poll.rs

use std::io;
use std::net;
use std::os::unix::io::AsRawFd;
use std::os::unix::io::RawFd;
use std::time;

#[repr(C, packed)]
pub struct Descriptor {
    fd: RawFd,
    events: libc::c_short,
    revents: libc::c_short,
}

impl From<net::TcpStream> for Descriptor {
    fn from(s: net::TcpStream) -> Self {
        Self {
            fd: s.as_raw_fd(),
            events: 0,
            revents: 0,
        }
    }
}

#[allow(non_camel_case_types)]
type nfds_t = libc::c_ulong;

#[derive(Debug, Copy, Clone)]
pub enum Poll {
    Timeout,
    Selected(usize),
}

pub fn poll(fds: &mut [Descriptor], timeout: time::Duration) -> Result<Poll, io::Error> {
    let timeout = timeout.as_millis() as libc::c_int;

    let result = unsafe {
        libc::poll(
            fds.as_mut_ptr() as *mut libc::pollfd,
            fds.len() as nfds_t,
            timeout,
        )
    };

    if result == 0 {
        Ok(Poll::Timeout)
    } else if result > 0 {
        Ok(Poll::Selected(result as usize))
    } else {
        Err(io::Error::last_os_error())
    }
}