use etherparse::*;
use std::io::Write;

fn main() {
    let with_udp_checksum = true;

    //Any struct implementing the "Write" trait can be used to write to (e.g. File).
    //For this example lets use a simple Vec as it implements the write trait.
    let mut out = Vec::<u8>::with_capacity(
        //lets reserve enough memory to avoid unnecessary allocations
        Ethernet2Header::LEN + Ipv4Header::MAX_LEN + UdpHeader::LEN + 8, //payload
    );

    //setup the actual payload of the udp packet
    let udp_payload = [1, 2, 3, 4, 5, 6, 7, 8];

    //Lets start out with an ethernet II header containing the mac addresses
    Ethernet2Header {
        destination: [1, 2, 3, 4, 5, 6],
        source: [11, 12, 13, 14, 15, 16],
        ether_type: ether_type::IPV4,
    }
    .write(&mut out)
    .unwrap();

    //create the ipv4 header with the helper function
    //Note: It is also possible to define the rest of the header values via Ipv4Header {...}
    let ip_header = Ipv4Header::new(
        //payload length
        (UdpHeader::LEN + udp_payload.len()) as u16,
        20,                //time to live
        ip_number::UDP,    //contained protocol is udp
        [192, 168, 1, 42], //source ip address
        [192, 168, 1, 1],  //destination ip address
    )
    .unwrap();

    //write the ipv4 header
    //
    //The "write" call automatically calculates the ipv4 checksum.
    //Alternatively "write_raw" can be used to skip the checksum
    //calculation and just write out the checksum set in the header.
    ip_header.write(&mut out).unwrap();

    //write the udp header
    //
    //There is the option to write it with a checksum or without.
    //If yes, the ipv4 header & payload are needed to calculate the header
    if with_udp_checksum {
        UdpHeader::with_ipv4_checksum(
            0,            //source port
            42,           //destination port
            &ip_header,   //ip header
            &udp_payload, //udp payload
        )
        .unwrap()
        .write(&mut out)
        .unwrap();
    } else {
        //write the header with the checksum disabled
        UdpHeader::without_ipv4_checksum(
            0,                 //source port
            42,                //destination port
            udp_payload.len(), //payload length
        )
        .unwrap()
        .write(&mut out)
        .unwrap();
    }

    out.write_all(&udp_payload).unwrap();

    println!("{:?}", &out);
}