Added preview view to admin

As the frontend serve view now uses renditions, previews are now
generated with their own view to prevent loads of unneeded renditions
being created.

wagtail/wagtailimages/admin_urls.py

@@ -9,6 +9,7 @@ urlpatterns = [
     url(r'^(\d+)/delete/$', images.delete, name='wagtailimages_delete_image'),
     url(r'^(\d+)/generate_url/$', images.url_generator, name='wagtailimages_url_generator'),
     url(r'^(\d+)/generate_url/(.*)/$', images.generate_url, name='wagtailimages_generate_url'),
+    url(r'^(\d+)/preview/(.*)/$', images.preview, name='wagtailimages_preview'),
     url(r'^add/$', images.add, name='wagtailimages_add_image'),
     url(r'^usage/(\d+)/$', images.usage, name='wagtailimages_image_usage'),
 

wagtail/wagtailimages/static/wagtailimages/js/image-url-generator.js

@@ -58,7 +58,7 @@ $(function() {
             $.getJSON(generatorUrl.replace('__filterspec__', filterSpec))
                 .done(function(data) {
                     $result.val(data['url']);
-                    $preview.attr('src', data['local_url']);
+                    $preview.attr('src', data['preview_url']);
                     $loadingMask.removeClass('loading');
                 })
                 .fail(function(data) {

wagtail/wagtailimages/tests/test_admin_views.py

@@ -517,7 +517,7 @@ class TestGenerateURLView(TestCase, WagtailTestUtils):
         # Check JSON
         content_json = json.loads(response.content.decode())
 
-        self.assertEqual(set(content_json.keys()), set(['url', 'local_url']))
+        self.assertEqual(set(content_json.keys()), set(['url', 'preview_url']))
 
         expected_url = 'http://localhost/images/%(signature)s/%(image_id)d/fill-800x600/' % {
             'signature': urlquote(generate_signature(self.image.id, 'fill-800x600').decode()),
@@ -525,11 +525,8 @@ class TestGenerateURLView(TestCase, WagtailTestUtils):
         }
         self.assertEqual(content_json['url'], expected_url)
 
-        expected_local_url = '/images/%(signature)s/%(image_id)d/fill-800x600/' % {
-            'signature': urlquote(generate_signature(self.image.id, 'fill-800x600').decode()),
-            'image_id': self.image.id,
-        }
-        self.assertEqual(content_json['local_url'], expected_local_url)
+        expected_preview_url = reverse('wagtailimages_preview', args=(self.image.id, 'fill-800x600'))
+        self.assertEqual(content_json['preview_url'], expected_preview_url)
 
     def test_get_bad_permissions(self):
         """
@@ -585,3 +582,41 @@ class TestGenerateURLView(TestCase, WagtailTestUtils):
         self.assertJSONEqual(response.content.decode(), json.dumps({
             'error': 'Invalid filter spec.',
         }))
+
+
+class TestPreviewView(TestCase, WagtailTestUtils):
+    def setUp(self):
+        # Create an image for running tests on
+        self.image = Image.objects.create(
+            title="Test image",
+            file=get_test_image_file(),
+        )
+
+        # Login
+        self.user = self.login()
+
+    def test_get(self):
+        """
+        Test a valid GET request to the view
+        """
+        # Get the image
+        response = self.client.get(reverse('wagtailimages_preview', args=(self.image.id, 'fill-800x600')))
+
+        # Check response
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response['Content-Type'], 'image/jpeg')
+
+    def test_get_invalid_filter_spec(self):
+        """
+        Test that an invalid filter spec returns a 400 response
+
+        This is very unlikely to happen in reality. A user would have
+        to create signature for the invalid filter spec which can't be
+        done with Wagtails built in URL generator. We should test it
+        anyway though.
+        """
+        # Get the image
+        response = self.client.get(reverse('wagtailimages_preview', args=(self.image.id, 'bad-filter-spec')))
+
+        # Check response
+        self.assertEqual(response.status_code, 400)

wagtail/wagtailimages/views/images.py

@@ -180,7 +180,20 @@ def generate_url(request, image_id, filter_spec):
     except Site.DoesNotExist:
         site_root_url = Site.objects.first().root_url
 
-    return json_response({'url': site_root_url + url, 'local_url': url}, status=200)
+    # Generate preview url
+    preview_url = reverse('wagtailimages_preview', args=(image_id, filter_spec))
+
+    return json_response({'url': site_root_url + url, 'preview_url': preview_url}, status=200)
+
+
+@permission_required('wagtailadmin.access_admin')
+def preview(request, image_id, filter_spec):
+    image = get_object_or_404(get_image_model(), id=image_id)
+
+    try:
+        return Filter(spec=filter_spec).process_image(image.file.file, HttpResponse(content_type='image/jpeg'), focal_point=image.get_focal_point())
+    except Filter.InvalidFilterSpecError:
+        return HttpResponse("Invalid filter spec: " + filter_spec, content_type='text/plain', status=400)
 
 
 @permission_required('wagtailadmin.access_admin')  # more specific permission tests are applied within the view