mirror of
https://github.com/django/django.git
synced 2024-11-29 22:56:46 +01:00
291 lines
11 KiB
Plaintext
291 lines
11 KiB
Plaintext
==========
|
|
Middleware
|
|
==========
|
|
|
|
Middleware is a framework of hooks into Django's request/response processing.
|
|
It's a light, low-level "plugin" system for globally altering Django's input
|
|
or output.
|
|
|
|
Each middleware component is responsible for doing some specific function. For
|
|
example, Django includes a middleware component,
|
|
:class:`~django.middleware.transaction.TransactionMiddleware`, that wraps the
|
|
processing of each HTTP request in a database transaction.
|
|
|
|
This document explains how middleware works, how you activate middleware, and
|
|
how to write your own middleware. Django ships with some built-in middleware
|
|
you can use right out of the box. They're documented in the :doc:`built-in
|
|
middleware reference </ref/middleware>`.
|
|
|
|
Activating middleware
|
|
=====================
|
|
|
|
To activate a middleware component, add it to the
|
|
:setting:`MIDDLEWARE_CLASSES` tuple in your Django settings.
|
|
|
|
In :setting:`MIDDLEWARE_CLASSES`, each middleware component is represented by
|
|
a string: the full Python path to the middleware's class name. For example,
|
|
here's the default value created by :djadmin:`django-admin.py startproject
|
|
<startproject>`::
|
|
|
|
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',
|
|
)
|
|
|
|
A Django installation doesn't require any middleware —
|
|
:setting:`MIDDLEWARE_CLASSES` can be empty, if you'd like — but it's strongly
|
|
suggested that you at least use
|
|
:class:`~django.middleware.common.CommonMiddleware`.
|
|
|
|
The order in :setting:`MIDDLEWARE_CLASSES` matters because a middleware can
|
|
depend on other middleware. For instance,
|
|
:class:`~django.contrib.auth.middleware.AuthenticationMiddleware` stores the
|
|
authenticated user in the session; therefore, it must run after
|
|
:class:`~django.contrib.sessions.middleware.SessionMiddleware`.
|
|
|
|
Hooks and application order
|
|
===========================
|
|
|
|
During the request phase, before calling the view, Django applies middleware
|
|
in the order it's defined in :setting:`MIDDLEWARE_CLASSES`, top-down. Two
|
|
hooks are available:
|
|
|
|
* :meth:`process_request`
|
|
* :meth:`process_view`
|
|
|
|
During the response phase, after calling the view, middleware are applied in
|
|
reverse order, from the bottom up. Three hooks are available:
|
|
|
|
* :meth:`process_exception` (only if the view raised an exception)
|
|
* :meth:`process_template_response` (only for template responses)
|
|
* :meth:`process_response`
|
|
|
|
.. image:: _images/middleware.*
|
|
:alt: middleware application order
|
|
:width: 481
|
|
:height: 409
|
|
|
|
If you prefer, you can also think of it like an onion: each middleware class
|
|
is a "layer" that wraps the view.
|
|
|
|
The behavior of each hook is described below.
|
|
|
|
Writing your own middleware
|
|
===========================
|
|
|
|
Writing your own middleware is easy. Each middleware component is a single
|
|
Python class that defines one or more of the following methods:
|
|
|
|
.. _request-middleware:
|
|
|
|
``process_request``
|
|
-------------------
|
|
|
|
.. method:: process_request(self, request)
|
|
|
|
``request`` is an :class:`~django.http.HttpRequest` object.
|
|
|
|
``process_request()`` is called on each request, before Django decides which
|
|
view to execute.
|
|
|
|
It should return either ``None`` or an :class:`~django.http.HttpResponse`
|
|
object. If it returns ``None``, Django will continue processing this request,
|
|
executing any other ``process_request()`` middleware, then, ``process_view()``
|
|
middleware, and finally, the appropriate view. If it returns an
|
|
:class:`~django.http.HttpResponse` object, Django won't bother calling any
|
|
other request, view or exception middleware, or the appropriate view; it'll
|
|
apply response middleware to that :class:`~django.http.HttpResponse`, and
|
|
return the result.
