import struct
from socket import htons, IPPROTO_TCP
from common import checksum
class layer(object):
pass
class TCP(object):
def __init__(self, srcp, dstp):
self.srcp = srcp
self.dstp = dstp
self.seqn = 10
self.ackn = 0
self.offset = 5 # Data offset: 5x4 = 20 bytes
self.reserved = 0
self.urg = 0
self.ack = 0
self.psh = 0
self.rst = 0
self.syn = 1
self.fin = 0
self.window = htons(5840)
self.checksum = 0
self.urgp = 0
self.payload = ""
def pack(self, src, dst):
data_offset = (self.offset << 4) + 0
flags = self.fin + (self.syn << 1) + (self.rst << 2) + (self.psh << 3) + (self.ack << 4) + (self.urg << 5)
tcp_header = struct.pack('!HHLLBBHHH',
self.srcp,
self.dstp,
self.seqn,
self.ackn,
data_offset,
flags,
self.window,
self.checksum,
self.urgp)
#pseudo header fields
#source_ip = src
#destination_ip = dst
reserved = 0
protocol = IPPROTO_TCP
total_length = len(tcp_header) + len(self.payload)
# Pseudo header
psh = struct.pack("!4s4sBBH",
src,
dst,
reserved,
protocol,
total_length)
psh = psh + tcp_header + self.payload
tcp_checksum = checksum(psh)
tcp_header = struct.pack("!HHLLBBH",
self.srcp,
self.dstp,
self.seqn,
self.ackn,
data_offset,
flags,
self.window)
tcp_header+= struct.pack('H', tcp_checksum) + struct.pack('!H', self.urgp)
return tcp_header
def unpack(self, packet):
cflags = { # Control flags
32:"U",
16:"A",
8:"P",
4:"R",
2:"S",
1:"F"}
_tcp = layer()
_tcp.thl = (ord(packet[12])>>4) * 4
_tcp.options = packet[20:_tcp.thl]
_tcp.payload = packet[_tcp.thl:]
tcph = struct.unpack("!HHLLBBHHH", packet[:20])
_tcp.srcp = tcph[0] # source port
_tcp.dstp = tcph[1] # destination port
_tcp.seq = tcph[2] # sequence number
_tcp.ack = hex(tcph[3]) # acknowledgment number
_tcp.flags = ""
for f in cflags:
if tcph[5] & f:
_tcp.flags+=cflags[f]
_tcp.window = tcph[6] # window
_tcp.checksum = hex(tcph[7]) # checksum
_tcp.urg = tcph[8] # urgent pointer
_tcp.list = [
_tcp.srcp,
_tcp.dstp,
_tcp.seq,
_tcp.ack,
_tcp.thl,
_tcp.flags,
_tcp.window,
_tcp.checksum,
_tcp.urg,
_tcp.options,
_tcp.payload]
return _tcp
