[bug] fix order of multipart serialization when writing to couch

The couch backend makes use of attachments and multipart structure for
writing the document to the couch database. For that to work, the order
in which attachments are described must match the actual order in which
attachments are written to the couch http stream.

This was not being properly taken care of, and eventually the json
serializer was arbitrarilly ordering the attachments description in a
way that it didn't match the actual order of attachments writing.

This commit fixes that by using json.dumps() sort_keys parameter and
making sure conflicts are always written before content.

1 files changed, 12 insertions, 1 deletions

diff --git a/common/src/leap/soledad/common/couch/__init__.py b/common/src/leap/soledad/common/couch/__init__.py
index ca0c2855..ba3192a4 100644
--- a/common/src/leap/soledad/common/couch/__init__.py
+++ b/common/src/leap/soledad/common/couch/__init__.py
@@ -714,7 +714,18 @@ class CouchDatabase(object):
         if not self.batching:
             buf = StringIO()
             envelope = MultipartWriter(buf)
-            envelope.add('application/json', json.dumps(couch_doc))
+            # the order in which attachments are described inside the
+            # serialization of the couch document must match the order in which
+            # they are actually written in the multipart structure. Because of
+            # that, we use `sorted_keys=True` in the json serialization (so
+            # "u1db_conflicts" comes before "u1db_content" on the couch
+            # document attachments description), and also reverse the order of
+            # the parts before writing them, so the "conflict" part is written
+            # before the "content" part.
+            envelope.add(
+                'application/json',
+                json.dumps(couch_doc, sort_keys=True))
+            parts.reverse()
             for part in parts:
                 envelope.add('application/octet-stream', part)
             envelope.close()