|
|
|
|
.. _view-middleware:
|
|
|
|
``process_view``
|
|
----------------
|
|
|
|
.. method:: process_view(self, request, view_func, view_args, view_kwargs)
|
|
|
|
``request`` is an :class:`~django.http.HttpRequest` object. ``view_func`` is
|
|
the Python function that Django is about to use. (It's the actual function
|
|
object, not the name of the function as a string.) ``view_args`` is a list of
|
|
positional arguments that will be passed to the view, and ``view_kwargs`` is a
|
|
dictionary of keyword arguments that will be passed to the view. Neither
|
|
``view_args`` nor ``view_kwargs`` include the first view argument
|
|
(``request``).
|
|
|
|
``process_view()`` is called just before Django calls the view.
|
|
|
|
It should return either ``None`` or an :class:`~django.http.HttpResponse`
|
|
object. If it returns ``None``, Django will continue processing this request,
|
|
executing any other ``process_view()`` middleware and, then, the appropriate
|
|
view. If it returns an :class:`~django.http.HttpResponse` object, Django won't
|
|
bother calling any other view or exception middleware, or the appropriate
|
|
view; it'll apply response middleware to that
|
|
:class:`~django.http.HttpResponse`, and return the result.
|
|
|
|
.. note::
|
|
|
|
Accessing :attr:`request.POST <django.http.HttpRequest.POST>` or
|
|
:attr:`request.REQUEST <django.http.HttpRequest.REQUEST>` inside middleware
|
|
from ``process_request`` or ``process_view`` will prevent any view running
|
|
after the middleware from being able to :ref:`modify the upload handlers
|
|
for the request <modifying_upload_handlers_on_the_fly>`, and should
|
|
normally be avoided.
|
|
|
|
The :class:`~django.middleware.csrf.CsrfViewMiddleware` class can be
|
|
considered an exception, as it provides the
|
|
:func:`~django.views.decorators.csrf.csrf_exempt` and
|
|
:func:`~django.views.decorators.csrf.csrf_protect` decorators which allow
|
|
views to explicitly control at what point the CSRF validation should occur.
|
|
|
|
.. _template-response-middleware:
|
|
|
|
``process_template_response``
|
|
-----------------------------
|
|
|
|
.. method:: process_template_response(self, request, response)
|
|
|
|
``request`` is an :class:`~django.http.HttpRequest` object. ``response`` is
|
|
the :class:`~django.template.response.TemplateResponse` object (or equivalent)
|
|
returned by a Django view or by a middleware.
|
|
|
|
``process_template_response()`` is called just after the view has finished
|
|
executing, if the response instance has a ``render()`` method, indicating that
|
|
it is a :class:`~django.template.response.TemplateResponse` or equivalent.
|
|
|
|
It must return a response object that implements a ``render`` method. It could
|
|
alter the given ``response`` by changing ``response.template_name`` and
|
|
``response.context_data``, or it could create and return a brand-new
|
|
:class:`~django.template.response.TemplateResponse` or equivalent.
|
|
|
|
You don't need to explicitly render responses -- responses will be
|
|
automatically rendered once all template response middleware has been
|
|
called.
|
|
|
|
Middleware are run in reverse order during the response phase, which
|
|
includes ``process_template_response()``.
|
|
|
|
.. _response-middleware:
|
|
|
|
``process_response``
|
|
--------------------
|
|
|
|
.. method:: process_response(self, request, response)
|
|
|
|
``request`` is an :class:`~django.http.HttpRequest` object. ``response`` is
|
|
the :class:`~django.http.HttpResponse` or
|
|
:class:`~django.http.StreamingHttpResponse` object returned by a Django view
|
|
or by a middleware.
|
|
|
|
``process_response()`` is called on all responses before they're returned to
|
|
the browser.
|
|
|
|
It must return an :class:`~django.http.HttpResponse` or
|
|
:class:`~django.http.StreamingHttpResponse` object. It could alter the given
|
|
``response``, or it could create and return a brand-new
|
|
:class:`~django.http.HttpResponse` or
|
|
:class:`~django.http.StreamingHttpResponse`.
