rust-chg: install signal handlers to forward signals to server

I use sync::Once as a synchronization primitive because it's quite easy
to use, and is good enough to prevent data race in these C functions.

rust/chg/src/main.rs

@@ -1,51 +1,59
 // 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.
 
 extern crate chg;
 extern crate futures;
 extern crate tokio;
 extern crate tokio_hglib;
 
 use chg::{ChgClientExt, ChgUiHandler};
 use chg::locator;
+use chg::procutil;
 use futures::sync::oneshot;
 use std::env;
 use std::io;
 use std::process;
 use tokio::prelude::*;
 use tokio_hglib::UnixClient;
 
 fn main() {
     let code = run().unwrap_or_else(|err| {
         eprintln!("chg: abort: {}", err);
         255
     });
     process::exit(code);
 }
 
 fn run() -> io::Result<i32> {
     let current_dir = env::current_dir()?;
     let sock_path = locator::prepare_server_socket_path()?;
     let handler = ChgUiHandler::new();
     let (result_tx, result_rx) = oneshot::channel();
     let fut = UnixClient::connect(sock_path)
         .and_then(|client| {
             client.set_current_dir(current_dir)
         })
         .and_then(|client| {
             client.attach_io(io::stdin(), io::stdout(), io::stderr())
         })
         .and_then(|client| {
+            let pid = client.server_spec().process_id.unwrap();
+            let pgid = client.server_spec().process_group_id;
+            procutil::setup_signal_handler_once(pid, pgid)?;
+            Ok(client)
+        })
+        .and_then(|client| {
             client.run_command_chg(handler, env::args_os().skip(1))
         })
         .map(|(_client, _handler, code)| {
+            procutil::restore_signal_handler_once()?;
             Ok(code)
         })
         .or_else(|err| Ok(Err(err)))  // pass back error to caller
         .map(|res| result_tx.send(res).unwrap());
     tokio::run(fut);
     result_rx.wait().unwrap_or(Err(io::Error::new(io::ErrorKind::Other,
                                                   "no exit code set")))
 }

rust/chg/src/procutil.rs

@@ -1,43 +1,87
 // 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.
 
 //! Low-level utility for signal and process handling.
 
-use libc::{self, c_int, size_t, ssize_t};
+use libc::{self, c_int, pid_t, size_t, ssize_t};
 use std::io;
 use std::os::unix::io::RawFd;
+use std::sync;
 
 #[link(name = "procutil", kind = "static")]
 extern "C" {
     // sendfds.c
     fn sendfds(sockfd: c_int, fds: *const c_int, fdlen: size_t) -> ssize_t;
+
+    // sighandlers.c
+    fn setupsignalhandler(pid: pid_t, pgid: pid_t) -> c_int;
+    fn restoresignalhandler() -> c_int;
 }
 
 /// Returns the effective uid of the current process.
 pub fn get_effective_uid() -> u32 {
     unsafe { libc::geteuid() }
 }
 
 /// Changes the given fd to blocking mode.
 pub fn set_blocking_fd(fd: RawFd) -> io::Result<()> {
     let flags = unsafe { libc::fcntl(fd, libc::F_GETFL) };
     if flags < 0 {
         return Err(io::Error::last_os_error());
     }
     let r = unsafe { libc::fcntl(fd, libc::F_SETFL, flags & !libc::O_NONBLOCK) };
     if r < 0 {
         return Err(io::Error::last_os_error())
     }
     Ok(())
 }
 
 /// Sends file descriptors via the given socket.
 pub fn send_raw_fds(sock_fd: RawFd, fds: &[RawFd]) -> io::Result<()> {
     let r = unsafe { sendfds(sock_fd, fds.as_ptr(), fds.len() as size_t) };
     if r < 0 {
         return Err(io::Error::last_os_error());
     }
     Ok(())
 }
+
+static SETUP_SIGNAL_HANDLER: sync::Once = sync::Once::new();
+static RESTORE_SIGNAL_HANDLER: sync::Once = sync::Once::new();
+
+/// Installs signal handlers to forward signals to the server.
+///
+/// # Safety
+///
+/// This touches global states, and thus synchronized as a one-time
+/// initialization function.
+pub fn setup_signal_handler_once(pid: u32, pgid: Option<u32>) -> io::Result<()> {
+    let pid_signed = pid as i32;
+    let pgid_signed = pgid.map(|n| n as i32).unwrap_or(0);
+    let mut r = 0;
+    SETUP_SIGNAL_HANDLER.call_once(|| {
+        r = unsafe { setupsignalhandler(pid_signed, pgid_signed) };
+    });
+    if r < 0 {
+        return Err(io::Error::last_os_error());
+    }
+    Ok(())
+}
+
+/// Restores the original signal handlers.
+///
+/// # Safety
+///
+/// This touches global states, and thus synchronized as a one-time
+/// initialization function.
+pub fn restore_signal_handler_once() -> io::Result<()> {
+    let mut r = 0;
+    RESTORE_SIGNAL_HANDLER.call_once(|| {
+        r = unsafe { restoresignalhandler() };
+    });
+    if r < 0 {
+        return Err(io::Error::last_os_error());
+    }
+    Ok(())
+}