async-process/src/lib.rs

752 lines
23 KiB
Rust

//! Async interface for working with processes.
//!
//! This crate is an async version of [`std::process`].
//!
//! # Implementation
//!
//! A background thread named "async-process" is lazily created on first use, which waits for
//! spawned child processes to exit and then calls the `wait()` syscall to clean up the "zombie"
//! processes. This is unlike the `process` API in the standard library, where dropping a running
//! `Child` leaks its resources.
//!
//! This crate uses [`async-io`] for async I/O on Unix-like systems and [`blocking`] for async I/O
//! on Windows.
//!
//! [`async-io`]: https://docs.rs/async-io
//! [`blocking`]: https://docs.rs/blocking
//!
//! # Examples
//!
//! Spawn a process and collect its output:
//!
//! ```no_run
//! # futures_lite::future::block_on(async {
//! use async_process::Command;
//!
//! let out = Command::new("echo").arg("hello").arg("world").output().await?;
//! assert_eq!(out.stdout, b"hello world\n");
//! # std::io::Result::Ok(()) });
//! ```
//!
//! Read the output line-by-line as it gets produced:
//!
//! ```no_run
//! # futures_lite::future::block_on(async {
//! use async_process::{Command, Stdio};
//! use futures_lite::{AsyncBufReadExt, StreamExt, io::BufReader};
//!
//! let mut child = Command::new("find")
//! .arg(".")
//! .stdout(Stdio::piped())
//! .spawn()?;
//!
//! let mut lines = BufReader::new(child.stdout.take().unwrap()).lines();
//!
//! while let Some(line) = lines.next().await {
//! println!("{}", line?);
//! }
//! # std::io::Result::Ok(()) });
//! ```
#![cfg_attr(unix, forbid(unsafe_code))]
#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
use std::ffi::OsStr;
use std::fmt;
use std::future::Future;
use std::path::Path;
use std::pin::Pin;
use std::sync::{Arc, Mutex};
use std::task::{Context, Poll};
use std::thread;
use async_channel::{Receiver, Sender};
#[cfg(unix)]
use async_io::Async;
#[cfg(windows)]
use blocking::Unblock;
use futures_lite::{future, io, AsyncReadExt};
use once_cell::sync::Lazy;
#[doc(no_inline)]
pub use std::process::{ExitStatus, Output, Stdio};
/// A spawned child process.
///
/// The process can be in running or exited state. Use [`status()`][`Child::status()`] or
/// [`output()`][`Child::output()`] to wait for it to exit.
///
/// If the [`Child`] is dropped, the process keeps running in the background.
///
/// # Examples
///
/// Spawn a process and wait for it to complete:
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// Command::new("cp").arg("a.txt").arg("b.txt").status().await?;
/// # std::io::Result::Ok(()) });
/// ```
pub struct Child {
/// The handle for writing to the child's standard input (stdin), if it has been captured.
pub stdin: Option<ChildStdin>,
/// The handle for reading from the child's standard output (stdout), if it has been captured.
pub stdout: Option<ChildStdout>,
/// The handle for reading from the child's standard error (stderr), if it has been captured.
pub stderr: Option<ChildStderr>,
/// The inner handle to the child process.
child: Arc<Mutex<std::process::Child>>,
/// A channel that gets closed when the process exits.
exited: Receiver<()>,
}
impl Child {
/// Wraps the inner child process handle and registers it in the global process list.
///
/// The "async-process" thread waits for processes in the global list and cleans up the
/// resources when they exit.
fn new(mut child: std::process::Child) -> io::Result<Child> {
cfg_if::cfg_if! {
if #[cfg(windows)] {
use std::os::windows::io::AsRawHandle;
use std::sync::mpsc;
use winapi::um::{
winbase::{RegisterWaitForSingleObject, INFINITE},
winnt::{BOOLEAN, HANDLE, PVOID, WT_EXECUTEINWAITTHREAD, WT_EXECUTEONLYONCE},
};
// This channel is used to simulate SIGCHLD on Windows.
static SIGCHLD: Lazy<(mpsc::SyncSender<()>, Mutex<mpsc::Receiver<()>>)> =
Lazy::new(|| {
let (s, r) = mpsc::sync_channel(1);
(s, Mutex::new(r))
});
// Called when a child exits.
unsafe extern "system" fn callback(_: PVOID, _: BOOLEAN) {
let _ = SIGCHLD.0.try_send(());
}
// Register this child process to invoke `callback` on exit.
