tokio/tests/stdio.rs

extern crate futures;
#[macro_use]
extern crate tokio_core;
extern crate tokio_process;
#[macro_use]
extern crate log;
extern crate env_logger;

use std::env;
use std::io;
use std::process::{Stdio, ExitStatus};

use futures::{Future, BoxFuture};
use futures::stream::{self, Stream};
use tokio_core::io::{read_until, write_all};
use tokio_core::reactor::{Core, Handle};
use tokio_process::{Command, Child};

fn cat(handle: &Handle) -> Command {
    let mut path = env::current_exe().unwrap();
    path.pop();
    if path.ends_with("deps") {
        path.pop();
    }
    path.push("cat");
    let mut cmd = Command::new(path, handle);
    cmd.stdin(Stdio::piped())
       .stdout(Stdio::piped());
    cmd
}

fn feed_cat(mut cat: Child, n: usize) -> BoxFuture<ExitStatus, io::Error> {
    let stdin = cat.stdin().take().unwrap();
    let stdout = cat.stdout().take().unwrap();

    debug!("starting to feed");
    // Produce n lines on the child's stdout.
    let numbers = stream::iter((0..n).into_iter().map(Ok));
    let write = numbers.fold(stdin, |stdin, i| {
        debug!("sending line {} to child", i);
        write_all(stdin, format!("line {}\n", i).into_bytes()).map(|p| p.0)
    }).map(|_| ());

    // Try to read `n + 1` lines, ensuring the last one is empty
    // (i.e. EOF is reached after `n` lines.
    let reader = io::BufReader::new(stdout);
    let expected_numbers = stream::iter((0..n + 1).map(Ok));
    let read = expected_numbers.fold((reader, 0), move |(reader, i), _| {
        let done = i >= n;
        debug!("starting read from child");
        read_until(reader, b'\n', Vec::new()).and_then(move |(reader, vec)| {
            debug!("read line {} from child ({} bytes, done: {})",
                   i, vec.len(), done);
            match (done, vec.len()) {
                (false, 0) => {
                    Err(io::Error::new(io::ErrorKind::BrokenPipe, "broken pipe"))
                },
                (true, n) if n != 0 => {
                    Err(io::Error::new(io::ErrorKind::Other, "extraneous data"))
                },
                _ => {
                    let s = std::str::from_utf8(&vec).unwrap();
                    let expected = format!("line {}\n", i);
                    if done || s == expected {
                        Ok((reader, i + 1))
                    } else {
                        Err(io::Error::new(io::ErrorKind::Other, "unexpected data"))
                    }
                }
            }
        })
    });

    // Compose reading and writing concurrently.
    write.join(read).and_then(|_| cat).boxed()
}

#[test]
/// Check for the following properties when feeding stdin and
/// consuming stdout of a cat-like process:
///
/// - A number of lines that amounts to a number of bytes exceeding a
///   typical OS buffer size can be fed to the child without
///   deadlock. This tests that we also consume the stdout
///   concurrently; otherwise this would deadlock.
///
/// - We read the same lines from the child that we fed it.
//
/// - The child does produce EOF on stdout after the last line.
fn feed_a_lot() {
    let _ = ::env_logger::init();

    let mut lp = Core::new().unwrap();
    let cmd = cat(&lp.handle());
    let child = cmd.spawn().and_then(|child| {
        feed_cat(child, 10000)
    });
    let status = lp.run(child).unwrap();
    assert_eq!(status.code(), Some(0));
}