323 lines
10 KiB
Python
323 lines
10 KiB
Python
# Copyright (C) 2013 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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"""
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Logical Link Control(LLC, IEEE 802.2) parser/serializer
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http://standards.ieee.org/getieee802/download/802.2-1998.pdf
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LLC format::
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+-----------------+--------------+
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| DSAP address | 8 bits |
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+-----------------+--------------+
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| SSAP address | 8 bits |
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+-----------------+--------------+
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| Control | 8 or 16 bits |
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+-----------------+--------------+
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DSAP address field::
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LSB
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+-----+---+---+---+---+---+---+---+
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| I/G | D | D | D | D | D | D | D |
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+-----+---+---+---+---+---+---+---+
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I/G bit = 0 : Individual DSAP
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I/G bit = 1 : Group DSA
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D : DSAP address
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SSAP address field::
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LSB
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+-----+---+---+---+---+---+---+---+
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| C/R | S | S | S | S | S | S | S |
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+-----+---+---+---+---+---+---+---+
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C/R bit = 0 : Command
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C/R bit = 1 : Response
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S : SSAP address
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Control field:
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Information transfer
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command/response
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(I-format PDU)::
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1 2 3 4 5 6 7 8 9 10-16
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+---+---+---+---+---+---+---+---+-----+------+
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| 0 | N(S) | P/F | N(R) |
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+---+---+---+---+---+---+---+---+-----+------+
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Supervisory
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commands/responses
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(S-format PDUs)::
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1 2 3 4 5 6 7 8 9 10-16
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+---+---+---+---+---+---+---+---+-----+------+
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| 1 0 | S S | 0 0 0 0 | P/F | N(R) |
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+---+---+---+---+---+---+---+---+-----+------+
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Unnumbered
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commands/responses
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(U-format PDUs)::
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1 2 3 4 5 6 7 8
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+---+---+----+---+-----+---+----+---+
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| 1 1 | M1 M1 | P/F | M2 M2 M2 |
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+---+---+----+---+-----+---+----+---+
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N(S) : sender send sequence number (Bit 2=lower-order-bit)
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N(R) : sender receive sequence number (Bit 10=lower-order-bit)
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S : supervisory function bit
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M1/M2: modifier function bit
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P/F : poll bit - command LLC PDUs
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final bit - response LLC PDUs
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"""
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import struct
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from . import bpdu
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from . import packet_base
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from os_ken.lib import stringify
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SAP_BPDU = 0x42
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class llc(packet_base.PacketBase):
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"""LLC(IEEE 802.2) 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
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order.
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__init__ takes the corresponding args in this order.
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.. tabularcolumns:: |l|L|
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=============== ===============================================
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Attribute Description
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=============== ===============================================
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dsap_addr Destination service access point address field \
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includes I/G bit at least significant bit.
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ssap_addr Source service access point address field \
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includes C/R bit at least significant bit.
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control Control field \
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[16 bits for formats that include sequence \
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numbering, and 8 bits for formats that do not]. \
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Either os_ken.lib.packet.llc.ControlFormatI or \
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os_ken.lib.packet.llc.ControlFormatS or \
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os_ken.lib.packet.llc.ControlFormatU object.
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=============== ===============================================
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"""
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_PACK_STR = '!BB'
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_PACK_LEN = struct.calcsize(_PACK_STR)
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_CTR_TYPES = {}
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_CTR_PACK_STR = '!2xB'
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_MIN_LEN = _PACK_LEN
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@staticmethod
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def register_control_type(register_cls):
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llc._CTR_TYPES[register_cls.TYPE] = register_cls
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return register_cls
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def __init__(self, dsap_addr, ssap_addr, control):
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super(llc, self).__init__()
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assert getattr(control, 'TYPE', None) in self._CTR_TYPES
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self.dsap_addr = dsap_addr
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self.ssap_addr = ssap_addr
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self.control = control
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@classmethod
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def parser(cls, buf):
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assert len(buf) >= cls._PACK_LEN
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(dsap_addr, ssap_addr) = struct.unpack_from(cls._PACK_STR, buf)
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(control,) = struct.unpack_from(cls._CTR_PACK_STR, buf)
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ctrl = cls._get_control(control)
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control, information = ctrl.parser(buf[cls._PACK_LEN:])
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return (cls(dsap_addr, ssap_addr, control),
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cls.get_packet_type(dsap_addr), information)
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def serialize(self, payload, prev):
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addr = struct.pack(self._PACK_STR, self.dsap_addr, self.ssap_addr)
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control = self.control.serialize()
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return addr + control
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@classmethod
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def _get_control(cls, buf):
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key = buf & 0b1 if buf & 0b1 == ControlFormatI.TYPE else buf & 0b11
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return cls._CTR_TYPES[key]
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@llc.register_control_type
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class ControlFormatI(stringify.StringifyMixin):
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"""LLC sub encoder/decoder class for control I-format field.
