zeroconf: do not crash if socket being read is closed by another thread

In zeroconf/__init__.py, there is:

    server = Zeroconf.Zeroconf(ip)
    l = listener()
    Zeroconf.ServiceBrowser(server, "_hg._tcp.local.", l)
    time.sleep(1)
    server.close()

`server.close()` closes the underlying socket while the `ServiceBrowser` may
still have a background thread reading the socket. There could be a race
condition where the reading thread reads the closed socket, resulting in
EBADF crash. This patch catches the exception.

This makes test-paths.t pass with chg.

Differential Revision: https://phab.mercurial-scm.org/D919

hgext/zeroconf/Zeroconf.py

@@ -1,1680 +1,1690 b''
 from __future__ import absolute_import, print_function
 
 """ Multicast DNS Service Discovery for Python, v0.12
     Copyright (C) 2003, Paul Scott-Murphy
 
     This module provides a framework for the use of DNS Service Discovery
     using IP multicast.  It has been tested against the JRendezvous
     implementation from <a href="http://strangeberry.com">StrangeBerry</a>,
     and against the mDNSResponder from Mac OS X 10.3.8.
 
     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, see
     <http://www.gnu.org/licenses/>.
 
 """
 
 """0.12 update - allow selection of binding interface
          typo fix - Thanks A. M. Kuchlingi
          removed all use of word 'Rendezvous' - this is an API change"""
 
 """0.11 update - correction to comments for addListener method
                  support for new record types seen from OS X
                   - IPv6 address
                   - hostinfo
                  ignore unknown DNS record types
                  fixes to name decoding
                  works alongside other processes using port 5353 (e.g. Mac OS X)
                  tested against Mac OS X 10.3.2's mDNSResponder
                  corrections to removal of list entries for service browser"""
 
 """0.10 update - Jonathon Paisley contributed these corrections:
                  always multicast replies, even when query is unicast
                  correct a pointer encoding problem
                  can now write records in any order
                  traceback shown on failure
                  better TXT record parsing
                  server is now separate from name
                  can cancel a service browser
 
                  modified some unit tests to accommodate these changes"""
 
 """0.09 update - remove all records on service unregistration
                  fix DOS security problem with readName"""
 
 """0.08 update - changed licensing to LGPL"""
 
 """0.07 update - faster shutdown on engine
                  pointer encoding of outgoing names
                  ServiceBrowser now works
                  new unit tests"""
 
 """0.06 update - small improvements with unit tests
                  added defined exception types
                  new style objects
                  fixed hostname/interface problem
                  fixed socket timeout problem
                  fixed addServiceListener() typo bug
                  using select() for socket reads
                  tested on Debian unstable with Python 2.2.2"""
 
 """0.05 update - ensure case insensitivity on domain names
                  support for unicast DNS queries"""
 
 """0.04 update - added some unit tests
                  added __ne__ adjuncts where required
                  ensure names end in '.local.'
                  timeout on receiving socket for clean shutdown"""
 
 __author__ = "Paul Scott-Murphy"
 __email__ = "paul at scott dash murphy dot com"
 __version__ = "0.12"
 
+import errno
 import itertools
 import select
 import socket
 import string
 import struct
 import threading
 import time
 import traceback
 
 __all__ = ["Zeroconf", "ServiceInfo", "ServiceBrowser"]
 
 # hook for threads
 
 globals()['_GLOBAL_DONE'] = 0
 
 # Some timing constants
 
 _UNREGISTER_TIME = 125
 _CHECK_TIME = 175
 _REGISTER_TIME = 225
 _LISTENER_TIME = 200
 _BROWSER_TIME = 500
 
 # Some DNS constants
 
 _MDNS_ADDR = '224.0.0.251'
 _MDNS_PORT = 5353
 _DNS_PORT = 53
 _DNS_TTL = 60 * 60 # one hour default TTL
 
 _MAX_MSG_TYPICAL = 1460 # unused
 _MAX_MSG_ABSOLUTE = 8972
 
 _FLAGS_QR_MASK = 0x8000 # query response mask
 _FLAGS_QR_QUERY = 0x0000 # query
 _FLAGS_QR_RESPONSE = 0x8000 # response
 
 _FLAGS_AA = 0x0400 # Authoritative answer
 _FLAGS_TC = 0x0200 # Truncated
 _FLAGS_RD = 0x0100 # Recursion desired
 _FLAGS_RA = 0x8000 # Recursion available
 
 _FLAGS_Z = 0x0040 # Zero
 _FLAGS_AD = 0x0020 # Authentic data
 _FLAGS_CD = 0x0010 # Checking disabled
 
 _CLASS_IN = 1
 _CLASS_CS = 2
 _CLASS_CH = 3
 _CLASS_HS = 4
 _CLASS_NONE = 254
 _CLASS_ANY = 255
 _CLASS_MASK = 0x7FFF
 _CLASS_UNIQUE = 0x8000
 
 _TYPE_A = 1
 _TYPE_NS = 2
 _TYPE_MD = 3
 _TYPE_MF = 4
 _TYPE_CNAME = 5
 _TYPE_SOA = 6
 _TYPE_MB = 7
 _TYPE_MG = 8
 _TYPE_MR = 9
 _TYPE_NULL = 10
 _TYPE_WKS = 11
 _TYPE_PTR = 12
 _TYPE_HINFO = 13
 _TYPE_MINFO = 14
 _TYPE_MX = 15
 _TYPE_TXT = 16
 _TYPE_AAAA = 28
 _TYPE_SRV = 33
 _TYPE_ANY = 255
 
 # Mapping constants to names
 
 _CLASSES = { _CLASS_IN : "in",
              _CLASS_CS : "cs",
              _CLASS_CH : "ch",
              _CLASS_HS : "hs",
              _CLASS_NONE : "none",
              _CLASS_ANY : "any" }
 
 _TYPES = { _TYPE_A : "a",
            _TYPE_NS : "ns",
            _TYPE_MD : "md",
            _TYPE_MF : "mf",
            _TYPE_CNAME : "cname",
            _TYPE_SOA : "soa",
            _TYPE_MB : "mb",
            _TYPE_MG : "mg",
            _TYPE_MR : "mr",
            _TYPE_NULL : "null",
            _TYPE_WKS : "wks",
            _TYPE_PTR : "ptr",
            _TYPE_HINFO : "hinfo",
            _TYPE_MINFO : "minfo",
            _TYPE_MX : "mx",
            _TYPE_TXT : "txt",
            _TYPE_AAAA : "quada",
            _TYPE_SRV : "srv",
            _TYPE_ANY : "any" }
 
