Passing multiple FD over an Unix Socket in a single Control Message doesn't work

[roblabla]

For some reason, passing multiple FD over a Unix Domain Socket doesn't seem to work. Below is some test code that is supposed to send two fd over a Unix Socket along with 8 bytes of data. For some reason, only one FD is sent though, the other is lost in the void.

extern crate nix;

use std::os::unix::net::UnixDatagram;
use std::os::unix::io::{RawFd, AsRawFd};
use nix::sys::socket::{CmsgSpace, ControlMessage, MsgFlags, sendmsg, recvmsg};
use nix::sys::uio::IoVec;


fn main() {
    let (send, receive) = UnixDatagram::pair().unwrap();
    let thread = std::thread::spawn(move || {
        let mut buf = [0u8; 8];
        let iovec = [IoVec::from_mut_slice(&mut buf)];
        let mut space = CmsgSpace::<[RawFd; 2]>::new();
        let (paneid, fds) = match recvmsg(receive.as_raw_fd(), &iovec, Some(&mut space), MsgFlags::empty()) {
            Ok(msg) => {
                let mut iter = msg.cmsgs();
                if let Some(ControlMessage::ScmRights(fds)) = iter.next() {
                    (iovec[0].as_slice(), fds.to_vec())
                } else {
                    panic!();
                }
            },
            Err(_) => {
                panic!();
            }
        };
        println!("paneid = {:?}, fds = {:?}", paneid, fds);
    });

    let slice = [1u8, 2u8, 3u8, 4u8, 5u8, 6u8, 7u8, 8u8];
    let iov = [IoVec::from_slice(&slice)];
    let arr = [0, 1]; // Pass stdin and stdout
    let cmsg = [ControlMessage::ScmRights(&arr)];
    sendmsg(send.as_raw_fd(), &iov, &cmsg, MsgFlags::empty(), None).unwrap();
    thread.join().unwrap();
}

The output is paneid = [1, 2, 3, 4, 5, 6, 7, 8], fds = [6]

[roblabla]

Similarly, sending multiple control messages doesn't seem to work either. The following code panics at runtime on the sendmsg line, with the error thread 'main' panicked at 'called``Result::unwrap()``on an``Err``value: Sys(EBADF)', src/libcore/result.rs:788 :

extern crate nix;

use std::os::unix::net::UnixDatagram;
use std::os::unix::io::{RawFd, AsRawFd};
use nix::sys::socket::{CmsgSpace, ControlMessage, MsgFlags, sendmsg, recvmsg};
use nix::sys::uio::IoVec;


fn main() {
    let (send, receive) = UnixDatagram::pair().unwrap();
    let thread = std::thread::spawn(move || {
        let mut buf = [0u8; 8];
        let iovec = [IoVec::from_mut_slice(&mut buf)];
        let mut space = CmsgSpace::<([RawFd; 1], CmsgSpace<[RawFd; 1]>)>::new();
        let (paneid, fds) = match recvmsg(receive.as_raw_fd(), &iovec, Some(&mut space), MsgFlags::empty()) {
            Ok(msg) => {
                let mut iter = msg.cmsgs();
                let fdone;
                let fdtwo;
                if let Some(ControlMessage::ScmRights(fds)) = iter.next() {
                    fdone = fds[0];
                } else {
                    panic!();
                }
                if let Some(ControlMessage::ScmRights(fds)) = iter.next() {
                    fdtwo = fds[0];
                } else {
                    panic!();
                }
                (iovec[0].as_slice(), [fdone, fdtwo])
            },
            Err(_) => {
                panic!();
            }
        };
        println!("paneid = {:?}, fds = {:?}", paneid, fds);
    });

    let slice = [1u8, 2u8, 3u8, 4u8, 5u8, 6u8, 7u8, 8u8];
    let iov = [IoVec::from_slice(&slice)];
    let arrone = [0];
    let arrtwo = [1]; // pass stdin and stdout
    let cmsg = [ControlMessage::ScmRights(&arrone), ControlMessage::ScmRights(&arrtwo)];
    sendmsg(send.as_raw_fd(), &iov, &cmsg, MsgFlags::empty(), None).unwrap();
    thread.join().unwrap();
}