- It won't fail if there are no file descriptors available
- No error handling needed: the call always succeeds and random bytes are always returned
Don't worry the name is historic it does not us the arc4 cipher any longer, at least on OpenBSD. They switched to chacha20 as stream cipher.
The analog of zx_cprng_draw is getentropy(2): http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/... except zx_cprng_draw kills the process, while getentropy returns an error.