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 using an event loop.

extern crate futures;
extern crate tokio;
extern crate tokio_process;

use std::process::Command;

use futures::Future;
use tokio_process::CommandExt;

fn main() {
    // 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")
        .map(|status| println!("exit status: {}", status))
        .map_err(|e| panic!("failed to wait for exit: {}", e));

    // Send the future to the tokio runtime for execution
    tokio::run(future)
}

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

extern crate futures;
extern crate tokio;
extern crate tokio_process;

use std::process::Command;

use futures::Future;
use tokio_process::CommandExt;

fn main() {
    // 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 future = output.map_err(|e| panic!("failed to collect output: {}", e))
        .map(|output| {
            assert!(output.status.success());
            assert_eq!(output.stdout, b"hello world\n");
        });

    tokio::run(future);
}

We can also read input line by line.

extern crate futures;
extern crate tokio;
extern crate tokio_process;
extern crate tokio_io;

use std::io;
use std::process::{Command, Stdio};

use futures::{Future, Stream};
use tokio_process::{CommandExt, Child};

fn print_lines(mut cat: Child) -> Box<Future<Item = (), Error = ()> + Send + 'static> {
    let stdout = cat.stdout().take().unwrap();
    let reader = io::BufReader::new(stdout);
    let lines = tokio_io::io::lines(reader);
    let cycle = lines.for_each(|l| {
        println!("Line: {}", l);
        Ok(())
    });

    let future = cycle.join(cat)
        .map(|_| ())
        .map_err(|e| panic!("{}", e));

    Box::new(future)
}

fn main() {
    let mut cmd = Command::new("cat");
    cmd.stdout(Stdio::piped());

    let future = print_lines(cmd.spawn_async().expect("failed to spawn command"));
    tokio::run(future);
}

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.