Stdout does panic in pipe

[gemmarx]

In a 64-bit Linux box, the code below fails to write, and dies with a panic message only in a pipeline.

fn main() {
    use std::io::Write;

    let buf = "\n".as_bytes();
    for _ in 1..2000 {
        std::io::stdout().write(buf).unwrap();
    }
}

#This is ok.
$ rustc main.rs
$ ./main

#However, this calls a panic.
$ ./main | head -0
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 32, message: "Broken pipe" } }', ../src/libcore/result.rs:788
note: Run with `RUST_BACKTRACE=1` for a backtrace.

On the other hand, following two codes work with no trouble.

fn main() {
    use std::io::Write;

    let buf = "\n".as_bytes();
    for _ in 1..100 {
        std::io::stdout().write(buf).unwrap();
    }
}

fn main() {
    use libc::{c_int, size_t, c_void};

    let fd: c_int = 1;
    let buf = "\n".as_bytes();
    for _ in 1..2000 { unsafe {
        libc::write(fd,
                    buf.as_ptr() as *const c_void,
                    buf.len() as size_t);
    } }
}

What's happened?
It seems to be a buggy behaviour.
( rustc version is 1.12.0-nightly (feeca94 2016-07-26) )

[nagisa]

As the message: "Broken pipe" implies, the stuff you’re piping into exits before your code finishes writing all your newlines.

The 2nd program likely finishes because it manages to write all of its stuff before head -0 exits. The 3rd program has different behaviour from the 1st or 2nd programs – it does not check the return code of libc::write, essentially ignoring the errors.

It seems to me that its working as it should be working.

[gemmarx]

Oh, thank you very much. I get it.

It sounds natural to handle exceptions neatly when bytes to write are to be greater than the buffer size of pipeline (maybe 1024?).

This means that print! or write! macro family is not good to use in pipeline because they cannot catch the errors, right?

[nagisa]

write! allows you to handle the errors just fine (it returns a Result). print! does not.

[gemmarx]

That reminds me!

Thank you, nagisa-san.

[gemmarx]

In my short research, "wc" command in coreutils projict and exa at least have this panic problem.
They have lost some values as a filter command.
There could be more appropriate affordance for Stdout.