Local transform on files before sending?

[David Howe]

Matt McCutchen wrote:
> On Sun, 2009-02-08 at 20:28 -0600, Michael Gardner wrote:
>> Is it possible to have rsync do a transform on each file before sending
>> it? This would be useful for things like individually compressed or
>> encrypted backups, or in my case, syncing lossy copies of my FLAC music
>> to an mp3 player or laptop.
> 
> This feature is provided by a maintained patch, which is not very
> mature:
> 
> http://rsync.samba.org/ftp/rsync/patches/source-filter_dest-filter.diff
> 
> Like many others, this patch is perhaps worthy but no one has shown an
> interest in working on it recently.  If you are willing to improve the
> patch to the point that it meets your needs, that would be great.

I can see this particular example being excessively cpu intensive though
- having to re-encode an entire directory of lossless files as a
different format so you can compute the hash - plus of course its
possible that some encoding processes could be non-deterministic.

Only way I can think of to avoid is to keep some sort of pre-computed
transform index - original vs re-encoded hash and filename - and check
against original hash and filename locally, re-encoded hash and filename
remotely.