playing around with a DNS packet definition for libpnet

dns_packet.rs

//! DNS packet abstraction

use packet::Packet;

use pnet_macros::types::*;

/// Represents an UDP Packet
#[packet]
pub struct Dns {
    id: u16be,
    qr: u1,
    op: u4,
    aa: u1,
    tc: u1,
    rd: u1,
    ra: u1,
    z: u1,
    ad: u1,
    cd: u1,
    rcode: u4,
    qd_count: u16be,
    an_count: u16be,
    ns_count: u16be,
    ar_count: u16be,
    length: u32,
    #[length = "length"]
    len_datas: Vec<LenData>,
    #[payload]
    payload: Vec<u8>
}

/// Represents the query in a DNS packet
#[packet]
pub struct LenData {
    length: u8,
    #[length = "length"]
    data: Vec<u8>,
    #[payload]
    payload: Vec<u8>
}

/*
payload here might be tricky. for future reference I am adding a simple DNS packet(as hex) and description of each part. 
DNS portion of packet:
ca 76 01 00 00 01 00 00 00 00 00 00 04 74 65 73 74 03 63 6f 6d 00 01 00 01
breakdown:
QID             ca 76
FLAGS           01 00
    breakdown of flags by bit:
    0(QR) 0000(opcode) 0(AA) 0(TC) 1(RD) 0(RA) 0(Z) 0(AD) 0(CD) 0000(RCODE)
Questions       00 01
Answer RRs      00 00
Authority RRs   00 00
Additional RRs  00 00
this is the end of the header. now we have the query itself (for the A record of test.com)
04 74 65 73 74  read as 4 characters, 't', 'e', 's', 't'
03 63 6f 6d     read as 3 characters, 'c', 'o', 'm'
00              end of qname
00 01           Type: A record
00 01           Class: IN (internet. this is most queries)
*/