 # utility functions
 
 def currentTimeMillis():
     """Current system time in milliseconds"""
     return time.time() * 1000
 
 # Exceptions
 
 class NonLocalNameException(Exception):
     pass
 
 class NonUniqueNameException(Exception):
     pass
 
 class NamePartTooLongException(Exception):
     pass
 
 class AbstractMethodException(Exception):
     pass
 
 class BadTypeInNameException(Exception):
     pass
 
 class BadDomainName(Exception):
     def __init__(self, pos):
         Exception.__init__(self, "at position %s" % pos)
 
 class BadDomainNameCircular(BadDomainName):
     pass
 
 # implementation classes
 
 class DNSEntry(object):
     """A DNS entry"""
 
     def __init__(self, name, type, clazz):
         self.key = string.lower(name)
         self.name = name
         self.type = type
         self.clazz = clazz & _CLASS_MASK
         self.unique = (clazz & _CLASS_UNIQUE) != 0
 
     def __eq__(self, other):
         """Equality test on name, type, and class"""
         if isinstance(other, DNSEntry):
             return (self.name == other.name and self.type == other.type and
                     self.clazz == other.clazz)
         return 0
 
     def __ne__(self, other):
         """Non-equality test"""
         return not self.__eq__(other)
 
     def getClazz(self, clazz):
         """Class accessor"""
         try:
             return _CLASSES[clazz]
         except KeyError:
             return "?(%s)" % (clazz)
 
     def getType(self, type):
         """Type accessor"""
         try:
             return _TYPES[type]
         except KeyError:
             return "?(%s)" % (type)
 
     def toString(self, hdr, other):
         """String representation with additional information"""
         result = ("%s[%s,%s" %
             (hdr, self.getType(self.type), self.getClazz(self.clazz)))
         if self.unique:
             result += "-unique,"
         else:
             result += ","
         result += self.name
         if other is not None:
             result += ",%s]" % (other)
         else:
             result += "]"
         return result
 
 class DNSQuestion(DNSEntry):
     """A DNS question entry"""
 
     def __init__(self, name, type, clazz):
         if not name.endswith(".local."):
             raise NonLocalNameException(name)
         DNSEntry.__init__(self, name, type, clazz)
 
     def answeredBy(self, rec):
         """Returns true if the question is answered by the record"""
         return (self.clazz == rec.clazz and
                 (self.type == rec.type or self.type == _TYPE_ANY) and
                 self.name == rec.name)
 
     def __repr__(self):
         """String representation"""
         return DNSEntry.toString(self, "question", None)
 
 
 class DNSRecord(DNSEntry):
     """A DNS record - like a DNS entry, but has a TTL"""
 
     def __init__(self, name, type, clazz, ttl):
         DNSEntry.__init__(self, name, type, clazz)
         self.ttl = ttl
         self.created = currentTimeMillis()
 
     def __eq__(self, other):
         """Tests equality as per DNSRecord"""
         if isinstance(other, DNSRecord):
             return DNSEntry.__eq__(self, other)
         return 0
 
     def suppressedBy(self, msg):
         """Returns true if any answer in a message can suffice for the
         information held in this record."""
         for record in msg.answers:
             if self.suppressedByAnswer(record):
                 return 1
         return 0
 
     def suppressedByAnswer(self, other):
         """Returns true if another record has same name, type and class,
         and if its TTL is at least half of this record's."""
         if self == other and other.ttl > (self.ttl / 2):
             return 1
         return 0
 
     def getExpirationTime(self, percent):
         """Returns the time at which this record will have expired
         by a certain percentage."""
         return self.created + (percent * self.ttl * 10)
 
     def getRemainingTTL(self, now):
         """Returns the remaining TTL in seconds."""
         return max(0, (self.getExpirationTime(100) - now) / 1000)
 
     def isExpired(self, now):
         """Returns true if this record has expired."""
         return self.getExpirationTime(100) <= now
 
     def isStale(self, now):
         """Returns true if this record is at least half way expired."""
         return self.getExpirationTime(50) <= now
 
     def resetTTL(self, other):
         """Sets this record's TTL and created time to that of
         another record."""
         self.created = other.created
         self.ttl = other.ttl
 
     def write(self, out):
         """Abstract method"""
         raise AbstractMethodException
 
     def toString(self, other):
         """String representation with additional information"""
         arg = ("%s/%s,%s" %
             (self.ttl, self.getRemainingTTL(currentTimeMillis()), other))
         return DNSEntry.toString(self, "record", arg)
 
 class DNSAddress(DNSRecord):
     """A DNS address record"""
 
     def __init__(self, name, type, clazz, ttl, address):
         DNSRecord.__init__(self, name, type, clazz, ttl)
         self.address = address
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
         out.writeString(self.address, len(self.address))
 
     def __eq__(self, other):
         """Tests equality on address"""
         if isinstance(other, DNSAddress):
             return self.address == other.address
         return 0
 
     def __repr__(self):
         """String representation"""
         try:
             return socket.inet_ntoa(self.address)
         except Exception:
             return self.address
 
 class DNSHinfo(DNSRecord):
     """A DNS host information record"""
 
     def __init__(self, name, type, clazz, ttl, cpu, os):
         DNSRecord.__init__(self, name, type, clazz, ttl)
         self.cpu = cpu
         self.os = os
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
         out.writeString(self.cpu, len(self.cpu))
         out.writeString(self.os, len(self.os))
 
     def __eq__(self, other):
         """Tests equality on cpu and os"""
         if isinstance(other, DNSHinfo):
             return self.cpu == other.cpu and self.os == other.os
         return 0
 
     def __repr__(self):
         """String representation"""
         return self.cpu + " " + self.os
 
 class DNSPointer(DNSRecord):
     """A DNS pointer record"""
 
     def __init__(self, name, type, clazz, ttl, alias):
         DNSRecord.__init__(self, name, type, clazz, ttl)
         self.alias = alias
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
         out.writeName(self.alias)
 
     def __eq__(self, other):
         """Tests equality on alias"""
         if isinstance(other, DNSPointer):
             return self.alias == other.alias
         return 0
 
     def __repr__(self):
         """String representation"""
         return self.toString(self.alias)
 
