[Owncloud] Syncing and Time Synchronization

[Bart Visscher]

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. 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.


> 
> 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.

Bart
> 
> Best,
> 
> Klaas
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