Maybe write to a readonly file should panic?

[alexniver]

Hi, I'm new to rust and tokio.

in std::fs::File, write to a read only File, will panic. like code below.

use std::{fs::File, io::Write};

fn main() -> std::io::Result<()> {
    let mut buffer = File::open("foo.txt")?; // readonly

    // Writes some prefix of the byte string, not necessarily all of it.
    buffer.write(b"some bytes")?;
    Ok(())
}

out put error:

Error: Os { code: 9, kind: Uncategorized, message: "Bad file descriptor" }

but in tokio::fs::File, write to a read only file, return success, and file not change.

use tokio::{
    fs::File,
    io::{self, AsyncWriteExt},
};

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut f = File::open("foo.txt").await?; // read only
    let n = f.write(b"some bytesaaaaa").await?;

    println!("write {} bytes", n);

    Ok(())
}

output :

write 15 bytes

my tokio version: tokio = {version="1", features=["full"]}

why tokio not panic? or I do something wrong?

[Darksonn]

For technical reasons, errors are not reported until the following flush or write. If you try to flush, you should get the error.

[alexniver]

OK! Thanks.