Appendix G: Request and Response Objects · Mastering Django: Core

Django uses request and response objects to pass state through the system. When a page is requested, Django creates an [`HttpRequest`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest "HttpRequest") object that contains metadata about the request. Then Django loads the appropriate view, passing the [`HttpRequest`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest "HttpRequest") as the first argument to the view function. Each view is responsible for returning an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") object. This document explains the APIs for [`HttpRequest`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest "HttpRequest") and [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") objects, which are defined in the`django.http` module. [TOC=3] ## HttpRequest objects *class *`HttpRequest` ### Attributes All attributes should be considered read-only, unless stated otherwise below. `session` is a notable exception. `HttpRequest.``scheme` A string representing the scheme of the request (`http` or `https` usually). `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 [`HttpRequest.read()`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.read "HttpRequest.read"). `HttpRequest.``path` A string representing the full path to the requested page, not including the domain. Example: `"/music/bands/the_beatles/"` `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 [`path`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.path "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/"`. `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() ~~~ `HttpRequest.``encoding` 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. `HttpRequest.``GET` A dictionary-like object containing all given HTTP GET parameters. See the [`QueryDict`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict "QueryDict") documentation below. `HttpRequest.``POST` A dictionary-like object containing all given HTTP POST parameters, providing that the request contains form data. See the [`QueryDict`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict "QueryDict") documentation below. If you need to access raw or non-form data posted in the request, access this through the [`HttpRequest.body`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.body "HttpRequest.body") attribute instead. Its 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 shouldnt 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`. `HttpRequest.``COOKIES` A standard Python dictionary containing all cookies. Keys and values are strings. `HttpRequest.``FILES` A dictionary-like object containing all uploaded files. Each key in `FILES` is the `name` from the `<inputtype="file" name="" />`. Each value in `FILES` is an `UploadedFile`. 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. `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 clients 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`. `HttpRequest.``user` An object of type `AUTH_USER_MODEL` representing the currently logged-in user. If the user isnt 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`](http://masteringdjango.com/django-request-and-response-objects/chapter_19.html#django.contrib.auth.middleware.AuthenticationMiddleware "django.contrib.auth.middleware.AuthenticationMiddleware") activated. `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. `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 how-django-processes-a-request for details. `HttpRequest.``resolver_match` An instance of `ResolverMatch` representing the resolved url. This attribute is only set after url resolving took place, which means its 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 `HttpRequest.``get_host`() Returns the originating host of the request using information from the `HTTP_X_FORWARDED_HOST` (if`USE_X_FORWARDED_HOST` is enabled) and `HTTP_HOST` headers, in that order. If they dont provide a value, the method uses a combination of `SERVER_NAME` and `SERVER_PORT` as detailed in [PEP 3333](https://www.python.org/dev/peps/pep-3333). Example: `"127.0.0.1:8000"` Note The [`get_host()`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.get_host "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 [`get_host()`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.get_host "HttpRequest.get_host") for instance, [`CommonMiddleware`](http://masteringdjango.com/django-request-and-response-objects/chapter_19.html#django.middleware.common.CommonMiddleware "django.middleware.common.CommonMiddleware") or [`CsrfViewMiddleware`](http://masteringdjango.com/django-request-and-response-objects/chapter_19.html#django.middleware.csrf.CsrfViewMiddleware "django.middleware.csrf.CsrfViewMiddleware"). `HttpRequest.``get_full_path`() Returns the `path`, plus an appended query string, if applicable. Example: `"/music/bands/the_beatles/?print=true"` `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"` `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 cryptographic signing for more information. `HttpRequest.