rust/library/std/src/sys/unix/pipe.rs

use crate::io::{self, IoSlice, IoSliceMut};
use crate::mem;
use crate::sys::fd::FileDesc;
use crate::sys::{cvt, cvt_r};

////////////////////////////////////////////////////////////////////////////////
// Anonymous pipes
////////////////////////////////////////////////////////////////////////////////

pub struct AnonPipe(FileDesc);

pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
    let mut fds = [0; 2];

    // The only known way right now to create atomically set the CLOEXEC flag is
    // to use the `pipe2` syscall. This was added to Linux in 2.6.27, glibc 2.9
    // and musl 0.9.3, and some other targets also have it.
    cfg_if::cfg_if! {
        if #[cfg(any(
            target_os = "dragonfly",
            target_os = "freebsd",
            target_os = "linux",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "redox"
        ))] {
            cvt(unsafe { libc::pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) })?;
            Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))))
        } else {
            cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;

            let fd0 = FileDesc::new(fds[0]);
            let fd1 = FileDesc::new(fds[1]);
            fd0.set_cloexec()?;
            fd1.set_cloexec()?;
            Ok((AnonPipe(fd0), AnonPipe(fd1)))
        }
    }
}

impl AnonPipe {
    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.0.read(buf)
    }

    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        self.0.read_vectored(bufs)
    }

    #[inline]
    pub fn is_read_vectored(&self) -> bool {
        self.0.is_read_vectored()
    }

    pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
        self.0.write(buf)
    }

    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        self.0.write_vectored(bufs)
    }

    #[inline]
    pub fn is_write_vectored(&self) -> bool {
        self.0.is_write_vectored()
    }

    pub fn fd(&self) -> &FileDesc {
        &self.0
    }
    pub fn into_fd(self) -> FileDesc {
        self.0
    }
}

pub fn read2(p1: AnonPipe, v1: &mut Vec<u8>, p2: AnonPipe, v2: &mut Vec<u8>) -> io::Result<()> {
    // Set both pipes into nonblocking mode as we're gonna be reading from both
    // in the `select` loop below, and we wouldn't want one to block the other!
    let p1 = p1.into_fd();
    let p2 = p2.into_fd();
    p1.set_nonblocking(true)?;
    p2.set_nonblocking(true)?;

    let mut fds: [libc::pollfd; 2] = unsafe { mem::zeroed() };
    fds[0].fd = p1.raw();
    fds[0].events = libc::POLLIN;
    fds[1].fd = p2.raw();
    fds[1].events = libc::POLLIN;
    loop {
        // wait for either pipe to become readable using `poll`
        cvt_r(|| unsafe { libc::poll(fds.as_mut_ptr(), 2, -1) })?;

        if fds[0].revents != 0 && read(&p1, v1)? {
            p2.set_nonblocking(false)?;
            return p2.read_to_end(v2).map(drop);
        }
        if fds[1].revents != 0 && read(&p2, v2)? {
            p1.set_nonblocking(false)?;
            return p1.read_to_end(v1).map(drop);
        }
    }

    // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
    // EAGAIN. If we hit EOF, then this will happen because the underlying
    // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
    // this case we flip the other fd back into blocking mode and read
    // whatever's leftover on that file descriptor.
    fn read(fd: &FileDesc, dst: &mut Vec<u8>) -> Result<bool, io::Error> {
        match fd.read_to_end(dst) {
            Ok(_) => Ok(true),
            Err(e) => {
                if e.raw_os_error() == Some(libc::EWOULDBLOCK)
                    || e.raw_os_error() == Some(libc::EAGAIN)
                {
                    Ok(false)
                } else {
                    Err(e)
                }
            }
        }
    }
}