[Storagesync] Some preliminary investigations on ownCloud

[Linhui Sun <[e-mail]>]

Hi all,

As I mentioned before, I think the developers could benefit from the IETF
standards. The ownCloud (https://owncloud.org/) is just an example. It is
developed for those who do not trust commercial storage services and want
to build their own network-based storage services. The ownCloud is using
WebDAV (RFC4918) to achieve the data sync. IMO, the WebDAV is designed for
distributed work but not for the sync. Thus, I made some preliminary
investigations on how the ownCloud uses WebDAV for sync purposes. A brief
summary of what I've found is in the following, please correct me if I am
wrong.

I installed the ownCloud server (v8.2.1) on the CentOS7, and the client is
a desktop client on Windows.

1. To find whether there is a change to the synced directory, the client
continuously sends PROPFIND to the server at regular intervals (around 34
seconds under my observation). The server will respond a 207 Multi-Status
Response to tell whether the main directory has been changed. To perform
this regular check, the client will open a new TCP connection to send the
PROPFIND, the server will close the existing TCP connection after
responding the 207 Multi-Status Response. For the next check, the client
will open another new TCP connection.

2. Every time adding (or creating) a new file to the local folder, the
client will open a new TCP connection (if there is no connection existing)
to send the file asap. The client will first send several PROPFINDs to find
out which sub-directory has been changed. And then it sends the file using
PUT. The server will respond a 201 Created Response and then terminate the
connection. Currently, I haven't found any application layer chunking, all
the segmentation are performed by TCP.

3. Every time I delete (or rename) a file locally, the client will also
open a new TCP connection to send several PROPFINDs to find out which file
has been removed (or renamed). Then it will send DELETE (or MOVE). The
server will respond a 204 No Content Response (or 201 Created Response) and
then terminate the connection.

4. I open a file and frequently edit and save it (actually this is what I
usually do with the Dropbox). The client will send the whole file to the
server every time I save the file.

To summarize, it seems that the ownCloud makes heavily use of PROPFIND to
achieve the sync process. Each sync operation (e.g. upload, modify and
etc.) will start with sending one or more PROPFINDs. And currently, if I
add a file to the server (directly from the server side via web interface),
the client cannot find the change. I need to interrupt the sync and recover
it to make the client be aware of the change and download the newly added
file. I'm not sure whether this is caused by the sync mechanism or an
improper server configuration. I need to investigate this further and also
how the ownCloud works for multiple clients (or devices).

For ISS, I think ownCloud has demonstrated to some extent that similar IETF
protocols could be deployed and employed. The intention of this message is
to investigate the current state of using WebDAV for sync purposes to see
what needs to be improved here and whether we need new protocols.

Comments are welcome : )

Regards,
Linhui