#
cargo_util/
read2.rs

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    pub use self::imp::read2;

    #[cfg(unix)]
    mod imp {
        use libc::{c_int, fcntl, F_GETFL, F_SETFL, O_NONBLOCK};
        use std::io;
        use std::io::prelude::*;
        use std::mem;
        use std::os::unix::prelude::*;
        use std::process::{ChildStderr, ChildStdout};

        fn set_nonblock(fd: c_int) -> io::Result<()> {
            let flags = unsafe { fcntl(fd, F_GETFL) };
            if flags == -1 || unsafe { fcntl(fd, F_SETFL, flags | O_NONBLOCK) } == -1 {
                return Err(io::Error::last_os_error());
            }
            Ok(())
        }

        pub fn read2(
            mut out_pipe: ChildStdout,
            mut err_pipe: ChildStderr,
            data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
        ) -> io::Result<()> {
            set_nonblock(out_pipe.as_raw_fd())?;
            set_nonblock(err_pipe.as_raw_fd())?;

            let mut out_done = false;
            let mut err_done = false;
            let mut out = Vec::new();
            let mut err = Vec::new();

            let mut fds: [libc::pollfd; 2] = unsafe { mem::zeroed() };
            fds[0].fd = out_pipe.as_raw_fd();
            fds[0].events = libc::POLLIN;
            fds[1].fd = err_pipe.as_raw_fd();
            fds[1].events = libc::POLLIN;
            let mut nfds = 2;
            let mut errfd = 1;

            while nfds > 0 {
                // wait for either pipe to become readable using `poll`
                let r = unsafe { libc::poll(fds.as_mut_ptr(), nfds, -1) };
                if r == -1 {
                    let err = io::Error::last_os_error();
                    if err.kind() == io::ErrorKind::Interrupted {
                        continue;
                    }
                    return Err(err);
                }

                // 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.
                let handle = |res: io::Result<_>| match res {
                    Ok(_) => Ok(true),
                    Err(e) => {
                        if e.kind() == io::ErrorKind::WouldBlock {
                            Ok(false)
                        } else {
                            Err(e)
                        }
                    }
                };
                if !err_done && fds[errfd].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
                    err_done = true;
                    nfds -= 1;
                }
                data(false, &mut err, err_done);
                if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? {
                    out_done = true;
                    fds[0].fd = err_pipe.as_raw_fd();
                    errfd = 0;
                    nfds -= 1;
                }
                data(true, &mut out, out_done);
            }
            Ok(())
        }
    }

    #[cfg(windows)]
    mod imp {
        use std::io;
        use std::os::windows::prelude::*;
        use std::process::{ChildStderr, ChildStdout};
        use std::slice;

        use miow::iocp::{CompletionPort, CompletionStatus};
        use miow::pipe::NamedPipe;
        use miow::Overlapped;
        use windows_sys::Win32::Foundation::ERROR_BROKEN_PIPE;

        struct Pipe<'a> {
            dst: &'a mut Vec<u8>,
            overlapped: Overlapped,
            pipe: NamedPipe,
            done: bool,
        }

        pub fn read2(
            out_pipe: ChildStdout,
            err_pipe: ChildStderr,
            data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
        ) -> io::Result<()> {
            let mut out = Vec::new();
            let mut err = Vec::new();

            let port = CompletionPort::new(1)?;
            port.add_handle(0, &out_pipe)?;
            port.add_handle(1, &err_pipe)?;

            unsafe {
                let mut out_pipe = Pipe::new(out_pipe, &mut out);
                let mut err_pipe = Pipe::new(err_pipe, &mut err);

                out_pipe.read()?;
                err_pipe.read()?;

                let mut status = [CompletionStatus::zero(), CompletionStatus::zero()];

                while !out_pipe.done || !err_pipe.done {
                    for status in port.get_many(&mut status, None)? {
                        if status.token() == 0 {
                            out_pipe.complete(status);
                            data(true, out_pipe.dst, out_pipe.done);
                            out_pipe.read()?;
                        } else {
                            err_pipe.complete(status);
                            data(false, err_pipe.dst, err_pipe.done);
                            err_pipe.read()?;
                        }
                    }
                }

                Ok(())
            }
        }

        impl<'a> Pipe<'a> {
            unsafe fn new<P: IntoRawHandle>(p: P, dst: &'a mut Vec<u8>) -> Pipe<'a> {
                Pipe {
                    dst,
                    pipe: NamedPipe::from_raw_handle(p.into_raw_handle()),
                    overlapped: Overlapped::zero(),
                    done: false,
                }
            }

            unsafe fn read(&mut self) -> io::Result<()> {
                let dst = slice_to_end(self.dst);
                match self.pipe.read_overlapped(dst, self.overlapped.raw()) {
                    Ok(_) => Ok(()),
                    Err(e) => {
                        if e.raw_os_error() == Some(ERROR_BROKEN_PIPE as i32) {
                            self.done = true;
                            Ok(())
                        } else {
                            Err(e)
                        }
                    }
                }
            }

            unsafe fn complete(&mut self, status: &CompletionStatus) {
                let prev = self.dst.len();
                self.dst.set_len(prev + status.bytes_transferred() as usize);
                if status.bytes_transferred() == 0 {
                    self.done = true;
                }
            }
        }

        unsafe fn slice_to_end(v: &mut Vec<u8>) -> &mut [u8] {
            if v.capacity() == 0 {
                v.reserve(16);
            }
            if v.capacity() == v.len() {
                v.reserve(1);
            }
            slice::from_raw_parts_mut(v.as_mut_ptr().add(v.len()), v.capacity() - v.len())
        }
    }