path: root/docs/ref/request-response.txt

.. _ref-request-response:

============================
Request and response objects
============================

.. module:: django.http
   :synopsis: Classes dealing with HTTP requests and responses.

Quick overview
==============

Django uses request and response objects to pass state through the system.

When a page is requested, Django creates an :class:`HttpRequest` object that
contains metadata about the request. Then Django loads the appropriate view,
passing the :class:`HttpRequest` as the first argument to the view function.
Each view is responsible for returning an :class:`HttpResponse` object.

This document explains the APIs for :class:`HttpRequest` and
:class:`HttpResponse` objects.

HttpRequest objects
===================

.. class:: HttpRequest

Attributes
----------

All attributes except ``session`` should be considered read-only.

.. attribute:: HttpRequest.path

   A string representing the full path to the requested page, not including
   the domain.

   Example: ``"/music/bands/the_beatles/"``

.. attribute:: HttpRequest.method

    A string representing the HTTP method used in the request. This is
    guaranteed to be uppercase. Example::

        if request.method == 'GET':
            do_something()
        elif request.method == 'POST':
            do_something_else()

.. attribute:: HttpRequest.encoding

    .. versionadded:: 1.0

    A string representing the current encoding used to decode form submission
    data (or ``None``, which means the ``DEFAULT_CHARSET`` setting is used).
    You can write to this attribute to change the encoding used when accessing
    the form data. Any subsequent attribute accesses (such as reading from
    ``GET`` or ``POST``) will use the new ``encoding`` value.  Useful if you
    know the form data is not in the ``DEFAULT_CHARSET`` encoding.

.. attribute:: HttpRequest.GET

    A dictionary-like object containing all given HTTP GET parameters. See the
    ``QueryDict`` documentation below.

.. attribute:: HttpRequest.POST

    A dictionary-like object containing all given HTTP POST parameters. See the
    ``QueryDict`` documentation below.

    It's possible that a request can come in via POST with an empty ``POST``
    dictionary -- if, say, a form is requested via the POST HTTP method but
    does not include form data. Therefore, you shouldn't use ``if request.POST``
    to check for use of the POST method; instead, use ``if request.method ==
    "POST"`` (see above).

    Note: ``POST`` does *not* include file-upload information. See ``FILES``.

.. attribute:: HttpRequest.REQUEST

    For convenience, a dictionary-like object that searches ``POST`` first,
    then ``GET``. Inspired by PHP's ``$_REQUEST``.

    For example, if ``GET = {"name": "john"}`` and ``POST = {"age": '34'}``,
    ``REQUEST["name"]`` would be ``"john"``, and ``REQUEST["age"]`` would be
    ``"34"``.

    It's strongly suggested that you use ``GET`` and ``POST`` instead of
    ``REQUEST``, because the former are more explicit.

.. attribute:: HttpRequest.COOKIES

    A standard Python dictionary containing all cookies. Keys and values are
    strings.

.. attribute:: HttpRequest.FILES

    A dictionary-like object containing all uploaded files. Each key in
    ``FILES`` is the ``name`` from the ``<input type="file" name="" />``. Each
    value in ``FILES`` is an ``UploadedFile`` object containing the following
    attributes:

        * ``read(num_bytes=None)`` -- Read a number of bytes from the file.
        * ``name`` -- The name of the uploaded file.
        * ``size`` -- The size, in bytes, of the uploaded file.
        * ``chunks(chunk_size=None)`` -- A generator that yields sequential
          chunks of data.

    See :ref:`topics-files` for more information.

    Note that ``FILES`` will only contain data if the request method was POST
    and the ``<form>`` that posted to the request had
    ``enctype="multipart/form-data"``. Otherwise, ``FILES`` will be a blank
    dictionary-like object.

    .. versionchanged:: 1.0

    In previous versions of Django, ``request.FILES`` contained simple ``dict``
    objects representing uploaded files. This is no longer true -- files are
    represented by ``UploadedFile`` objects as described below.

    These ``UploadedFile`` objects will emulate the old-style ``dict``
    interface, but this is deprecated and will be removed in the next release of
    Django.