 class DNSText(DNSRecord):
     """A DNS text record"""
 
     def __init__(self, name, type, clazz, ttl, text):
         DNSRecord.__init__(self, name, type, clazz, ttl)
         self.text = text
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
         out.writeString(self.text, len(self.text))
 
     def __eq__(self, other):
         """Tests equality on text"""
         if isinstance(other, DNSText):
             return self.text == other.text
         return 0
 
     def __repr__(self):
         """String representation"""
         if len(self.text) > 10:
             return self.toString(self.text[:7] + "...")
         else:
             return self.toString(self.text)
 
 class DNSService(DNSRecord):
     """A DNS service record"""
 
     def __init__(self, name, type, clazz, ttl, priority, weight, port, server):
         DNSRecord.__init__(self, name, type, clazz, ttl)
         self.priority = priority
         self.weight = weight
         self.port = port
         self.server = server
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
         out.writeShort(self.priority)
         out.writeShort(self.weight)
         out.writeShort(self.port)
         out.writeName(self.server)
 
     def __eq__(self, other):
         """Tests equality on priority, weight, port and server"""
         if isinstance(other, DNSService):
             return (self.priority == other.priority and
                     self.weight == other.weight and
                     self.port == other.port and
                     self.server == other.server)
         return 0
 
     def __repr__(self):
         """String representation"""
         return self.toString("%s:%s" % (self.server, self.port))
 
 class DNSIncoming(object):
     """Object representation of an incoming DNS packet"""
 
     def __init__(self, data):
         """Constructor from string holding bytes of packet"""
         self.offset = 0
         self.data = data
         self.questions = []
         self.answers = []
         self.numquestions = 0
         self.numanswers = 0
         self.numauthorities = 0
         self.numadditionals = 0
 
         self.readHeader()
         self.readQuestions()
         self.readOthers()
 
     def readHeader(self):
         """Reads header portion of packet"""
         format = '!HHHHHH'
         length = struct.calcsize(format)
         info = struct.unpack(format,
                              self.data[self.offset:self.offset + length])
         self.offset += length
 
         self.id = info[0]
         self.flags = info[1]
         self.numquestions = info[2]
         self.numanswers = info[3]
         self.numauthorities = info[4]
         self.numadditionals = info[5]
 
     def readQuestions(self):
         """Reads questions section of packet"""
         format = '!HH'
         length = struct.calcsize(format)
         for i in range(0, self.numquestions):
             name = self.readName()
             info = struct.unpack(format,
                                  self.data[self.offset:self.offset + length])
             self.offset += length
 
             try:
                 question = DNSQuestion(name, info[0], info[1])
                 self.questions.append(question)
             except NonLocalNameException:
                 pass
 
     def readInt(self):
         """Reads an integer from the packet"""
         format = '!I'
         length = struct.calcsize(format)
         info = struct.unpack(format,
                              self.data[self.offset:self.offset + length])
         self.offset += length
         return info[0]
 
     def readCharacterString(self):
         """Reads a character string from the packet"""
         length = ord(self.data[self.offset])
         self.offset += 1
         return self.readString(length)
 
     def readString(self, len):
         """Reads a string of a given length from the packet"""
         format = '!' + str(len) + 's'
         length = struct.calcsize(format)
         info = struct.unpack(format,
                              self.data[self.offset:self.offset + length])
         self.offset += length
         return info[0]
 
     def readUnsignedShort(self):
         """Reads an unsigned short from the packet"""
         format = '!H'
         length = struct.calcsize(format)
         info = struct.unpack(format,
                              self.data[self.offset:self.offset + length])
         self.offset += length
         return info[0]
 
     def readOthers(self):
         """Reads answers, authorities and additionals section of the packet"""
         format = '!HHiH'
         length = struct.calcsize(format)
         n = self.numanswers + self.numauthorities + self.numadditionals
         for i in range(0, n):
             domain = self.readName()
             info = struct.unpack(format,
                                  self.data[self.offset:self.offset + length])
             self.offset += length
 
             rec = None
             if info[0] == _TYPE_A:
                 rec = DNSAddress(domain, info[0], info[1], info[2],
                                  self.readString(4))
             elif info[0] == _TYPE_CNAME or info[0] == _TYPE_PTR:
                 rec = DNSPointer(domain, info[0], info[1], info[2],
                                  self.readName())
             elif info[0] == _TYPE_TXT:
                 rec = DNSText(domain, info[0], info[1], info[2],
                               self.readString(info[3]))
             elif info[0] == _TYPE_SRV:
                 rec = DNSService(domain, info[0], info[1], info[2],
                                  self.readUnsignedShort(),
                                  self.readUnsignedShort(),
                                  self.readUnsignedShort(),
                                  self.readName())
             elif info[0] == _TYPE_HINFO:
                 rec = DNSHinfo(domain, info[0], info[1], info[2],
                                self.readCharacterString(),
                                self.readCharacterString())
             elif info[0] == _TYPE_AAAA:
                 rec = DNSAddress(domain, info[0], info[1], info[2],
                                  self.readString(16))
             else:
                 # Try to ignore types we don't know about
                 # this may mean the rest of the name is
                 # unable to be parsed, and may show errors
                 # so this is left for debugging.  New types
                 # encountered need to be parsed properly.
                 #
                 #print "UNKNOWN TYPE = " + str(info[0])
                 #raise BadTypeInNameException
                 self.offset += info[3]
 
             if rec is not None:
                 self.answers.append(rec)
 
     def isQuery(self):
         """Returns true if this is a query"""
         return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_QUERY
 
     def isResponse(self):
         """Returns true if this is a response"""
         return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_RESPONSE
 
     def readUTF(self, offset, len):
         """Reads a UTF-8 string of a given length from the packet"""
         return self.data[offset:offset + len].decode('utf-8')
 
     def readName(self):
         """Reads a domain name from the packet"""
         result = ''
         off = self.offset
         next = -1
         first = off
 
         while True:
             len = ord(self.data[off])
             off += 1
             if len == 0:
                 break
             t = len & 0xC0
             if t == 0x00:
                 result = ''.join((result, self.readUTF(off, len) + '.'))
                 off += len
             elif t == 0xC0:
                 if next < 0:
                     next = off + 1
                 off = ((len & 0x3F) << 8) | ord(self.data[off])
                 if off >= first:
                     raise BadDomainNameCircular(off)
                 first = off
             else:
                 raise BadDomainName(off)
 
