Fixed #7581 -- Added streaming responses.

Thanks mrmachine and everyone else involved on this long-standing ticket.

django/http/__init__.py

@@ -528,18 +528,23 @@ def parse_cookie(cookie):
 class BadHeaderError(ValueError):
     pass
 
-class HttpResponse(object):
-    """A basic HTTP response, with content and dictionary-accessed headers."""
+class HttpResponseBase(object):
+    """
+    An HTTP response base class with dictionary-accessed headers.
+
+    This class doesn't handle content. It should not be used directly.
+    Use the HttpResponse and StreamingHttpResponse subclasses instead.
+    """
 
     status_code = 200
 
-    def __init__(self, content='', content_type=None, status=None,
-            mimetype=None):
+    def __init__(self, content_type=None, status=None, mimetype=None):
         # _headers is a mapping of the lower-case name to the original case of
         # the header (required for working with legacy systems) and the header
         # value. Both the name of the header and its value are ASCII strings.
         self._headers = {}
         self._charset = settings.DEFAULT_CHARSET
+        self._closable_objects = []
         if mimetype:
             warnings.warn("Using mimetype keyword argument is deprecated, use"
                           " content_type instead", PendingDeprecationWarning)
@@ -547,26 +552,24 @@ class HttpResponse(object):
         if not content_type:
             content_type = "%s; charset=%s" % (settings.DEFAULT_CONTENT_TYPE,
                     self._charset)
-        # content is a bytestring. See the content property methods.
-        self.content = content
         self.cookies = SimpleCookie()
         if status:
             self.status_code = status
 
         self['Content-Type'] = content_type
 
-    def serialize(self):
-        """Full HTTP message, including headers, as a bytestring."""
+    def serialize_headers(self):
+        """HTTP headers as a bytestring."""
         headers = [
             ('%s: %s' % (key, value)).encode('us-ascii')
             for key, value in self._headers.values()
         ]
-        return b'\r\n'.join(headers) + b'\r\n\r\n' + self.content
+        return b'\r\n'.join(headers)
 
     if six.PY3:
-        __bytes__ = serialize
+        __bytes__ = serialize_headers
     else:
-        __str__ = serialize
+        __str__ = serialize_headers
 
     def _convert_to_charset(self, value, charset, mime_encode=False):
         """Converts headers key/value to ascii/latin1 native strings.
@@ -690,24 +693,75 @@ class HttpResponse(object):
         self.set_cookie(key, max_age=0, path=path, domain=domain,
                         expires='Thu, 01-Jan-1970 00:00:00 GMT')
 
+    # Common methods used by subclasses
+
+    def make_bytes(self, value):
+        """Turn a value into a bytestring encoded in the output charset."""
+        # For backwards compatibility, this method supports values that are
+        # unlikely to occur in real applications. It has grown complex and
+        # should be refactored. It also overlaps __next__. See #18796.
+        if self.has_header('Content-Encoding'):
+            if isinstance(value, int):
+                value = six.text_type(value)
+            if isinstance(value, six.text_type):
+                value = value.encode('ascii')
+            # force conversion to bytes in case chunk is a subclass
+            return bytes(value)
+        else:
+            return force_bytes(value, self._charset)
+
+    # These methods partially implement the file-like object interface.
+    # See http://docs.python.org/lib/bltin-file-objects.html
+
+    # The WSGI server must call this method upon completion of the request.
+    # See http://blog.dscpl.com.au/2012/10/obligations-for-calling-close-on.html
+    def close(self):
+        for closable in self._closable_objects:
+            closable.close()
+
+    def write(self, content):
+        raise Exception("This %s instance is not writable" % self.__class__.__name__)
+
+    def flush(self):
+        pass
+
+    def tell(self):
+        raise Exception("This %s instance cannot tell its position" % self.__class__.__name__)
+
+class HttpResponse(HttpResponseBase):
+    """
+    An HTTP response class with a string as content.
+
+    This content that can be read, appended to or replaced.
+    """
+
+    streaming = False
+
+    def __init__(self, content='', *args, **kwargs):
+        super(HttpResponse, self).__init__(*args, **kwargs)
+        # Content is a bytestring. See the `content` property methods.
+        self.content = content
+
+    def serialize(self):
+        """Full HTTP message, including headers, as a bytestring."""
+        return self.serialize_headers() + b'\r\n\r\n' + self.content
+
+    if six.PY3:
+        __bytes__ = serialize
+    else:
+        __str__ = serialize
+
     @property
     def content(self):
-        if self.has_header('Content-Encoding'):
-            def make_bytes(value):
-                if isinstance(value, int):
-                    value = six.text_type(value)
-                if isinstance(value, six.text_type):
-                    value = value.encode('ascii')
-                # force conversion to bytes in case chunk is a subclass
-                return bytes(value)
-            return b''.join(make_bytes(e) for e in self._container)
-        return b''.join(force_bytes(e, self._charset) for e in self._container)
+        return b''.join(self.make_bytes(e) for e in self._container)
 
