We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Return empty json for empty bundles in ASR
Return empty json for empty bundles in ASR. Unclear whether ASR can handle 204 responses so let's default to empty json. 

See also https://bugzilla.mozilla.org/show_bug.cgi?id=1511640

History:
 - https://github.com/mozmeao/snippets-service/commit/4936f2371e341690def9be40a72abdd32205b0c9
 - https://github.com/mozmeao/snippets-service/commit/cb0fc0ca63af4ed3786342e17c2f50d2fc6dc5c4

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `snippets/base/views.py`
Content:
```
1 import json
2 import logging
3 
4 from distutils.util import strtobool
5 
6 from django.conf import settings
7 from django.contrib.auth.decorators import permission_required
8 from django.core.exceptions import ValidationError
9 from django.http import Http404, HttpResponse, HttpResponseBadRequest, HttpResponseRedirect
10 from django.shortcuts import get_object_or_404, render
11 from django.utils.functional import lazy
12 from django.views.decorators.cache import cache_control
13 from django.views.decorators.csrf import csrf_exempt
14 from django.views.decorators.http import require_POST
15 from django.views.generic import TemplateView
16 
17 from django_statsd.clients import statsd
18 from raven.contrib.django.models import client as sentry_client
19 
20 from snippets.base import util
21 from snippets.base.bundles import ASRSnippetBundle, SnippetBundle
22 from snippets.base.decorators import access_control
23 from snippets.base.encoders import JSONSnippetEncoder
24 from snippets.base.models import ASRSnippet, Client, JSONSnippet, Snippet, SnippetTemplate
25 from snippets.base.util import get_object_or_none
26 
27 
28 def _bundle_timeout():
29     return getattr(settings, 'SNIPPET_BUNDLE_TIMEOUT')
30 SNIPPET_BUNDLE_TIMEOUT = lazy(_bundle_timeout, int)()  # noqa
31 
32 
33 class HomeView(TemplateView):
34     template_name = 'base/home.jinja'
35 
36 
37 @cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)
38 @access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)
39 def fetch_snippets(request, **kwargs):
40     """
41     Return one of the following responses:
42     - 200 with empty body when the bundle is empty
43     - 302 to a bundle URL after generating it if not cached.
44     """
45     statsd.incr('serve.snippets')
46 
47     client = Client(**kwargs)
48     if client.startpage_version == 6:
49         bundle = ASRSnippetBundle(client)
50     else:
51         bundle = SnippetBundle(client)
52     if bundle.empty:
53         statsd.incr('bundle.empty')
54         # This is not a 204 because Activity Stream expects content, even if
55         # it's empty.
56         return HttpResponse(status=200, content='')
57     elif bundle.cached:
58         statsd.incr('bundle.cached')
59     else:
60         statsd.incr('bundle.generate')
61         bundle.generate()
62 
63     return HttpResponseRedirect(bundle.url)
64 
65 
66 @cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)
67 @access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)
68 def fetch_json_snippets(request, **kwargs):
69     statsd.incr('serve.json_snippets')
70     client = Client(**kwargs)
71     matching_snippets = (JSONSnippet.objects
72                          .filter(published=True)
73                          .match_client(client)
74                          .filter_by_available())
75     return HttpResponse(json.dumps(matching_snippets, cls=JSONSnippetEncoder),
76                         content_type='application/json')
77 
78 
79 def preview_asr_snippet(request, uuid):
80     try:
81         snippet = get_object_or_404(ASRSnippet, uuid=uuid)
82     except ValidationError:
83         # Raised when UUID is a badly formed hexadecimal UUID string
84         raise Http404()
85 
86     bundle_content = json.dumps({
87         'messages': [snippet.render(preview=True)],
88     })
89     return HttpResponse(bundle_content, content_type='application/json')
90 
91 
92 @csrf_exempt
93 @permission_required('base.change_snippet')
94 def preview_snippet(request):
95     """
96     Build a snippet using info from the POST parameters, and preview that
97     snippet on a mock about:home page.
98     """
99     try:
100         template_id = int(request.POST.get('template_id', None))
101     except (TypeError, ValueError):
102         return HttpResponseBadRequest()
103 
104     template = get_object_or_none(SnippetTemplate, id=template_id)
105     data = request.POST.get('data', None)
106 
107     # Validate that data is JSON.
108     try:
109         json.loads(data)
110     except (TypeError, ValueError):
111         data = None
112 
113     # If your parameters are wrong, I have no sympathy for you.
