Crate tokio_process

An implementation of asynchronous process management for Tokio.

This crate provides a CommandExt trait to enhance the functionality of the Command type in the standard library. The three methods provided by this trait mirror the "spawning" methods in the standard library. The CommandExt trait in this crate, though, returns "future aware" types that interoperate with Tokio. The asynchronous process support is provided through signal handling on Unix and system APIs on Windows.

Examples

Here's an example program which will spawn echo hello world and then wait for it complete.

#![feature(async_await)]

use std::process::Command;
use tokio_process::CommandExt;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Use the standard library's `Command` type to build a process and
    // then execute it via the `CommandExt` trait.
    let child = Command::new("echo").arg("hello").arg("world")
                        .spawn_async();

    // Make sure our child succeeded in spawning and process the result
    let future = child.expect("failed to spawn");

    // Await until the future (and the command) completes
    let status = future.await?;
    println!("the command exited with: {}", status);
    Ok(())
}

Next, let's take a look at an example where we not only spawn echo hello world but we also capture its output.

#![feature(async_await)]

use std::process::Command;
use tokio_process::CommandExt;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Like above, but use `output_async` which returns a future instead of
    // immediately returning the `Child`.
    let output = Command::new("echo").arg("hello").arg("world")
                        .output_async();

    let output = output.await?;

    assert!(output.status.success());
    assert_eq!(output.stdout, b"hello world\n");
    Ok(())
}

We can also read input line by line.

#![feature(async_await)]

use futures_util::stream::StreamExt;
use std::process::{Command, Stdio};
use tokio::codec::{FramedRead, LinesCodec};
use tokio_process::CommandExt;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut cmd = Command::new("cat");

    // Specify that we want the command's standard output piped back to us.
    // By default, standard input/output/error will be inherited from the
    // current process (for example, this means that standard input will
    // come from the keyboard and standard output/error will go directly to
    // the terminal if this process is invoked from the command line).
    cmd.stdout(Stdio::piped());

    let mut child = cmd.spawn_async()
        .expect("failed to spawn command");

    let stdout = child.stdout().take()
        .expect("child did not have a handle to stdout");

    let mut reader = FramedRead::new(stdout, LinesCodec::new());

    // Ensure the child process is spawned in the runtime so it can
    // make progress on its own while we await for any output.
    tokio::spawn(async {
        let status = child.await
            .expect("child process encountered an error");

        println!("child status was: {}", status);
    });

    while let Some(line) = reader.next().await {
        println!("Line: {}", line?);
    }

    Ok(())
}

Caveats

While similar to the standard library, this crate's Child type differs importantly in the behavior of drop. In the standard library, a child process will continue running after the instance of std::process::Child is dropped. In this crate, however, because tokio_process::Child is a future of the child's ExitStatus, a child process is terminated if tokio_process::Child is dropped. The behavior of the standard library can be regained with the Child::forget method.

Structs

Child	Representation of a child process spawned onto an event loop.
ChildStderr	The standard error stream for spawned children.
ChildStdin	The standard input stream for spawned children.
ChildStdout	The standard output stream for spawned children.
OutputAsync	Future returned by the CommandExt::output_async method.
StatusAsync	Future returned by the CommandExt::status_async method.
WaitWithOutput	Future returned from the Child::wait_with_output method.

Traits

CommandExt

Extensions provided by this crate to the Command type in the standard library.