     @content.setter
     def content(self, value):
         if hasattr(value, '__iter__') and not isinstance(value, (bytes, six.string_types)):
             self._container = value
             self._base_content_is_iter = True
+            if hasattr(value, 'close'):
+                self._closable_objects.append(value)
         else:
             self._container = [value]
             self._base_content_is_iter = False
@@ -727,25 +781,85 @@ class HttpResponse(object):
 
     next = __next__             # Python 2 compatibility
 
-    def close(self):
-        if hasattr(self._container, 'close'):
-            self._container.close()
-
-    # The remaining methods partially implement the file-like object interface.
-    # See http://docs.python.org/lib/bltin-file-objects.html
     def write(self, content):
         if self._base_content_is_iter:
-            raise Exception("This %s instance is not writable" % self.__class__)
+            raise Exception("This %s instance is not writable" % self.__class__.__name__)
         self._container.append(content)
 
-    def flush(self):
-        pass
-
     def tell(self):
         if self._base_content_is_iter:
-            raise Exception("This %s instance cannot tell its position" % self.__class__)
+            raise Exception("This %s instance cannot tell its position" % self.__class__.__name__)
         return sum([len(chunk) for chunk in self])
 
+class StreamingHttpResponse(HttpResponseBase):
+    """
+    A streaming HTTP response class with an iterator as content.
+
+    This should only be iterated once, when the response is streamed to the
+    client. However, it can be appended to or replaced with a new iterator
+    that wraps the original content (or yields entirely new content).
+    """
+
+    streaming = True
+
+    def __init__(self, streaming_content=(), *args, **kwargs):
+        super(StreamingHttpResponse, self).__init__(*args, **kwargs)
+        # `streaming_content` should be an iterable of bytestrings.
+        # See the `streaming_content` property methods.
+        self.streaming_content = streaming_content
+
+    @property
+    def content(self):
+        raise AttributeError("This %s instance has no `content` attribute. "
+            "Use `streaming_content` instead." % self.__class__.__name__)
+
+    @property
+    def streaming_content(self):
+        return self._iterator
+
+    @streaming_content.setter
+    def streaming_content(self, value):
+        # Ensure we can never iterate on "value" more than once.
+        self._iterator = iter(value)
+        if hasattr(value, 'close'):
+            self._closable_objects.append(value)
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        return self.make_bytes(next(self._iterator))
+
+    next = __next__             # Python 2 compatibility
+
+class CompatibleStreamingHttpResponse(StreamingHttpResponse):
+    """
+    This class maintains compatibility with middleware that doesn't know how
+    to handle the content of a streaming response by exposing a `content`
+    attribute that will consume and cache the content iterator when accessed.
+
+    These responses will stream only if no middleware attempts to access the
+    `content` attribute. Otherwise, they will behave like a regular response,
+    and raise a `PendingDeprecationWarning`.
+    """
+    @property
+    def content(self):
+        warnings.warn(
+            'Accessing the `content` attribute on a streaming response is '
+            'deprecated. Use the `streaming_content` attribute instead.',
+            PendingDeprecationWarning)
+        content = b''.join(self)
+        self.streaming_content = [content]
+        return content
+
+    @content.setter
+    def content(self, content):
+        warnings.warn(
+            'Accessing the `content` attribute on a streaming response is '
+            'deprecated. Use the `streaming_content` attribute instead.',
+            PendingDeprecationWarning)
+        self.streaming_content = [content]
+
 class HttpResponseRedirectBase(HttpResponse):
     allowed_schemes = ['http', 'https', 'ftp']
 

