django/docs/ref/request-response.txt

============================
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, which are defined in the :mod:`django.http`
module.

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

.. class:: HttpRequest

.. _httprequest-attributes:

Attributes
----------

All attributes should be considered read-only, unless stated otherwise below.
``session`` is a notable exception.

.. attribute:: HttpRequest.scheme

   .. versionadded:: 1.7

   A string representing the scheme of the request (``http`` or ``https``
   usually).

.. attribute:: HttpRequest.body

    The raw HTTP request body as a byte string. This is useful for processing
    data in different ways than conventional HTML forms: binary images,
    XML payload etc. For processing conventional form data, use ``HttpRequest.POST``.

    You can also read from an HttpRequest using a file-like interface. See
    :meth:`HttpRequest.read()`.

.. attribute:: HttpRequest.path

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

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

.. attribute:: HttpRequest.path_info

    Under some Web server configurations, the portion of the URL after the
    host name is split up into a script prefix portion and a path info
    portion. The ``path_info`` attribute always contains the path info portion
    of the path, no matter what Web server is being used. Using this instead
    of :attr:`~HttpRequest.path` can make your code easier to move between
    test and deployment servers.

    For example, if the ``WSGIScriptAlias`` for your application is set to
    ``"/minfo"``, then ``path`` might be ``"/minfo/music/bands/the_beatles/"``
    and ``path_info`` would be ``"/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

    A string representing the current encoding used to decode form submission
    data (or ``None``, which means the :setting:`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 :setting:`DEFAULT_CHARSET` encoding.

.. attribute:: HttpRequest.GET

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

.. attribute:: HttpRequest.POST

    A dictionary-like object containing all given HTTP POST parameters,
    providing that the request contains form data. See the
    :class:`QueryDict` documentation below. If you need to access raw or
    non-form data posted in the request, access this through the
    :attr:`HttpRequest.body` attribute instead.

    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

    .. deprecated:: 1.7
        Use the more explicit ``GET`` and ``POST`` instead.

    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 :class:`~django.core.files.uploadedfile.UploadedFile`.

    See :doc:`/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.

.. 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`` -- the length of the request body (as a string).
    * ``CONTENT_TYPE`` -- the MIME type of the request body.
    * ``HTTP_ACCEPT_ENCODING`` -- Acceptable encodings for the response.
    * ``HTTP_ACCEPT_LANGUAGE`` -- Acceptable languages for the response.
    * ``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 (as a string).

    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

    An object of type :setting:`AUTH_USER_MODEL` representing the currently
    logged-in user. If the user isn't currently logged in, ``user`` will be set
    to an instance of :class:`django.contrib.auth.models.AnonymousUser`. You
    can tell them apart with
    :meth:`~django.contrib.auth.models.User.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
    :class:`~django.contrib.auth.middleware.AuthenticationMiddleware`
    activated. For more, see :doc:`/topics/auth/index`.

.. 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 :doc:`session documentation
    </topics/http/sessions>` for full details.

.. 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 :setting:`ROOT_URLCONF`
    setting. See :ref:`how-django-processes-a-request` for details.

.. attribute:: HttpRequest.resolver_match

    An instance of :class:`~django.core.urlresolvers.ResolverMatch` representing
    the resolved url. This attribute is only set after url resolving took place,
    which means it's available in all views but not in middleware methods which
    are executed before url resolving takes place (like ``process_request``, you
    can use ``process_view`` instead).


Methods
-------

.. method:: HttpRequest.get_host()

    Returns the originating host of the request using information from the
    ``HTTP_X_FORWARDED_HOST`` (if :setting:`USE_X_FORWARDED_HOST` is enabled)
    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:`3333`.

    Example: ``"127.0.0.1:8000"``

    .. note:: The :meth:`~HttpRequest.get_host()` method fails when the host is
        behind multiple proxies. One solution is to use middleware to rewrite
        the proxy headers, as in the following example::

            class MultipleProxyMiddleware(object):
                FORWARDED_FOR_FIELDS = [
                    'HTTP_X_FORWARDED_FOR',
                    'HTTP_X_FORWARDED_HOST',
                    'HTTP_X_FORWARDED_SERVER',
                ]

                def process_request(self, request):
                    """
                    Rewrites the proxy headers so that only the most
                    recent proxy is used.
                    """
                    for field in self.FORWARDED_FOR_FIELDS:
                        if field in request.META:
                            if ',' in request.META[field]:
                                parts = request.META[field].split(',')
                                request.META[field] = parts[-1].strip()

        This middleware should be positioned before any other middleware that
        relies on the value of :meth:`~HttpRequest.get_host()` -- for instance,
        :class:`~django.middleware.common.CommonMiddleware` or
        :class:`~django.middleware.csrf.CsrfViewMiddleware`.

