:`session documentation

</topics/http/sessions>`.

Authentication middleware

-------------------------

.. module:: django.contrib.auth.middleware

  :synopsis: Authentication middleware.

.. class:: AuthenticationMiddleware

Adds the ``user`` attribute, representing the currently-logged-in user, to

every incoming ``HttpRequest`` object. See :doc:`Authentication in Web requests

</topics/auth>`.

CSRF protection middleware

--------------------------

.. module:: django.middleware.csrf

   :synopsis: Middleware adding protection against Cross Site Request

              Forgeries.

.. class:: CsrfMiddleware

.. versionadded:: 1.0

Adds protection against Cross Site Request Forgeries by adding hidden form

fields to POST forms and checking requests for the correct value. See the

:doc:`Cross Site Request Forgery protection documentation </ref/contrib/csrf>`.

Transaction middleware

----------------------

.. module:: django.middleware.transaction

   :synopsis: Middleware binding a database transaction to each Web request.

.. class:: TransactionMiddleware

Binds commit and rollback to the request/response phase. If a view function

runs successfully, a commit is done. If it fails with an exception, a rollback

is done.

The order of this middleware in the stack is important: middleware modules

running outside of it run with commit-on-save - the default Django behavior.

Middleware modules running inside it (coming later in the stack) will be under

the same transaction control as the view functions.

See the :doc:`transaction management documentation </topics/db/transactions>`.