> NFS used to use XDR and some variant of RPC to work but I am not sure it does any more.

Yep, still does [1]. Even 4.1 and 4.2 (the most modern variants of NFS) all start with .x files and XDR encoding. The ancient names codified by Sun still exist and still work (and the tooling still works for introspection as a nice bonus).

[1] https://github.com/nfs-ganesha/nfs-ganesha/tree/next/src/Pro...