rsync (Was: Call for Community Feedback: Retiring IETF FTP Service)

[Job Snijders <[e-mail]>]

On Thu, Nov 26, 2020 at 04:26:24PM +0000, Dave Cridland wrote:
> On Wed, 25 Nov 2020 at 18:03, Lyndon Nerenberg <[e-mail]> wrote:
> 
> > The cluster I use doesn't support rsync
> 
> I appreciate this is slightly off-topic, but given the consistent
> suggestion that "rsync" should replace FTP, perhaps this is the best place
> to ask - I can find an implementation of rsync easily enough, but I can't
> find the specification published as an open standard anywhere - do you know
> where I can find it?

Fun question!

The RSYNC algorithm is outlined in these (excellent) papers by Andrew
Tridgell: https://rsync.samba.org/~tridge/phd_thesis.pdf and
https://www.andrew.cmu.edu/course/15-749/READINGS/required/cas/tridgell96.pdf

Currently only two interoperable implementations of the RSYNC protocol exist:

GPL rsync, aka 'the original'
    source: https://github.com/WayneD/rsync
    web: https://rsync.samba.org/
    initial release: 1996

openrsync, a clean-room implementation by the OpenBSD project
    source: https://cvsweb.openbsd.org/src/usr.bin/rsync/
    web: https://www.openrsync.org/
    initial release: 2019

To produce openrsync the paper was very helpful, but also some reverse
engineering was required: ktrace, 'rsync -vvvv', and lots of tcpdump. In
hindsight a specification in the form of a IETF RFC would've been very
helpful :-)

Currently the closest thing to a specification about what happens on the
wire probably is the notes compiled during the openrsync development,
the notes can be found here (mandoc format): https://github.com/openbsd/src/blob/master/usr.bin/rsync/rsync.5

For your convenience i put a HTML version up here: http://sobornost.net/~job/rsync.5.html

Kind regards,

Job