.. attribute:: HttpRequest.META

    A standard Python dictionary containing all available HTTP headers.
    Available headers depend on the client and server, but here are some
    examples:

        * ``CONTENT_LENGTH``
        * ``CONTENT_TYPE``
        * ``HTTP_ACCEPT_ENCODING``
        * ``HTTP_ACCEPT_LANGUAGE``
        * ``HTTP_HOST`` -- The HTTP Host header sent by the client.
        * ``HTTP_REFERER`` -- The referring page, if any.
        * ``HTTP_USER_AGENT`` -- The client's user-agent string.
        * ``QUERY_STRING`` -- The query string, as a single (unparsed) string.
        * ``REMOTE_ADDR`` -- The IP address of the client.
        * ``REMOTE_HOST`` -- The hostname of the client.
        * ``REMOTE_USER`` -- The user authenticated by the web server, if any.
        * ``REQUEST_METHOD`` -- A string such as ``"GET"`` or ``"POST"``.
        * ``SERVER_NAME`` -- The hostname of the server.
        * ``SERVER_PORT`` -- The port of the server.

    With the exception of ``CONTENT_LENGTH`` and ``CONTENT_TYPE``, as given
    above, any HTTP headers in the request are converted to ``META`` keys by
    converting all characters to uppercase, replacing any hyphens with
    underscores and adding an ``HTTP_`` prefix to the name. So, for example, a
    header called ``X-Bender`` would be mapped to the ``META`` key
    ``HTTP_X_BENDER``.

.. attribute:: HttpRequest.user

    A ``django.contrib.auth.models.User`` object representing the currently
    logged-in user. If the user isn't currently logged in, ``user`` will be set
    to an instance of ``django.contrib.auth.models.AnonymousUser``. You
    can tell them apart with ``is_authenticated()``, like so::

        if request.user.is_authenticated():
            # Do something for logged-in users.
        else:
            # Do something for anonymous users.

    ``user`` is only available if your Django installation has the
    ``AuthenticationMiddleware`` activated. For more, see
    :ref:`topics-auth`.

.. attribute:: HttpRequest.session

    A readable-and-writable, dictionary-like object that represents the current
    session. This is only available if your Django installation has session
    support activated. See the :ref:`session documentation
    <topics-http-sessions>` for full details.

.. attribute:: HttpRequest.raw_post_data

    The raw HTTP POST data. This is only useful for advanced processing. Use
    ``POST`` instead.

.. attribute:: HttpRequest.urlconf

    Not defined by Django itself, but will be read if other code (e.g., a custom
    middleware class) sets it. When present, this will be used as the root
    URLconf for the current request, overriding the ``ROOT_URLCONF`` setting.
    See :ref:`how-django-processes-a-request` for details.

Methods
-------

.. method:: HttpRequest.get_host()

   .. versionadded:: 1.0

   Returns the originating host of the request using information from the
   ``HTTP_X_FORWARDED_HOST`` and ``HTTP_HOST`` headers (in that order). If
   they don't provide a value, the method uses a combination of
   ``SERVER_NAME`` and ``SERVER_PORT`` as detailed in `PEP 333`_.

   .. _PEP 333: http://www.python.org/dev/peps/pep-0333/

   Example: ``"127.0.0.1:8000"``

.. method:: HttpRequest.get_full_path()

   Returns the ``path``, plus an appended query string, if applicable.

   Example: ``"/music/bands/the_beatles/?print=true"``

.. method:: HttpRequest.build_absolute_uri(location)

   .. versionadded:: 1.0

   Returns the absolute URI form of ``location``. If no location is provided,
   the location will be set to ``request.get_full_path()``.

   If the location is already an absolute URI, it will not be altered.
   Otherwise the absolute URI is built using the server variables available in
   this request.

   Example: ``"http://example.com/music/bands/the_beatles/?print=true"``

.. method:: HttpRequest.is_secure()

   Returns ``True`` if the request is secure; that is, if it was made with
   HTTPS.

.. method:: HttpRequest.is_ajax()

   .. versionadded:: 1.0

   Returns ``True`` if the request was made via an ``XMLHttpRequest``, by
   checking the ``HTTP_X_REQUESTED_WITH`` header for the string
   ``'XMLHttpRequest'``. The following major JavaScript libraries all send this
   header:

       * jQuery
       * Dojo
       * MochiKit
       * MooTools
       * Prototype
       * YUI

   If you write your own XMLHttpRequest call (on the browser side), you'll
   have to set this header manually if you want ``is_ajax()`` to work.


QueryDict objects
-----------------

.. class:: QueryDict

In an :class:`HttpRequest` object, the ``GET`` and ``POST`` attributes are instances
of ``django.http.QueryDict``. :class:`QueryDict` is a dictionary-like
class customized to deal with multiple values for the same key. This is
necessary because some HTML form elements, notably
``<select multiple="multiple">``, pass multiple values for the same key.

``QueryDict`` instances are immutable, unless you create a ``copy()`` of them.
That means you can't change attributes of ``request.POST`` and ``request.GET``
directly.

