diff -r 44840bcc411a -r 74da9d999cd7 rust/chg/src/clientext.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/chg/src/clientext.rs	Mon Sep 24 18:57:54 2018 +0900
@@ -0,0 +1,51 @@
+// 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.
+
+//! cHg extensions to command server client.
+
+use std::ffi::OsStr;
+use std::os::unix::io::AsRawFd;
+use tokio_hglib::{Client, Connection};
+
+use super::attachio::AttachIo;
+use super::message;
+use super::runcommand::ChgRunCommand;
+use super::uihandler::SystemHandler;
+
+pub trait ChgClientExt<C>
+    where C: Connection + AsRawFd,
+{
+    /// Attaches the client file descriptors to the server.
+    fn attach_io<I, O, E>(self, stdin: I, stdout: O, stderr: E) -> AttachIo<C, I, O, E>
+        where I: AsRawFd,
+              O: AsRawFd,
+              E: AsRawFd;
+
+    /// Runs the specified Mercurial command with cHg extension.
+    fn run_command_chg<I, P, H>(self, handler: H, args: I) -> ChgRunCommand<C, H>
+        where I: IntoIterator<Item = P>,
+              P: AsRef<OsStr>,
+              H: SystemHandler;
+}
+
+impl<C> ChgClientExt<C> for Client<C>
+    where C: Connection + AsRawFd,
+{
+    fn attach_io<I, O, E>(self, stdin: I, stdout: O, stderr: E) -> AttachIo<C, I, O, E>
+        where I: AsRawFd,
+              O: AsRawFd,
+              E: AsRawFd,
+    {
+        AttachIo::with_client(self, stdin, stdout, Some(stderr))
+    }
+
+    fn run_command_chg<I, P, H>(self, handler: H, args: I) -> ChgRunCommand<C, H>
+        where I: IntoIterator<Item = P>,
+              P: AsRef<OsStr>,
+              H: SystemHandler,
+    {
+        ChgRunCommand::with_client(self, handler, message::pack_args_os(args))
+    }
+}