simplesshd/rsync/rsyncsh.txt

rsyncsh
Copyright (C) 2001 by Martin Pool

This is a quick hack to build an interactive shell around rsync, the
same way we have the ftp, lftp and ncftp programs for the FTP
protocol.  The key application for this is connecting to a public
rsync server, such as rsync.kernel.org, change down through and list
directories, and finally pull down the file you want.

rsync is somewhat ill-at-ease as an interactive operation, since every
network connection is used to carry out exactly one operation.  rsync
kind of "forks across the network" passing the options and filenames
to operate upon, and the connection is closed when the transfer is
complete.  (This might be fixed in the future, either by adapting the
current protocol to allow chained operations over a single socket, or
by writing a new protocol that better supports interactive use.)

So, rsyncsh runs a new rsync command and opens a new socket for every
(network-based) command you type.

This has two consequences.  Firstly, there is more command latency
than is really desirable.  More seriously, if the connection cannot be
done automatically, because for example it uses SSH with a password,
then you will need to enter the password every time.  We might even
fix this in the future, though, by having a way to automatically feed
the password to SSH if it's entered once.