|
|
|
|
Unlike the ``process_request()`` and ``process_view()`` methods, the
|
|
``process_response()`` method is always called, even if the
|
|
``process_request()`` and ``process_view()`` methods of the same middleware
|
|
class were skipped (because an earlier middleware method returned an
|
|
:class:`~django.http.HttpResponse`). In particular, this means that your
|
|
``process_response()`` method cannot rely on setup done in
|
|
``process_request()``.
|
|
|
|
Finally, remember that during the response phase, middleware are applied in
|
|
reverse order, from the bottom up. This means classes defined at the end of
|
|
:setting:`MIDDLEWARE_CLASSES` will be run first.
|
|
|
|
Dealing with streaming responses
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. versionchanged:: 1.5
|
|
|
|
``response`` may also be an :class:`~django.http.StreamingHttpResponse`
|
|
object.
|
|
|
|
Unlike :class:`~django.http.HttpResponse`,
|
|
:class:`~django.http.StreamingHttpResponse` does not have a ``content``
|
|
attribute. As a result, middleware can no longer assume that all responses
|
|
will have a ``content`` attribute. If they need access to the content, they
|
|
must test for streaming responses and adjust their behavior accordingly::
|
|
|
|
if response.streaming:
|
|
response.streaming_content = wrap_streaming_content(response.streaming_content)
|
|
else:
|
|
response.content = alter_content(response.content)
|
|
|
|
.. note::
|
|
|
|
``streaming_content`` should be assumed to be too large to hold in memory.
|
|
Response middleware may wrap it in a new generator, but must not consume
|
|
it. Wrapping is typically implemented as follows::
|
|
|
|
def wrap_streaming_content(content)
|
|
for chunk in content:
|
|
yield alter_content(chunk)
|
|
|
|
.. _exception-middleware:
|
|
|
|
``process_exception``
|
|
---------------------
|
|
|
|
.. method:: process_exception(self, request, exception)
|
|
|
|
``request`` is an :class:`~django.http.HttpRequest` object. ``exception`` is an
|
|
``Exception`` object raised by the view function.
|
|
|
|
Django calls ``process_exception()`` when a view raises an exception.
|
|
``process_exception()`` should return either ``None`` or an
|
|
:class:`~django.http.HttpResponse` object. If it returns an
|
|
:class:`~django.http.HttpResponse` object, the template response and response
|
|
middleware will be applied, and the resulting response returned to the
|
|
browser. Otherwise, default exception handling kicks in.
|
|
|
|
Again, middleware are run in reverse order during the response phase, which
|
|
includes ``process_exception``. If an exception middleware returns a response,
|
|
the middleware classes above that middleware will not be called at all.
|
|
|
|
``__init__``
|
|
------------
|
|
|
|
Most middleware classes won't need an initializer since middleware classes are
|
|
essentially placeholders for the ``process_*`` methods. If you do need some
|
|
global state you may use ``__init__`` to set up. However, keep in mind a couple
|
|
of caveats:
|
|
|
|
* Django initializes your middleware without any arguments, so you can't
|
|
define ``__init__`` as requiring any arguments.
|
|
|
|
* Unlike the ``process_*`` methods which get called once per request,
|
|
``__init__`` gets called only *once*, when the Web server responds to the
|
|
first request.
|
|
|
|
Marking middleware as unused
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
It's sometimes useful to determine at run-time whether a piece of middleware
|
|
should be used. In these cases, your middleware's ``__init__`` method may
|
|
raise :exc:`django.core.exceptions.MiddlewareNotUsed`. Django will then remove
|
|
that piece of middleware from the middleware process.
|
|
|
|
Guidelines
|
|
----------
|
|
|
|
* Middleware classes don't have to subclass anything.
|
|
|
|
* The middleware class can live anywhere on your Python path. All Django
|
|
cares about is that the :setting:`MIDDLEWARE_CLASSES` setting includes
|
|
the path to it.
|
|
|
|
* Feel free to look at :doc:`Django's available middleware
|
|
</ref/middleware>` for examples.
|
|
|
|
* If you write a middleware component that you think would be useful to
|
|
other people, contribute to the community! :doc:`Let us know
|
|
</internals/contributing/index>`, and we'll consider adding it to Django.
|