django/http/utils.py

@@ -26,10 +26,16 @@ def conditional_content_removal(request, response):
     responses. Ensures compliance with RFC 2616, section 4.3.
     """
     if 100 <= response.status_code < 200 or response.status_code in (204, 304):
-       response.content = ''
-       response['Content-Length'] = 0
+        if response.streaming:
+            response.streaming_content = []
+        else:
+            response.content = ''
+        response['Content-Length'] = '0'
     if request.method == 'HEAD':
-        response.content = ''
+        if response.streaming:
+            response.streaming_content = []
+        else:
+            response.content = ''
     return response
 
 def fix_IE_for_attach(request, response):

django/middleware/common.py

@@ -113,14 +113,18 @@ class CommonMiddleware(object):
         if settings.USE_ETAGS:
             if response.has_header('ETag'):
                 etag = response['ETag']
+            elif response.streaming:
+                etag = None
             else:
                 etag = '"%s"' % hashlib.md5(response.content).hexdigest()
-            if response.status_code >= 200 and response.status_code < 300 and request.META.get('HTTP_IF_NONE_MATCH') == etag:
-                cookies = response.cookies
-                response = http.HttpResponseNotModified()
-                response.cookies = cookies
-            else:
-                response['ETag'] = etag
+            if etag is not None:
+                if (200 <= response.status_code < 300
+                    and request.META.get('HTTP_IF_NONE_MATCH') == etag):
+                    cookies = response.cookies
+                    response = http.HttpResponseNotModified()
+                    response.cookies = cookies
+                else:
+                    response['ETag'] = etag
 
         return response
 

django/middleware/gzip.py

@@ -1,6 +1,6 @@
 import re
 
-from django.utils.text import compress_string
+from django.utils.text import compress_sequence, compress_string
 from django.utils.cache import patch_vary_headers
 
 re_accepts_gzip = re.compile(r'\bgzip\b')
@@ -13,7 +13,7 @@ class GZipMiddleware(object):
     """
     def process_response(self, request, response):
         # It's not worth attempting to compress really short responses.
-        if len(response.content) < 200:
+        if not response.streaming and len(response.content) < 200:
             return response
 
         patch_vary_headers(response, ('Accept-Encoding',))
@@ -32,15 +32,21 @@ class GZipMiddleware(object):
         if not re_accepts_gzip.search(ae):
             return response
 
-        # Return the compressed content only if it's actually shorter.
-        compressed_content = compress_string(response.content)
-        if len(compressed_content) >= len(response.content):
-            return response
+        if response.streaming:
+            # Delete the `Content-Length` header for streaming content, because
+            # we won't know the compressed size until we stream it.
+            response.streaming_content = compress_sequence(response.streaming_content)
+            del response['Content-Length']
+        else:
+            # Return the compressed content only if it's actually shorter.
+            compressed_content = compress_string(response.content)
+            if len(compressed_content) >= len(response.content):
+                return response
+            response.content = compressed_content
+            response['Content-Length'] = str(len(response.content))
 
         if response.has_header('ETag'):
             response['ETag'] = re.sub('"$', ';gzip"', response['ETag'])
-
-        response.content = compressed_content
         response['Content-Encoding'] = 'gzip'
-        response['Content-Length'] = str(len(response.content))
+
         return response

django/middleware/http.py

@@ -10,7 +10,7 @@ class ConditionalGetMiddleware(object):
     """
     def process_response(self, request, response):
         response['Date'] = http_date()
-        if not response.has_header('Content-Length'):
+        if not response.streaming and not response.has_header('Content-Length'):
             response['Content-Length'] = str(len(response.content))
 
         if response.has_header('ETag'):

django/test/testcases.py

@@ -596,7 +596,9 @@ class TransactionTestCase(SimpleTestCase):
             msg_prefix + "Couldn't retrieve content: Response code was %d"
             " (expected %d)" % (response.status_code, status_code))
         text = force_text(text, encoding=response._charset)
-        content = response.content.decode(response._charset)
+        content = b''.join(response).decode(response._charset)
+        # Avoid ResourceWarning about unclosed files.
+        response.close()
         if html:
             content = assert_and_parse_html(self, content, None,
                 "Response's content is not valid HTML:")

django/utils/cache.py

@@ -95,7 +95,8 @@ def get_max_age(response):
             pass
 
 def _set_response_etag(response):
-    response['ETag'] = '"%s"' % hashlib.md5(response.content).hexdigest()
+    if not response.streaming:
+        response['ETag'] = '"%s"' % hashlib.md5(response.content).hexdigest()
     return response
 
 def patch_response_headers(response, cache_timeout=None):

django/utils/text.py

@@ -288,6 +288,37 @@ def compress_string(s):
     zfile.close()
     return zbuf.getvalue()
 
