Fixed #17942 -- Added a JsonResponse class to more easily create JSON encoded responses.

Thanks leahculver for the suggestion and Erik Romijn,
Simon Charette, and Marc Tamlyn for the reviews.

django/http/__init__.py

@@ -5,7 +5,7 @@ from django.http.response import (HttpResponse, StreamingHttpResponse,
     HttpResponseRedirect, HttpResponsePermanentRedirect,
     HttpResponseNotModified, HttpResponseBadRequest, HttpResponseForbidden,
     HttpResponseNotFound, HttpResponseNotAllowed, HttpResponseGone,
-    HttpResponseServerError, Http404, BadHeaderError)
+    HttpResponseServerError, Http404, BadHeaderError, JsonResponse)
 from django.http.utils import (fix_location_header,
     conditional_content_removal, fix_IE_for_attach, fix_IE_for_vary)
 
@@ -16,6 +16,6 @@ __all__ = [
     'HttpResponsePermanentRedirect', 'HttpResponseNotModified',
     'HttpResponseBadRequest', 'HttpResponseForbidden', 'HttpResponseNotFound',
     'HttpResponseNotAllowed', 'HttpResponseGone', 'HttpResponseServerError',
-    'Http404', 'BadHeaderError', 'fix_location_header',
+    'Http404', 'BadHeaderError', 'fix_location_header', 'JsonResponse',
     'conditional_content_removal', 'fix_IE_for_attach', 'fix_IE_for_vary',
 ]

django/http/response.py

@@ -1,8 +1,9 @@
 from __future__ import unicode_literals
 
 import datetime
-import time
+import json
 import sys
+import time
 from email.header import Header
 try:
     from urllib.parse import urlparse
@@ -13,6 +14,7 @@ from django.conf import settings
 from django.core import signals
 from django.core import signing
 from django.core.exceptions import DisallowedRedirect
+from django.core.serializers.json import DjangoJSONEncoder
 from django.http.cookie import SimpleCookie
 from django.utils import six, timezone
 from django.utils.encoding import force_bytes, force_text, iri_to_uri
@@ -456,3 +458,25 @@ class HttpResponseServerError(HttpResponse):
 
 class Http404(Exception):
     pass
+
+
+class JsonResponse(HttpResponse):
+    """
+    An HTTP response class that consumes data to be serialized to JSON.
+
+    :param data: Data to be dumped into json. By default only ``dict`` objects
+      are allowed to be passed due to a security flaw before EcmaScript 5. See
+      the ``safe`` parameter for more information.
+    :param encoder: Should be an json encoder class. Defaults to
+      ``django.core.serializers.json.DjangoJSONEncoder``.
+    :param safe: Controls if only ``dict`` objects may be serialized. Defaults
+      to ``True``.
+    """
+
+    def __init__(self, data, encoder=DjangoJSONEncoder, safe=True, **kwargs):
+        if safe and not isinstance(data, dict):
+            raise TypeError('In order to allow non-dict objects to be '
+                'serialized set the safe parameter to False')
+        kwargs.setdefault('content_type', 'application/json')
+        data = json.dumps(data, cls=encoder)
+        super(JsonResponse, self).__init__(content=data, **kwargs)

docs/ref/request-response.txt

@@ -823,6 +823,74 @@ types of HTTP responses. Like ``HttpResponse``, these subclasses live in
     :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:`~exceptions.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:`~exceptions.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

docs/releases/1.7.txt

@@ -671,15 +671,19 @@ Templates
 * The new :tfilter:`truncatechars_html` filter truncates a string to be no
   longer than the specified number of characters, taking HTML into account.
 
-Requests
+Requests and Responses
-^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^
 
 * The new :attr:`HttpRequest.scheme <django.http.HttpRequest.scheme>` attribute
   specifies the scheme of the request (``http`` or ``https`` normally).
 
+
 * The shortcut :func:`redirect() <django.shortcuts.redirect>` now supports
   relative URLs.
 
+* The new :class:`~django.http.JsonResponse` subclass of
+  :class:`~django.http.HttpResponse` helps easily create JSON-encoded responses.
+
 Tests
 ^^^^^
 

docs/topics/serialization.txt

@@ -216,6 +216,8 @@ the auth.User model has such a relation to the auth.Permission model::
 
 This example links the given user with the permission models with PKs 46 and 47.
 