         if next >= 0:
             self.offset = next
         else:
             self.offset = off
 
         return result
 
 
 class DNSOutgoing(object):
     """Object representation of an outgoing packet"""
 
     def __init__(self, flags, multicast=1):
         self.finished = 0
         self.id = 0
         self.multicast = multicast
         self.flags = flags
         self.names = {}
         self.data = []
         self.size = 12
 
         self.questions = []
         self.answers = []
         self.authorities = []
         self.additionals = []
 
     def addQuestion(self, record):
         """Adds a question"""
         self.questions.append(record)
 
     def addAnswer(self, inp, record):
         """Adds an answer"""
         if not record.suppressedBy(inp):
             self.addAnswerAtTime(record, 0)
 
     def addAnswerAtTime(self, record, now):
         """Adds an answer if if does not expire by a certain time"""
         if record is not None:
             if now == 0 or not record.isExpired(now):
                 self.answers.append((record, now))
 
     def addAuthoritativeAnswer(self, record):
         """Adds an authoritative answer"""
         self.authorities.append(record)
 
     def addAdditionalAnswer(self, record):
         """Adds an additional answer"""
         self.additionals.append(record)
 
     def writeByte(self, value):
         """Writes a single byte to the packet"""
         format = '!c'
         self.data.append(struct.pack(format, chr(value)))
         self.size += 1
 
     def insertShort(self, index, value):
         """Inserts an unsigned short in a certain position in the packet"""
         format = '!H'
         self.data.insert(index, struct.pack(format, value))
         self.size += 2
 
     def writeShort(self, value):
         """Writes an unsigned short to the packet"""
         format = '!H'
         self.data.append(struct.pack(format, value))
         self.size += 2
 
     def writeInt(self, value):
         """Writes an unsigned integer to the packet"""
         format = '!I'
         self.data.append(struct.pack(format, int(value)))
         self.size += 4
 
     def writeString(self, value, length):
         """Writes a string to the packet"""
         format = '!' + str(length) + 's'
         self.data.append(struct.pack(format, value))
         self.size += length
 
     def writeUTF(self, s):
         """Writes a UTF-8 string of a given length to the packet"""
         utfstr = s.encode('utf-8')
         length = len(utfstr)
         if length > 64:
             raise NamePartTooLongException
         self.writeByte(length)
         self.writeString(utfstr, length)
 
     def writeName(self, name):
         """Writes a domain name to the packet"""
 
         try:
             # Find existing instance of this name in packet
             #
             index = self.names[name]
         except KeyError:
             # No record of this name already, so write it
             # out as normal, recording the location of the name
             # for future pointers to it.
             #
             self.names[name] = self.size
             parts = name.split('.')
             if parts[-1] == '':
                 parts = parts[:-1]
             for part in parts:
                 self.writeUTF(part)
             self.writeByte(0)
             return
 
         # An index was found, so write a pointer to it
         #
         self.writeByte((index >> 8) | 0xC0)
         self.writeByte(index)
 
     def writeQuestion(self, question):
         """Writes a question to the packet"""
         self.writeName(question.name)
         self.writeShort(question.type)
         self.writeShort(question.clazz)
 
     def writeRecord(self, record, now):
         """Writes a record (answer, authoritative answer, additional) to
         the packet"""
         self.writeName(record.name)
         self.writeShort(record.type)
         if record.unique and self.multicast:
             self.writeShort(record.clazz | _CLASS_UNIQUE)
         else:
             self.writeShort(record.clazz)
         if now == 0:
             self.writeInt(record.ttl)
         else:
             self.writeInt(record.getRemainingTTL(now))
         index = len(self.data)
         # Adjust size for the short we will write before this record
         #
         self.size += 2
         record.write(self)
         self.size -= 2
 
         length = len(''.join(self.data[index:]))
         self.insertShort(index, length) # Here is the short we adjusted for
 
     def packet(self):
         """Returns a string containing the packet's bytes
 
         No further parts should be added to the packet once this
         is done."""
         if not self.finished:
             self.finished = 1
             for question in self.questions:
                 self.writeQuestion(question)
             for answer, time_ in self.answers:
                 self.writeRecord(answer, time_)
             for authority in self.authorities:
                 self.writeRecord(authority, 0)
             for additional in self.additionals:
                 self.writeRecord(additional, 0)
 
             self.insertShort(0, len(self.additionals))
             self.insertShort(0, len(self.authorities))
             self.insertShort(0, len(self.answers))
             self.insertShort(0, len(self.questions))
             self.insertShort(0, self.flags)
             if self.multicast:
                 self.insertShort(0, 0)
             else:
                 self.insertShort(0, self.id)
         return ''.join(self.data)
 
 
 class DNSCache(object):
     """A cache of DNS entries"""
 
     def __init__(self):
         self.cache = {}
 
     def add(self, entry):
         """Adds an entry"""
         try:
             list = self.cache[entry.key]
         except KeyError:
             list = self.cache[entry.key] = []
         list.append(entry)
 
     def remove(self, entry):
         """Removes an entry"""
         try:
             list = self.cache[entry.key]
             list.remove(entry)
         except KeyError:
             pass
 
     def get(self, entry):
         """Gets an entry by key.  Will return None if there is no
         matching entry."""
         try:
             list = self.cache[entry.key]
             return list[list.index(entry)]
         except (KeyError, ValueError):
             return None
 
     def getByDetails(self, name, type, clazz):
         """Gets an entry by details.  Will return None if there is
         no matching entry."""
         entry = DNSEntry(name, type, clazz)
         return self.get(entry)
 
     def entriesWithName(self, name):
         """Returns a list of entries whose key matches the name."""
         try:
             return self.cache[name]
         except KeyError:
             return []
 
     def entries(self):
         """Returns a list of all entries"""
         try:
             return list(itertools.chain.from_iterable(self.cache.values()))
         except Exception:
             return []
 
 
 class Engine(threading.Thread):
     """An engine wraps read access to sockets, allowing objects that
     need to receive data from sockets to be called back when the
     sockets are ready.
 
     A reader needs a handle_read() method, which is called when the socket
     it is interested in is ready for reading.
 