+class StreamingBuffer(object):
+    def __init__(self):
+        self.vals = []
+
+    def write(self, val):
+        self.vals.append(val)
+
+    def read(self):
+        ret = b''.join(self.vals)
+        self.vals = []
+        return ret
+
+    def flush(self):
+        return
+
+    def close(self):
+        return
+
+# Like compress_string, but for iterators of strings.
+def compress_sequence(sequence):
+    buf = StreamingBuffer()
+    zfile = GzipFile(mode='wb', compresslevel=6, fileobj=buf)
+    # Output headers...
+    yield buf.read()
+    for item in sequence:
+        zfile.write(item)
+        zfile.flush()
+        yield buf.read()
+    zfile.close()
+    yield buf.read()
+
 ustring_re = re.compile("([\u0080-\uffff])")
 
 def javascript_quote(s, quote_double_quotes=False):

django/views/generic/base.py

@@ -99,7 +99,7 @@ class View(object):
         """
         response = http.HttpResponse()
         response['Allow'] = ', '.join(self._allowed_methods())
-        response['Content-Length'] = 0
+        response['Content-Length'] = '0'
         return response
 
     def _allowed_methods(self):

django/views/static.py

@@ -14,7 +14,8 @@ try:
 except ImportError:     # Python 2
     from urllib import unquote
 
-from django.http import Http404, HttpResponse, HttpResponseRedirect, HttpResponseNotModified
+from django.http import (CompatibleStreamingHttpResponse, Http404,
+    HttpResponse, HttpResponseRedirect, HttpResponseNotModified)
 from django.template import loader, Template, Context, TemplateDoesNotExist
 from django.utils.http import http_date, parse_http_date
 from django.utils.translation import ugettext as _, ugettext_noop
@@ -62,8 +63,7 @@ def serve(request, path, document_root=None, show_indexes=False):
     if not was_modified_since(request.META.get('HTTP_IF_MODIFIED_SINCE'),
                               statobj.st_mtime, statobj.st_size):
         return HttpResponseNotModified()
-    with open(fullpath, 'rb') as f:
-        response = HttpResponse(f.read(), content_type=mimetype)
+    response = CompatibleStreamingHttpResponse(open(fullpath, 'rb'), content_type=mimetype)
     response["Last-Modified"] = http_date(statobj.st_mtime)
     if stat.S_ISREG(statobj.st_mode):
         response["Content-Length"] = statobj.st_size

docs/ref/request-response.txt

@@ -566,13 +566,21 @@ file-like object::
 Passing iterators
 ~~~~~~~~~~~~~~~~~
 
-Finally, you can pass ``HttpResponse`` an iterator rather than passing it
-hard-coded strings. If you use this technique, follow these guidelines:
+Finally, you can pass ``HttpResponse`` an iterator rather than strings. If you
+use this technique, the iterator should return strings.
 
-* The iterator should return strings.
-* If an :class:`HttpResponse` has been initialized with an iterator as its
-  content, you can't use the :class:`HttpResponse` instance as a file-like
-  object. Doing so will raise ``Exception``.
+.. versionchanged:: 1.5
+
+    Passing an iterator as content to :class:`HttpResponse` creates a
+    streaming response if (and only if) no middleware accesses the
+    :attr:`HttpResponse.content` attribute before the response is returned.
+
+    If you want to guarantee that your response will stream to the client, you
+    should use the new :class:`StreamingHttpResponse` class instead.
+
+If an :class:`HttpResponse` instance has been initialized with an iterator as
+its content, you can't use it as a file-like object. Doing so will raise an
+exception.
 
 Setting headers
 ~~~~~~~~~~~~~~~
@@ -614,6 +622,13 @@ Attributes
 
     The `HTTP Status code`_ for the response.
 
