need to modify file data before storing it on destination

[Kyle Jones]

jw schultz writes:
 > [...]
 > As i hope you can see i am not exactly oposed the idea of
 > compressed repositories with an rsync interface.  I just
 > don't think it belongs in the rsyncd utility.

Sure.  This is why I suggested something general, essentially a
callback from within rsync so I can have other UNIX tools operate
on the data.  rsync does do things that I want--- update file
permissions / ownerships / time stamps, mirror a directory tree,
keep track of hard links.  I want the callback from within rsync
because I want to continue to enjoy these features and not have
to implement them separately.  Also if I want to keep unencrypted
data from hitting the remote disk, there's no way I can implement
it without a callback from within rsync.  Compression I could do
by noting each file that rsync updates and compressing each one,
careful to maintain hard links in the process.

But there are other uses for --remotefilter.  Suppose I have a
image repository and a matching repository of thumbnails.  With
--remotefilter I can use rsync to keep these trees sync'd by
specifying a filter that will take an image on input and produce
a thumbnail on output.  The same sort of thing could be done for
sound files and intro clips, book documents and tables of
contents, even iterative functions and graphics files displaying
fractals.  You just have to expand your definition of
"synchronization" and "equivalence".  I see rsync as a framework
for doing synchronization and I think it would make the tool more
useful if the definition of synchronization could be more
general.