     Writers are not implemented here, because we only send short
     packets.
     """
 
     def __init__(self, zeroconf):
         threading.Thread.__init__(self)
         self.zeroconf = zeroconf
         self.readers = {} # maps socket to reader
         self.timeout = 5
         self.condition = threading.Condition()
         self.start()
 
     def run(self):
         while not globals()['_GLOBAL_DONE']:
             rs = self.getReaders()
             if len(rs) == 0:
                 # No sockets to manage, but we wait for the timeout
                 # or addition of a socket
                 #
                 self.condition.acquire()
                 self.condition.wait(self.timeout)
                 self.condition.release()
             else:
                 try:
                     rr, wr, er = select.select(rs, [], [], self.timeout)
                     for sock in rr:
                         try:
                             self.readers[sock].handle_read()
                         except Exception:
                             if not globals()['_GLOBAL_DONE']:
                                 traceback.print_exc()
                 except Exception:
                     pass
 
     def getReaders(self):
         self.condition.acquire()
         result = self.readers.keys()
         self.condition.release()
         return result
 
     def addReader(self, reader, socket):
         self.condition.acquire()
         self.readers[socket] = reader
         self.condition.notify()
         self.condition.release()
 
     def delReader(self, socket):
         self.condition.acquire()
         del self.readers[socket]
         self.condition.notify()
         self.condition.release()
 
     def notify(self):
         self.condition.acquire()
         self.condition.notify()
         self.condition.release()
 
 class Listener(object):
     """A Listener is used by this module to listen on the multicast
     group to which DNS messages are sent, allowing the implementation
     to cache information as it arrives.
 
     It requires registration with an Engine object in order to have
     the read() method called when a socket is available for reading."""
 
     def __init__(self, zeroconf):
         self.zeroconf = zeroconf
         self.zeroconf.engine.addReader(self, self.zeroconf.socket)
 
     def handle_read(self):
-        data, (addr, port) = self.zeroconf.socket.recvfrom(_MAX_MSG_ABSOLUTE)
+        data = addr = port = None
+        sock = self.zeroconf.socket
+        try:
+            data, (addr, port) = sock.recvfrom(_MAX_MSG_ABSOLUTE)
+        except socket.error as e:
+            if e.errno == errno.EBADF:
+                # some other thread may close the socket
+                return
+            else:
+                raise
         self.data = data
         msg = DNSIncoming(data)
         if msg.isQuery():
             # Always multicast responses
             #
             if port == _MDNS_PORT:
                 self.zeroconf.handleQuery(msg, _MDNS_ADDR, _MDNS_PORT)
             # If it's not a multicast query, reply via unicast
             # and multicast
             #
             elif port == _DNS_PORT:
                 self.zeroconf.handleQuery(msg, addr, port)
                 self.zeroconf.handleQuery(msg, _MDNS_ADDR, _MDNS_PORT)
         else:
             self.zeroconf.handleResponse(msg)
 
 
 class Reaper(threading.Thread):
     """A Reaper is used by this module to remove cache entries that
     have expired."""
 
     def __init__(self, zeroconf):
         threading.Thread.__init__(self)
         self.zeroconf = zeroconf
         self.start()
 
     def run(self):
         while True:
             self.zeroconf.wait(10 * 1000)
             if globals()['_GLOBAL_DONE']:
                 return
             now = currentTimeMillis()
             for record in self.zeroconf.cache.entries():
                 if record.isExpired(now):
                     self.zeroconf.updateRecord(now, record)
                     self.zeroconf.cache.remove(record)
 
 
 class ServiceBrowser(threading.Thread):
     """Used to browse for a service of a specific type.
 
     The listener object will have its addService() and
     removeService() methods called when this browser
     discovers changes in the services availability."""
 
     def __init__(self, zeroconf, type, listener):
         """Creates a browser for a specific type"""
         threading.Thread.__init__(self)
         self.zeroconf = zeroconf
         self.type = type
         self.listener = listener
         self.services = {}
         self.nexttime = currentTimeMillis()
         self.delay = _BROWSER_TIME
         self.list = []
 
         self.done = 0
 
         self.zeroconf.addListener(self, DNSQuestion(self.type, _TYPE_PTR,
                                                     _CLASS_IN))
         self.start()
 
     def updateRecord(self, zeroconf, now, record):
         """Callback invoked by Zeroconf when new information arrives.
 
         Updates information required by browser in the Zeroconf cache."""
         if record.type == _TYPE_PTR and record.name == self.type:
             expired = record.isExpired(now)
             try:
                 oldrecord = self.services[record.alias.lower()]
                 if not expired:
                     oldrecord.resetTTL(record)
                 else:
                     del self.services[record.alias.lower()]
                     callback = (lambda x:
                         self.listener.removeService(x, self.type, record.alias))
                     self.list.append(callback)
                     return
             except Exception:
                 if not expired:
                     self.services[record.alias.lower()] = record
                     callback = (lambda x:
                         self.listener.addService(x, self.type, record.alias))
                     self.list.append(callback)
 
             expires = record.getExpirationTime(75)
             if expires < self.nexttime:
                 self.nexttime = expires
 
     def cancel(self):
         self.done = 1
         self.zeroconf.notifyAll()
 
     def run(self):
         while True:
             event = None
             now = currentTimeMillis()
             if len(self.list) == 0 and self.nexttime > now:
                 self.zeroconf.wait(self.nexttime - now)
             if globals()['_GLOBAL_DONE'] or self.done:
                 return
             now = currentTimeMillis()
 
             if self.nexttime <= now:
                 out = DNSOutgoing(_FLAGS_QR_QUERY)
                 out.addQuestion(DNSQuestion(self.type, _TYPE_PTR, _CLASS_IN))
                 for record in self.services.values():
                     if not record.isExpired(now):
                         out.addAnswerAtTime(record, now)
                 self.zeroconf.send(out)
                 self.nexttime = now + self.delay
                 self.delay = min(20 * 1000, self.delay * 2)
 
             if len(self.list) > 0:
                 event = self.list.pop(0)
 
             if event is not None:
                 event(self.zeroconf)
 
 
 class ServiceInfo(object):
     """Service information"""
 
     def __init__(self, type, name, address=None, port=None, weight=0,
                  priority=0, properties=None, server=None):
         """Create a service description.
 
