#13 Doc: st_*msg() un-necessarily constrained to UDP

[MarkD]

Both st_sendmsg() and st_recvmsg() caution that "A file descriptor object identifier (see st_netfd_t) representing a UDP socket", but I don't think that constraint is valid. I've long used by st_sendmsg() and st_recvmsg() on a TCP socket to do, inter alia, fd-passing and the st library does just fine.

My suspicion is that this reference to UDP is just an artifact of a copy/paste of st_sendto() and st_recvfrom().

In any event, I think that restriction on UDP sockets should be removed from the docs or clarified as to when it does not work for TCP.