```rust
// Copy a file 4096 bytes at a time
use std::fs::File;
use std::io::{self, Read, Write};

fn main() -> io::Result<()> {
    let mut ifile = File::open("src.txt")?;
    let mut ofile = File::create("output.txt")?;
    let mut buffer = [0u8; 4096];

    loop {
        let bytes_read = ifile.read(&mut buffer)?;
        println!("Bytes read: {}", &bytes_read);
        if bytes_read == 0 { break; }

        ofile.write_all(&buffer[0..bytes_read])?;
        println!("Written: {}", &bytes_read);
    }
    println!("Done");
    Ok(())
}
```