Merge pull request #742 from kobotoolbox/hotfix-zip-exports

Disable seeking when writing ZIP exports

onadata/libs/utils/viewer_tools.py

@@ -227,6 +227,17 @@ def enketo_url(form_url, id_string, instance_xml=None,
 def create_attachments_zipfile(attachments, output_file=None):
     if not output_file:
         output_file = NamedTemporaryFile()
+    else:
+        # Disable seeking in a way understood by Python's zipfile module. See
+        # https://github.com/python/cpython/blob/ca2009d72a52a98bf43aafa9ad270a4fcfabfc89/Lib/zipfile.py#L1270-L1274
+        # This is a workaround for https://github.com/kobotoolbox/kobocat/issues/475
+        # and https://github.com/jschneier/django-storages/issues/566
+        def no_seeking(*a, **kw):
+            raise AttributeError(
+                'Seeking disabled! See '
+                'https://github.com/kobotoolbox/kobocat/issues/475'
+            )
+        output_file.seek = no_seeking
 
     storage = get_storage_class()()
     with zipfile.ZipFile(output_file, 'w', zipfile.ZIP_STORED, allowZip64=True) as zip_file: