80 lines
3.1 KiB
Python
80 lines
3.1 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 typing import Dict, List, Set, Tuple
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from ._dns import DNSQuestion, DNSRecord
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from .const import _DUPLICATE_QUESTION_INTERVAL
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# The QuestionHistory is used to implement Duplicate Question Suppression
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# https://datatracker.ietf.org/doc/html/rfc6762#section-7.3
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_float = float
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class QuestionHistory:
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"""Remember questions and known answers."""
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def __init__(self) -> None:
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"""Init a new QuestionHistory."""
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self._history: Dict[DNSQuestion, Tuple[float, Set[DNSRecord]]] = {}
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def add_question_at_time(self, question: DNSQuestion, now: _float, known_answers: Set[DNSRecord]) -> None:
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"""Remember a question with known answers."""
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self._history[question] = (now, known_answers)
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def suppresses(self, question: DNSQuestion, now: _float, known_answers: Set[DNSRecord]) -> bool:
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"""Check to see if a question should be suppressed.
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https://datatracker.ietf.org/doc/html/rfc6762#section-7.3
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When multiple queriers on the network are querying
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for the same resource records, there is no need for them to all be
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repeatedly asking the same question.
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"""
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previous_question = self._history.get(question)
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# There was not previous question in the history
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if not previous_question:
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return False
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than, previous_known_answers = previous_question
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# The last question was older than 999ms
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if now - than > _DUPLICATE_QUESTION_INTERVAL:
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return False
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# The last question has more known answers than
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# we knew so we have to ask
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if previous_known_answers - known_answers:
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return False
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return True
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def async_expire(self, now: _float) -> None:
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"""Expire the history of old questions."""
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removes: List[DNSQuestion] = []
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for question, now_known_answers in self._history.items():
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than, _ = now_known_answers
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if now - than > _DUPLICATE_QUESTION_INTERVAL:
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removes.append(question)
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for question in removes:
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del self._history[question]
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def clear(self) -> None:
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"""Clear the history."""
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self._history.clear()
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