Is there a way to send ancillary data with 0.16 Io, and if not, is there a way to cleanly integrate it into the io system?
Yes, but only over datagram sockets, not connected ones. It’s currently a known limitation, but fixing Io doesn’t seem to be the priority for the next couple of Zig releases.
“for the next couple” seems to directly contradict what Andrew wrote here in response to you.
Andrew expressed that maybe we can discuss the strategy in a few weeks. Zig 0.17 was supposed to be a short cycle, so let’s just say I’m not as optimistic about 0.18. I’ll be extremely happy to he proven wrong.
I actually put up a PR for exchanging control data with Stream just now!