         type: fully qualified service type name
         name: fully qualified service name
         address: IP address as unsigned short, network byte order
         port: port that the service runs on
         weight: weight of the service
         priority: priority of the service
         properties: dictionary of properties (or a string holding the bytes for
                     the text field)
         server: fully qualified name for service host (defaults to name)"""
 
         if not name.endswith(type):
             raise BadTypeInNameException
         self.type = type
         self.name = name
         self.address = address
         self.port = port
         self.weight = weight
         self.priority = priority
         if server:
             self.server = server
         else:
             self.server = name
         self.setProperties(properties)
 
     def setProperties(self, properties):
         """Sets properties and text of this info from a dictionary"""
         if isinstance(properties, dict):
             self.properties = properties
             list = []
             result = ''
             for key in properties:
                 value = properties[key]
                 if value is None:
                     suffix = ''
                 elif isinstance(value, str):
                     suffix = value
                 elif isinstance(value, int):
                     if value:
                         suffix = 'true'
                     else:
                         suffix = 'false'
                 else:
                     suffix = ''
                 list.append('='.join((key, suffix)))
             for item in list:
                 result = ''.join((result, struct.pack('!c', chr(len(item))),
                                   item))
             self.text = result
         else:
             self.text = properties
 
     def setText(self, text):
         """Sets properties and text given a text field"""
         self.text = text
         try:
             result = {}
             end = len(text)
             index = 0
             strs = []
             while index < end:
                 length = ord(text[index])
                 index += 1
                 strs.append(text[index:index + length])
                 index += length
 
             for s in strs:
                 eindex = s.find('=')
                 if eindex == -1:
                     # No equals sign at all
                     key = s
                     value = 0
                 else:
                     key = s[:eindex]
                     value = s[eindex + 1:]
                     if value == 'true':
                         value = 1
                     elif value == 'false' or not value:
                         value = 0
 
                 # Only update non-existent properties
                 if key and result.get(key) is None:
                     result[key] = value
 
             self.properties = result
         except Exception:
             traceback.print_exc()
             self.properties = None
 
     def getType(self):
         """Type accessor"""
         return self.type
 
     def getName(self):
         """Name accessor"""
         if self.type is not None and self.name.endswith("." + self.type):
             return self.name[:len(self.name) - len(self.type) - 1]
         return self.name
 
     def getAddress(self):
         """Address accessor"""
         return self.address
 
     def getPort(self):
         """Port accessor"""
         return self.port
 
     def getPriority(self):
         """Priority accessor"""
         return self.priority
 
     def getWeight(self):
         """Weight accessor"""
         return self.weight
 
     def getProperties(self):
         """Properties accessor"""
         return self.properties
 
     def getText(self):
         """Text accessor"""
         return self.text
 
     def getServer(self):
         """Server accessor"""
         return self.server
 
     def updateRecord(self, zeroconf, now, record):
         """Updates service information from a DNS record"""
         if record is not None and not record.isExpired(now):
             if record.type == _TYPE_A:
                 #if record.name == self.name:
                 if record.name == self.server:
                     self.address = record.address
             elif record.type == _TYPE_SRV:
                 if record.name == self.name:
                     self.server = record.server
                     self.port = record.port
                     self.weight = record.weight
                     self.priority = record.priority
                     #self.address = None
                     self.updateRecord(zeroconf, now,
                                       zeroconf.cache.getByDetails(self.server,
                                       _TYPE_A, _CLASS_IN))
             elif record.type == _TYPE_TXT:
                 if record.name == self.name:
                     self.setText(record.text)
 
     def request(self, zeroconf, timeout):
         """Returns true if the service could be discovered on the
         network, and updates this object with details discovered.
         """
         now = currentTimeMillis()
         delay = _LISTENER_TIME
         next = now + delay
         last = now + timeout
         result = 0
         try:
             zeroconf.addListener(self, DNSQuestion(self.name, _TYPE_ANY,
                                                    _CLASS_IN))
             while (self.server is None or self.address is None or
                    self.text is None):
                 if last <= now:
                     return 0
                 if next <= now:
                     out = DNSOutgoing(_FLAGS_QR_QUERY)
                     out.addQuestion(DNSQuestion(self.name, _TYPE_SRV,
                                                 _CLASS_IN))
                     out.addAnswerAtTime(
                         zeroconf.cache.getByDetails(self.name,
                                                     _TYPE_SRV,
                                                     _CLASS_IN),
                                         now)
                     out.addQuestion(DNSQuestion(self.name, _TYPE_TXT,
                                                 _CLASS_IN))
                     out.addAnswerAtTime(
                         zeroconf.cache.getByDetails(self.name, _TYPE_TXT,
                                                     _CLASS_IN),
                                         now)
                     if self.server is not None:
                         out.addQuestion(
                             DNSQuestion(self.server, _TYPE_A, _CLASS_IN))
                         out.addAnswerAtTime(
                             zeroconf.cache.getByDetails(self.server, _TYPE_A,
                                                         _CLASS_IN),
                                             now)
                     zeroconf.send(out)
                     next = now + delay
                     delay = delay * 2
 
                 zeroconf.wait(min(next, last) - now)
                 now = currentTimeMillis()
             result = 1
         finally:
             zeroconf.removeListener(self)
 
         return result
 
     def __eq__(self, other):
         """Tests equality of service name"""
         if isinstance(other, ServiceInfo):
             return other.name == self.name
         return 0
 
     def __ne__(self, other):
         """Non-equality test"""
         return not self.__eq__(other)
 
     def __repr__(self):
         """String representation"""
         result = ("service[%s,%s:%s," %
             (self.name, socket.inet_ntoa(self.getAddress()), self.port))
         if self.text is None:
             result += "None"
         else:
             if len(self.text) < 20:
                 result += self.text
             else:
                 result += self.text[:17] + "..."
         result += "]"
         return result
 
 
 class Zeroconf(object):
     """Implementation of Zeroconf Multicast DNS Service Discovery
 