``is_secure`() Returns `True` if the request is secure; that is, if it was made with HTTPS. `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), youll have to set this header manually if you want `is_ajax()` to work. If a response varies on whether or not its requested via AJAX and you are using some form of caching like Djangos [`cache middleware`](http://masteringdjango.com/django-request-and-response-objects/chapter_19.html#module-django.middleware.cache "django.middleware.cache: Middleware for the site-wide cache."), you should decorate the view with `vary_on_headers('HTTP_X_REQUESTED_WITH')` so that the responses are properly cached. `HttpRequest.``read`(*size=None*) `HttpRequest.``readline`() `HttpRequest.``readlines`() `HttpRequest.``xreadlines`() `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 [`HttpRequest`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest "HttpRequest") object, the `GET` and `POST` attributes are instances of `django.http.QueryDict`, 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>`, pass multiple values for the same key. The `QueryDict`s at `request.POST` and `request.GET` will be immutable when accessed in a normal request/response cycle. To get a mutable version you need to use `.copy()`. ### Methods [`QueryDict`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict "QueryDict") implements all the standard dictionary methods because its a subclass of dictionary. Exceptions are outlined here: `QueryDict.``__init__`(*query_string=None*, *mutable=False*, *encoding=None*) Instantiates a `QueryDict` object based on `query_string`. ~~~ >>> QueryDict('a=1&a=2&c=3') <QueryDict: {'a': ['1', '2'], 'c': ['3']}> ~~~ If `query_string` is not passed in, the resulting `QueryDict` will be empty (it will have no keys or values). Most `QueryDict`s you encounter, and in particular those at `request.POST` and `request.GET`, will be immutable. If you are instantiating one yourself, you can make it mutable by passing `mutable=True` to its `__init__()`. Strings for setting both keys and values will be converted from `encoding` to unicode. If encoding is not set, it defaults to `DEFAULT_CHARSET`. Changed in version 1.8: In previous versions, `query_string` was a required positional argument. `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 Pythons standard `KeyError`, so you can stick to catching `KeyError`.) `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` (such as one that was created via `copy()`). `QueryDict.``__contains__`(*key*) Returns `True` if the given key is set. This lets you do, e.g., `if "foo" in request.GET`. `QueryDict.``get`(*key*, *default*) Uses the same logic as `__getitem__()` above, with a hook for returning a default value if the key doesnt exist. `QueryDict.``setdefault`(*key*, *default*) Just like the standard dictionary `setdefault()` method, except it uses `__setitem__()` internally. `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', mutable=True) >>> q.update({'a': '2'}) >>> q.getlist('a') ['1', '2'] >>> q['a'] # returns the last ['2'] ~~~ `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')] ~~~ `QueryDict.``iteritems`() Just like the standard dictionary `iteritems()` method. Like [`QueryDict.items()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.items "QueryDict.items") this uses the same last-value logic as [`QueryDict.__getitem__()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.__getitem__ "QueryDict.__getitem__"). `QueryDict.``iterlists`() Like [`QueryDict.iteritems()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.iteritems "QueryDict.iteritems") except it includes all values, as a list, for each member of the dictionary. `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'] ~~~ `QueryDict.``itervalues`() Just like [`QueryDict.values()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.values "QueryDict.values"), except an iterator. In addition, `QueryDict` has the following methods: `QueryDict.``copy`() Returns a copy of the object, using `copy.deepcopy()` from the Python standard library. This copy will be mutable even if the original was not. `QueryDict.``getlist`(*key*, *default*) Returns the data with the requested key, as a Python list. Returns an empty list if the key doesnt exist and no default value was provided. Its guaranteed to return a list of some sort unless the default value was no list. `QueryDict.``setlist`(*key*, *list_*) Sets the given key to `list_` (unlike `__setitem__()`). `QueryDict.``appendlist`(*key*, *item*) Appends an item to the internal list associated with key. `QueryDict.``setlistdefault`(*key*, *default_list*) Just like `setdefault`, except it takes a list of values instead of a single value. `QueryDict.``lists`() Like [`items()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.items "QueryDict.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'])] ~~~ `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'] ~~~ `QueryDict.``popitem`() Removes an arbitrary member of the dictionary (since theres 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']) ~~~ `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 [`QueryDict.