Find the position of the last non-zero byte in a file

main.rs

use std::io::{prelude::*, SeekFrom};

const CHUNK: usize = 512 * 1024 * 1024;

fn main() {
    let path = std::env::args_os().nth(1).unwrap();
    let mut file = std::fs::File::open(path).unwrap();

    let mut position = file.seek(SeekFrom::End(-(CHUNK as i64))).unwrap();

    let mut buffer = vec![0; CHUNK];
    loop {
        file.read_exact(&mut buffer).unwrap();
        
        if let Some(index) = buffer.iter().rposition(|&byte| byte != 0) {
            println!("{}", position + index as u64);
            return;
        }

        print!(".");
        std::io::stdout().flush().unwrap();
        position = file.seek(SeekFrom::Current(-(CHUNK as i64 * 2))).unwrap();
    }
}