114     if data is None or template is None:
115         return HttpResponseBadRequest()
116 
117     # Build a snippet that isn't saved so we can render it.
118     snippet = Snippet(template=template, data=data)
119 
120     if strtobool(request.POST.get('activity_stream', 'false')):
121         template_name = 'base/preview_as.jinja'
122         preview_client = Client(5, 'Firefox', '57.0', 'default', 'default', 'en-US',
123                                 'release', 'default', 'default', 'default')
124     else:
125         template_name = 'base/preview.jinja'
126         preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',
127                                 'release', 'default', 'default', 'default')
128 
129     skip_boilerplate = request.POST.get('skip_boilerplate', 'false')
130     skip_boilerplate = strtobool(skip_boilerplate)
131     if skip_boilerplate:
132         template_name = 'base/preview_without_shell.jinja'
133 
134     return render(request, template_name, {
135         'snippets_json': json.dumps([snippet.to_dict()]),
136         'client': preview_client,
137         'preview': True,
138         'current_firefox_major_version': util.current_firefox_major_version(),
139     })
140 
141 
142 def show_snippet(request, snippet_id, uuid=False):
143     preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',
144                             'release', 'default', 'default', 'default')
145 
146     if uuid:
147         snippet = get_object_or_404(Snippet, uuid=snippet_id)
148     else:
149         snippet = get_object_or_404(Snippet, pk=snippet_id)
150         if not snippet.published and not request.user.is_authenticated:
151             raise Http404()
152 
153     template = 'base/preview.jinja'
154     if snippet.on_startpage_5:
155         template = 'base/preview_as.jinja'
156     return render(request, template, {
157         'snippets_json': json.dumps([snippet.to_dict()]),
158         'client': preview_client,
159         'preview': True,
160         'current_firefox_major_version': util.current_firefox_major_version(),
161     })
162 
163 
164 @csrf_exempt
165 @require_POST
166 def csp_violation_capture(request):
167     data = sentry_client.get_data_from_request(request)
168     data.update({
169         'level': logging.INFO,
170         'logger': 'CSP',
171     })
172     try:
173         csp_data = json.loads(request.body)
174     except ValueError:
175         # Cannot decode CSP violation data, ignore
176         return HttpResponseBadRequest('Invalid CSP Report')
177 
178     try:
179         blocked_uri = csp_data['csp-report']['blocked-uri']
180     except KeyError:
181         # Incomplete CSP report
182         return HttpResponseBadRequest('Incomplete CSP Report')
183 
184     sentry_client.captureMessage(
185         message='CSP Violation: {}'.format(blocked_uri),
186         data=data)
187 
188     return HttpResponse('Captured CSP violation, thanks for reporting.')
189
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/snippets/base/views.py b/snippets/base/views.py
--- a/snippets/base/views.py
+++ b/snippets/base/views.py
@@ -51,6 +51,11 @@
         bundle = SnippetBundle(client)
     if bundle.empty:
         statsd.incr('bundle.empty')
+
+        if client.startpage_version == 6:
+            # Return valid JSON for Activity Stream Router
+            return HttpResponse(status=200, content='{}')
+
         # This is not a 204 because Activity Stream expects content, even if
         # it's empty.
         return HttpResponse(status=200, content='')

{"golden_diff": "diff --git a/snippets/base/views.py b/snippets/base/views.py\n--- a/snippets/base/views.py\n+++ b/snippets/base/views.py\n@@ -51,6 +51,11 @@\n         bundle = SnippetBundle(client)\n     if bundle.empty:\n         statsd.incr('bundle.empty')\n+\n+        if client.startpage_version == 6:\n+            # Return valid JSON for Activity Stream Router\n+            return HttpResponse(status=200, content='{}')\n+\n         # This is not a 204 because Activity Stream expects content, even if\n         # it's empty.