Allow to upload only when sync attribute matches
Protocols like WebDAV allow to run an upload only under certain conditions, e.g. when the file on the server has a known etag
. We should implement support for this, as this allows to implement a robust server-first sync strategy (if we don't, we cannot guarantee that the file on the server was not updated between querying recent state information and trying the upload).
Edit: If possible, the same probably should be implemented for the delete job as well.
Edited by Martin Hoeher