Kristaps Dzonsons has developed a clean-room implementation of rsync, based on The rsync Algorithm by Andrew Tridgell and Paul Mackerras. It’s licensed under BSD/ISC, and leverages OpenBSD’s native
unveil security systems.
I predominantly use FreeBSD, so I was encouraged by the portability section of the README:
This is possible (I think?) with FreeBSD’s Capsicum, but Linux’s security facilities are a mess, and will take an expert hand to properly secure.
I’m looking forward to someone smarter than me figuring out how this would work on FreeBSD; one fewer GPL package is always a good thing. rsync isn’t just a nice thing to have, it makes my work and personal projects possible.