use std::convert::TryInto;

#[derive(Default, Debug, Clone, Copy)]
#[repr(C, packed)]
struct Header {
    timestamp_ns: i64,
    message_id: u16,
    message_version: u16,
    sequence_number: u16,
    reserved: u32,
    length_bytes: u16,
}

fn main() {
    let mut header = Header::default();
    header.message_id = 4;
    header.length_bytes = 42;

    let bytes: [u8; std::mem::size_of::<Header>()] = unsafe { std::mem::transmute(header) };
    println!("{:?}", bytes);

    // Now say you only have a byte slice
    let byte_slice: &[u8] = &bytes[..];

    // Get a fixed-size array from the slice
    let byte_array: &[u8; std::mem::size_of::<Header>()] = byte_slice.try_into().unwrap();

    let header_again: Header = unsafe { std::mem::transmute(*byte_array) };
    println!("{:?}", header_again);
}