iptrap 1.0.9

A fast, stateless TCP sinkhole
Documentation 
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use std::mem::size_of;

use rand;

use crate::packetdissector::{EtherHeader, IpHeader, TcpHeader};
use crate::packetdissector::{ETHERTYPE_IP, IPPROTO_TCP};

#[repr(C, packed)]
#[derive(Copy, Clone)]
pub struct EmptyTcpPacket {
    pub etherhdr: EtherHeader,
    pub iphdr: IpHeader,
    pub tcphdr: TcpHeader,
    pub tcpoptions: [u8; 4],
}

impl Default for EmptyTcpPacket {
    fn default() -> Self {
        Self::new()
    }
}

impl EmptyTcpPacket {
    pub fn new() -> EmptyTcpPacket {
        let etherhdr = EtherHeader {
            ether_dhost: [0u8; 6],
            ether_shost: [0u8; 6],
            ether_type: ETHERTYPE_IP.to_be(),
        };
        let tcpoptions = [0x2u8, 0x4u8, 0x5u8, 0xb4u8];
        let iphdr = IpHeader {
            ip_vhl: (4u8 << 4) | (size_of::<IpHeader>() as u8 / 4u8),
            ip_tos: 0u8,
            ip_len: ((size_of::<IpHeader>() + size_of::<TcpHeader>() + tcpoptions.len()) as u16)
                .to_be(),
            ip_id: rand::random(),
            ip_off: 0u16,
            ip_ttl: 42u8,
            ip_p: IPPROTO_TCP,
            ip_sum: 0u16,
            ip_src: [0u8; 4],
            ip_dst: [0u8; 4],
        };
        assert!(tcpoptions.len().is_multiple_of(4));
        let tcphdr = TcpHeader {
            th_sport: 0u16,
            th_dport: 0u16,
            th_seq: 0u32,
            th_ack: 0u32,
            th_off_x2: (((size_of::<TcpHeader>() + tcpoptions.len()) / 4) as u8) << 4,
            th_flags: 0u8,
            th_win: 65535u16,
            th_sum: 0u16,
            th_urp: 0u16,
        };
        EmptyTcpPacket {
            etherhdr,
            iphdr,
            tcphdr,
            tcpoptions,
        }
    }
}