+.. _serialization-formats-json:
+
 JSON
 ~~~~
 

tests/httpwrappers/tests.py

@@ -2,18 +2,20 @@
 from __future__ import unicode_literals
 
 import copy
+import json
 import os
 import pickle
 import unittest
 import warnings
 
 from django.core.exceptions import SuspiciousOperation
+from django.core.serializers.json import DjangoJSONEncoder
 from django.core.signals import request_finished
 from django.db import close_old_connections
 from django.http import (QueryDict, HttpResponse, HttpResponseRedirect,
                          HttpResponsePermanentRedirect, HttpResponseNotAllowed,
                          HttpResponseNotModified, StreamingHttpResponse,
-                         SimpleCookie, BadHeaderError,
+                         SimpleCookie, BadHeaderError, JsonResponse,
                          parse_cookie)
 from django.test import TestCase
 from django.utils.encoding import smart_str, force_text
@@ -451,6 +453,35 @@ class HttpResponseSubclassesTests(TestCase):
         self.assertContains(response, 'Only the GET method is allowed', status_code=405)
 
 
+class JsonResponseTests(TestCase):
+    def test_json_response_non_ascii(self):
+        data = {'key': 'łóżko'}
+        response = JsonResponse(data)
+        self.assertEqual(json.loads(response.content.decode()), data)
+
+    def test_json_response_raises_type_error_with_default_setting(self):
+        with self.assertRaisesMessage(TypeError,
+                'In order to allow non-dict objects to be serialized set the '
+                'safe parameter to False'):
+            JsonResponse([1, 2, 3])
+
+    def test_json_response_text(self):
+        response = JsonResponse('foobar', safe=False)
+        self.assertEqual(json.loads(response.content.decode()), 'foobar')
+
+    def test_json_response_list(self):
+        response = JsonResponse(['foo', 'bar'], safe=False)
+        self.assertEqual(json.loads(response.content.decode()), ['foo', 'bar'])
+
+    def test_json_response_custom_encoder(self):
+        class CustomDjangoJSONEncoder(DjangoJSONEncoder):
+            def encode(self, o):
+                return json.dumps({'foo': 'bar'})
+
+        response = JsonResponse({}, encoder=CustomDjangoJSONEncoder)
+        self.assertEqual(json.loads(response.content.decode()), {'foo': 'bar'})
+
+
 class StreamingHttpResponseTests(TestCase):
     def test_streaming_response(self):
         r = StreamingHttpResponse(iter(['hello', 'world']))

tests/view_tests/generic_urls.py

@@ -56,3 +56,8 @@ urlpatterns += patterns('view_tests.views',
     (r'^shortcuts/render/dirs/$', 'render_with_dirs'),
     (r'^shortcuts/render/current_app_conflict/$', 'render_view_with_current_app_conflict'),
 )
+
+# json response
+urlpatterns += patterns('view_tests.views',
+    (r'^json/response/$', 'json_response_view'),
+)

tests/view_tests/tests/test_json.py

@@ -0,0 +1,22 @@
+# encoding: utf8
+from __future__ import unicode_literals
+
+import json
+
+from django.test import TestCase
+
+
+class JsonResponseTests(TestCase):
+    urls = 'view_tests.generic_urls'
+
+    def test_json_response(self):
+        response = self.client.get('/json/response/')
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(
+            response['content-type'], 'application/json')
+        self.assertEqual(json.loads(response.content.decode()), {
+            'a': [1, 2, 3],
+            'foo': {'bar': 'baz'},
+            'timestamp': '2013-05-19T20:00:00',
+            'value': '3.14',
+        })

tests/view_tests/views.py

@@ -1,11 +1,13 @@
 from __future__ import unicode_literals
 
+import datetime
+import decimal
 import os
 import sys
 
 from django.core.exceptions import PermissionDenied, SuspiciousOperation
 from django.core.urlresolvers import get_resolver
-from django.http import HttpResponse, HttpResponseRedirect
+from django.http import HttpResponse, HttpResponseRedirect, JsonResponse
 from django.shortcuts import render_to_response, render
 from django.template import Context, RequestContext, TemplateDoesNotExist
 from django.views.debug import technical_500_response, SafeExceptionReporterFilter
@@ -334,3 +336,13 @@ def multivalue_dict_key_error(request):
         exc_info = sys.exc_info()
         send_log(request, exc_info)
         return technical_500_response(request, *exc_info)
+
+
+def json_response_view(request):
+    return JsonResponse({
+        'a': [1, 2, 3],
+        'foo': {'bar': 'baz'},
+        # Make sure datetime and Decimal objects would be serialized properly
+        'timestamp': datetime.datetime(2013, 5, 19, 20),
+        'value': decimal.Decimal('3.14'),
+    })