let mut wait_object = std::ptr::null_mut();
let ret = unsafe {
RegisterWaitForSingleObject(
&mut wait_object,
child.as_raw_handle() as HANDLE,
Some(callback),
std::ptr::null_mut(),
INFINITE,
WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE,
)
};
if ret == 0 {
return Err(io::Error::last_os_error());
}
// Waits for the next SIGCHLD signal.
fn wait_sigchld() {
let _ = SIGCHLD.1.lock().unwrap().recv();
}
// Wraps a sync I/O type into an async I/O type.
fn wrap<T>(io: T) -> io::Result<Unblock<T>> {
Ok(Unblock::new(io))
}
} else if #[cfg(unix)] {
static SIGNALS: Lazy<signal_hook::iterator::Signals> = Lazy::new(|| {
signal_hook::iterator::Signals::new(&[signal_hook::SIGCHLD])
.expect("cannot set signal handler for SIGCHLD")
});
// Make sure the signal handler is registered before interacting with the process.
Lazy::force(&SIGNALS);
// Waits for the next SIGCHLD signal.
fn wait_sigchld() {
SIGNALS.forever().next();
}
// Wraps a sync I/O type into an async I/O type.
fn wrap<T: std::os::unix::io::AsRawFd>(io: T) -> io::Result<Async<T>> {
Async::new(io)
}
}
}
// An entry in the list of running child processes.
struct Entry {
child: Arc<Mutex<std::process::Child>>,
_exited: Sender<()>,
}
// The global list of running child processes.
static CHILDREN: Lazy<Mutex<Vec<Entry>>> = Lazy::new(|| {
// Start a thread that handles SIGCHLD and notifies tasks when child processes exit.
thread::Builder::new()
.name("async-process".to_string())
.spawn(move || {
loop {
// Wait for the next SIGCHLD signal.
wait_sigchld();
// Remove processes that have exited. When an entry is removed from this
// `Vec`, its associated `Sender` is dropped, thus disconnecting the
// channel and waking up the task waiting on the `Receiver`.
CHILDREN.lock().unwrap().retain(|entry| {
let mut child = entry.child.lock().unwrap();
child.try_wait().expect("error waiting a child").is_none()
});
}
})
.expect("cannot spawn async-process thread");
Mutex::new(Vec::new())
});
// Convert sync I/O types into async I/O types.
let stdin = child.stdin.take().map(wrap).transpose()?.map(ChildStdin);
let stdout = child.stdout.take().map(wrap).transpose()?.map(ChildStdout);
let stderr = child.stderr.take().map(wrap).transpose()?.map(ChildStderr);
// Register the child process in the global list.
let child = Arc::new(Mutex::new(child));
let (sender, exited) = async_channel::bounded(1);
CHILDREN.lock().unwrap().push(Entry {
child: child.clone(),
_exited: sender,
});
Ok(Child {
stdin,
stdout,
stderr,
child,
exited,
})
}
/// Returns the OS-assigned process identifier associated with this child.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let mut child = Command::new("ls").spawn()?;
/// println!("id: {}", child.id());
/// # std::io::Result::Ok(()) });
/// ```
pub fn id(&self) -> u32 {
self.child.lock().unwrap().id()
}
/// Forces the child process to exit.
///
/// If the child has already exited, an [`InvalidInput`] error is returned.
///
/// This is equivalent to sending a SIGKILL on Unix platforms.
///
/// [`InvalidInput`]: `std::io::ErrorKind::InvalidInput`
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let mut child = Command::new("yes").spawn()?;
/// child.kill()?;
/// println!("exit status: {}", child.status().await?);
/// # std::io::Result::Ok(()) });
/// ```
pub fn kill(&mut self) -> io::Result<()> {
self.child.lock().unwrap().kill()
}
/// Returns the exit status if the process has exited.
///
/// Unlike [`status()`][`Child::status()`], this method will not drop the stdin handle.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let mut child = Command::new("ls").spawn()?;
///
/// match child.try_status()? {
/// None => println!("still running"),
/// Some(status) => println!("exited with: {}", status),
/// }
/// # std::io::Result::Ok(()) });
/// ```
pub fn try_status(&mut self) -> io::Result<Option<ExitStatus>> {
self.child.lock().unwrap().try_wait()
}
/// Drops the stdin handle and waits for the process to exit.
///
/// Closing the stdin of the process helps avoid deadlocks. It ensures that the process does
/// not block waiting for input from the parent process while the parent waits for the child to
/// exit.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::{Command, Stdio};
///
/// let mut child = Command::new("cp")
/// .arg("a.txt")
/// .arg("b.txt")
/// .spawn()?;
///
/// println!("exit status: {}", child.status().await?);
/// # std::io::Result::Ok(()) });
/// ```
pub fn status(&mut self) -> impl Future<Output = io::Result<ExitStatus>> {
self.stdin.take();
let child = self.child.clone();
let exited = self.exited.clone();
async move {
let _ = exited.recv().await;
child.lock().unwrap().wait()
}
}
/// Drops the stdin handle and collects the output of the process.
