115 lines
4.2 KiB
Python
115 lines
4.2 KiB
Python
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""" Multicast DNS Service Discovery for Python, v0.14-wmcbrine
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Copyright 2003 Paul Scott-Murphy, 2014 William McBrine
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This module provides a framework for the use of DNS Service Discovery
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using IP multicast.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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"""
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from operator import attrgetter
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from typing import Dict, List, Set
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from .._dns import DNSQuestion, DNSRecord
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from .._protocol.outgoing import DNSOutgoing
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from ..const import _FLAGS_AA, _FLAGS_QR_RESPONSE
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_AnswerWithAdditionalsType = Dict[DNSRecord, Set[DNSRecord]]
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int_ = int
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MULTICAST_DELAY_RANDOM_INTERVAL = (20, 120)
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NAME_GETTER = attrgetter('name')
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_FLAGS_QR_RESPONSE_AA = _FLAGS_QR_RESPONSE | _FLAGS_AA
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float_ = float
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class QuestionAnswers:
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"""A group of answers to a question."""
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__slots__ = ('ucast', 'mcast_now', 'mcast_aggregate', 'mcast_aggregate_last_second')
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def __init__(
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self,
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ucast: _AnswerWithAdditionalsType,
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mcast_now: _AnswerWithAdditionalsType,
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mcast_aggregate: _AnswerWithAdditionalsType,
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mcast_aggregate_last_second: _AnswerWithAdditionalsType,
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) -> None:
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"""Initialize a QuestionAnswers."""
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self.ucast = ucast
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self.mcast_now = mcast_now
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self.mcast_aggregate = mcast_aggregate
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self.mcast_aggregate_last_second = mcast_aggregate_last_second
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def __repr__(self) -> str:
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"""Return a string representation of this QuestionAnswers."""
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return (
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f'QuestionAnswers(ucast={self.ucast}, mcast_now={self.mcast_now}, '
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f'mcast_aggregate={self.mcast_aggregate}, '
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f'mcast_aggregate_last_second={self.mcast_aggregate_last_second})'
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)
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class AnswerGroup:
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"""A group of answers scheduled to be sent at the same time."""
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__slots__ = ('send_after', 'send_before', 'answers')
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def __init__(self, send_after: float_, send_before: float_, answers: _AnswerWithAdditionalsType) -> None:
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self.send_after = send_after # Must be sent after this time
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self.send_before = send_before # Must be sent before this time
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self.answers = answers
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def construct_outgoing_multicast_answers(answers: _AnswerWithAdditionalsType) -> DNSOutgoing:
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"""Add answers and additionals to a DNSOutgoing."""
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out = DNSOutgoing(_FLAGS_QR_RESPONSE_AA, True)
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_add_answers_additionals(out, answers)
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return out
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def construct_outgoing_unicast_answers(
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answers: _AnswerWithAdditionalsType, ucast_source: bool, questions: List[DNSQuestion], id_: int_
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) -> DNSOutgoing:
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"""Add answers and additionals to a DNSOutgoing."""
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out = DNSOutgoing(_FLAGS_QR_RESPONSE_AA, False, id_)
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# Adding the questions back when the source is legacy unicast behavior
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if ucast_source:
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for question in questions:
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out.add_question(question)
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_add_answers_additionals(out, answers)
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return out
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def _add_answers_additionals(out: DNSOutgoing, answers: _AnswerWithAdditionalsType) -> None:
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# Find additionals and suppress any additionals that are already in answers
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sending: Set[DNSRecord] = set(answers)
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# Answers are sorted to group names together to increase the chance
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# that similar names will end up in the same packet and can reduce the
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# overall size of the outgoing response via name compression
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for answer in sorted(answers, key=NAME_GETTER):
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out.add_answer_at_time(answer, 0)
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additionals = answers[answer]
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for additional in additionals:
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if additional not in sending:
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out.add_additional_answer(additional)
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sending.add(additional)
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