Methods
-------

:class:`QueryDict` implements all the standard dictionary methods, because it's
a subclass of dictionary. Exceptions are outlined here:

.. method:: QueryDict.__getitem__(key)

    Returns the value for the given key. If the key has more than one value,
    ``__getitem__()`` returns the last value. Raises
    ``django.utils.datastructure.MultiValueDictKeyError`` if the key does not
    exist. (This is a subclass of Python's standard ``KeyError``, so you can
    stick to catching ``KeyError``.)

.. method:: QueryDict.__setitem__(key, value)

    Sets the given key to ``[value]`` (a Python list whose single element is
    ``value``). Note that this, as other dictionary functions that have side
    effects, can only be called on a mutable ``QueryDict`` (one that was created
    via ``copy()``).

.. method:: QueryDict.__contains__(key)

    Returns ``True`` if the given key is set. This lets you do, e.g., ``if "foo"
    in request.GET``.

.. method:: QueryDict.get(key, default)

    Uses the same logic as ``__getitem__()`` above, with a hook for returning a
    default value if the key doesn't exist.

.. method:: QueryDict.setdefault(key, default)

    Just like the standard dictionary ``setdefault()`` method, except it uses
    ``__setitem__`` internally.

.. method:: QueryDict.update(other_dict)

    Takes either a ``QueryDict`` or standard dictionary. Just like the standard
    dictionary ``update()`` method, except it *appends* to the current
    dictionary items rather than replacing them. For example::

          >>> q = QueryDict('a=1')
          >>> q = q.copy() # to make it mutable
          >>> q.update({'a': '2'})
          >>> q.getlist('a')
          ['1', '2']
          >>> q['a'] # returns the last
          ['2']

.. method:: QueryDict.items()

    Just like the standard dictionary ``items()`` method, except this uses the
    same last-value logic as ``__getitem()__``. For example::

           >>> q = QueryDict('a=1&a=2&a=3')
           >>> q.items()
           [('a', '3')]
           
.. method:: QueryDict.iteritems()

    Just like the standard dictionary ``iteritems()`` method. Like
    :meth:`QueryDict.items()` this uses the same last-value logic as
    :meth:`QueryDict.__getitem()__`.

.. method:: QueryDict.iterlists()

    Like :meth:`QueryDict.iteritems()` except it includes all values, as a list,
    for each member of the dictionary.

.. method:: QueryDict.values()

    Just like the standard dictionary ``values()`` method, except this uses the
    same last-value logic as ``__getitem()__``. For example::

           >>> q = QueryDict('a=1&a=2&a=3')
           >>> q.values()
           ['3']

.. method:: QueryDict.itervalues()

    Just like :meth:`QueryDict.values()`, except an iterator.

In addition, ``QueryDict`` has the following methods:

.. method:: QueryDict.copy()

    Returns a copy of the object, using ``copy.deepcopy()`` from the Python
    standard library. The copy will be mutable -- that is, you can change its
    values.

.. method:: QueryDict.getlist(key)

    Returns the data with the requested key, as a Python list. Returns an
    empty list if the key doesn't exist. It's guaranteed to return a list of
    some sort.

.. method:: QueryDict.setlist(key, list_)

    Sets the given key to ``list_`` (unlike ``__setitem__()``).

.. method:: QueryDict.appendlist(key, item)

    Appends an item to the internal list associated with key.

.. method:: QueryDict.setlistdefault(key, default_list)

    Just like ``setdefault``, except it takes a list of values instead of a
    single value.

.. method:: QueryDict.lists()

    Like :meth:`items()`, except it includes all values, as a list, for each
    member of the dictionary. For example::

         >>> q = QueryDict('a=1&a=2&a=3')
         >>> q.lists()
         [('a', ['1', '2', '3'])]

.. method:: QueryDict.urlencode()

    Returns a string of the data in query-string format.
    Example: ``"a=2&b=3&b=5"``.

HttpResponse objects
====================

.. class:: HttpResponse

In contrast to :class:`HttpRequest` objects, which are created automatically by
Django, :class:`HttpResponse` objects are your responsibility. Each view you
write is responsible for instantiating, populating and returning an
:class:`HttpResponse`.

The :class:`HttpResponse` class lives in the ``django.http`` module.