///
/// Closing the stdin of the process helps avoid deadlocks. It ensures that the process does
/// not block waiting for input from the parent process while the parent waits for the child to
/// exit.
///
/// In order to capture the output of the process, [`Command::stdout()`] and
/// [`Command::stderr()`] must be configured with [`Stdio::piped()`].
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::{Command, Stdio};
///
/// let child = Command::new("ls")
/// .stdout(Stdio::piped())
/// .stderr(Stdio::piped())
/// .spawn()?;
///
/// let out = child.output().await?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn output(mut self) -> impl Future<Output = io::Result<Output>> {
// A future that waits for the exit status.
let status = self.status();
// A future that collects stdout.
let stdout = self.stdout.take();
let stdout = async move {
let mut v = Vec::new();
if let Some(mut s) = stdout {
s.read_to_end(&mut v).await?;
}
Ok(v)
};
// A future that collects stderr.
let stderr = self.stderr.take();
let stderr = async move {
let mut v = Vec::new();
if let Some(mut s) = stderr {
s.read_to_end(&mut v).await?;
}
Ok(v)
};
async move {
let (status, (stdout, stderr)) =
future::try_join(status, future::try_join(stdout, stderr)).await?;
Ok(Output {
status,
stdout,
stderr,
})
}
}
}
impl fmt::Debug for Child {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Child")
.field("stdin", &self.stdin)
.field("stdout", &self.stdout)
.field("stderr", &self.stderr)
.finish()
}
}
/// A handle to a child process's standard input (stdin).
///
/// When a [`ChildStdin`] is dropped, the underlying handle gets clossed. If the child process was
/// previously blocked on input, it becomes unblocked after dropping.
#[derive(Debug)]
pub struct ChildStdin(
#[cfg(windows)] Unblock<std::process::ChildStdin>,
#[cfg(unix)] Async<std::process::ChildStdin>,
);
impl io::AsyncWrite for ChildStdin {
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Pin::new(&mut self.0).poll_write(cx, buf)
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Pin::new(&mut self.0).poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Pin::new(&mut self.0).poll_close(cx)
}
}
/// A handle to a child process's standard output (stdout).
///
/// When a [`ChildStdout`] is dropped, the underlying handle gets closed.
#[derive(Debug)]
pub struct ChildStdout(
#[cfg(windows)] Unblock<std::process::ChildStdout>,
#[cfg(unix)] Async<std::process::ChildStdout>,
);
impl io::AsyncRead for ChildStdout {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<io::Result<usize>> {
Pin::new(&mut self.0).poll_read(cx, buf)
}
}
/// A handle to a child process's standard error (stderr).
///
/// When a [`ChildStderr`] is dropped, the underlying handle gets closed.
#[derive(Debug)]
pub struct ChildStderr(
#[cfg(windows)] Unblock<std::process::ChildStderr>,
#[cfg(unix)] Async<std::process::ChildStderr>,
);
impl io::AsyncRead for ChildStderr {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<io::Result<usize>> {
Pin::new(&mut self.0).poll_read(cx, buf)
}
}
/// A builder for spawning processes.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let output = if cfg!(target_os = "windows") {
/// Command::new("cmd").args(&["/C", "echo hello"]).output().await?
/// } else {
/// Command::new("sh").arg("-c").arg("echo hello").output().await?
/// };
/// # std::io::Result::Ok(()) });
/// ```
#[derive(Debug)]
pub struct Command {
cmd: std::process::Command,
stdin: Option<Stdio>,
stdout: Option<Stdio>,
stderr: Option<Stdio>,
}
impl Command {
/// Constructs a new [`Command`] for launching `program`.
///
/// The initial configuration (the working directory and environment variables) is inherited
/// from the current process.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// ```
pub fn new<S: AsRef<OsStr>>(program: S) -> Command {
Command {
cmd: std::process::Command::new(program),
stdin: None,
stdout: None,
stderr: None,
}
}
/// Adds a single argument to pass to the program.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("echo");
/// cmd.arg("hello");
/// cmd.arg("world");
/// ```
pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command {
self.cmd.arg(arg);
self
}
/// Adds multiple arguments to pass to the program.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("echo");
/// cmd.args(&["hello", "world"]);
/// ```
pub fn args<I, S>(&mut self, args: I) -> &mut Command
where
I: IntoIterator<Item = S>,
S: AsRef<OsStr>,
{
self.cmd.args(args);
self
}
/// Configures an environment variable for the new process.