+.. attribute:: HttpResponse.streaming
+
+    This is always ``False``.
+
+    This attribute exists so middleware can treat streaming responses
+    differently from regular responses.
+
 Methods
 -------
 
@@ -781,3 +796,63 @@ types of HTTP responses. Like ``HttpResponse``, these subclasses live in
     method, Django will treat it as emulating a
     :class:`~django.template.response.SimpleTemplateResponse`, and the
     ``render`` method must itself return a valid response object.
+
+StreamingHttpResponse objects
+=============================
+
+.. versionadded:: 1.5
+
+.. 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
+generating large CSV files.
+
+.. admonition:: Performance considerations
+
+    Django is designed for short-lived requests. Streaming responses will tie
+    a worker process and keep a database connection idle in transaction 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.
+
+* Any iterators that have a ``close()`` method and are assigned as content will
+  be closed automatically after the response has been iterated.
+
+: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.streaming
+
+    This is always ``True``.

docs/releases/1.5.txt

@@ -84,6 +84,24 @@ For one-to-one relationships, both sides can be cached. For many-to-one
 relationships, only the single side of the relationship can be cached. This
 is particularly helpful in combination with ``prefetch_related``.
 
+Explicit support for streaming responses
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before Django 1.5, it was possible to create a streaming response by passing
+an iterator to :class:`~django.http.HttpResponse`. But this was unreliable:
+any middleware that accessed the :attr:`~django.http.HttpResponse.content`
+attribute would consume the iterator prematurely.
+
+You can now explicitly generate a streaming response with the new
+:class:`~django.http.StreamingHttpResponse` class. This class exposes a
+:class:`~django.http.StreamingHttpResponse.streaming_content` attribute which
+is an iterator.
+
+Since :class:`~django.http.StreamingHttpResponse` does not have a ``content``
+attribute, middleware that need access to the response content must test for
+streaming responses and behave accordingly. See :ref:`response-middleware` for
+more information.
+
 ``{% verbatim %}`` template tag
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/topics/http/middleware.txt

@@ -164,6 +164,23 @@ an earlier middleware method returned an :class:`~django.http.HttpResponse`
 classes are applied in reverse order, from the bottom up. This means classes
 defined at the end of :setting:`MIDDLEWARE_CLASSES` will be run first.
 
+.. versionchanged:: 1.5
+    ``response`` may also be an :class:`~django.http.StreamingHttpResponse`
+    object.
+
+Unlike :class:`~django.http.HttpResponse`,
+:class:`~django.http.StreamingHttpResponse` does not have a ``content``
+attribute. As a result, middleware can no longer assume that all responses
+will have a ``content`` attribute. If they need access to the content, they
+must test for streaming responses and adjust their behavior accordingly::
+
+    if response.streaming:
+        response.streaming_content = wrap_streaming_content(response.streaming_content)
+    else:
+        response.content = wrap_content(response.content)
+
+``streaming_content`` should be assumed to be too large to hold in memory.
+Middleware may wrap it in a new generator, but must not consume it.
 
 .. _exception-middleware:
 

tests/regressiontests/cache/tests.py

@@ -19,7 +19,8 @@ from django.core.cache import get_cache
 from django.core.cache.backends.base import (CacheKeyWarning,
     InvalidCacheBackendError)
 from django.db import router
-from django.http import HttpResponse, HttpRequest, QueryDict
+from django.http import (HttpResponse, HttpRequest, StreamingHttpResponse,
+    QueryDict)
 from django.middleware.cache import (FetchFromCacheMiddleware,
     UpdateCacheMiddleware, CacheMiddleware)
 from django.template import Template
@@ -1416,6 +1417,29 @@ class CacheI18nTest(TestCase):
         # reset the language
         translation.deactivate()
 
+    @override_settings(
+            CACHE_MIDDLEWARE_KEY_PREFIX="test",
+            CACHE_MIDDLEWARE_SECONDS=60,
+            USE_ETAGS=True,
+    )
+    def test_middleware_with_streaming_response(self):
+        # cache with non empty request.GET
+        request = self._get_request_cache(query_string='foo=baz&other=true')
+
+        # first access, cache must return None
+        get_cache_data = FetchFromCacheMiddleware().process_request(request)
+        self.assertEqual(get_cache_data, None)
+
+        # pass streaming response through UpdateCacheMiddleware.
+        content = 'Check for cache with QUERY_STRING and streaming content'
+        response = StreamingHttpResponse(content)
+        UpdateCacheMiddleware().process_response(request, response)
+
+        # second access, cache must still return None, because we can't cache
+        # streaming response.
+        get_cache_data = FetchFromCacheMiddleware().process_request(request)
+        self.assertEqual(get_cache_data, None)
+
 
