Current File : //lib/python3/dist-packages/zeroconf/_history.py
""" Multicast DNS Service Discovery for Python, v0.14-wmcbrine
Copyright 2003 Paul Scott-Murphy, 2014 William McBrine
This module provides a framework for the use of DNS Service Discovery
using IP multicast.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA
"""
from typing import Dict, Set, Tuple
from ._dns import DNSQuestion, DNSRecord
from .const import _DUPLICATE_QUESTION_INTERVAL
# The QuestionHistory is used to implement Duplicate Question Suppression
# https://datatracker.ietf.org/doc/html/rfc6762#section-7.3
class QuestionHistory:
def __init__(self) -> None:
self._history: Dict[DNSQuestion, Tuple[float, Set[DNSRecord]]] = {}
def add_question_at_time(self, question: DNSQuestion, now: float, known_answers: Set[DNSRecord]) -> None:
"""Remember a question with known answers."""
self._history[question] = (now, known_answers)
def suppresses(self, question: DNSQuestion, now: float, known_answers: Set[DNSRecord]) -> bool:
"""Check to see if a question should be suppressed.
https://datatracker.ietf.org/doc/html/rfc6762#section-7.3
When multiple queriers on the network are querying
for the same resource records, there is no need for them to all be
repeatedly asking the same question.
"""
previous_question = self._history.get(question)
# There was not previous question in the history
if not previous_question:
return False
than, previous_known_answers = previous_question
# The last question was older than 999ms
if now - than > _DUPLICATE_QUESTION_INTERVAL:
return False
# The last question has more known answers than
# we knew so we have to ask
if previous_known_answers - known_answers:
return False
return True
def async_expire(self, now: float) -> None:
"""Expire the history of old questions."""
removes = [
question
for question, now_known_answers in self._history.items()
if now - now_known_answers[0] > _DUPLICATE_QUESTION_INTERVAL
]
for question in removes:
del self._history[question]
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