.. 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)

   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.get_signed_cookie(key, default=RAISE_ERROR, salt='', max_age=None)

   Returns a cookie value for a signed cookie, or raises a
   ``django.core.signing.BadSignature`` exception if the signature is
   no longer valid. If you provide the ``default`` argument the exception
   will be suppressed and that default value will be returned instead.

   The optional ``salt`` argument can be used to provide extra protection
   against brute force attacks on your secret key. If supplied, the
   ``max_age`` argument will be checked against the signed timestamp
   attached to the cookie value to ensure the cookie is not older than
   ``max_age`` seconds.

   For example::

          >>> request.get_signed_cookie('name')
          'Tony'
          >>> request.get_signed_cookie('name', salt='name-salt')
          'Tony' # assuming cookie was set using the same salt
          >>> request.get_signed_cookie('non-existing-cookie')
          ...
          KeyError: 'non-existing-cookie'
          >>> request.get_signed_cookie('non-existing-cookie', False)
          False
          >>> request.get_signed_cookie('cookie-that-was-tampered-with')
          ...
          BadSignature: ...
          >>> request.get_signed_cookie('name', max_age=60)
          ...
          SignatureExpired: Signature age 1677.3839159 > 60 seconds
          >>> request.get_signed_cookie('name', False, max_age=60)
          False

   See :doc:`cryptographic signing </topics/signing>` for more information.

.. method:: HttpRequest.is_secure()

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

.. method:: HttpRequest.is_ajax()

   Returns ``True`` if the request was made via an ``XMLHttpRequest``, by
   checking the ``HTTP_X_REQUESTED_WITH`` header for the string
   ``'XMLHttpRequest'``. Most modern JavaScript libraries send this header.
   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.

.. method:: HttpRequest.read(size=None)
.. method:: HttpRequest.readline()
.. method:: HttpRequest.readlines()
.. method:: HttpRequest.xreadlines()
.. method:: HttpRequest.__iter__()

    Methods implementing a file-like interface for reading from an
    HttpRequest instance. This makes it possible to consume an incoming
    request in a streaming fashion. A common use-case would be to process a
    big XML payload with iterative parser without constructing a whole
    XML tree in memory.

    Given this standard interface, an HttpRequest instance can be
    passed directly to an XML parser such as ElementTree::

        import xml.etree.ElementTree as ET
        for element in ET.iterparse(request):
            process(element)


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.datastructures.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, default)

    Returns the data with the requested key, as a Python list. Returns an
    empty list if the key doesn't exist and no default value was provided.
    It's guaranteed to return a list of some sort unless the default value
    was no list.

.. 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.pop(key)

    Returns a list of values for the given key and removes them from the
    dictionary. Raises ``KeyError`` if the key does not exist. For example::

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

.. method:: QueryDict.popitem()

    Removes an arbitrary member of the dictionary (since there's no concept
    of ordering), and returns a two value tuple containing the key and a list
    of all values for the key. Raises ``KeyError`` when called on an empty
    dictionary. For example::

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

.. method:: QueryDict.dict()

    Returns ``dict`` representation of ``QueryDict``. For every (key, list)
    pair in ``QueryDict``, ``dict`` will have (key, item), where item is one
    element of the list, using same logic as :meth:`QueryDict.__getitem__()`::

        >>> q = QueryDict('a=1&a=3&a=5')
        >>> q.dict()
        {'a': '5'}

.. method:: QueryDict.urlencode([safe])

    Returns a string of the data in query-string format. Example::

        >>> q = QueryDict('a=2&b=3&b=5')
        >>> q.urlencode()
        'a=2&b=3&b=5'

    Optionally, urlencode can be passed characters which
    do not require encoding. For example::

        >>> q = QueryDict('', mutable=True)
        >>> q['next'] = '/a&b/'
        >>> q.urlencode(safe='/')
        'next=/a%26b/'

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 :mod:`django.http` module.

Usage
-----

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

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

    >>> from django.http import HttpResponse
    >>> response = HttpResponse("Here's the text of the Web page.")
    >>> response = HttpResponse("Text only, please.", content_type="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>")

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

Finally, you can pass ``HttpResponse`` an iterator rather than strings.
``HttpResponse`` will consume the iterator immediately, store its content as a
string, and discard it.