 @override_settings(
         CACHES={

tests/regressiontests/httpwrappers/abc.txt

@@ -0,0 +1 @@
+random content

tests/regressiontests/httpwrappers/tests.py

@@ -2,12 +2,13 @@
 from __future__ import unicode_literals
 
 import copy
+import os
 import pickle
 
 from django.core.exceptions import SuspiciousOperation
 from django.http import (QueryDict, HttpResponse, HttpResponseRedirect,
                          HttpResponsePermanentRedirect, HttpResponseNotAllowed,
-                         HttpResponseNotModified,
+                         HttpResponseNotModified, StreamingHttpResponse,
                          SimpleCookie, BadHeaderError,
                          parse_cookie)
 from django.test import TestCase
@@ -351,7 +352,6 @@ class HttpResponseTests(unittest.TestCase):
             self.assertRaises(SuspiciousOperation,
                               HttpResponsePermanentRedirect, url)
 
-
 class HttpResponseSubclassesTests(TestCase):
     def test_redirect(self):
         response = HttpResponseRedirect('/redirected/')
@@ -379,6 +379,113 @@ class HttpResponseSubclassesTests(TestCase):
             content_type='text/html')
         self.assertContains(response, 'Only the GET method is allowed', status_code=405)
 
+class StreamingHttpResponseTests(TestCase):
+    def test_streaming_response(self):
+        r = StreamingHttpResponse(iter(['hello', 'world']))
+
+        # iterating over the response itself yields bytestring chunks.
+        chunks = list(r)
+        self.assertEqual(chunks, [b'hello', b'world'])
+        for chunk in chunks:
+            self.assertIsInstance(chunk, six.binary_type)
+
+        # and the response can only be iterated once.
+        self.assertEqual(list(r), [])
+
+        # even when a sequence that can be iterated many times, like a list,
+        # is given as content.
+        r = StreamingHttpResponse(['abc', 'def'])
+        self.assertEqual(list(r), [b'abc', b'def'])
+        self.assertEqual(list(r), [])
+
+        # streaming responses don't have a `content` attribute.
+        self.assertFalse(hasattr(r, 'content'))
+
+        # and you can't accidentally assign to a `content` attribute.
+        with self.assertRaises(AttributeError):
+            r.content = 'xyz'
+
+        # but they do have a `streaming_content` attribute.
+        self.assertTrue(hasattr(r, 'streaming_content'))
+
+        # that exists so we can check if a response is streaming, and wrap or
+        # replace the content iterator.
+        r.streaming_content = iter(['abc', 'def'])
+        r.streaming_content = (chunk.upper() for chunk in r.streaming_content)
+        self.assertEqual(list(r), [b'ABC', b'DEF'])
+
+        # coercing a streaming response to bytes doesn't return a complete HTTP
+        # message like a regular response does. it only gives us the headers.
+        r = StreamingHttpResponse(iter(['hello', 'world']))
+        self.assertEqual(
+            six.binary_type(r), b'Content-Type: text/html; charset=utf-8')
+
+        # and this won't consume its content.
+        self.assertEqual(list(r), [b'hello', b'world'])
+
+        # additional content cannot be written to the response.
+        r = StreamingHttpResponse(iter(['hello', 'world']))
+        with self.assertRaises(Exception):
+            r.write('!')
+
+        # and we can't tell the current position.
+        with self.assertRaises(Exception):
+            r.tell()
+
+class FileCloseTests(TestCase):
+    def test_response(self):
+        filename = os.path.join(os.path.dirname(__file__), 'abc.txt')
+
+        # file isn't closed until we close the response.
+        file1 = open(filename)
+        r = HttpResponse(file1)
+        self.assertFalse(file1.closed)
+        r.close()
+        self.assertTrue(file1.closed)
+
+        # don't automatically close file when we finish iterating the response.
+        file1 = open(filename)
+        r = HttpResponse(file1)
+        self.assertFalse(file1.closed)
+        list(r)
+        self.assertFalse(file1.closed)
+        r.close()
+        self.assertTrue(file1.closed)
+
+        # when multiple file are assigned as content, make sure they are all
+        # closed with the response.
+        file1 = open(filename)
+        file2 = open(filename)
+        r = HttpResponse(file1)
+        r.content = file2
+        self.assertFalse(file1.closed)
+        self.assertFalse(file2.closed)
+        r.close()
+        self.assertTrue(file1.closed)
+        self.assertTrue(file2.closed)
+
+    def test_streaming_response(self):
+        filename = os.path.join(os.path.dirname(__file__), 'abc.txt')
+
+        # file isn't closed until we close the response.
+        file1 = open(filename)
+        r = StreamingHttpResponse(file1)
+        self.assertFalse(file1.closed)
+        r.close()
+        self.assertTrue(file1.closed)
+
+        # when multiple file are assigned as content, make sure they are all
+        # closed with the response.
+        file1 = open(filename)
+        file2 = open(filename)
+        r = StreamingHttpResponse(file1)
+        r.streaming_content = file2
+        self.assertFalse(file1.closed)
+        self.assertFalse(file2.closed)
+        r.close()
+        self.assertTrue(file1.closed)
+        self.assertTrue(file2.closed)
+
 class CookieTests(unittest.TestCase):
     def test_encode(self):
         """

