Use tempfile.SpooledTemporaryFile() instead of raw BytesIO (#767)

* Use tempfile.SpooledTemporaryFile() instead of raw BytesIO
* Fix test to call .read() instead of .getvalue()

CTFd/utils/exports/__init__.py

@@ -14,6 +14,7 @@ import os
 import re
 import six
 import zipfile
+import tempfile
 
 
 class CTFdSerializer(JSONSerializer):
@@ -56,7 +57,7 @@ def export_ctf():
     db = dataset.connect(get_app_config('SQLALCHEMY_DATABASE_URI'))
 
     # Backup database
-    backup = six.BytesIO()
+    backup = tempfile.SpooledTemporaryFile()
 
     backup_zip = zipfile.ZipFile(backup, 'w')
 

tests/utils/test_exports.py

@@ -27,7 +27,7 @@ def test_export_ctf():
             backup = export_ctf()
 
             with open('export.zip', 'wb') as f:
-                f.write(backup.getvalue())
+                f.write(backup.read())
             os.remove('export.zip')
     destroy_ctfd(app)