If you need the response to be streamed from the iterator to the client, you
must use the :class:`StreamingHttpResponse` class instead.

Setting header fields
~~~~~~~~~~~~~~~~~~~~~

To set or remove a header field in your response, treat it like a dictionary::

    >>> response = HttpResponse()
    >>> response['Age'] = 120
    >>> del response['Age']

Note that unlike a dictionary, ``del`` doesn't raise ``KeyError`` if the header
field doesn't exist.

For setting the ``Cache-Control`` and ``Vary`` header fields, it is recommended
to use the :func:`~django.utils.cache.patch_cache_control` and
:func:`~django.utils.cache.patch_vary_headers` methods from
:mod:`django.utils.cache`, since these fields can have multiple, comma-separated
values. The "patch" methods ensure that other values, e.g. added by a
middleware, are not removed.

HTTP header fields cannot contain newlines. An attempt to set a header field
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
``content_type`` argument and set the ``Content-Disposition`` header. For example,
this is how you might return a Microsoft Excel spreadsheet::

    >>> response = HttpResponse(my_data, content_type='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 bytestring representing the content, encoded from a Unicode
    object if necessary.

.. attribute:: HttpResponse.status_code

    The `HTTP status code`_ for the response.

.. attribute:: HttpResponse.reason_phrase

    The HTTP reason phrase for the response.

.. attribute:: HttpResponse.streaming

    This is always ``False``.

    This attribute exists so middleware can treat streaming responses
    differently from regular responses.

Methods
-------

.. method:: HttpResponse.__init__(content='', content_type=None, status=200, reason=None)

    Instantiates an ``HttpResponse`` object with the given page content and
    content type.

    ``content`` should 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. If it is not
    an iterator or a string, it will be converted to a string when
    accessed.

    ``content_type`` is the MIME type optionally completed by a character set
    encoding and is used to fill the HTTP ``Content-Type`` header. If not
    specified, it is formed by the :setting:`DEFAULT_CONTENT_TYPE` and
    :setting:`DEFAULT_CHARSET` settings, by default: "`text/html; charset=utf-8`".

    Historically, this parameter was called ``mimetype`` (now deprecated).

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

    ``reason`` is the HTTP response phrase. If not provided, a default phrase
    will be used.

.. 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-insensitive.

.. method:: HttpResponse.__getitem__(header)

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

.. 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, httponly=False)

    Sets a cookie. The parameters are the same as in the
    :class:`~http.cookies.Morsel` cookie 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.
      If ``expires`` is not specified, it will be calculated.
    * ``expires`` should either be a string in the format
      ``"Wdy, DD-Mon-YY HH:MM:SS GMT"`` or a ``datetime.datetime`` object
      in UTC. If ``expires`` is a ``datetime`` object, the ``max_age``
      will be calculated.
    * 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.
    * Use ``httponly=True`` if you want to prevent client-side
      JavaScript from having access to the cookie.

      HTTPOnly_ is a flag included in a Set-Cookie HTTP response
      header. It is not part of the :rfc:`2109` standard for cookies,
      and it isn't honored consistently by all browsers. However,
      when it is honored, it can be a useful way to mitigate the
      risk of client side script accessing the protected cookie
      data.

    .. _HTTPOnly: https://www.owasp.org/index.php/HTTPOnly

    .. warning::

        Both :rfc:`2109` and :rfc:`6265` state that user agents should support
        cookies of at least 4096 bytes. For many browsers this is also the
        maximum size. Django will not raise an exception if there's an attempt
        to store a cookie of more than 4096 bytes, but many browsers will not
        set the cookie correctly.

.. method:: HttpResponse.set_signed_cookie(key, value, salt='', max_age=None, expires=None, path='/', domain=None, secure=None, httponly=True)

    Like :meth:`~HttpResponse.set_cookie()`, but
    :doc:`cryptographic signing </topics/signing>` the cookie before setting
    it. Use in conjunction with :meth:`HttpRequest.get_signed_cookie`.
    You can use the optional ``salt`` argument for added key strength, but
    you will need to remember to pass it to the corresponding
    :meth:`HttpRequest.get_signed_cookie` call.

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

.. class:: HttpResponseRedirect

    The first argument to the constructor is required -- the path to redirect
    to. This can be a fully qualified URL
    (e.g. ``'http://www.yahoo.com/search/'``) or an absolute path with no
    domain (e.g. ``'/search/'``). See :class:`HttpResponse` for other optional
    constructor arguments. Note that this returns an HTTP status code 302.

    .. attribute:: HttpResponseRedirect.url

        This read-only attribute represents the URL the response will redirect