///
/// Note that environment variable names are case-insensitive (but case-preserving) on Windows,
/// and case-sensitive on all other platforms.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// cmd.env("PATH", "/bin");
/// ```
pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Command
where
K: AsRef<OsStr>,
V: AsRef<OsStr>,
{
self.cmd.env(key, val);
self
}
/// Configures multiple environment variables for the new process.
///
/// Note that environment variable names are case-insensitive (but case-preserving) on Windows,
/// and case-sensitive on all other platforms.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// cmd.envs(vec![("PATH", "/bin"), ("TERM", "xterm-256color")]);
/// ```
pub fn envs<I, K, V>(&mut self, vars: I) -> &mut Command
where
I: IntoIterator<Item = (K, V)>,
K: AsRef<OsStr>,
V: AsRef<OsStr>,
{
self.cmd.envs(vars);
self
}
/// Removes an environment variable mapping.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// cmd.env_remove("PATH");
/// ```
pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command {
self.cmd.env_remove(key);
self
}
/// Removes all environment variable mappings.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// cmd.env_clear();
/// ```
pub fn env_clear(&mut self) -> &mut Command {
self.cmd.env_clear();
self
}
/// Configures the working directory for the new process.
///
/// # Examples
///
/// ```
/// use async_process::Command;
///
/// let mut cmd = Command::new("ls");
/// cmd.current_dir("/");
/// ```
pub fn current_dir<P: AsRef<Path>>(&mut self, dir: P) -> &mut Command {
self.cmd.current_dir(dir);
self
}
/// Configures the standard input (stdin) for the new process.
///
/// # Examples
///
/// ```
/// use async_process::{Command, Stdio};
///
/// let mut cmd = Command::new("cat");
/// cmd.stdin(Stdio::null());
/// ```
pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
self.stdin = Some(cfg.into());
self
}
/// Configures the standard output (stdout) for the new process.
///
/// # Examples
///
/// ```
/// use async_process::{Command, Stdio};
///
/// let mut cmd = Command::new("ls");
/// cmd.stdout(Stdio::piped());
/// ```
pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
self.stdout = Some(cfg.into());
self
}
/// Configures the standard error (stderr) for the new process.
///
/// # Examples
///
/// ```
/// use async_process::{Command, Stdio};
///
/// let mut cmd = Command::new("ls");
/// cmd.stderr(Stdio::piped());
/// ```
pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
self.stderr = Some(cfg.into());
self
}
/// Executes the command and returns the [`Child`] handle to it.
///
/// If not configured, stdin, stdout and stderr will be set to [`Stdio::inherit()`].
///
/// After spawning the process, stdin, stdout, and stderr become unconfigured again.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let child = Command::new("ls").spawn()?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn spawn(&mut self) -> io::Result<Child> {
let (stdin, stdout, stderr) = (self.stdin.take(), self.stdout.take(), self.stderr.take());
self.cmd.stdin(stdin.unwrap_or(Stdio::inherit()));
self.cmd.stdout(stdout.unwrap_or(Stdio::inherit()));
self.cmd.stderr(stderr.unwrap_or(Stdio::inherit()));
Child::new(self.cmd.spawn()?)
}
/// Executes the command, waits for it to exit, and returns the exit status.
///
/// If not configured, stdin, stdout and stderr will be set to [`Stdio::inherit()`].
///
/// After spawning the process, stdin, stdout, and stderr become unconfigured again.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let status = Command::new("cp")
/// .arg("a.txt")
/// .arg("b.txt")
/// .status()
/// .await?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn status(&mut self) -> impl Future<Output = io::Result<ExitStatus>> {
let child = self.spawn();
async { child?.status().await }
}
/// Executes the command and collects its output.
///
/// If not configured, stdin will be set to [`Stdio::null()`], and stdout and stderr will be
/// set to [`Stdio::piped()`].
///
/// After spawning the process, stdin, stdout, and stderr become unconfigured again.
///
/// # Examples
///
/// ```no_run
/// # futures_lite::future::block_on(async {
/// use async_process::Command;
///
/// let child = Command::new("ls").spawn()?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn output(&mut self) -> impl Future<Output = io::Result<Output>> {
let (stdin, stdout, stderr) = (self.stdin.take(), self.stdout.take(), self.stderr.take());
self.cmd.stdin(stdin.unwrap_or(Stdio::null()));
self.cmd.stdout(stdout.unwrap_or(Stdio::piped()));
self.cmd.stderr(stderr.unwrap_or(Stdio::piped()));
let child = self.cmd.spawn();
async { Child::new(child?)?.output().await }
}
}