3837a84eec
The patch teaches packet library to truncate padding octets. Change packet_base.parser() to return (header, next_type, rest_of_packet) The protocol class that knows its payload length should rest_of_packet where padding octets at the last of packet is truncated. As bonus, - fix ipv6 parser as ipv6 header doesn't have options. It seems copy-and-paste from ipv4 - improve ipv4, tcp a bit Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp> Cc: Shaun Crampton <Shaun.Crampton@metaswitch.com> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
101 lines
3.4 KiB
Python
101 lines
3.4 KiB
Python
# Copyright (C) 2012 Nippon Telegraph and Telephone Corporation.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import struct
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from . import packet_base
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from . import packet_utils
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class tcp(packet_base.PacketBase):
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"""TCP (RFC 793) header encoder/decoder class.
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An instance has the following attributes at least.
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Most of them are same to the on-wire counterparts but in host byte order.
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__init__ takes the correspondig args in this order.
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============== ====================
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Attribute Description
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============== ====================
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src_port Source Port
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dst_port Destination Port
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seq Sequence Number
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ack Acknowledgement Number
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offset Data Offset
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bits Control Bits
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window_size Window
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csum Checksum \
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(0 means automatically-calculate when encoding)
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urgent Urgent Pointer
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option An bytearray containing Options and following Padding. \
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None if no options.
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============== ====================
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"""
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_PACK_STR = '!HHIIBBHHH'
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_MIN_LEN = struct.calcsize(_PACK_STR)
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def __init__(self, src_port, dst_port, seq, ack, offset,
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bits, window_size, csum, urgent, option=None):
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super(tcp, self).__init__()
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self.src_port = src_port
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self.dst_port = dst_port
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self.seq = seq
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self.ack = ack
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self.offset = offset
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self.bits = bits
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self.window_size = window_size
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self.csum = csum
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self.urgent = urgent
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self.option = option
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def __len__(self):
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return self.offset * 4
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@classmethod
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def parser(cls, buf):
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(src_port, dst_port, seq, ack, offset, bits, window_size,
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csum, urgent) = struct.unpack_from(cls._PACK_STR, buf)
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offset = offset >> 4
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bits = bits & 0x3f
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length = offset * 4
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if length > tcp._MIN_LEN:
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option = buf[tcp._MIN_LEN:length]
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else:
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option = None
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msg = cls(src_port, dst_port, seq, ack, offset, bits,
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window_size, csum, urgent, option)
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return msg, None, buf[length:]
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def serialize(self, payload, prev):
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length = len(self)
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h = bytearray(length)
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offset = self.offset << 4
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struct.pack_into(tcp._PACK_STR, h, 0, self.src_port, self.dst_port,
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self.seq, self.ack, offset, self.bits,
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self.window_size, self.csum, self.urgent)
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if self.option:
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assert (length - tcp._MIN_LEN) >= len(self.option)
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h[tcp._MIN_LEN:tcp._MIN_LEN + len(self.option)] = self.option
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if self.csum == 0:
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total_length = length + len(payload)
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self.csum = packet_utils.checksum_ip(prev, total_length,
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h + payload)
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struct.pack_into('!H', h, 16, self.csum)
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return h
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