.rs

try!(file.seek(SeekFrom::Start(file_pos)));;
    try!(pad.seek(SeekFrom::Start(pad_pos)));

    let mut file_reader = BufStream::with_capacities(BUF_SIZE, BUF_SIZE, file).take(size);
    let mut pad_reader = BufStream::with_capacities(BUF_SIZE, BUF_SIZE, pad).take(size);

    loop {
        let mut read_buf_size;
        let mut read_pad_size;
        
        {
            let buf = try!(file_reader.fill_buf());
            let pad = try!(pad_reader.fill_buf());

            if buf.is_empty() || pad.is_empty() {
                break;
            }
            read_buf_size = buf.len();
            read_pad_size = pad.len();

            try!(file.write_all(&xor(buf, pad)));
        }

        file_reader.consume(read_buf_size);
        pad_reader.consume(read_pad_size);
    }