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" % self.v)
hl = self.hl * 4
# verify the checksum
self.sum = struct.unpack('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('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('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 = packet + self.data
self.__packet = inet.iph2net(packet)
return self.__packet
def __disassemble(self, raw_packet, cksum=1):
packet = inet.net2updh(raw_packet)
if cksum and packet[6:8] != '\000\000':
our_cksum = inet.cksum(packet)
if our_cksum != 0:
raise ValueError(packet)
elts = map(lambda x:x & 0xffff, struct.unpack('hhhh', packet[:8]))
[self.sport, self.dport, self.ulen, self.sum] = elts
self.data = packet[8:]
def assemble(self, cksum=1):
self.ulen = 8 + len(self.data)
begin = struct.pack('hhh', self.sport, self.dport, self.ulen)
packet = begin + '\000\000' + self.data
if cksum:
self.sum = inet.cksum(packet)
packet = begin + struct.pack('h', self.sum) + self.data
self.__packet = inet.udph2net(packet)
return self.__packet