fuzz: use thread to bypass the limitation of output

[sylvestre]

No description provided.

[samueltardieu]

I think there might be a simpler way of writing this using scoped threads, join handles, and the fact that the uumain function can run onto the current thread, without requiring MPSC channels, something like (untested):

    let (uumain_exit_status, stdout, stderr) = thread::scope(|s| {
        let out = s.spawn(|| read_from_fd(pipe_stdout_fds[0]));
        let err = s.spawn(|| read_from_fd(pipe_stderr_fds[0]));
        (uumain_function(args), out.join().unwrap(), err.join().unwrap())
    });

Scoped threads have been introduced in Rust 1.63, but even without using them the code using the join handle to transfer the out/err streams is simpler than using MPSC channels.

[sylvestre]

Looks nicer indeed but still freezes
with

let (uumain_exit_status, captured_stdout, captured_stderr) = thread::scope(|s| {
    let out = s.spawn(|| read_from_fd(pipe_stdout_fds[0]));
    let err = s.spawn(|| read_from_fd(pipe_stderr_fds[0]));

    (uumain_function(args_clone.into_iter()), out.join().unwrap(), err.join().unwrap())
});

[samueltardieu]

Yes, because stdout/stderr for the child are not closed in the main thread so the threads don't terminate and will block on join. By trying

    let (uumain_exit_status, captured_stdout, captured_stderr) = thread::scope(|s| {
        let out = s.spawn(|| read_from_fd(pipe_stdout_fds[0]));
        let err = s.spawn(|| read_from_fd(pipe_stderr_fds[0]));
        let status = uumain_function(args.to_owned().into_iter());
        io::stdout().flush().unwrap();
        io::stderr().flush().unwrap();
        unsafe {
            close(pipe_stdout_fds[1]);
            close(pipe_stderr_fds[1]);
            close(STDOUT_FILENO);
            close(STDERR_FILENO);
        }
        (status, out.join().unwrap(), err.join().unwrap())
    });

(and removing two close() below)

it looks like it works as expected. And it fails but because the output of seq -38 -17.207520895356907 -9727 is really different between GNU coreutils and uutils.

[sylvestre]

Much better, thanks

it found an issue (but i can't reproduce locally yet)

Test Type: seq
Input: ["0.8262287413206764"]
Rust stdout:
GNU stdout: 1

Discrepancy detected: stdout differs
thread '<unnamed>' panicked at fuzz_targets/fuzz_common.rs:360:13:
Test failed for seq: ["0.8262287413206764"]