Implementation

pcapkit.foundation.reassembly.tcp contains Reassembly only, which reconstructs fragmented TCP packets back to origin.

Terminology

tcp.packet

Data structure for TCP datagram reassembly (TCP_Reassembly.reassembly) is as following:

packet_dict = Info(
  bufid = tuple(
      ip.src,                     # source IP address
      tcp.srcport,                # source port
      ip.dst,                     # destination IP address
      tcp.dstport,                # destination port
  ),
  dsn = tcp.seq,                  # data sequence number
  ack = tcp.ack,                  # acknowledgement number
  num = frame.number,             # original packet range number
  syn = tcp.flags.syn,            # synchronise flag
  fin = tcp.flags.fin,            # finish flag
  rst = tcp.flags.rst,            # reset connection flag
  len = tcp.raw_len,              # payload length, header excludes
  first = tcp.seq,                # this sequence number
  last = tcp.seq + tcp.raw_len,   # next (wanted) sequence number
  header = tcp.packet.header,     # raw bytes type header
  payload = tcp.raw,              # raw bytearray type payload
)

tcp.datagram

Data structure for reassembled TCP datagram (element from TCP_Reassembly.datagram tuple) is as following:

(tuple) datagram
 |--> (Info) data
 |     |--> 'completed' : (bool) True --> implemented
 |     |--> 'id' : (Info) original packet identifier
 |     |            |--> 'src' --> (tuple)
 |     |            |               |--> (IPv4Address) ip.src
 |     |            |               |--> (int) tcp.srcport
 |     |            |--> 'dst' --> (tuple)
 |     |            |               |--> (IPv4Address) ip.dst
 |     |            |               |--> (int) tcp.dstport
 |     |            |--> 'ack' --> (int) original packet ACK number
 |     |--> 'index' : (tuple) packet numbers
 |     |               |--> (int) original packet range number
 |     |               |--> ...
 |     |--> 'header' : (bytes) initial TCP header
 |     |--> 'payload' : (bytes) reassembled payload
 |     |--> 'packet' : (Protocol) parsed reassembled payload
 |--> (Info) data
 |     |--> 'completed' : (bool) False --> not implemented
 |     |--> 'id' : (Info) original packet identifier
 |     |            |--> 'src' --> (tuple)
 |     |            |               |--> (IPv4Address) ip.src
 |     |            |               |--> (int) tcp.srcport
 |     |            |--> 'dst' --> (tuple)
 |     |            |               |--> (IPv4Address) ip.dst
 |     |            |               |--> (int) tcp.dstport
 |     |            |--> 'ack' --> (int) original packet ACK number
 |     |--> 'index' : (tuple) packet numbers
 |     |               |--> (int) original packet range number
 |     |               |--> ...
 |     |--> 'header' : (bytes) initial TCP header
 |     |--> 'payload' : (tuple) partially reassembled payload
 |     |                 |--> (bytes) payload fragment
 |     |                 |--> ...
 |     |--> 'packet' : (None) not implemented
 |--> (Info) data ...

tcp.buffer

Data structure for internal buffering when performing reassembly algorithms (TCP_Reassembly._buffer) is as following:

(dict) buffer --> memory buffer for reassembly
 |--> (tuple) BUFID : (dict)
 |       |--> ip.src      |
 |       |--> ip.dst      |
 |       |--> tcp.srcport |
 |       |--> tcp.dstport |
 |                        |--> 'hdl' : (list) hole descriptor list
 |                        |             |--> (Info) hole --> hole descriptor
 |                        |                   |--> "first" --> (int) start of hole
 |                        |                   |--> "last" --> (int) stop of hole
 |                        |--> 'hdr' : (bytes) initial TCP header
 |                        |--> 'ack' : (dict) ACK list
 |                                      |--> (int) ACK : (dict)
 |                                      |                 |--> 'ind' : (list) list of reassembled packets
 |                                      |                 |             |--> (int) packet range number
 |                                      |                 |--> 'isn' : (int) ISN of payload buffer
 |                                      |                 |--> 'len' : (int) length of payload buffer
 |                                      |                 |--> 'raw' : (bytearray) reassembled payload,
 |                                      |                                          holes set to b'\x00'
 |                                      |--> (int) ACK ...
 |                                      |--> ...
 |--> (tuple) BUFID ...

Data Structures