Function send_packet 

async fn send_packet(
    socket: &UnixSeqpacket,
    packet: &[IoSlice<'_>],
    hangup: Pin<&mut impl Future<Output = ()>>,
    token: &CancellationToken,
    draining: bool,
) -> Result<bool>

Send a packet, false if the client went away or does not take it in time. A client which does not read keeps a send waiting, until it hangs up or, once the container exited, for at most DRAIN_MAX_WAIT. Each packet gets that long, so that a slow client still gets the output which was there already.