def __disassemble(self, raw_packet, cksum=0):
# The kernel computes the checksum, even on a raw packet.
packet = inet.net2iph(raw_packet)
b1 = ord(packet[0])
self.v = (b1 >> 4) & 0x0f
self.hl = b1 & 0x0f
if self.v != IPVERSION:
raise ValueError("cannot handle IPv{:d} packets".format(self.v))
hl = self.hl * 4
# verify the checksum
self.sum = struct.unpack(b'h', packet[10:12])[0] & 0xffff
if cksum:
our_cksum = inet.cksum(packet[:20])
if our_cksum != 0:
raise ValueError(packet)
# unpack the fields
elts = struct.unpack(b'cchhhcc', packet[:hl - 10])
# struct didn't do !<> when this was written
self.tos = ord(elts[1])
self.len = elts[2] & 0xffff
self.id = elts[3] & 0xffff
self.off = elts[4] & 0xffff
self.ttl = ord(elts[5])
self.p = ord(elts[6])
self.data = packet[hl:]
self.src = packet[hl - 8:hl - 4]
self.dst = packet[hl - 4:hl]
self.__unparse_addrs()
def assemble(self, cksum=0):
""" Get a packet suitable for sending over an IP socket. """
# make sure all the data is ready
self.len = self.hl * 4 + len(self.data)
self.__parse_addrs()
# create the packet
header = struct.pack(
b'cchhhcc',
chr((self.v & 0x0f) << 4 | (self.hl & 0x0f)), # 4bits each
chr(self.tos & 0xff),
self.len,
self.id,
self.off, # what about flags?
chr(self.ttl & 0xff),
chr(self.p & 0xff))
if cksum:
self.sum = inet.cksum(header + '\000\000' + self.__src +
self.__dst)
packet = header + struct.pack('h',
self.sum) + self.__src + self.__dst
else:
packet = header + '\000\000' + self.__src + self.__dst
packet += self.data
self.__packet = inet.iph2net(packet)
return self.__packet
def __disassemble(self, packet, cksum=1):
if cksum:
our_cksum = inet.cksum(packet)
if our_cksum != 0:
raise ValueError(packet)
self.type = ord(packet[0])
self.code = ord(packet[1])
elts = struct.unpack('hhh', packet[2:8])
[self.cksum, self.id, self.seq] = [x & 0xffff for x in elts]
self.data = packet[8:]
def assemble(self, cksum=1):
idseq = struct.pack('hh', self.id, self.seq)
packet = chr(self.type) + chr(
self.code) + '\000\000' + idseq + self.data
if cksum:
self.cksum = inet.cksum(packet)
packet = chr(self.type) + chr(self.code) + struct.pack(
'H', self.cksum) + idseq + self.data
# Don't need to do any byte-swapping, because idseq is
# appplication defined and others are single byte values.
self.__packet = packet
return self.__packet
def __compute_cksum(self):
"Use inet.cksum instead"
return inet.cksum(self.packet)
packet = self.packet
if len(packet) & 1:
packet = packet + '\0'
words = array.array('h', packet)
sum = 0
for word in words:
sum = sum + (word & 0xffff)
hi = sum >> 16
lo = sum & 0xffff
sum = hi + lo
sum = sum + (sum >> 16)
return (~sum) & 0xffff