def _decode(self, msg, query):
msg = BitStream(msg)
header = msg[:self.HEADER_SIZE].unpack(self.HDR_FMT)
id, ctl, qc, rc, _, ac = header
ctl = BitStream(bin(ctl))
_, opcode, aa, tc, rd, ra, _, rcode = ctl.unpack(self.CTL_FMT)
if rcode == 1:
raise FormatError(self.raw_msg)
elif rcode == 2:
raise ServerError(self.raw_msg)
elif rcode == 3:
raise InvalidNameError(self.raw_msg)
elif rcode == 5:
raise ServerRefusedError(self.raw_msg)
if tc == 1:
raise ResponseTruncatedError(self.raw_msg)
self.ra = ra
self.aa = aa
self.rc = rc
self.ac = ac
question = msg[96:]
for _ in range(qc):
_, question = decode_name(msg, question)
question = question[32:] # Move past QTYPE and QCLASS
resp = question
name = True
names = []
for _ in range(rc):
name, answer, rtype, ttl, resp = seek_response(resp, msg)
self.responses.append((name, answer, rtype, ttl))
for _ in range(ac):
name, answer, rtype, ttl, resp = seek_response(resp, msg)
self.additional.append((name, answer, rtype, ttl))
def from_bytes(buf):
bs = BitStream(bytes=buf)
pkt = IPv4Packet()
pkt.version = bs.read('uint:4')
pkt.ihl = bs.read('uint:4')
pkt.dscp = bs.read('uint:6')
pkt.ecn = bs.read('uint:2')
pkt.total_length = bs.read('uint:16')
pkt.ident = bs.read('uint:16')
pkt.flag_reserved = bs.read('bool')
pkt.flag_dont_fragment = bs.read('bool')
pkt.flag_more_fragments = bs.read('bool')
pkt.fragment_offset = bs.read('uint:13')
pkt.time_to_live = bs.read('uint:8')
pkt.protocol = bs.read('uint:8')
# TODO The checksum field is the 16 bit one's complement of the one's
# complement sum of all 16 bit words in the header. For purposes of
# computing the checksum, the value of the checksum field is zero.
pkt.header_checksum = bs.read('uint:16')
pkt.source = ipaddress.IPv4Address(bs.read('uint:32'))
pkt.destination = ipaddress.IPv4Address(bs.read('uint:32'))
if pkt.ihl == 5:
pkt.options = None
elif pkt.ihl >= 6 and pkt.ihl <= 15:
pkt.options = []
while (True):
if bs.bytepos >= pkt.ihl * 4:
break
#TODO padding (always ends on 32 bit boundary; implicit end of list)
option = {}
option['copy'] = bs.read('bool')
option['class'] = bs.read('uint:2')
option['number'] = bs.read('uint:5')
if option['class'] == IPv4Packet.CLASS_CONTROL:
if option[
'number'] == IPv4Packet.NUMBER_END_OF_OPTION_LIST:
# end of options list
# no length or data
break
elif option['number'] == IPv4Packet.NUMBER_NO_OPERATION:
# no operation
# no length or data
pass
elif option['number'] == IPv4Packet.NUMBER_SECURITY:
# Security RFC 791
# 11 octet length
option['length'] = bs.unpack('uint:8')
if option['length'] != 11:
raise RuntimeError(
'Security IP Option with length other than 11')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
elif option[
'number'] == IPv4Packet.NUMBER_LOOSE_SOURCE_ROUTING:
# Loose Source Routing
# var octet length
option['length'] = bs.unpack('uint:8')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
elif option['number'] == IPv4Packet.NUMBER_RECORD_ROUTE:
# Record Route
# var octet length
option['length'] = bs.unpack('uint:8')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
elif option['number'] == IPv4Packet.NUMBER_STREAM_ID:
# Stream ID
# 4 octet length
option['length'] = bs.unpack('uint:8')
if option['length'] != 4:
raise RuntimeError(
'Stream ID IP Option with length other than 4')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
elif option[
'number'] == IPv4Packet.NUMBER_STRICT_SOURCE_ROUTING:
# Strict Source Routing
# var octet length
option['length'] = bs.unpack('uint:8')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
else:
raise RuntimeError('Unknown IP option: ' \
+ 'class: ' + str(option['class'] \
+ ', number: ' + str(option['number'])))
elif option['class'] == IPv4Packet.CLASS_DEBUG_MEASURE:
if option[
'number'] == IPv4Packet.NUMBER_INTERNET_TIMESTAMP:
# Internet Timestamp
# var octet length
option['length'] = bs.unpack('uint:8')
option['data'] = bs.unpack('bytes:' +
str(option['length'] - 2))
else:
raise RuntimeError('Unknown IP option: ' \
+ 'class: ' + str(option['class'] \
+ ', number: ' + str(option['number'])))
else:
raise RuntimeError('Unknown IP option class: ' +
str(option['class']))
else:
raise RuntimeError('Invalid IHL value for packet: ' + str(pkt.ihl))
pkt.data = buf[(pkt.ihl * 4):]
return pkt
