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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 struct
from . import packet_base
from os_ken.lib import type_desc
class mpls(packet_base.PacketBase):
"""MPLS (RFC 3032) header encoder/decoder class.
NOTE: When decoding, this implementation assumes that the inner protocol
is IPv4.
An instance has the following attributes at least.
Most of them are same to the on-wire counterparts but in host byte order.
__init__ takes the corresponding args in this order.
============== ====================
Attribute Description
============== ====================
label Label Value
exp Experimental Use
bsb Bottom of Stack
ttl Time To Live
============== ====================
"""
_PACK_STR = '!I'
_MIN_LEN = struct.calcsize(_PACK_STR)
def __init__(self, label=0, exp=0, bsb=1, ttl=255):
super(mpls, self).__init__()
self.label = label
self.exp = exp
self.bsb = bsb
self.ttl = ttl
@classmethod
def parser(cls, buf):
(label,) = struct.unpack_from(cls._PACK_STR, buf)
ttl = label & 0xff
bsb = (label >> 8) & 1
exp = (label >> 9) & 7
label = label >> 12
msg = cls(label, exp, bsb, ttl)
if bsb:
from . import ipv4
return msg, ipv4.ipv4, buf[msg._MIN_LEN:]
else:
return msg, mpls, buf[msg._MIN_LEN:]
def serialize(self, payload, prev):
val = self.label << 12 | self.exp << 9 | self.bsb << 8 | self.ttl
return struct.pack(mpls._PACK_STR, val)
def label_from_bin(buf):
"""
Converts binary representation label to integer.
:param buf: Binary representation of label.
:return: MPLS Label and BoS bit.
"""
mpls_label = type_desc.Int3.to_user(bytes(buf))
return mpls_label >> 4, mpls_label & 1
def label_to_bin(mpls_label, is_bos=True):
"""
Converts integer label to binary representation.
:param mpls_label: MPLS Label.
:param is_bos: BoS bit.
:return: Binary representation of label.
"""
return type_desc.Int3.from_user(mpls_label << 4 | is_bos)
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