zond-engine 0.5.0

A lightweight, fast, and highly concurrent networking backend for packet crafting, protocol fingerprinting, and host discovery.
Documentation 
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// Copyright (c) 2026 Erik Lening (hollowpointer) and Contributors
//
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at
// https://mozilla.org/MPL/2.0/.

use std::net::IpAddr;

use anyhow::Context;
use pnet::packet::tcp::{MutableTcpPacket, TcpOption, TcpPacket};

const MIN_TCP_HDR_LEN: usize = 24;
const WORD_IN_BYTES: usize = 4;
const SYN_FLAG: u8 = 1 << 1;

pub fn create_packet(
    src_addr: &IpAddr,
    dst_addr: &IpAddr,
    src_port: u16,
    dst_port: u16,
    seq_num: u32,
) -> anyhow::Result<Vec<u8>> {
    let mut buffer: Vec<u8> = vec![0u8; MIN_TCP_HDR_LEN];
    {
        let mut tcp: MutableTcpPacket =
            MutableTcpPacket::new(&mut buffer).context("creating tcp packet")?;
        tcp.set_source(src_port);
        tcp.set_destination(dst_port);
        tcp.set_data_offset((MIN_TCP_HDR_LEN / WORD_IN_BYTES) as u8);
        tcp.set_sequence(seq_num);
        tcp.set_acknowledgement(0);
        tcp.set_flags(SYN_FLAG);
        tcp.set_window(1024);
        tcp.set_checksum(0);

        let mut tcp_options: Vec<TcpOption> = Vec::new();
        let mss: TcpOption = TcpOption::mss(1412);
        tcp_options.push(mss);
        tcp.set_options(&tcp_options);

        let tcp_packet: TcpPacket = tcp.to_immutable();
        let checksum = match (src_addr, dst_addr) {
            (IpAddr::V4(src), IpAddr::V4(dst)) => {
                pnet::packet::tcp::ipv4_checksum(&tcp_packet, src, dst)
            }
            (IpAddr::V6(src), IpAddr::V6(dst)) => {
                pnet::packet::tcp::ipv6_checksum(&tcp_packet, src, dst)
            }
            _ => anyhow::bail!("IP version mismatch"),
        };

        tcp.set_checksum(checksum);
    }
    Ok(buffer)
}

pub fn from_u8(bytes: &'_ [u8]) -> anyhow::Result<TcpPacket<'_>> {
    TcpPacket::new(bytes).context("truncated or invalid TCP packet")
}