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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
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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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send_sequence_number sender send sequence number
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pf_bit poll/final bit
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receive_sequence_number sender receive sequence number
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======================== ===============================
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"""
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TYPE = 0b0
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_PACK_STR = '!H'
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_PACK_LEN = struct.calcsize(_PACK_STR)
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def __init__(self, send_sequence_number=0, pf_bit=0,
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receive_sequence_number=0):
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super(ControlFormatI, self).__init__()
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self.send_sequence_number = send_sequence_number
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self.pf_bit = pf_bit
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self.receive_sequence_number = receive_sequence_number
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@classmethod
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def parser(cls, buf):
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assert len(buf) >= cls._PACK_LEN
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(control,) = struct.unpack_from(cls._PACK_STR, buf)
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assert (control >> 8) & 0b1 == cls.TYPE
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send_sequence_number = (control >> 9) & 0b1111111
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pf_bit = (control >> 8) & 0b1
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receive_sequence_number = (control >> 1) & 0b1111111
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return cls(send_sequence_number, pf_bit,
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receive_sequence_number), buf[cls._PACK_LEN:]
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def serialize(self):
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control = (self.send_sequence_number << 9 |
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self.TYPE << 8 |
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self.receive_sequence_number << 1 |
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self.pf_bit)
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return struct.pack(self._PACK_STR, control)
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@llc.register_control_type
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class ControlFormatS(stringify.StringifyMixin):
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"""LLC sub encoder/decoder class for control S-format field.
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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
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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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supervisory_function supervisory function bit
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pf_bit poll/final bit
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receive_sequence_number sender receive sequence number
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======================== ===============================
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"""
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TYPE = 0b01
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_PACK_STR = '!H'
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_PACK_LEN = struct.calcsize(_PACK_STR)
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def __init__(self, supervisory_function=0, pf_bit=0,
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receive_sequence_number=0):
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super(ControlFormatS, self).__init__()
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self.supervisory_function = supervisory_function
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self.pf_bit = pf_bit
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self.receive_sequence_number = receive_sequence_number
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@classmethod
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def parser(cls, buf):
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assert len(buf) >= cls._PACK_LEN
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(control,) = struct.unpack_from(cls._PACK_STR, buf)
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assert (control >> 8) & 0b11 == cls.TYPE
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supervisory_function = (control >> 10) & 0b11
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pf_bit = (control >> 8) & 0b1
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receive_sequence_number = (control >> 1) & 0b1111111
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return cls(supervisory_function, pf_bit,
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receive_sequence_number), buf[cls._PACK_LEN:]
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def serialize(self):
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control = (self.supervisory_function << 10 |
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self.TYPE << 8 |
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self.receive_sequence_number << 1 |
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self.pf_bit)
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return struct.pack(self._PACK_STR, control)
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@llc.register_control_type
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class ControlFormatU(stringify.StringifyMixin):
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"""LLC sub encoder/decoder class for control U-format field.
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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
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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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modifier_function1 modifier function bit
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pf_bit poll/final bit
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modifier_function2 modifier function bit
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======================== ===============================
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"""
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TYPE = 0b11
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_PACK_STR = '!B'
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_PACK_LEN = struct.calcsize(_PACK_STR)
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def __init__(self, modifier_function1=0, pf_bit=0, modifier_function2=0):
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super(ControlFormatU, self).__init__()
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self.modifier_function1 = modifier_function1
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self.pf_bit = pf_bit
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self.modifier_function2 = modifier_function2
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@classmethod
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def parser(cls, buf):
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assert len(buf) >= cls._PACK_LEN
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(control,) = struct.unpack_from(cls._PACK_STR, buf)
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assert control & 0b11 == cls.TYPE
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modifier_function1 = (control >> 2) & 0b11
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pf_bit = (control >> 4) & 0b1
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modifier_function2 = (control >> 5) & 0b111
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return cls(modifier_function1, pf_bit,
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modifier_function2), buf[cls._PACK_LEN:]
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def serialize(self):
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control = (self.modifier_function2 << 5 |
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self.pf_bit << 4 |
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self.modifier_function1 << 2 |
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self.TYPE)
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return struct.pack(self._PACK_STR, control)
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llc.register_packet_type(bpdu.bpdu, SAP_BPDU)
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llc.set_classes(llc._CTR_TYPES)
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