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# Copyright (C) 2012 Nippon Telegraph and Telephone Corporation.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import array
import socket
import struct
from os_ken.lib import addrconv
def carry_around_add(a, b):
c = a + b
return (c & 0xffff) + (c >> 16)
def checksum(data):
data = bytes(data) # input can be bytearray.
if len(data) % 2:
data += b'\x00'
s = sum(array.array('H', data))
s = (s & 0xffff) + (s >> 16)
s += (s >> 16)
return socket.ntohs(~s & 0xffff)
# avoid circular import
_IPV4_PSEUDO_HEADER_PACK_STR = '!4s4sxBH'
_IPV6_PSEUDO_HEADER_PACK_STR = '!16s16sI3xB'
def checksum_ip(ipvx, length, payload):
"""
calculate checksum of IP pseudo header
IPv4 pseudo header
UDP RFC768
TCP RFC793 3.1
0 7 8 15 16 23 24 31
+--------+--------+--------+--------+
| source address |
+--------+--------+--------+--------+
| destination address |
+--------+--------+--------+--------+
| zero |protocol| length |
+--------+--------+--------+--------+
IPv6 pseudo header
RFC2460 8.1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upper-Layer Packet Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zero | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
"""
if ipvx.version == 4:
header = struct.pack(_IPV4_PSEUDO_HEADER_PACK_STR,
addrconv.ipv4.text_to_bin(ipvx.src),
addrconv.ipv4.text_to_bin(ipvx.dst),
ipvx.proto, length)
elif ipvx.version == 6:
header = struct.pack(_IPV6_PSEUDO_HEADER_PACK_STR,
addrconv.ipv6.text_to_bin(ipvx.src),
addrconv.ipv6.text_to_bin(ipvx.dst),
length, ipvx.nxt)
else:
raise ValueError('Unknown IP version %d' % ipvx.version)
buf = header + payload
return checksum(buf)
_MODX = 4102
def fletcher_checksum(data, offset):
"""
Fletcher Checksum -- Refer to RFC1008
calling with offset == _FLETCHER_CHECKSUM_VALIDATE will validate the
checksum without modifying the buffer; a valid checksum returns 0.
"""
c0 = 0
c1 = 0
pos = 0
length = len(data)
data = bytearray(data)
data[offset:offset + 2] = [0] * 2
while pos < length:
tlen = min(length - pos, _MODX)
for d in data[pos:pos + tlen]:
c0 += d
c1 += c0
c0 %= 255
c1 %= 255
pos += tlen
x = ((length - offset - 1) * c0 - c1) % 255
if x <= 0:
x += 255
y = 510 - c0 - x
if y > 255:
y -= 255
data[offset] = x
data[offset + 1] = y
return (x << 8) | (y & 0xff)
|