\n         return HttpResponse(status=200, content='')\n", "issue": "Return empty json for empty bundles in ASR\nReturn empty json for empty bundles in ASR. Unclear whether ASR can handle 204 responses so let's default to empty json. \r\n\r\nSee also https://bugzilla.mozilla.org/show_bug.cgi?id=1511640\r\n\r\nHistory:\r\n - https://github.com/mozmeao/snippets-service/commit/4936f2371e341690def9be40a72abdd32205b0c9\r\n - https://github.com/mozmeao/snippets-service/commit/cb0fc0ca63af4ed3786342e17c2f50d2fc6dc5c4\n", "before_files": [{"content": "import json\nimport logging\n\nfrom distutils.util import strtobool\n\nfrom django.conf import settings\nfrom django.contrib.auth.decorators import permission_required\nfrom django.core.exceptions import ValidationError\nfrom django.http import Http404, HttpResponse, HttpResponseBadRequest, HttpResponseRedirect\nfrom django.shortcuts import get_object_or_404, render\nfrom django.utils.functional import lazy\nfrom django.views.decorators.cache import cache_control\nfrom django.views.decorators.csrf import csrf_exempt\nfrom django.views.decorators.http import require_POST\nfrom django.views.generic import TemplateView\n\nfrom django_statsd.clients import statsd\nfrom raven.contrib.django.models import client as sentry_client\n\nfrom snippets.base import util\nfrom snippets.base.bundles import ASRSnippetBundle, SnippetBundle\nfrom snippets.base.decorators import access_control\nfrom snippets.base.encoders import JSONSnippetEncoder\nfrom snippets.base.models import ASRSnippet, Client, JSONSnippet, Snippet, SnippetTemplate\nfrom snippets.base.util import get_object_or_none\n\n\ndef _bundle_timeout():\n    return getattr(settings, 'SNIPPET_BUNDLE_TIMEOUT')\nSNIPPET_BUNDLE_TIMEOUT = lazy(_bundle_timeout, int)()  # noqa\n\n\nclass HomeView(TemplateView):\n    template_name = 'base/home.jinja'\n\n\n@cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)\n@access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)\ndef fetch_snippets(request, **kwargs):\n    \"\"\"\n    Return one of the following responses:\n    - 200 with empty body when the bundle is empty\n    - 302 to a bundle URL after generating it if not cached.\n    \"\"\"\n    statsd.incr('serve.snippets')\n\n    client = Client(**kwargs)\n    if client.startpage_version == 6:\n        bundle = ASRSnippetBundle(client)\n    else:\n        bundle = SnippetBundle(client)\n    if bundle.empty:\n        statsd.incr('bundle.empty')\n        # This is not a 204 because Activity Stream expects content, even if\n        # it's empty.\n        return HttpResponse(status=200, content='')\n    elif bundle.cached:\n        statsd.incr('bundle.cached')\n    else:\n        statsd.incr('bundle.generate')\n        bundle.generate()\n\n    return HttpResponseRedirect(bundle.url)\n\n\n@cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)\n@access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)\ndef fetch_json_snippets(request, **kwargs):\n    statsd.incr('serve.json_snippets')\n    client = Client(**kwargs)\n    matching_snippets = (JSONSnippet.objects\n                         .filter(published=True)\n                         .match_client(client)\n                         .filter_by_available())\n    return HttpResponse(json.dumps(matching_snippets, cls=JSONSnippetEncoder),\n                        content_type='application/json')\n\n\ndef preview_asr_snippet(request, uuid):\n    try:\n        snippet = get_object_or_404(ASRSnippet, uuid=uuid)\n    except ValidationError:\n        # Raised when UUID is a badly formed hexadecimal UUID string\n        raise Http404()\n\n    bundle_content = json.dumps({\n        'messages': [snippet.render(preview=True)],\n    })\n    return HttpResponse(bundle_content, content_type='application/json')\n\n\n@csrf_exempt\n@permission_required('base.change_snippet')\ndef preview_snippet(request):\n    \"\"\"\n    Build a snippet using info from the POST parameters, and preview that\n    snippet on a mock about:home page.\n    \"\"\"\n    try:\n        template_id = int(request.POST.get('template_id', None))\n    except (TypeError, ValueError):\n        return HttpResponseBadRequest()\n\n    template = get_object_or_none(SnippetTemplate, id=template_id)\n    data = request.POST.get('data', None)\n\n    # Validate that data is JSON.\n    try:\n        json.loads(data)\n    except (TypeError, ValueError):\n        data = None\n\n    # If your parameters are wrong, I have no sympathy for you.\n    if data is None or template is None:\n        return HttpResponseBadRequest()\n\n    # Build a snippet that isn't saved so we can render it.