Ensure that >400 level HTTP errors are properly handled

Fixes: #1072

We discovored that the API endpoint to get an enketo edit url
encountered >400 level errors it did not properly set the HTTP
status code and instead returned the edit url as false.

This set of commits fixes that by raising an EnketoError exception
which has a friendly default error message that can be overriden.

onadata/apps/api/tests/viewsets/test_data_viewset.py

@@ -43,6 +43,14 @@ def enketo_mock(url, request):
     return response
 
 
+@urlmatch(netloc=r'(.*\.)?enketo\.ona\.io$')
+def enketo_mock_http_413(url, request):
+    response = requests.Response()
+    response.status_code = 413
+    response._content = ''
+    return response
+
+
 def _data_list(formid):
     return [{
         u'id': formid,
@@ -1128,6 +1136,11 @@ def test_get_enketo_edit_url(self):
                 response.data['url'],
                 "https://hmh2a.enketo.ona.io")
 
+        with HTTMock(enketo_mock_http_413):
+            response = view(request, pk=formid, dataid=dataid)
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(response.get('Cache-Control'), None)
+
     def test_get_form_public_data(self):
         self._make_submissions()
         view = DataViewSet.as_view({'get': 'list'})

onadata/apps/api/viewsets/data_viewset.py

@@ -254,7 +254,7 @@ def enketo(self, request, *args, **kwargs):
                     data["url"] = get_enketo_edit_url(
                         request, self.object, return_url)
                 except EnketoError as e:
-                    data['detail'] = "{}".format(e)
+                    raise ParseError(str(e))
             else:
                 raise PermissionDenied(_(u"You do not have edit permissions."))
 

onadata/libs/utils/viewer_tools.py

@@ -11,6 +11,7 @@
 from django.core.files.uploadedfile import InMemoryUploadedFile
 from django.core.mail import mail_admins
 from django.utils.translation import ugettext as _
+from django.utils.translation import ugettext_lazy
 
 from onadata.libs.utils import common_tags
 
@@ -22,7 +23,18 @@ class MyError(Exception):
 
 
 class EnketoError(Exception):
-    pass
+
+    default_message = ugettext_lazy("There was a problem with your submission"
+                                    " or form. Please contact support.")
+
+    def __init__(self, message=None):
+        if message is None:
+            self.message = self.default_message
+        else:
+            self.message = message
+
+    def __str__(self):
+        return "{}".format(self.message)
 
 
 def image_urls_for_form(xform):
@@ -120,8 +132,8 @@ def report_exception(subject, info, exc_info=None):
         info += u"".join(traceback.format_exception(*exc_info))
 
     if settings.DEBUG:
-        print subject
-        print info
+        print(subject)
+        print(info)
     else:
         mail_admins(subject=subject, message=info)
 
@@ -189,7 +201,6 @@ def enketo_url(form_url,
     req = requests.post(
         url, data=values, auth=(settings.ENKETO_API_TOKEN, ''),
         verify=getattr(settings, 'VERIFY_SSL', True))
-
     if req.status_code in [200, 201]:
         try:
             response = req.json()
@@ -208,7 +219,7 @@ def enketo_url(form_url,
         try:
             response = req.json()
         except ValueError:
-            pass
+            raise EnketoError()
         else:
             if 'message' in response:
                 raise EnketoError(response['message'])