Gracefully handle uploading the same item twice.

We were failing until now, but since the uid is sure to be unique,
we can just assume that if it's the same uid it's the same content.
This means we can just gracefully fail as the data is the same.

Until now, we were raising an error, but we now just do nothing
and consider it a success.

This is especially useful when a network error caused an item to
be uploaded but not updated on the client side.

django_etebase/serializers.py

@@ -30,6 +30,10 @@ User = get_user_model()
 def process_revisions_for_item(item, revision_data):
     chunks_objs = []
     chunks = revision_data.pop('chunks_relation')
+
+    revision = models.CollectionItemRevision(**revision_data, item=item)
+    revision.validate_unique()  # Verify there aren't any validation issues
+
     for chunk in chunks:
         uid = chunk[0]
         chunk_obj = models.CollectionItemChunk.objects.filter(uid=uid).first()
@@ -47,8 +51,9 @@ def process_revisions_for_item(item, revision_data):
         chunks_objs.append(chunk_obj)
 
     stoken = models.Stoken.objects.create()
+    revision.stoken = stoken
+    revision.save()
 
-    revision = models.CollectionItemRevision.objects.create(**revision_data, item=item, stoken=stoken)
     for chunk in chunks_objs:
         models.RevisionChunkRelation.objects.create(chunk=chunk, revision=revision)
     return revision
@@ -196,6 +201,9 @@ class CollectionItemRevisionSerializer(BetterErrorsMixin, serializers.ModelSeria
     class Meta:
         model = models.CollectionItemRevision
         fields = ('chunks', 'meta', 'uid', 'deleted')
+        extra_kwargs = {
+            'uid': {'validators': []},  # We deal with it in the serializers
+        }
 
 
 class CollectionItemSerializer(BetterErrorsMixin, serializers.ModelSerializer):
@@ -220,6 +228,10 @@ class CollectionItemSerializer(BetterErrorsMixin, serializers.ModelSerializer):
             instance, created = Model.objects.get_or_create(uid=uid, defaults=validated_data)
             cur_etag = instance.etag if not created else None
 
+            # If we are trying to update an up to date item, abort early and consider it a success
+            if cur_etag == revision_data.get('uid'):
+                return instance
+
             if validate_etag and cur_etag != etag:
                 raise EtebaseValidationError('wrong_etag', 'Wrong etag. Expected {} got {}'.format(cur_etag, etag),
                                              status_code=status.HTTP_409_CONFLICT)
@@ -231,7 +243,10 @@ class CollectionItemSerializer(BetterErrorsMixin, serializers.ModelSerializer):
                 current_revision.current = None
                 current_revision.save()
 
+            try:
                 process_revisions_for_item(instance, revision_data)
+            except django_exceptions.ValidationError as e:
+                self.transform_validation_error("content", e)
 
         return instance