use std::{io, mem};
use std::io::Read;

fn fill(r: &mut Read, mut buf: &mut [u8]) -> io::Result<()> {
    while buf.len() > 0 {
        match r.read(buf).unwrap() {
            0 => return Err(io::Error::new(io::ErrorKind::Other,
                                           "end of file reached")),
            n => buf = &mut mem::replace(&mut buf, &mut [])[n..],
        }
    }
    Ok(())
}

fn main() {
}