Tokio: File operations don't use the whole buffer

[lnicola]

tokio 0.2.4, see https://github.com/tokio-rs/tokio/blob/0d38936b35779b604770120da2e98560bbb6241f/tokio/src/io/blocking.rs#L29.

There's an unexpected 16 KB limit for IO operations, e.g. this will print 16384. It seems intended, but it's somewhat confusing.

async fn run() -> Result<(), std::io::Error> {
    let mut file = File::open("x.mkv").await?;
    let mut buf = [0u8; 32768];
    let size = file.read(&mut buf).await?;
    println!("{}", size);
    Ok(())
}

[carllerche]

Looking at your original issue, I think we can support better performance by working directly with Bytes. In that case, we can avoid the copying and instead send the bytes handle to the remote thread.

[blasrodri]

I’d like to work on this. Some guidance would be appreciated.
Especially around

I think we can support better performance by working directly with Bytes