Is it within scope to add something against closed stdio?

[hasezoey]

I have noticed that when flexi_logger is setup to use stderr (or even stdout) to print, it may panic if those descriptors are closed (thanks to eprintln / println), and in case a file errors AND the stderr (or stdout) are closed, it will also panic (because of the eprintln in file error case). (assuming flexi_logger is configured to also log to stderr / stdout)

I wanted to know if it is within scope to maybe make stdout & stderr failing not result in a panic before making a actual issue.

reproduction:

// process A
fn main() {
    let mut cmd = std::process::Command::new("processB");
    cmd.stdout(Stdio::null()).stderr(Stdio::piped());

    let spawned = cmd.spawn().unwrap();
    // exit
}

// process B
fn main() {
    let original_hook = std::panic::take_hook();
    std::panic::set_hook(Box::new(move |panic| {
        // this works because rust will execute the panic hook before unwinding
        let backtrace = std::backtrace::Backtrace::capture();

        let stringy = format!("Panic occured:\n{}\n{}", panic, backtrace);
        let file = std::fs::OpenOptions::new().create(true).append(true).open("/tmp/crash.log").map(|mut v| {
            v.write_all(stringy.as_bytes());
            v.flush();
        });

        original_hook(panic);
    }));
    loop {
        eprintln!("test");
        std::thread::sleep(Duration::from_secs(1));
    }
}

will log into the file:

Panic occured:
panicked at library/std/src/io/stdio.rs:1021:9:
failed printing to stderr: Broken pipe (os error 32)

when having it crash via flexi_logger, the backtrace indicates the following function is the problem:

flexi_logger/src/util.rs

Line 90 in 98f1e9a

fn try_to_write(s: &str) {

rustc 1.76.0
flexi_logger 0.27.4

[emabee]

Hi, yes, that seems to be easy to fix - by throwing messages away.
Would that be appropriate?

[hasezoey]

this would work for my use-case, i dont know if other users would want it to panic though (to get the old behavior), so maybe consider doing it as a option (to ignore or to panic on closed stdio fds, maybe separately from other fds like files, or maybe something in the case that is the only fd).

[emabee]

It's now available with version 0.28. See Logger::panic_if_error_channel_is_broken