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Edited the middleware doc for completeness, clarity, and consistency.

This commit is contained in:
Aymeric Augustin 2012-12-09 22:22:36 +01:00
parent ae8e97384b
commit be9f2919e0
2 changed files with 113 additions and 69 deletions
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2
django/core/handlers/base.py
View File

@ -134,7 +134,7 @@ class BaseHandler(object):
raise ValueError("The view %s.%s didn't return an HttpResponse object." % (callback.__module__, view_name))
# If the response supports deferred rendering, apply template
# response middleware and the render the response
# response middleware and then render the response
if hasattr(response, 'render') and callable(response.render):
for middleware_method in self._template_response_middleware:
response = middleware_method(request, response)

180
docs/topics/http/middleware.txt
View File

@ -4,25 +4,28 @@ 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
and/or output.
or output.
Each middleware component is responsible for doing some specific function. For
example, Django includes a middleware component, ``XViewMiddleware``, that adds
an ``"X-View"`` HTTP header to every response to a ``HEAD`` request.
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
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`
list 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 :setting:`MIDDLEWARE_CLASSES`
created by :djadmin:`django-admin.py startproject <startproject>`::
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',
@ -32,12 +35,33 @@ created by :djadmin:`django-admin.py startproject <startproject>`::
'django.contrib.messages.middleware.MessageMiddleware',
)
During the request phases (:meth:`process_request` and :meth:`process_view`),
Django applies middleware in the order it's defined in
:setting:`MIDDLEWARE_CLASSES`, top-down. During the response phases
(:meth:`process_template_response`, :meth:`process_response`, and
:meth:`process_exception`), the classes are applied in reverse order, from the
bottom up.
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.svg
:alt: middleware application order
@ -47,10 +71,7 @@ bottom up.
If you prefer, you can also think of it like an onion: each middleware class
is a "layer" that wraps the view.
A Django installation doesn't require any middleware -- e.g.,
: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 behavior of each hook is described below.
Writing your own middleware
===========================
@ -65,16 +86,19 @@ Python class that defines one or more of the following methods:
.. method:: process_request(self, request)
``request`` is an :class:`~django.http.HttpRequest` object. This method is
called on each request, before Django decides which view to execute.
``request`` is an :class:`~django.http.HttpRequest` object.
``process_request()`` should return either ``None`` or an
:class:`~django.http.HttpResponse` object. If it returns ``None``, Django will
continue processing this request, executing any other middleware and, then, 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 return that :class:`~django.http.HttpResponse`.
Response middleware is always called on every response.
``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:
@ -91,14 +115,15 @@ 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 request, view or exception middleware, or the appropriate
view; it'll return that :class:`~django.http.HttpResponse`. Response
middleware is always called on every response.
``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::
@ -122,19 +147,17 @@ middleware is always called on every response.
.. method:: process_template_response(self, request, response)
``request`` is an :class:`~django.http.HttpRequest` object. ``response`` is a
subclass of :class:`~django.template.response.SimpleTemplateResponse` (e.g.
:class:`~django.template.response.TemplateResponse`) or any response object
that implements a ``render`` method.
``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()`` 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.SimpleTemplateResponse` or equivalent.
``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.
``process_template_response()`` will only be called if the response
instance has a ``render()`` method, indicating that it is a
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
@ -142,7 +165,7 @@ 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.
includes ``process_template_response()``.
.. _response-middleware:
@ -151,21 +174,34 @@ includes process_template_response.
.. method:: process_response(self, request, response)
``request`` is an :class:`~django.http.HttpRequest` object. ``response`` is the
:class:`~django.http.HttpResponse` object returned by a Django view.
``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()`` must return an :class:`~django.http.HttpResponse`
object. It could alter the given ``response``, or it could create and return a
brand-new :class:`~django.http.HttpResponse`.
``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`
(this means that your ``process_response()`` method cannot rely on setup done in
``process_request()``, for example). In addition, during the response phase the
classes are applied in reverse order, from the bottom up. This means classes
defined at the end of :setting:`MIDDLEWARE_CLASSES` will be run first.
``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`
@ -180,10 +216,17 @@ 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 = wrap_content(response.content)
response.content = alter_content(response.content)
``streaming_content`` should be assumed to be too large to hold in memory.
Middleware may wrap it in a new generator, but must not consume it.
.. 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:
@ -198,8 +241,9 @@ Middleware may wrap it in a new generator, but must not consume it.
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 response will be returned to
the browser. Otherwise, default exception handling kicks in.
: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,
@ -224,9 +268,9 @@ 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
``django.core.exceptions.MiddlewareNotUsed``. Django will then remove that
piece of middleware from the middleware process.
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
----------