add a sendfile class based view implementation

docs/advanced_topics/images/image_serve_view.rst

@@ -97,3 +97,52 @@ method in your urls configuration:
 
        url(r'^images/([^/]*)/(\d*)/([^/]*)/[^/]*$', ServeView.as_view(action='redirect'), name='wagtailimages_serve'),
    ]
+
+Integration with django-sendfile
+--------------------------------
+
+`django-sendfile`_ offloads the job of transferring the image data to the web
+server instead of serving it directly from the Django application. This could
+greatly reduce server load in situations where your site has many images being
+downloaded but you're unable to use a :ref:`caching_proxy` or a CDN.
+
+.. _django-sendfile: https://github.com/johnsensible/django-sendfile
+
+You firstly need to install and configure django-sendfile and configure your
+web server to use it. If you haven't done this already, please refer to the
+`installation docs <https://github.com/johnsensible/django-sendfile#django-sendfile>`_.
+
+To serve images with django-sendfile, you can use the ``SendFileView`` class.
+This view can be used out of the box:
+
+.. code-block:: python
+
+   from wagtail.wagtailimages.views.serve import SendFileView
+
+   urlpatterns = [
+       ...
+
+       url(r'^images/([^/]*)/(\d*)/([^/]*)/[^/]*$', SendFileView.as_view(), name='wagtailimages_serve'),
+   ]
+
+You can customise it to override the backend defined in the ``SENDFILE_BACKEND``
+setting:
+
+.. code-block:: python
+
+    from wagtail.wagtailimages.views.serve import SendFileView
+    from project.sendfile_backends import MyCustomBackend
+
+    class MySendFileView(SendFileView):
+        backend = MyCustomBackend
+
+You can also customise it to serve private files. For example, if the only need
+is to be authenticated (e.g. for Django >= 1.9):
+
+.. code-block:: python
+
+    from django.contrib.auth.mixins import LoginRequiredMixin
+    from wagtail.wagtailimages.views.serve import SendFileView
+
+    class PrivateSendFileView(LoginRequiredMixin, SendFileView):
+        raise_exception = True

docs/advanced_topics/performance.rst

@@ -58,6 +58,8 @@ Wagtail is tested on SQLite, and should work on other Django-supported database
 Public users
 ~~~~~~~~~~~~
 
+.. _caching_proxy:
+
 Caching proxy
 -------------
 

wagtail/tests/dummy_sendfile_backend.py

@@ -0,0 +1,10 @@
+from __future__ import absolute_import, unicode_literals
+
+from django.http import HttpResponse
+
+
+def sendfile(request, filename, **kwargs):
+    """
+    Dummy sendfile backend implementation.
+    """
+    return HttpResponse('Dummy backend response')

wagtail/wagtailimages/tests/tests.py

@@ -1,11 +1,12 @@
 from __future__ import absolute_import, unicode_literals
 
 import os
+import unittest
 
 from django import forms, template
 from django.core.exceptions import ImproperlyConfigured
 from django.core.urlresolvers import reverse
-from django.test import TestCase
+from django.test import TestCase, override_settings
 from django.utils import six
 from mock import MagicMock
 from taggit.forms import TagField, TagWidget
@@ -21,6 +22,12 @@ from wagtail.wagtailimages.views.serve import ServeView, generate_signature, ver
 
 from .utils import Image, get_test_image_file
 
+try:
+    import sendfile  # noqa
+    sendfile_mod = True
+except:
+    sendfile_mod = False
+
 
 class TestImageTag(TestCase):
     def setUp(self):
@@ -354,6 +361,36 @@ class TestFrontendServeView(TestCase):
         self.assertEqual(response.status_code, 410)
 
 
+class TestFrontendSendfileView(TestCase):
+
+    def setUp(self):
+        self.image = Image.objects.create(
+            title="Test image",
+            file=get_test_image_file(),
+        )
+
+    @override_settings(SENDFILE_BACKEND='sendfile.backends.development')
+    @unittest.skipIf(not sendfile_mod, 'Missing django-sendfile app.')
+    def test_sendfile_nobackend(self):
+        signature = generate_signature(self.image.id, 'fill-800x600')
+        response = self.client.get(reverse('wagtailimages_sendfile',
+                                           args=(signature, self.image.id,
+                                                 'fill-800x600')))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response['Content-Type'], 'image/png')
+
+    @override_settings(SENDFILE_BACKEND='sendfile.backends.development')
+    def test_sendfile_dummy_backend(self):
+        signature = generate_signature(self.image.id, 'fill-800x600')
+        response = self.client.get(reverse('wagtailimages_sendfile_dummy',
+                                           args=(signature, self.image.id,
+                                                 'fill-800x600')))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertTrue(response.content, 'Dummy backend response')
+
+
 class TestRect(TestCase):
     def test_init(self):
         rect = Rect(100, 150, 200, 250)

wagtail/wagtailimages/tests/urls.py

@@ -2,10 +2,13 @@ from __future__ import absolute_import, unicode_literals
 
 from django.conf.urls import url
 
-from wagtail.wagtailimages.views.serve import ServeView
+from wagtail.tests import dummy_sendfile_backend
+from wagtail.wagtailimages.views.serve import SendFileView, ServeView
 
 urlpatterns = [
     url(r'^actions/serve/(.*)/(\d*)/(.*)/[^/]*', ServeView.as_view(action='serve'), name='wagtailimages_serve_action_serve'),
     url(r'^actions/redirect/(.*)/(\d*)/(.*)/[^/]*', ServeView.as_view(action='redirect'), name='wagtailimages_serve_action_redirect'),
     url(r'^custom_key/(.*)/(\d*)/(.*)/[^/]*', ServeView.as_view(key='custom'), name='wagtailimages_serve_custom_key'),
+    url(r'^sendfile/(.*)/(\d*)/(.*)/[^/]*', SendFileView.as_view(), name='wagtailimages_sendfile'),
+    url(r'^sendfile-dummy/(.*)/(\d*)/(.*)/[^/]*', SendFileView.as_view(backend=dummy_sendfile_backend.sendfile), name='wagtailimages_sendfile_dummy'),
 ]

wagtail/wagtailimages/views/serve.py

@@ -14,6 +14,7 @@ from django.utils.decorators import classonlymethod
 from django.utils.six import text_type
 from django.views.generic import View
 
+from wagtail.utils.sendfile import sendfile
 from wagtail.wagtailimages.exceptions import InvalidFilterSpecError
 from wagtail.wagtailimages.models import SourceImageIOError, get_image_model
 
@@ -78,3 +79,10 @@ class ServeView(View):
 
 
 serve = ServeView.as_view()
+
+
+class SendFileView(ServeView):
+    backend = None
+
+    def serve(self, rendition):
+        return sendfile(self.request, rendition.file.path, backend=self.backend)