\n    snippet = Snippet(template=template, data=data)\n\n    if strtobool(request.POST.get('activity_stream', 'false')):\n        template_name = 'base/preview_as.jinja'\n        preview_client = Client(5, 'Firefox', '57.0', 'default', 'default', 'en-US',\n                                'release', 'default', 'default', 'default')\n    else:\n        template_name = 'base/preview.jinja'\n        preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',\n                                'release', 'default', 'default', 'default')\n\n    skip_boilerplate = request.POST.get('skip_boilerplate', 'false')\n    skip_boilerplate = strtobool(skip_boilerplate)\n    if skip_boilerplate:\n        template_name = 'base/preview_without_shell.jinja'\n\n    return render(request, template_name, {\n        'snippets_json': json.dumps([snippet.to_dict()]),\n        'client': preview_client,\n        'preview': True,\n        'current_firefox_major_version': util.current_firefox_major_version(),\n    })\n\n\ndef show_snippet(request, snippet_id, uuid=False):\n    preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',\n                            'release', 'default', 'default', 'default')\n\n    if uuid:\n        snippet = get_object_or_404(Snippet, uuid=snippet_id)\n    else:\n        snippet = get_object_or_404(Snippet, pk=snippet_id)\n        if not snippet.published and not request.user.is_authenticated:\n            raise Http404()\n\n    template = 'base/preview.jinja'\n    if snippet.on_startpage_5:\n        template = 'base/preview_as.jinja'\n    return render(request, template, {\n        'snippets_json': json.dumps([snippet.to_dict()]),\n        'client': preview_client,\n        'preview': True,\n        'current_firefox_major_version': util.current_firefox_major_version(),\n    })\n\n\n@csrf_exempt\n@require_POST\ndef csp_violation_capture(request):\n    data = sentry_client.get_data_from_request(request)\n    data.update({\n        'level': logging.INFO,\n        'logger': 'CSP',\n    })\n    try:\n        csp_data = json.loads(request.body)\n    except ValueError:\n        # Cannot decode CSP violation data, ignore\n        return HttpResponseBadRequest('Invalid CSP Report')\n\n    try:\n        blocked_uri = csp_data['csp-report']['blocked-uri']\n    except KeyError:\n        # Incomplete CSP report\n        return HttpResponseBadRequest('Incomplete CSP Report')\n\n    sentry_client.captureMessage(\n        message='CSP Violation: {}'.format(blocked_uri),\n        data=data)\n\n    return HttpResponse('Captured CSP violation, thanks for reporting.')\n", "path": "snippets/base/views.py"}], "after_files": [{"content": "import json\nimport logging\n\nfrom distutils.util import strtobool\n\nfrom django.conf import settings\nfrom django.contrib.auth.decorators import permission_required\nfrom django.core.exceptions import ValidationError\nfrom django.http import Http404, HttpResponse, HttpResponseBadRequest, HttpResponseRedirect\nfrom django.shortcuts import get_object_or_404, render\nfrom django.utils.functional import lazy\nfrom django.views.decorators.cache import cache_control\nfrom django.views.decorators.csrf import csrf_exempt\nfrom django.views.decorators.http import require_POST\nfrom django.views.generic import TemplateView\n\nfrom django_statsd.clients import statsd\nfrom raven.contrib.django.models import client as sentry_client\n\nfrom snippets.base import util\nfrom snippets.base.bundles import ASRSnippetBundle, SnippetBundle\nfrom snippets.base.decorators import access_control\nfrom snippets.base.encoders import JSONSnippetEncoder\nfrom snippets.base.models import ASRSnippet, Client, JSONSnippet, Snippet, SnippetTemplate\nfrom snippets.base.util import get_object_or_none\n\n\ndef _bundle_timeout():\n    return getattr(settings, 'SNIPPET_BUNDLE_TIMEOUT')\nSNIPPET_BUNDLE_TIMEOUT = lazy(_bundle_timeout, int)()  # noqa\n\n\nclass HomeView(TemplateView):\n    template_name = 'base/home.jinja'\n\n\n@cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)\n@access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)\ndef fetch_snippets(request, **kwargs):\n    \"\"\"\n    Return one of the following responses:\n    - 200 with empty body when the bundle is empty\n    - 302 to a bundle URL after generating it if not cached.\n    \"\"\"\n    statsd.incr('serve.snippets')\n\n    client = Client(**kwargs)\n    if client.startpage_version == 6:\n        bundle = ASRSnippetBundle(client)\n    else:\n        bundle = SnippetBundle(client)\n    if bundle.empty:\n        statsd.incr('bundle.empty')\n\n        if client.startpage_version == 6:\n            # Return valid JSON for Activity Stream Router\n            return HttpResponse(status=200, content='{}')\n\n        # This is not a 204 because Activity Stream expects content, even if\n        # it's empty.