139 lines
4.5 KiB
Python
139 lines
4.5 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 array
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import six
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import socket
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import struct
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from os_ken.lib import addrconv
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def carry_around_add(a, b):
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c = a + b
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return (c & 0xffff) + (c >> 16)
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def checksum(data):
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data = six.binary_type(data) # input can be bytearray.
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if len(data) % 2:
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data += b'\x00'
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s = sum(array.array('H', data))
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s = (s & 0xffff) + (s >> 16)
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s += (s >> 16)
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return socket.ntohs(~s & 0xffff)
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# avoid circular import
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_IPV4_PSEUDO_HEADER_PACK_STR = '!4s4sxBH'
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_IPV6_PSEUDO_HEADER_PACK_STR = '!16s16sI3xB'
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def checksum_ip(ipvx, length, payload):
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"""
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calculate checksum of IP pseudo header
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IPv4 pseudo header
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UDP RFC768
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TCP RFC793 3.1
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0 7 8 15 16 23 24 31
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+--------+--------+--------+--------+
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| source address |
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+--------+--------+--------+--------+
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| destination address |
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+--------+--------+--------+--------+
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| zero |protocol| length |
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+--------+--------+--------+--------+
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IPv6 pseudo header
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RFC2460 8.1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+ +
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+ Source Address +
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+ +
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+ +
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+ Destination Address +
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+ +
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Upper-Layer Packet Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| zero | Next Header |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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"""
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if ipvx.version == 4:
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header = struct.pack(_IPV4_PSEUDO_HEADER_PACK_STR,
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addrconv.ipv4.text_to_bin(ipvx.src),
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addrconv.ipv4.text_to_bin(ipvx.dst),
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ipvx.proto, length)
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elif ipvx.version == 6:
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header = struct.pack(_IPV6_PSEUDO_HEADER_PACK_STR,
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addrconv.ipv6.text_to_bin(ipvx.src),
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addrconv.ipv6.text_to_bin(ipvx.dst),
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length, ipvx.nxt)
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else:
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raise ValueError('Unknown IP version %d' % ipvx.version)
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buf = header + payload
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return checksum(buf)
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_MODX = 4102
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def fletcher_checksum(data, offset):
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"""
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Fletcher Checksum -- Refer to RFC1008
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calling with offset == _FLETCHER_CHECKSUM_VALIDATE will validate the
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checksum without modifying the buffer; a valid checksum returns 0.
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"""
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c0 = 0
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c1 = 0
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pos = 0
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length = len(data)
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data = bytearray(data)
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data[offset:offset + 2] = [0] * 2
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while pos < length:
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tlen = min(length - pos, _MODX)
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for d in data[pos:pos + tlen]:
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c0 += d
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c1 += c0
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c0 %= 255
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c1 %= 255
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pos += tlen
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x = ((length - offset - 1) * c0 - c1) % 255
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if x <= 0:
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x += 255
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y = 510 - c0 - x
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if y > 255:
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y -= 255
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data[offset] = x
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data[offset + 1] = y
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return (x << 8) | (y & 0xff)
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