tests/regressiontests/middleware/tests.py

@@ -8,7 +8,7 @@ from io import BytesIO
 from django.conf import settings
 from django.core import mail
 from django.http import HttpRequest
-from django.http import HttpResponse
+from django.http import HttpResponse, StreamingHttpResponse
 from django.middleware.clickjacking import XFrameOptionsMiddleware
 from django.middleware.common import CommonMiddleware
 from django.middleware.http import ConditionalGetMiddleware
@@ -322,6 +322,12 @@ class ConditionalGetMiddlewareTest(TestCase):
         self.assertTrue('Content-Length' in self.resp)
         self.assertEqual(int(self.resp['Content-Length']), content_length)
 
+    def test_content_length_header_not_added(self):
+        resp = StreamingHttpResponse('content')
+        self.assertFalse('Content-Length' in resp)
+        resp = ConditionalGetMiddleware().process_response(self.req, resp)
+        self.assertFalse('Content-Length' in resp)
+
     def test_content_length_header_not_changed(self):
         bad_content_length = len(self.resp.content) + 10
         self.resp['Content-Length'] = bad_content_length
@@ -351,6 +357,29 @@ class ConditionalGetMiddlewareTest(TestCase):
         self.resp = ConditionalGetMiddleware().process_response(self.req, self.resp)
         self.assertEqual(self.resp.status_code, 200)
 
+    @override_settings(USE_ETAGS=True)
+    def test_etag(self):
+        req = HttpRequest()
+        res = HttpResponse('content')
+        self.assertTrue(
+            CommonMiddleware().process_response(req, res).has_header('ETag'))
+
+    @override_settings(USE_ETAGS=True)
+    def test_etag_streaming_response(self):
+        req = HttpRequest()
+        res = StreamingHttpResponse(['content'])
+        res['ETag'] = 'tomatoes'
+        self.assertEqual(
+            CommonMiddleware().process_response(req, res).get('ETag'),
+            'tomatoes')
+
+    @override_settings(USE_ETAGS=True)
+    def test_no_etag_streaming_response(self):
+        req = HttpRequest()
+        res = StreamingHttpResponse(['content'])
+        self.assertFalse(
+            CommonMiddleware().process_response(req, res).has_header('ETag'))
+
     # Tests for the Last-Modified header
 
     def test_if_modified_since_and_no_last_modified(self):
@@ -511,6 +540,7 @@ class GZipMiddlewareTest(TestCase):
     short_string = b"This string is too short to be worth compressing."
     compressible_string = b'a' * 500
     uncompressible_string = b''.join(six.int2byte(random.randint(0, 255)) for _ in xrange(500))
+    sequence = [b'a' * 500, b'b' * 200, b'a' * 300]
 
     def setUp(self):
         self.req = HttpRequest()
@@ -525,6 +555,8 @@ class GZipMiddlewareTest(TestCase):
         self.resp.status_code = 200
         self.resp.content = self.compressible_string
         self.resp['Content-Type'] = 'text/html; charset=UTF-8'
+        self.stream_resp = StreamingHttpResponse(self.sequence)
+        self.stream_resp['Content-Type'] = 'text/html; charset=UTF-8'
 
