rust/chg/src/attachio.rs

interfaces: introduce and use a protocol class for the `charencoding` module

See f2832de2a46c for details when this was done for the `bdiff` module.

This lets us dump the hack where the `pure` implementation was imported during
the type checking phase to provide signatures for the module methods it
provides.  Now the protocol classes are starting to shine, because these methods
are provided by `pure.charencoding` and `cext.parsers`, and references to
`cffi.charencoding` and `cext.charencoding` are forwarded to them as appropriate
by the `policy` module.  But none of that matters, as long as the module
returned provides the listed methods.

The interface was copy/pasted from the `pure` module, but `jsonescapeu8fallback`
is omitted because it is accessed from the `pure` module directly when the
escaping fails in the primary module's `jsonescapeu8()`.

// Copyright 2018 Yuya Nishihara <[e-mail]>
//
// 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<()> {
    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",
                ));
            }
        }
    }
}