// Copyright 2018 Yuya Nishihara <yuya@tcha.org>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Functions to send client-side fds over the command server channel.

use std::io;
use std::os::unix::io::AsRawFd;
use tokio_hglib::codec::ChannelMessage;
use tokio_hglib::{Connection, Protocol};

use crate::message;
use crate::procutil;

/// Sends client-side fds over the command server channel.
///
/// This works as follows:
/// 1. Client sends "attachio" request.
/// 2. Server sends back 1-byte input request.
/// 3. Client sends fds with 1-byte dummy payload in response.
/// 4. Server returns the number of the fds received.
///
/// The client-side fds may be dropped once duplicated to the server.
pub async fn attach_io(
    proto: &mut Protocol<impl Connection + AsRawFd>,
    stdin: &impl AsRawFd,
    stdout: &impl AsRawFd,
    stderr: &impl AsRawFd,
) -> io::Result<()> {
    // TODO: unindent
    {
        proto.send_command("attachio").await?;
        loop {
            match proto.fetch_response().await? {
                ChannelMessage::Data(b'r', data) => {
                    let fd_cnt = message::parse_result_code(data)?;
                    if fd_cnt == 3 {
                        return Ok(());
                    } else {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidData,
                            "unexpected attachio result",
                        ));
                    }
                }
                ChannelMessage::Data(..) => {
                    // just ignore data sent to uninteresting (optional) channel
                }
                ChannelMessage::InputRequest(1) => {
                    // this may fail with EWOULDBLOCK in theory, but the
                    // payload is quite small, and the send buffer should
                    // be empty so the operation will complete immediately
                    let sock_fd = proto.as_raw_fd();
                    let ifd = stdin.as_raw_fd();
                    let ofd = stdout.as_raw_fd();
                    let efd = stderr.as_raw_fd();
                    procutil::send_raw_fds(sock_fd, &[ifd, ofd, efd])?;
                }
                ChannelMessage::InputRequest(..)
                | ChannelMessage::LineRequest(..)
                | ChannelMessage::SystemRequest(..) => {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidData,
                        "unsupported request while attaching io",
                    ));
                }
            }
        }
    }
}