Usage
-----

Passing strings
~~~~~~~~~~~~~~~

Typical usage is to pass the contents of the page, as a string, to the
:class:`HttpResponse` constructor::

    >>> response = HttpResponse("Here's the text of the Web page.")
    >>> response = HttpResponse("Text only, please.", mimetype="text/plain")

But if you want to add content incrementally, you can use ``response`` as a
file-like object::

    >>> response = HttpResponse()
    >>> response.write("<p>Here's the text of the Web page.</p>")
    >>> response.write("<p>Here's another paragraph.</p>")

You can add and delete headers using dictionary syntax::

    >>> response = HttpResponse()
    >>> response['X-DJANGO'] = "It's the best."
    >>> del response['X-PHP']
    >>> response['X-DJANGO']
    "It's the best."

Note that ``del`` doesn't raise ``KeyError`` if the header doesn't exist.

Passing iterators
~~~~~~~~~~~~~~~~~

Finally, you can pass ``HttpResponse`` an iterator rather than passing it
hard-coded strings. If you use this technique, note the following:

    * The iterator should return strings.
    * ``HttpResponse.__init__()`` will read and store the iterator's contents.

Setting headers
~~~~~~~~~~~~~~~

To set a header in your response, just treat it like a dictionary::

    >>> response = HttpResponse()
    >>> response['Pragma'] = 'no-cache'

.. versionadded:: 1.1

HTTP headers cannot contain newlines. An attempt to set a header containing a
newline character (CR or LF) will raise ``BadHeaderError``

Telling the browser to treat the response as a file attachment
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To tell the browser to treat the response as a file attachment, use the
``mimetype`` argument and set the ``Content-Disposition`` header. For example,
this is how you might return a Microsoft Excel spreadsheet::

    >>> response = HttpResponse(my_data, mimetype='application/vnd.ms-excel')
    >>> response['Content-Disposition'] = 'attachment; filename=foo.xls'

There's nothing Django-specific about the ``Content-Disposition`` header, but
it's easy to forget the syntax, so we've included it here.

Attributes
----------

.. attribute:: HttpResponse.content

    A normal Python string representing the content, encoded from a Unicode
    object if necessary.

.. attribute :: HttpResponse.codec

    A class that contains the attribute ``name``, which contains an alias or
    name of a codec (from the module ``codecs``) that will be used to encode
    the response content. This value is set automatically in response to a
    ``request`` argument that contains an Accept-Charset header or content_type
    argument that contains a charset value. The priority for setting the codec/
    charset is specified in HttpResponse.charsets.

Methods
-------

.. method:: HttpResponse.__init__(content='', mimetype=None, status=200, content_type=DEFAULT_CONTENT_TYPE, request=None)

    Instantiates an ``HttpResponse`` object with the given page content (a
    string) and MIME type. The ``DEFAULT_CONTENT_TYPE`` is ``'text/html'``.

    ``content`` can be an iterator or a string. If it's an iterator, it should
    return strings, and those strings will be joined together to form the
    content of the response.

    ``status`` is the `HTTP Status code`_ for the response.

    .. versionadded:: 1.0

    ``content_type`` is an alias for ``mimetype``. Historically, this parameter
    was only called ``mimetype``, but since this is actually the value included
    in the HTTP ``Content-Type`` header, it can also include the character set
    encoding, which makes it more than just a MIME type specification.
    If ``mimetype`` is specified (not ``None``), that value is used.
    Otherwise, ``content_type`` is used. If neither is given, the
    ``DEFAULT_CONTENT_TYPE`` setting is used.

    .. versionadded:: 1.2

    ``request`` is the request that triggered this response. It can be used in
    the event that a view cares about dealing with request headers, in
    particular the Accept-Charset header.

.. method:: HttpResponse.__setitem__(header, value)

    Sets the given header name to the given value. Both ``header`` and
    ``value`` should be strings.

.. method:: HttpResponse.__delitem__(header)

    Deletes the header with the given name. Fails silently if the header
    doesn't exist. Case-sensitive.

.. method:: HttpResponse.__getitem__(header)

    Returns the value for the given header name. Case-sensitive.

.. method:: HttpResponse.has_header(header)

    Returns ``True`` or ``False`` based on a case-insensitive check for a
    header with the given name.

.. method:: HttpResponse.set_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=None)

    Sets a cookie. The parameters are the same as in the `cookie Morsel`_
    object in the Python standard library.

        * ``max_age`` should be a number of seconds, or ``None`` (default) if
          the cookie should last only as long as the client's browser session.
        * ``expires`` should be a string in the format
          ``"Wdy, DD-Mon-YY HH:MM:SS GMT"``.
        * Use ``domain`` if you want to set a cross-domain cookie. For example,