     @staticmethod
     def decompress(gzipped_string):
@@ -539,6 +571,15 @@ class GZipMiddlewareTest(TestCase):
         self.assertEqual(r.get('Content-Encoding'), 'gzip')
         self.assertEqual(r.get('Content-Length'), str(len(r.content)))
 
+    def test_compress_streaming_response(self):
+        """
+        Tests that compression is performed on responses with streaming content.
+        """
+        r = GZipMiddleware().process_response(self.req, self.stream_resp)
+        self.assertEqual(self.decompress(b''.join(r)), b''.join(self.sequence))
+        self.assertEqual(r.get('Content-Encoding'), 'gzip')
+        self.assertFalse(r.has_header('Content-Length'))
+
     def test_compress_non_200_response(self):
         """
         Tests that compression is performed on responses with a status other than 200.

tests/regressiontests/views/tests/static.py

@@ -31,28 +31,35 @@ class StaticTests(TestCase):
         media_files = ['file.txt', 'file.txt.gz']
         for filename in media_files:
             response = self.client.get('/views/%s/%s' % (self.prefix, filename))
+            response_content = b''.join(response)
+            response.close()
             file_path = path.join(media_dir, filename)
             with open(file_path, 'rb') as fp:
-                self.assertEqual(fp.read(), response.content)
-            self.assertEqual(len(response.content), int(response['Content-Length']))
+                self.assertEqual(fp.read(), response_content)
+            self.assertEqual(len(response_content), int(response['Content-Length']))
             self.assertEqual(mimetypes.guess_type(file_path)[1], response.get('Content-Encoding', None))
 
     def test_unknown_mime_type(self):
         response = self.client.get('/views/%s/file.unknown' % self.prefix)
+        response.close()
         self.assertEqual('application/octet-stream', response['Content-Type'])
 
     def test_copes_with_empty_path_component(self):
         file_name = 'file.txt'
         response = self.client.get('/views/%s//%s' % (self.prefix, file_name))
+        response_content = b''.join(response)
+        response.close()
         with open(path.join(media_dir, file_name), 'rb') as fp:
-            self.assertEqual(fp.read(), response.content)
+            self.assertEqual(fp.read(), response_content)
 
     def test_is_modified_since(self):
         file_name = 'file.txt'
         response = self.client.get('/views/%s/%s' % (self.prefix, file_name),
             HTTP_IF_MODIFIED_SINCE='Thu, 1 Jan 1970 00:00:00 GMT')
+        response_content = b''.join(response)
+        response.close()
         with open(path.join(media_dir, file_name), 'rb') as fp:
-            self.assertEqual(fp.read(), response.content)
+            self.assertEqual(fp.read(), response_content)
 
     def test_not_modified_since(self):
         file_name = 'file.txt'
@@ -74,9 +81,11 @@ class StaticTests(TestCase):
         invalid_date = 'Mon, 28 May 999999999999 28:25:26 GMT'
         response = self.client.get('/views/%s/%s' % (self.prefix, file_name),
                                    HTTP_IF_MODIFIED_SINCE=invalid_date)
+        response_content = b''.join(response)
+        response.close()
         with open(path.join(media_dir, file_name), 'rb') as fp:
-            self.assertEqual(fp.read(), response.content)
-        self.assertEqual(len(response.content),
+            self.assertEqual(fp.read(), response_content)
+        self.assertEqual(len(response_content),
                           int(response['Content-Length']))
 
     def test_invalid_if_modified_since2(self):
@@ -89,9 +98,11 @@ class StaticTests(TestCase):
         invalid_date = ': 1291108438, Wed, 20 Oct 2010 14:05:00 GMT'
         response = self.client.get('/views/%s/%s' % (self.prefix, file_name),
                                    HTTP_IF_MODIFIED_SINCE=invalid_date)
+        response_content = b''.join(response)
+        response.close()
         with open(path.join(media_dir, file_name), 'rb') as fp:
-            self.assertEqual(fp.read(), response.content)
-        self.assertEqual(len(response.content),
+            self.assertEqual(fp.read(), response_content)
+        self.assertEqual(len(response_content),
                           int(response['Content-Length']))