        to (equivalent to the ``Location`` response header).

.. 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 and no content should be added
    to this response. Use this to designate that a page hasn't been modified
    since the user's last request (status code 304).

.. class:: HttpResponseBadRequest

    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. The first argument
    to the constructor is required: 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.

.. note::

    If a custom subclass of :class:`HttpResponse` implements a ``render``
    method, Django will treat it as emulating a
    :class:`~django.template.response.SimpleTemplateResponse`, and the
    ``render`` method must itself return a valid response object.

JsonResponse objects
====================

.. versionadded:: 1.7

.. class:: JsonResponse

.. method:: JsonResponse.__init__(data, encoder=DjangoJSONEncoder, safe=True, **kwargs)

   An :class:`HttpResponse` subclass that helps to create a JSON-encoded
   response. It inherits most behavior from its superclass with a couple
   differences:

   Its default ``Content-Type`` header is set to ``application/json``.

   The first parameter, ``data``, should be a ``dict`` instance. If the ``safe``
   parameter is set to ``False`` (see below) it can be any JSON-serializable
   object.

   The ``encoder``, which defaults to
   ``django.core.serializers.json.DjangoJSONEncoder``, will be used to
   serialize the data. See :ref:`JSON serialization
   <serialization-formats-json>` for more details about this serializer.

   The ``safe`` boolean parameter defaults to ``True``. If it's set to ``False``,
   any object can be passed for serialization (otherwise only ``dict`` instances
   are allowed). If ``safe`` is ``True`` and a non-``dict`` object is passed as
   the first argument, a :exc:`TypeError` will be raised.

Usage
-----

Typical usage could look like::

    >>> from django.http import JsonResponse
    >>> response = JsonResponse({'foo': 'bar'})
    >>> response.content
    '{"foo": "bar"}'


Serializing non-dictionary objects
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to serialize objects other than ``dict`` you must set the ``safe``
parameter to ``False``::

    >>> response = JsonResponse([1, 2, 3], safe=False)

Without passing ``safe=False``, a :exc:`TypeError` will be raised.

.. warning::

    Before the `5th edition of EcmaScript
    <http://www.ecma-international.org/publications/standards/Ecma-262.htm>`_
    it was possible to poison the JavaScript ``Array`` constructor. For this
    reason, Django does not allow passing non-dict objects to the
    :class:`~django.http.JsonResponse` constructor by default.  However, most
    modern browsers implement EcmaScript 5 which removes this attack vector.
    Therefore it is possible to disable this security precaution.

Changing the default JSON encoder
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you need to use a differ JSON encoder class you can pass the ``encoder``
parameter to the constructor method::

    >>> response = JsonResponse(data, encoder=MyJSONEncoder)

.. _httpresponse-streaming:

StreamingHttpResponse objects
=============================

.. class:: StreamingHttpResponse

The :class:`StreamingHttpResponse` class is used to stream a response from
Django to the browser. You might want to do this if generating the response
takes too long or uses too much memory. For instance, it's useful for
:ref:`generating large CSV files <streaming-csv-files>`.

.. admonition:: Performance considerations

    Django is designed for short-lived requests. Streaming responses will tie
    a worker process for the entire duration of the response. This may result
    in poor performance.

    Generally speaking, you should perform expensive tasks outside of the
    request-response cycle, rather than resorting to a streamed response.

The :class:`StreamingHttpResponse` is not a subclass of :class:`HttpResponse`,
because it features a slightly different API. However, it is almost identical,
with the following notable differences:

* It should be given an iterator that yields strings as content.

* You cannot access its content, except by iterating the response object
  itself. This should only occur when the response is returned to the client.

* It has no ``content`` attribute. Instead, it has a
  :attr:`~StreamingHttpResponse.streaming_content` attribute.

* You cannot use the file-like object ``tell()`` or ``write()`` methods.
  Doing so will raise an exception.

:class:`StreamingHttpResponse` should only be used in situations where it is
absolutely required that the whole content isn't iterated before transferring
the data to the client. Because the content can't be accessed, many
middlewares can't function normally. For example the ``ETag`` and ``Content-
Length`` headers can't be generated for streaming responses.

Attributes
----------

.. attribute:: StreamingHttpResponse.streaming_content

    An iterator of strings representing the content.

.. attribute:: HttpResponse.status_code

    The `HTTP status code`_ for the response.

.. attribute:: HttpResponse.reason_phrase

    The HTTP reason phrase for the response.

.. attribute:: HttpResponse.streaming

    This is always ``True``.