procutil: make stream detection in make_line_buffered more correct and strict
In make_line_buffered(), we don’t want to wrap the stream if we know that lines
get flushed to the underlying raw stream already.
Previously, the heuristic was too optimistic. It assumed that any stream which
is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there
are buffered streams that aren’t instances of io.BufferedIOBase, like
Mercurial’s own winstdout.
The new logic is different in two ways:
First, only for the check, if unwraps any combination of WriteAllWrapper and
winstdout.
Second, it skips wrapping the stream only if it is an instance of io.RawIOBase
(or already wrapped). If it is an instance of io.BufferedIOBase, it gets
wrapped. In any other case, the function raises an exception. This ensures
that, if an unknown stream is passed or we add another wrapper in the future,
we don’t wrap the stream if it’s already line buffered or not wrap the stream
if it’s not line buffered. In fact, this was already helpful during development
of this change. Without it, I possibly would have forgot that WriteAllWrapper
needs to be ignored for the check, leading to unnecessary wrapping if stdout is
unbuffered.
The alternative would have been to always wrap unknown streams. However, I
don’t think that anyone would benefit from being less strict. We can expect
streams from the standard library to be subclassing either io.RawIOBase or
io.BufferedIOBase, so running Mercurial in the standard way should not regress
by this change. Py2exe might replace sys.stdout and sys.stderr, but that
currently breaks Mercurial anyway and also these streams don’t claim to be
interactive, so this function is not called for them.
// 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.
use async_trait::async_trait;
use std::io;
use std::os::unix::io::AsRawFd;
use std::os::unix::process::ExitStatusExt;
use std::process::Stdio;
use tokio;
use tokio::process::{Child, ChildStdin, Command};
use crate::message::CommandSpec;
use crate::procutil;
/// Callback to process shell command requests received from server.
#[async_trait]
pub trait SystemHandler {
type PagerStdin: AsRawFd;
/// Handles pager command request.
///
/// Returns the pipe to be attached to the server if the pager is spawned.
async fn spawn_pager(
&mut self,
spec: &CommandSpec,
) -> io::Result<Self::PagerStdin>;
/// Handles system command request.
///
/// Returns command exit code (positive) or signal number (negative).
async fn run_system(&mut self, spec: &CommandSpec) -> io::Result<i32>;
}
/// Default cHg implementation to process requests received from server.
pub struct ChgUiHandler {
pager: Option<Child>,
}
impl ChgUiHandler {
pub fn new() -> ChgUiHandler {
ChgUiHandler { pager: None }
}
/// Waits until the pager process exits.
pub async fn wait_pager(&mut self) -> io::Result<()> {
if let Some(p) = self.pager.take() {
p.await?;
}
Ok(())
}
}
#[async_trait]
impl SystemHandler for ChgUiHandler {
type PagerStdin = ChildStdin;
async fn spawn_pager(
&mut self,
spec: &CommandSpec,
) -> io::Result<Self::PagerStdin> {
let mut pager =
new_shell_command(&spec).stdin(Stdio::piped()).spawn()?;
let pin = pager.stdin.take().unwrap();
procutil::set_blocking_fd(pin.as_raw_fd())?;
// TODO: if pager exits, notify the server with SIGPIPE immediately.
// otherwise the server won't get SIGPIPE if it does not write
// anything. (issue5278)
// kill(peerpid, SIGPIPE);
self.pager = Some(pager);
Ok(pin)
}
async fn run_system(&mut self, spec: &CommandSpec) -> io::Result<i32> {
let status = new_shell_command(&spec).spawn()?.await?;
let code = status
.code()
.or_else(|| status.signal().map(|n| -n))
.expect("either exit code or signal should be set");
Ok(code)
}
}
fn new_shell_command(spec: &CommandSpec) -> Command {
let mut builder = Command::new("/bin/sh");
builder
.arg("-c")
.arg(&spec.command)
.current_dir(&spec.current_dir)
.env_clear()
.envs(spec.envs.iter().cloned());
builder
}