          ``domain=".lawrence.com"`` will set a cookie that is readable by
          the domains www.lawrence.com, blogs.lawrence.com and
          calendars.lawrence.com. Otherwise, a cookie will only be readable by
          the domain that set it.

    .. _`cookie Morsel`: http://docs.python.org/library/cookie.html#Cookie.Morsel

.. method:: HttpResponse.delete_cookie(key, path='/', domain=None)

    Deletes the cookie with the given key. Fails silently if the key doesn't
    exist.

    Due to the way cookies work, ``path`` and ``domain`` should be the same
    values you used in ``set_cookie()`` -- otherwise the cookie may not be
    deleted.

.. method:: HttpResponse.write(content)

    This method makes an :class:`HttpResponse` instance a file-like object.

.. method:: HttpResponse.flush()

    This method makes an :class:`HttpResponse` instance a file-like object.

.. method:: HttpResponse.tell()

    This method makes an :class:`HttpResponse` instance a file-like object.

.. _HTTP Status code: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10


.. _ref-httpresponse-subclasses:

HttpResponse subclasses
-----------------------

Django includes a number of :class:`HttpResponse` subclasses that handle
different types of HTTP responses. Like :class:`HttpResponse`, these subclasses
live in :mod:`django.http`.

.. class:: HttpResponseSendFile

    .. versionadded:: 1.2

    A special response class for efficient file serving. It informs the HTTP
    protocol handler to use platform-specific file serving mechanism (if
    available). The constructor takes three arguments -- the file path and,
    optionally, the file's content type and block size hint for handlers that
    need it.

    If the setting :setting:`SENDFILE_HEADER` is overridden (default None),
    HttpResponseSendFile will return that response header set as the file name given.
    If the file is unavailable, no content will be returned. Since certain servers
    do not allow direct access to the file system, it is not feasible to verify
    the file's existence beforehand.

    Be very careful with this method. It provides access to the filesystem that 
    must be controlled, and performs no verification of a file's existence in most
    cases.

    **Note:** Response middleware is bypassed by HttpResponseSendFile.

.. class:: HttpResponseStreaming

    .. versionadded:: 1.2

    A special response class that does not consume generators before returning
    the response. To do this, it bypasses middleware that is not useful for
    chunked responses, and is treated specially by middleware that is useful.

    It is primarily useful for sending large responses that would cause
    timeouts if sent with a normal HttpResponse.

    **Note:** Of the built-in response middleware, this class works correctly with:

    * :class:`django.middleware.common.CommonMiddleware`

    * :class:`django.middleware.gzip.GZipMiddleware`

    * :class:`django.middleware.http.ConditionalGetMiddleware`

    * :class:`django.contrib.csrf.middleware.CsrfMiddleware`

    Developers of third-party middleware who wish to make it work with this class
    should note that any time they access :class:`HttpResponseStreaming.content`, it will
    break the functionality of this class. Instead, replace :attr:`HttpResponseStreaming.content`
    by wrapping the value of :attr:`HttpResponseStreaming.content_generator`. :class:`django.middleware.gzip.GZipMiddleware`
    is a good example to follow. To inform the handler to send :class:`HttpResponseStreaming`
    responses through your middleware, add the class attribute ``streaming_safe = True``
    to your middleware class.

.. class:: HttpResponseRedirect

    The constructor takes a single argument -- the path to redirect to. This
    can be a fully qualified URL (e.g. ``'http://www.yahoo.com/search/'``) or an
    absolute URL with no domain (e.g. ``'/search/'``). Note that this returns
    an HTTP status code 302.

.. class:: HttpResponsePermanentRedirect

    Like :class:`HttpResponseRedirect`, but it returns a permanent redirect
    (HTTP status code 301) instead of a "found" redirect (status code 302).

.. class:: HttpResponseNotModified

    The constructor doesn't take any arguments. Use this to designate that a
    page hasn't been modified since the user's last request (status code 304).

.. class:: HttpResponseBadRequest

    .. versionadded:: 1.0

    Acts just like :class:`HttpResponse` but uses a 400 status code.

.. class:: HttpResponseNotFound

    Acts just like :class:`HttpResponse` but uses a 404 status code.

.. class:: HttpResponseForbidden

    Acts just like :class:`HttpResponse` but uses a 403 status code.

.. class:: HttpResponseNotAllowed

    Like :class:`HttpResponse`, but uses a 405 status code. Takes a single,
    required argument: a list of permitted methods (e.g. ``['GET', 'POST']``).

.. class:: HttpResponseGone

    Acts just like :class:`HttpResponse` but uses a 410 status code.

.. class:: HttpResponseServerError

    Acts just like :class:`HttpResponse` but uses a 500 status code.