old_contents: """ 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
  """
  
  import asyncio
  import socket
  from functools import lru_cache
  from typing import List
  
  import ifaddr
  
  
  from zeroconf import DNSIncoming, Zeroconf
  
  
  def _inject_responses(zc: Zeroconf, msgs: List[DNSIncoming]) -> None:
      """Inject a DNSIncoming response."""
      assert zc.loop is not None
  
      async def _wait_for_response():
          for msg in msgs:
              zc.handle_response(msg)
  
      asyncio.run_coroutine_threadsafe(_wait_for_response(), zc.loop).result()
  
  
  def _inject_response(zc: Zeroconf, msg: DNSIncoming) -> None:
      """Inject a DNSIncoming response."""
      _inject_responses(zc, [msg])
  
  
  def _wait_for_start(zc: Zeroconf) -> None:
      """Wait for all sockets to be up and running."""
      assert zc.loop is not None
      asyncio.run_coroutine_threadsafe(zc.async_wait_for_start(), zc.loop).result()
  
  
  @lru_cache(maxsize=None)
  def has_working_ipv6():
      """Return True if if the system can bind an IPv6 address."""
      if not socket.has_ipv6:
          return False
  
      try:
          sock = socket.socket(socket.AF_INET6)
          sock.bind(('::1', 0))
      except Exception:
          return False
      finally:
          if sock:
              sock.close()
  
      for iface in ifaddr.get_adapters():
          for addr in iface.ips:
              if addr.is_IPv6 and iface.index is not None:
                  return True
      return False
  
  
  def _clear_cache(zc):
      zc.cache.cache.clear()
      zc.question_history._history.clear()
  
new_contents: """ 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
  """
  
  import asyncio
  import socket
  from functools import lru_cache
  from typing import List
  
  import ifaddr
  
  
  from zeroconf import DNSIncoming, Zeroconf
  
  
  def _inject_responses(zc: Zeroconf, msgs: List[DNSIncoming]) -> None:
      """Inject a DNSIncoming response."""
      assert zc.loop is not None
  
      async def _wait_for_response():
          for msg in msgs:
              zc.handle_response(msg)
  
      asyncio.run_coroutine_threadsafe(_wait_for_response(), zc.loop).result()
  
  
  def _inject_response(zc: Zeroconf, msg: DNSIncoming) -> None:
      """Inject a DNSIncoming response."""
      _inject_responses(zc, [msg])
  
  
  def _wait_for_start(zc: Zeroconf) -> None:
      """Wait for all sockets to be up and running."""
      assert zc.loop is not None
      asyncio.run_coroutine_threadsafe(zc.async_wait_for_start(), zc.loop).result()
  
  
  @lru_cache(maxsize=None)
  def has_working_ipv6():
      """Return True if if the system can bind an IPv6 address."""
      if not socket.has_ipv6:
          return False
  
      sock = None
      try:
          sock = socket.socket(socket.AF_INET6)
          sock.bind(('::1', 0))
      except Exception:
          return False
      finally:
          if sock:
              sock.close()
  
      for iface in ifaddr.get_adapters():
          for addr in iface.ips:
              if addr.is_IPv6 and iface.index is not None:
                  return True
      return False
  
  
  def _clear_cache(zc):
      zc.cache.cache.clear()
      zc.question_history._history.clear()
  
subject: Fix test failure when has_working_ipv6 generates an exception (#1022)