__getitem__()`](http://masteringdjango.com/django-request-and-response-objects/#QueryDict.__getitem__ "QueryDict.__getitem__"): ~~~ >>> q = QueryDict('a=1&a=3&a=5') >>> q.dict() {'a': '5'} ~~~ `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 [`HttpRequest`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest "HttpRequest") objects, which are created automatically by Django, [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") objects are your responsibility. Each view you write is responsible for instantiating, populating and returning an[`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse"). The [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "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 [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "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[`StreamingHttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse "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` doesnt raise `KeyError` if the header field doesnt exist. For setting the `Cache-Control` and `Vary` header fields, it is recommended to use the `patch_cache_control()` and`patch_vary_headers()` methods from `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"' ~~~ Theres nothing Django-specific about the `Content-Disposition` header, but its easy to forget the syntax, so weve included it here. ### Attributes `HttpResponse.``content` A bytestring representing the content, encoded from a Unicode object if necessary. `HttpResponse.``charset` A string denoting the charset in which the response will be encoded. If not given at `HttpResponse`instantiation time, it will be extracted from `content_type` and if that is unsuccessful, the `DEFAULT_CHARSET`setting will be used. `HttpResponse.``status_code` The [HTTP status code](http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10) for the response. `HttpResponse.``reason_phrase` The HTTP reason phrase for the response. `HttpResponse.``streaming` This is always `False`. This attribute exists so middleware can treat streaming responses differently from regular responses. `HttpResponse.``closed` `True` if the response has been closed. ### Methods `HttpResponse.``__init__`(*content=”*, *content_type=None*, *status=200*, *reason=None*, *charset=None*) Instantiates an `HttpResponse` object with the given page content and content type. `content` should be an iterator or a string. If its 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 `DEFAULT_CONTENT_TYPE` and `DEFAULT_CHARSET`settings, by default: text/html; charset=utf-8. `status` is the [HTTP status code](http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10) for the response. `reason` is the HTTP response phrase. If not provided, a default phrase will be used. `charset` is the charset in which the response will be encoded. If not given it will be extracted from`content_type`, and if that is unsuccessful, the `DEFAULT_CHARSET` setting will be used. `HttpResponse.``__setitem__`(*header*, *value*) Sets the given header name to the given value. Both `header` and `value` should be strings. `HttpResponse.``__delitem__`(*header*) Deletes the header with the given name. Fails silently if the header doesnt exist. Case-insensitive. `HttpResponse.``__getitem__`(*header*) Returns the value for the given header name. Case-insensitive. `HttpResponse.``has_header`(*header*) Returns `True` or `False` based on a case-insensitive check for a header with the given name. `HttpResponse.``setdefault`(*header*, *value*) Sets a header unless it has already been set. `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 `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 clients 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](https://www.owasp.org/index.php/HTTPOnly) is a flag included in a Set-Cookie HTTP response header. It is not part of the [RFC 2109](https://tools.ietf.org/html/rfc2109.html) standard for cookies, and it isnt 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. Warning Both [RFC 2109](https://tools.ietf.org/html/rfc2109.html) and [RFC 6265](https://tools.ietf.org/html/rfc6265.html) 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 theres an attempt to store a cookie of more than 4096 bytes, but many browsers will not set the cookie correctly. `HttpResponse.``set_signed_cookie`(*key*, *value*, *salt=”*, *max_age=None*, *expires=None*, *path=’/’*, *domain=None*,*secure=None*, *httponly=True*) Like [`set_cookie()`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse.set_cookie "HttpResponse.set_cookie"), but cryptographic signing the cookie before setting it. Use in conjunction with[`HttpRequest.get_signed_cookie()`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.get_signed_cookie "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 [`HttpRequest.get_signed_cookie()`](http://masteringdjango.com/django-request-and-response-objects/#HttpRequest.get_signed_cookie "HttpRequest.get_signed_cookie") call. `HttpResponse.