write_tcp.rs

extern crate etherparse;
use etherparse::*;

fn main() {

    //setup the packet headers
    let builder = PacketBuilder::
    ethernet2([1,2,3,4,5,6],     //source mac
               [7,8,9,10,11,12]) //destionation mac
    .ipv4([192,168,1,1], //source ip
          [192,168,1,2], //desitionation ip
          20)            //time to life
    .tcp(21,    //source port 
         1234,  //desitnation port
         1,     //sequence number
         26180) //window size

    //set additional tcp header fields
    .ns() //set the ns flag
    //supported flags: ns(), fin(), syn(), rst(), psh(), ece(), cwr()
    .ack(123) //ack flag + the ack number
    .urg(23) //urg flag + urgent pointer

    //tcp header options
    .options(&[
        TcpOptionElement::Noop,
        TcpOptionElement::MaximumSegmentSize(1234)
    ]).unwrap();

    //payload of the tcp packet
    let payload = [1,2,3,4,5,6,7,8];
    
    //get some memory to store the result
    let mut result = Vec::<u8>::with_capacity(
                    builder.size(payload.len()));
    
    //serialize
    //this will automatically set all length fields, checksums and identifiers (ethertype & protocol)
    builder.write(&mut result, &payload).unwrap();
    println!("{:?}", result);
}