TCP segment: C++/STL parsing library

KS implementation details

License: CC0-1.0

This page hosts a formal specification of TCP segment using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.


Using Kaitai Struct in C++/STL usually consists of 3 steps.

  1. We need to create an STL input stream (std::istream).
    • One can open a stream for reading from a local file:
      #include <fstream>
      std::ifstream is("path/to/local/file.tcp_segment", std::ifstream::binary);
    • Or one can prepare a stream for reading from existing std::string str:
      #include <sstream>
      std::istringstream is(str);
    • Or one can parse arbitrary char* buffer in memory, given that we know its size:
      #include <sstream>
      const char buf[] = { ... };
      std::string str(buf, sizeof buf);
      std::istringstream is(str);
  2. We need to wrap our input stream into Kaitai stream:
    #include <kaitai/kaitaistream.h>
    kaitai::kstream ks(&is);
  3. And finally, we can invoke the parsing:
    tcp_segment_t data(&ks);

After that, one can get various attributes from the structure by invoking getter methods like:

data.src_port() // => get src port

C++/STL source code to parse TCP segment


#ifndef TCP_SEGMENT_H_
#define TCP_SEGMENT_H_

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "kaitai/kaitaistruct.h"

#include <stdint.h>

#error "Incompatible Kaitai Struct C++/STL API: version 0.7 or later is required"

class tcp_segment_t : public kaitai::kstruct {


    tcp_segment_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent = 0, tcp_segment_t* p__root = 0);

    void _read();


    uint16_t m_src_port;
    uint16_t m_dst_port;
    uint32_t m_seq_num;
    uint32_t m_ack_num;
    uint8_t m_b12;
    uint8_t m_b13;
    uint16_t m_window_size;
    uint16_t m_checksum;
    uint16_t m_urgent_pointer;
    std::string m_body;
    tcp_segment_t* m__root;
    kaitai::kstruct* m__parent;

    uint16_t src_port() const { return m_src_port; }
    uint16_t dst_port() const { return m_dst_port; }
    uint32_t seq_num() const { return m_seq_num; }
    uint32_t ack_num() const { return m_ack_num; }
    uint8_t b12() const { return m_b12; }
    uint8_t b13() const { return m_b13; }
    uint16_t window_size() const { return m_window_size; }
    uint16_t checksum() const { return m_checksum; }
    uint16_t urgent_pointer() const { return m_urgent_pointer; }
    std::string body() const { return m_body; }
    tcp_segment_t* _root() const { return m__root; }
    kaitai::kstruct* _parent() const { return m__parent; }

#endif  // TCP_SEGMENT_H_


// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "tcp_segment.h"

tcp_segment_t::tcp_segment_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent, tcp_segment_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = this;

void tcp_segment_t::_read() {
    m_src_port = m__io->read_u2be();
    m_dst_port = m__io->read_u2be();
    m_seq_num = m__io->read_u4be();
    m_ack_num = m__io->read_u4be();
    m_b12 = m__io->read_u1();
    m_b13 = m__io->read_u1();
    m_window_size = m__io->read_u2be();
    m_checksum = m__io->read_u2be();
    m_urgent_pointer = m__io->read_u2be();
    m_body = m__io->read_bytes_full();

tcp_segment_t::~tcp_segment_t() {