     Supports registration, unregistration, queries and browsing.
     """
     def __init__(self, bindaddress=None):
         """Creates an instance of the Zeroconf class, establishing
         multicast communications, listening and reaping threads."""
         globals()['_GLOBAL_DONE'] = 0
         if bindaddress is None:
             self.intf = socket.gethostbyname(socket.gethostname())
         else:
             self.intf = bindaddress
         self.group = ('', _MDNS_PORT)
         self.socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
         try:
             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
         except Exception:
             # SO_REUSEADDR should be equivalent to SO_REUSEPORT for
             # multicast UDP sockets (p 731, "TCP/IP Illustrated,
             # Volume 2"), but some BSD-derived systems require
             # SO_REUSEPORT to be specified explicitly.  Also, not all
             # versions of Python have SO_REUSEPORT available.  So
             # if you're on a BSD-based system, and haven't upgraded
             # to Python 2.3 yet, you may find this library doesn't
             # work as expected.
             #
             pass
         self.socket.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_TTL, "\xff")
         self.socket.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_LOOP, "\x01")
         try:
             self.socket.bind(self.group)
         except Exception:
             # Some versions of linux raise an exception even though
             # SO_REUSEADDR and SO_REUSEPORT have been set, so ignore it
             pass
         self.socket.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP,
             socket.inet_aton(_MDNS_ADDR) + socket.inet_aton('0.0.0.0'))
 
         self.listeners = []
         self.browsers = []
         self.services = {}
         self.servicetypes = {}
 
         self.cache = DNSCache()
 
         self.condition = threading.Condition()
 
         self.engine = Engine(self)
         self.listener = Listener(self)
         self.reaper = Reaper(self)
 
     def isLoopback(self):
         return self.intf.startswith("127.0.0.1")
 
     def isLinklocal(self):
         return self.intf.startswith("169.254.")
 
     def wait(self, timeout):
         """Calling thread waits for a given number of milliseconds or
         until notified."""
         self.condition.acquire()
         self.condition.wait(timeout / 1000)
         self.condition.release()
 
     def notifyAll(self):
         """Notifies all waiting threads"""
         self.condition.acquire()
         self.condition.notifyAll()
         self.condition.release()
 
     def getServiceInfo(self, type, name, timeout=3000):
         """Returns network's service information for a particular
         name and type, or None if no service matches by the timeout,
         which defaults to 3 seconds."""
         info = ServiceInfo(type, name)
         if info.request(self, timeout):
             return info
         return None
 
     def addServiceListener(self, type, listener):
         """Adds a listener for a particular service type.  This object
         will then have its updateRecord method called when information
         arrives for that type."""
         self.removeServiceListener(listener)
         self.browsers.append(ServiceBrowser(self, type, listener))
 
     def removeServiceListener(self, listener):
         """Removes a listener from the set that is currently listening."""
         for browser in self.browsers:
             if browser.listener == listener:
                 browser.cancel()
                 del browser
 
     def registerService(self, info, ttl=_DNS_TTL):
         """Registers service information to the network with a default TTL
         of 60 seconds.  Zeroconf will then respond to requests for
         information for that service.  The name of the service may be
         changed if needed to make it unique on the network."""
         self.checkService(info)
         self.services[info.name.lower()] = info
         if info.type in self.servicetypes:
             self.servicetypes[info.type] += 1
         else:
             self.servicetypes[info.type] = 1
         now = currentTimeMillis()
         nexttime = now
         i = 0
         while i < 3:
             if now < nexttime:
                 self.wait(nexttime - now)
                 now = currentTimeMillis()
                 continue
             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
             out.addAnswerAtTime(DNSPointer(info.type, _TYPE_PTR,
                 _CLASS_IN, ttl, info.name), 0)
             out.addAnswerAtTime(
                 DNSService(
                     info.name, _TYPE_SRV,
                     _CLASS_IN, ttl, info.priority, info.weight, info.port,
                     info.server),
                 0)
             out.addAnswerAtTime(
                 DNSText(info.name, _TYPE_TXT, _CLASS_IN, ttl, info.text),
                 0)
             if info.address:
                 out.addAnswerAtTime(DNSAddress(info.server, _TYPE_A,
                     _CLASS_IN, ttl, info.address), 0)
             self.send(out)
             i += 1
             nexttime += _REGISTER_TIME
 
     def unregisterService(self, info):
         """Unregister a service."""
         try:
             del self.services[info.name.lower()]
             if self.servicetypes[info.type] > 1:
                 self.servicetypes[info.type] -= 1
             else:
                 del self.servicetypes[info.type]
         except KeyError:
             pass
         now = currentTimeMillis()
         nexttime = now
         i = 0
         while i < 3:
             if now < nexttime:
                 self.wait(nexttime - now)
                 now = currentTimeMillis()
                 continue
             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
             out.addAnswerAtTime(
                 DNSPointer(info.type, _TYPE_PTR, _CLASS_IN, 0, info.name), 0)
             out.addAnswerAtTime(
                 DNSService(info.name, _TYPE_SRV,
                            _CLASS_IN, 0, info.priority, info.weight, info.port,
                            info.name),
                 0)
             out.addAnswerAtTime(DNSText(info.name, _TYPE_TXT,
                 _CLASS_IN, 0, info.text), 0)
             if info.address:
                 out.addAnswerAtTime(DNSAddress(info.server, _TYPE_A,
                     _CLASS_IN, 0, info.address), 0)
             self.send(out)
             i += 1
             nexttime += _UNREGISTER_TIME
 
     def unregisterAllServices(self):
         """Unregister all registered services."""
         if len(self.services) > 0:
             now = currentTimeMillis()
             nexttime = now
             i = 0
             while i < 3:
                 if now < nexttime:
                     self.wait(nexttime - now)
                     now = currentTimeMillis()
                     continue
                 out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
                 for info in self.services.values():
                     out.addAnswerAtTime(DNSPointer(info.type, _TYPE_PTR,
                         _CLASS_IN, 0, info.name), 0)
                     out.addAnswerAtTime(
                         DNSService(info.name, _TYPE_SRV,
                                    _CLASS_IN, 0, info.priority, info.weight,
                                    info.port, info.server),
                         0)
                     out.addAnswerAtTime(DNSText(info.name, _TYPE_TXT,
                         _CLASS_IN, 0, info.text), 0)
                     if info.address:
                         out.addAnswerAtTime(DNSAddress(info.server, _TYPE_A,
                            _CLASS_IN, 0, info.address), 0)
                 self.send(out)
                 i += 1
                 nexttime += _UNREGISTER_TIME
 
     def checkService(self, info):
         """Checks the network for a unique service name, modifying the
         ServiceInfo passed in if it is not unique."""
         now = currentTimeMillis()
         nexttime = now
         i = 0
         while i < 3:
             for record in self.cache.entriesWithName(info.type):
                 if (record.type == _TYPE_PTR and not record.isExpired(now) and
                     record.alias == info.name):
                     if (info.name.find('.') < 0):
                         info.name = ("%w.[%s:%d].%s" %
                             (info.name, info.address, info.port, info.type))
                         self.checkService(info)
                         return
                     raise NonUniqueNameException
             if now < nexttime:
                 self.wait(nexttime - now)
                 now = currentTimeMillis()
                 continue
             out = DNSOutgoing(_FLAGS_QR_QUERY | _FLAGS_AA)
             self.debug = out
             out.addQuestion(DNSQuestion(info.type, _TYPE_PTR, _CLASS_IN))
             out.addAuthoritativeAnswer(DNSPointer(info.type, _TYPE_PTR,
                 _CLASS_IN, _DNS_TTL, info.name))
             self.send(out)
             i += 1
             nexttime += _CHECK_TIME
 
