TCP is one of the core Internet protocols on transport layer (AKA OSI layer 4), providing stateful connections with error checking, guarantees of delivery, order of segments and avoidance of duplicate delivery.
This page hosts a formal specification of TCP (Transmission Control Protocol) segment using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.
The Python runtime library can be installed from PyPI:
python3 -m pip install kaitaistructParse a local file and get structure in memory:
data = TcpSegment.from_file("path/to/local/file.bin")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = TcpSegment(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.src_port # => Source port
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 9):
raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))
class TcpSegment(KaitaiStruct):
"""TCP is one of the core Internet protocols on transport layer (AKA
OSI layer 4), providing stateful connections with error checking,
guarantees of delivery, order of segments and avoidance of duplicate
delivery.
"""
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.src_port = self._io.read_u2be()
self.dst_port = self._io.read_u2be()
self.seq_num = self._io.read_u4be()
self.ack_num = self._io.read_u4be()
self.data_offset = self._io.read_bits_int_be(4)
self.reserved = self._io.read_bits_int_be(4)
self._io.align_to_byte()
self.flags = TcpSegment.Flags(self._io, self, self._root)
self.window_size = self._io.read_u2be()
self.checksum = self._io.read_u2be()
self.urgent_pointer = self._io.read_u2be()
if ((self.data_offset * 4) - 20) != 0:
self.options = self._io.read_bytes(((self.data_offset * 4) - 20))
self.body = self._io.read_bytes_full()
class Flags(KaitaiStruct):
"""TCP header flags as defined "TCP Header Flags" registry.
"""
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.cwr = self._io.read_bits_int_be(1) != 0
self.ece = self._io.read_bits_int_be(1) != 0
self.urg = self._io.read_bits_int_be(1) != 0
self.ack = self._io.read_bits_int_be(1) != 0
self.psh = self._io.read_bits_int_be(1) != 0
self.rst = self._io.read_bits_int_be(1) != 0
self.syn = self._io.read_bits_int_be(1) != 0
self.fin = self._io.read_bits_int_be(1) != 0
def __repr__(self):
return (u"|CWR" if self.cwr else u"") + (u"|ECE" if self.ece else u"") + (u"|URG" if self.urg else u"") + (u"|ACK" if self.ack else u"") + (u"|PSH" if self.psh else u"") + (u"|RST" if self.rst else u"") + (u"|SYN" if self.syn else u"") + (u"|FIN" if self.fin else u"")