94 lines
2.7 KiB
Python
94 lines
2.7 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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import six
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from . import packet_base
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from ryu.lib import type_desc
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class mpls(packet_base.PacketBase):
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"""MPLS (RFC 3032) header encoder/decoder class.
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NOTE: When decoding, this implementation assumes that the inner protocol
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is IPv4.
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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 corresponding args in this order.
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============== ====================
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Attribute Description
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============== ====================
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label Label Value
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exp Experimental Use
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bsb Bottom of Stack
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ttl Time To Live
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============== ====================
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"""
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_PACK_STR = '!I'
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_MIN_LEN = struct.calcsize(_PACK_STR)
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def __init__(self, label=0, exp=0, bsb=1, ttl=255):
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super(mpls, self).__init__()
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self.label = label
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self.exp = exp
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self.bsb = bsb
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self.ttl = ttl
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@classmethod
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def parser(cls, buf):
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(label,) = struct.unpack_from(cls._PACK_STR, buf)
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ttl = label & 0xff
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bsb = (label >> 8) & 1
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exp = (label >> 9) & 7
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label = label >> 12
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msg = cls(label, exp, bsb, ttl)
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if bsb:
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from . import ipv4
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return msg, ipv4.ipv4, buf[msg._MIN_LEN:]
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else:
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return msg, mpls, buf[msg._MIN_LEN:]
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def serialize(self, payload, prev):
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val = self.label << 12 | self.exp << 9 | self.bsb << 8 | self.ttl
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return struct.pack(mpls._PACK_STR, val)
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def label_from_bin(buf):
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"""
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Converts binary representation label to integer.
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:param buf: Binary representation of label.
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:return: MPLS Label and BoS bit.
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"""
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mpls_label = type_desc.Int3.to_user(six.binary_type(buf))
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return mpls_label >> 4, mpls_label & 1
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def label_to_bin(mpls_label, is_bos=True):
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"""
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Converts integer label to binary representation.
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:param mpls_label: MPLS Label.
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:param is_bos: BoS bit.
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:return: Binary representation of label.
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"""
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return type_desc.Int3.from_user(mpls_label << 4 | is_bos)
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