     def addListener(self, listener, question):
         """Adds a listener for a given question.  The listener will have
         its updateRecord method called when information is available to
         answer the question."""
         now = currentTimeMillis()
         self.listeners.append(listener)
         if question is not None:
             for record in self.cache.entriesWithName(question.name):
                 if question.answeredBy(record) and not record.isExpired(now):
                     listener.updateRecord(self, now, record)
         self.notifyAll()
 
     def removeListener(self, listener):
         """Removes a listener."""
         try:
             self.listeners.remove(listener)
             self.notifyAll()
         except Exception:
             pass
 
     def updateRecord(self, now, rec):
         """Used to notify listeners of new information that has updated
         a record."""
         for listener in self.listeners:
             listener.updateRecord(self, now, rec)
         self.notifyAll()
 
     def handleResponse(self, msg):
         """Deal with incoming response packets.  All answers
         are held in the cache, and listeners are notified."""
         now = currentTimeMillis()
         for record in msg.answers:
             expired = record.isExpired(now)
             if record in self.cache.entries():
                 if expired:
                     self.cache.remove(record)
                 else:
                     entry = self.cache.get(record)
                     if entry is not None:
                         entry.resetTTL(record)
                         record = entry
             else:
                 self.cache.add(record)
 
             self.updateRecord(now, record)
 
     def handleQuery(self, msg, addr, port):
         """Deal with incoming query packets.  Provides a response if
         possible."""
         out = None
 
         # Support unicast client responses
         #
         if port != _MDNS_PORT:
             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA, 0)
             for question in msg.questions:
                 out.addQuestion(question)
 
         for question in msg.questions:
             if question.type == _TYPE_PTR:
                 if question.name == "_services._dns-sd._udp.local.":
                     for stype in self.servicetypes.keys():
                         if out is None:
                             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
                         out.addAnswer(msg,
                                       DNSPointer(
                                           "_services._dns-sd._udp.local.",
                                            _TYPE_PTR, _CLASS_IN,
                                            _DNS_TTL, stype))
                 for service in self.services.values():
                     if question.name == service.type:
                         if out is None:
                             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
                         out.addAnswer(msg, DNSPointer(service.type, _TYPE_PTR,
                             _CLASS_IN, _DNS_TTL, service.name))
             else:
                 try:
                     if out is None:
                         out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
 
                     # Answer A record queries for any service addresses we know
                     if question.type == _TYPE_A or question.type == _TYPE_ANY:
                         for service in self.services.values():
                             if service.server == question.name.lower():
                                 out.addAnswer(msg,
                                     DNSAddress(question.name, _TYPE_A,
                                                _CLASS_IN | _CLASS_UNIQUE,
                                                _DNS_TTL, service.address))
 
                     service = self.services.get(question.name.lower(), None)
                     if not service: continue
 
                     if (question.type == _TYPE_SRV or
                         question.type == _TYPE_ANY):
                         out.addAnswer(msg,
                             DNSService(question.name, _TYPE_SRV,
                                        _CLASS_IN | _CLASS_UNIQUE,
                                        _DNS_TTL, service.priority,
                                        service.weight, service.port,
                                        service.server))
                     if (question.type == _TYPE_TXT or
                         question.type == _TYPE_ANY):
                         out.addAnswer(msg, DNSText(question.name, _TYPE_TXT,
                             _CLASS_IN | _CLASS_UNIQUE, _DNS_TTL, service.text))
                     if question.type == _TYPE_SRV:
                         out.addAdditionalAnswer(
                             DNSAddress(service.server, _TYPE_A,
                                        _CLASS_IN | _CLASS_UNIQUE,
                                        _DNS_TTL, service.address))
                 except Exception:
                     traceback.print_exc()
 
         if out is not None and out.answers:
             out.id = msg.id
             self.send(out, addr, port)
 
     def send(self, out, addr=_MDNS_ADDR, port=_MDNS_PORT):
         """Sends an outgoing packet."""
         # This is a quick test to see if we can parse the packets we generate
         #temp = DNSIncoming(out.packet())
         try:
             self.socket.sendto(out.packet(), 0, (addr, port))
         except Exception:
             # Ignore this, it may be a temporary loss of network connection
             pass
 
     def close(self):
         """Ends the background threads, and prevent this instance from
         servicing further queries."""
         if globals()['_GLOBAL_DONE'] == 0:
             globals()['_GLOBAL_DONE'] = 1
             self.notifyAll()
             self.engine.notify()
             self.unregisterAllServices()
             self.socket.setsockopt(socket.SOL_IP, socket.IP_DROP_MEMBERSHIP,
                 socket.inet_aton(_MDNS_ADDR) + socket.inet_aton('0.0.0.0'))
             self.socket.close()
 
 # Test a few module features, including service registration, service
 # query (for Zoe), and service unregistration.
 
 if __name__ == '__main__':
     print("Multicast DNS Service Discovery for Python, version", __version__)
     r = Zeroconf()
     print("1. Testing registration of a service...")
     desc = {'version':'0.10','a':'test value', 'b':'another value'}
     info = ServiceInfo("_http._tcp.local.",
                        "My Service Name._http._tcp.local.",
         socket.inet_aton("127.0.0.1"), 1234, 0, 0, desc)
     print("   Registering service...")
     r.registerService(info)
     print("   Registration done.")
     print("2. Testing query of service information...")
     print("   Getting ZOE service:",
         str(r.getServiceInfo("_http._tcp.local.", "ZOE._http._tcp.local.")))
     print("   Query done.")
     print("3. Testing query of own service...")
     print("   Getting self:",
         str(r.getServiceInfo("_http._tcp.local.",
                              "My Service Name._http._tcp.local.")))
     print("   Query done.")
     print("4. Testing unregister of service information...")
     r.unregisterService(info)
     print("   Unregister done.")
     r.close()