``delete_cookie`(*key*, *path=’/’*, *domain=None*) Deletes the cookie with the given key. Fails silently if the key doesnt 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. `HttpResponse.``write`(*content*) This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") instance a file-like object. `HttpResponse.``flush`() This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") instance a file-like object. `HttpResponse.``tell`() This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") instance a file-like object. `HttpResponse.``getvalue`() Returns the value of [`HttpResponse.content`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse.content "HttpResponse.content"). This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") instance a stream-like object. `HttpResponse.``writable`() Always `True`. This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") instance a stream-like object. `HttpResponse.``writelines`(*lines*) Writes a list of lines to the response. Line separators are not added. This method makes an [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse")instance a stream-like object. ### HttpResponse subclasses Django includes a number of `HttpResponse` subclasses that handle different types of HTTP responses. Like`HttpResponse`, these subclasses live in `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 [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse")for other optional constructor arguments. Note that this returns an HTTP status code 302. `url` This read-only attribute represents the URL the response will redirect to (equivalent to the `Location`response header). *class *`HttpResponsePermanentRedirect` Like [`HttpResponseRedirect`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponseRedirect "HttpResponseRedirect"), but it returns a permanent redirect (HTTP status code 301) instead of a found redirect (status code 302). *class *`HttpResponseNotModified` The constructor doesnt take any arguments and no content should be added to this response. Use this to designate that a page hasnt been modified since the users last request (status code 304). *class *`HttpResponseBadRequest` Acts just like [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") but uses a 400 status code. *class *`HttpResponseNotFound` Acts just like [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") but uses a 404 status code. *class *`HttpResponseForbidden` Acts just like [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") but uses a 403 status code. *class *`HttpResponseNotAllowed` Like [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "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 [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") but uses a 410 status code. *class *`HttpResponseServerError` Acts just like [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") but uses a 500 status code. Note If a custom subclass of [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "HttpResponse") implements a `render` method, Django will treat it as emulating a`SimpleTemplateResponse`, and the `render` method must itself return a valid response object. ## JsonResponse objects *class *`JsonResponse` `JsonResponse.``__init__`(*data*, *encoder=DjangoJSONEncoder*, *safe=True*, ***kwargs*) An [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "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. The `safe` boolean parameter defaults to `True`. If its 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 `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 `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 `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 different JSON encoder class you can pass the `encoder` parameter to the constructor method: ~~~ >>> response = JsonResponse(data, encoder=MyJSONEncoder) ~~~ ## StreamingHttpResponse objects *class *`StreamingHttpResponse` The [`StreamingHttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse "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, its useful for generating large CSV files . 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 [`StreamingHttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse "StreamingHttpResponse") is not a subclass of [`HttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#HttpResponse "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 [`streaming_content`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse.streaming_content "StreamingHttpResponse.streaming_content") attribute. * You cannot use the file-like object `tell()` or `write()` methods. Doing so will raise an exception. [`StreamingHttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse "StreamingHttpResponse") should only be used in situations where it is absolutely required that the whole content isnt iterated before transferring the data to the client. Because the content cant be accessed, many middlewares cant function normally. For example the `ETag` and `Content- Length` headers cant be generated for streaming responses. ### Attributes `StreamingHttpResponse.``streaming_content` An iterator of strings representing the content. `StreamingHttpResponse.