\n        return HttpResponse(status=200, content='')\n    elif bundle.cached:\n        statsd.incr('bundle.cached')\n    else:\n        statsd.incr('bundle.generate')\n        bundle.generate()\n\n    return HttpResponseRedirect(bundle.url)\n\n\n@cache_control(public=True, max_age=SNIPPET_BUNDLE_TIMEOUT)\n@access_control(max_age=SNIPPET_BUNDLE_TIMEOUT)\ndef fetch_json_snippets(request, **kwargs):\n    statsd.incr('serve.json_snippets')\n    client = Client(**kwargs)\n    matching_snippets = (JSONSnippet.objects\n                         .filter(published=True)\n                         .match_client(client)\n                         .filter_by_available())\n    return HttpResponse(json.dumps(matching_snippets, cls=JSONSnippetEncoder),\n                        content_type='application/json')\n\n\ndef preview_asr_snippet(request, uuid):\n    try:\n        snippet = get_object_or_404(ASRSnippet, uuid=uuid)\n    except ValidationError:\n        # Raised when UUID is a badly formed hexadecimal UUID string\n        raise Http404()\n\n    bundle_content = json.dumps({\n        'messages': [snippet.render(preview=True)],\n    })\n    return HttpResponse(bundle_content, content_type='application/json')\n\n\n@csrf_exempt\n@permission_required('base.change_snippet')\ndef preview_snippet(request):\n    \"\"\"\n    Build a snippet using info from the POST parameters, and preview that\n    snippet on a mock about:home page.\n    \"\"\"\n    try:\n        template_id = int(request.POST.get('template_id', None))\n    except (TypeError, ValueError):\n        return HttpResponseBadRequest()\n\n    template = get_object_or_none(SnippetTemplate, id=template_id)\n    data = request.POST.get('data', None)\n\n    # Validate that data is JSON.\n    try:\n        json.loads(data)\n    except (TypeError, ValueError):\n        data = None\n\n    # If your parameters are wrong, I have no sympathy for you.\n    if data is None or template is None:\n        return HttpResponseBadRequest()\n\n    # Build a snippet that isn't saved so we can render it.\n    snippet = Snippet(template=template, data=data)\n\n    if strtobool(request.POST.get('activity_stream', 'false')):\n        template_name = 'base/preview_as.jinja'\n        preview_client = Client(5, 'Firefox', '57.0', 'default', 'default', 'en-US',\n                                'release', 'default', 'default', 'default')\n    else:\n        template_name = 'base/preview.jinja'\n        preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',\n                                'release', 'default', 'default', 'default')\n\n    skip_boilerplate = request.POST.get('skip_boilerplate', 'false')\n    skip_boilerplate = strtobool(skip_boilerplate)\n    if skip_boilerplate:\n        template_name = 'base/preview_without_shell.jinja'\n\n    return render(request, template_name, {\n        'snippets_json': json.dumps([snippet.to_dict()]),\n        'client': preview_client,\n        'preview': True,\n        'current_firefox_major_version': util.current_firefox_major_version(),\n    })\n\n\ndef show_snippet(request, snippet_id, uuid=False):\n    preview_client = Client(4, 'Firefox', '24.0', 'default', 'default', 'en-US',\n                            'release', 'default', 'default', 'default')\n\n    if uuid:\n        snippet = get_object_or_404(Snippet, uuid=snippet_id)\n    else:\n        snippet = get_object_or_404(Snippet, pk=snippet_id)\n        if not snippet.published and not request.user.is_authenticated:\n            raise Http404()\n\n    template = 'base/preview.jinja'\n    if snippet.on_startpage_5:\n        template = 'base/preview_as.jinja'\n    return render(request, template, {\n        'snippets_json': json.dumps([snippet.to_dict()]),\n        'client': preview_client,\n        'preview': True,\n        'current_firefox_major_version': util.current_firefox_major_version(),\n    })\n\n\n@csrf_exempt\n@require_POST\ndef csp_violation_capture(request):\n    data = sentry_client.get_data_from_request(request)\n    data.update({\n        'level': logging.INFO,\n        'logger': 'CSP',\n    })\n    try:\n        csp_data = json.loads(request.body)\n    except ValueError:\n        # Cannot decode CSP violation data, ignore\n        return HttpResponseBadRequest('Invalid CSP Report')\n\n    try:\n        blocked_uri = csp_data['csp-report']['blocked-uri']\n    except KeyError:\n        # Incomplete CSP report\n        return HttpResponseBadRequest('Incomplete CSP Report')\n\n    sentry_client.captureMessage(\n        message='CSP Violation: {}'.format(blocked_uri),\n        data=data)\n\n    return HttpResponse('Captured CSP violation, thanks for reporting.')\n", "path": "snippets/base/views.py"}]}