[Owncloud] Syncing and Time Synchronization

[Klaas Freitag]

On 18.07.2012 14:31, Bart Visscher wrote:
Hi,

> On Wed, Jul 18, 2012 at 10:31:13AM +0200, Klaas Freitag wrote:
>> For that, the best would be if the ownCloud WebDAV server would
>> provide another WebDAV property that returns the md5-sum of the file
>> or file list. That probably means that the md5 sum needs to be
>> calculated on every file change on the server and be stored in the
>> fs cache.
>
> I think you could use the etag for that, this is a standard property in
> WebDAV.
AFAIU Etags could help us here if the PUT of a new file to the server 
would have an ETag in the response which could be stored on the client. 
On subsequent sync runs, the Etag could be checked to see if it has 
changed. Yet, currently I can neither see an etag in the PUT response 
nor in a GET. That is probably because the getETag implementation in 
lib/connector/sabre/file.php returns null. So that would still have to 
be implemented.

> For transfering big files, i have looked at the librsync
> protocol/way. This uses a rolling checksum and a strong hash. The hash
> is md4 which is implemented by php. The rolling checksum is not
> implemented by php, I made a version in php, but this proved to be
> slow (1 second/MB on a fast machine). There is a PECL extension, but i
> think that as owncloud we should also have an alternative.
Yes, but that is another problem, right?
>
>
>>
>> Is that doable? Who can help with that?
>
> I we use the etag property we should calculate this when it is needed,
> not when the file changes. File can change multiple times in between
> etag requests.
Well, calculating an MD5 at least takes some time, so it would be better 
to get that out of the DB rather than calculating it on request.

regards,

Klaas