``status_code` The [HTTP status code](http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10) for the response. `StreamingHttpResponse.``reason_phrase` The HTTP reason phrase for the response. `StreamingHttpResponse.``streaming` This is always `True`. ## FileResponse objects *class *`FileResponse` [`FileResponse`](http://masteringdjango.com/django-request-and-response-objects/#FileResponse "FileResponse") is a subclass of [`StreamingHttpResponse`](http://masteringdjango.com/django-request-and-response-objects/#StreamingHttpResponse "StreamingHttpResponse") optimized for binary files. It uses [wsgi.file_wrapper](https://www.python.org/dev/peps/pep-3333/#optional-platform-specific-file-handling) if provided by the wsgi server, otherwise it streams the file out in small chunks. `FileResponse` expects a file open in binary mode like so: ~~~ >>> from django.http import FileResponse >>> response = FileResponse(open('myfile.png', 'rb')) ~~~ ## Error views Django comes with a few views by default for handling HTTP errors. To override these with your own custom views, see customizing-error-views. ### The 404 (page not found) view `defaults.``page_not_found`(*request*, *template_name=’404.html’*) When you raise `Http404` from within a view, Django loads a special view devoted to handling 404 errors. By default, its the view `django.views.defaults.page_not_found()`, which either produces a very simple Not Found message or loads and renders the template `404.html` if you created it in your root template directory. The default 404 view will pass one variable to the template: `request_path`, which is the URL that resulted in the error. Three things to note about 404 views: * The 404 view is also called if Django doesnt find a match after checking every regular expression in the URLconf. * The 404 view is passed a `RequestContext` and will have access to variables supplied by your template context processors (e.g. `MEDIA_URL`). * If `DEBUG` is set to `True` (in your settings module), then your 404 view will never be used, and your URLconf will be displayed instead, with some debug information. ### The 500 (server error) view `defaults.``server_error`(*request*, *template_name=’500.html’*) Similarly, Django executes special-case behavior in the case of runtime errors in view code. If a view results in an exception, Django will, by default, call the view `django.views.defaults.server_error`, which either produces a very simple Server Error message or loads and renders the template `500.html` if you created it in your root template directory. The default 500 view passes no variables to the `500.html` template and is rendered with an empty `Context` to lessen the chance of additional errors. If `DEBUG` is set to `True` (in your settings module), then your 500 view will never be used, and the traceback will be displayed instead, with some debug information. ### The 403 (HTTP Forbidden) view `defaults.``permission_denied`(*request*, *template_name=’403.html’*) In the same vein as the 404 and 500 views, Django has a view to handle 403 Forbidden errors. If a view results in a 403 exception then Django will, by default, call the view`django.views.defaults.permission_denied`. This view loads and renders the template `403.html` in your root template directory, or if this file does not exist, instead serves the text 403 Forbidden, as per [RFC 2616](https://tools.ietf.org/html/rfc2616.html) (the HTTP 1.1 Specification). `django.views.defaults.permission_denied` is triggered by a `PermissionDenied` exception. To deny access in a view you can use code like this: ~~~ from django.core.exceptions import PermissionDenied def edit(request, pk): if not request.user.is_staff: raise PermissionDenied # ... ~~~ ### The 400 (bad request) view `defaults.``bad_request`(*request*, *template_name=’400.html’*) When a `SuspiciousOperation` is raised in Django, it may be handled by a component of Django (for example resetting the session data). If not specifically handled, Django will consider the current request a bad request instead of a server error. `django.views.defaults.bad_request`, is otherwise very similar to the `server_error` view, but returns with the status code 400 indicating that the error condition was the result of a client operation. `bad_request` views are also only used when `DEBUG` is `False`. ## Customizing error views The default error views in Django should suffice for most Web applications, but can easily be overridden if you need any custom behavior. Simply specify the handlers as seen below in your URLconf (setting them anywhere else will have no effect). The `page_not_found()` view is overridden by `handler404`: ~~~ handler404 = 'mysite.views.my_custom_page_not_found_view' ~~~ The `server_error()` view is overridden by `handler500`: ~~~ handler500 = 'mysite.views.my_custom_error_view' ~~~ The `permission_denied()` view is overridden by `handler403`: ~~~ handler403 = 'mysite.views.my_custom_permission_denied_view' ~~~ The `bad_request()` view is overridden by `handler400`: ~~~ handler400 = 'mysite.views.my_custom_bad_request_view' ~~~