cappie/protocol.py

   1 #!/usr/bin/python
   2 ###############################################################################
   3 #                                                                             #
   4 # Cappie                                                                      #
   5 # Copyright (C) 2010 Michael Tremer                                           #
   6 #                                                                             #
   7 # This program is free software: you can redistribute it and/or modify        #
   8 # it under the terms of the GNU General Public License as published by        #
   9 # the Free Software Foundation, either version 3 of the License, or           #
  10 # (at your option) any later version.                                         #
  11 #                                                                             #
  12 # This program is distributed in the hope that it will be useful,             #
  13 # but WITHOUT ANY WARRANTY; without even the implied warranty of              #
  14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               #
  15 # GNU General Public License for more details.                                #
  16 #                                                                             #
  17 # You should have received a copy of the GNU General Public License           #
  18 # along with this program.  If not, see <http://www.gnu.org/licenses/>.       #
  19 #                                                                             #
  20 ###############################################################################
  21
  22 import struct
  23
  24 from constants import *
  25 from errors import *
  26
  27 def val2int(val):
  28         return int("".join(["%02d" % ord(c) for c in val]), 16)
  29
  30 def val2ip4(val):
  31         return ".".join(["%d" % ord(i) for i in val])
  32
  33 def val2mac(val):
  34         return ":".join(["%02x" % ord(i) for i in val])
  35
  36 def decode_packet(data):
  37         for func in (decode_arp_packet,):
  38                 try:
  39                         p = func(data)
  40                 except PacketTypeError:
  41                         continue
  42
  43                 return p
  44
  45         raise PacketTypeError, "Could not determine type of packet"
  46
  47 def decode_arp_packet(data):
  48         operationmap = {
  49                 1 : OPERATION_REQUEST,
  50                 2 : OPERATION_RESPONSE,
  51         }
  52
  53         #if not len(data) == 42:
  54         #       raise DecodeError, "Data has wrong length: %d" % len(data)
  55
  56         ret = {
  57                 "type" : TYPE_ARP,
  58         }
  59
  60         #"hwtype" : data[:2],
  61         protocol = val2int(struct.unpack("!2s", data[12:14])[0])
  62         hw_addr_size = val2int(struct.unpack("!1s", data[18:19])[0])
  63         hw_prot_size = val2int(struct.unpack("!1s", data[19:20])[0])
  64         operation = val2int(struct.unpack("!2s", data[20:22])[0])
  65
  66         # Sanity checks
  67         if not protocol == 0x0806:
  68                 raise PacketTypeError, "Not an ARP packet"
  69
  70         # TODO Must check hwtype here...
  71
  72         try:
  73                 ret["operation"] = operationmap[operation]
  74         except KeyError:
  75                 raise DecodeError, "Unknown operation type"
  76
  77         address_length = hw_addr_size + hw_prot_size
  78         unpack_str = "!%ss%ss" % (hw_addr_size, hw_prot_size)
  79
  80         ret["source_address"], ret["source_ip_address"] = \
  81                 struct.unpack(unpack_str, data[22:22 + address_length])
  82
  83         ret["destination_address"], ret["destination_ip_address"] = \
  84                 struct.unpack(unpack_str, data[22 + address_length:22 + address_length * 2])
  85
  86         for i in ("source_address", "destination_address"):
  87                 ret[i] = val2mac(ret[i])
  88
  89         for i in ("source_ip_address", "destination_ip_address"):
  90                 ret[i] = val2ip4(ret[i])
  91
  92         return ret
  93
  94 def decode_ndp_packet(data):
  95         raise PacketTypeError