Zeroconf.py

   1 """ Multicast DNS Service Discovery for Python, v0.12-wmcbrine
   2     Copyright (C) 2003, Paul Scott-Murphy
   3
   4     This module provides a framework for the use of DNS Service Discovery
   5     using IP multicast.  It has been tested against the JRendezvous
   6     implementation from <a href="http://strangeberry.com">StrangeBerry</a>,
   7     and against the mDNSResponder from Mac OS X 10.3.8.
   8
   9     This library is free software; you can redistribute it and/or
  10     modify it under the terms of the GNU Lesser General Public
  11     License as published by the Free Software Foundation; either
  12     version 2.1 of the License, or (at your option) any later version.
  13
  14     This library is distributed in the hope that it will be useful,
  15     but WITHOUT ANY WARRANTY; without even the implied warranty of
  16     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17     Lesser General Public License for more details.
  18
  19     You should have received a copy of the GNU Lesser General Public
  20     License along with this library; if not, write to the Free Software
  21     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  22
  23 """
  24
  25 """0.12-wmcbrine update - see git for changes"""
  26
  27 """0.12 update - allow selection of binding interface
  28          typo fix - Thanks A. M. Kuchlingi
  29          removed all use of word 'Rendezvous' - this is an API change"""
  30
  31 """0.11 update - correction to comments for addListener method
  32                  support for new record types seen from OS X
  33                   - IPv6 address
  34                   - hostinfo
  35                  ignore unknown DNS record types
  36                  fixes to name decoding
  37                  works alongside other processes using port 5353
  38                  (e.g. on Mac OS X)
  39                  tested against Mac OS X 10.3.2's mDNSResponder
  40                  corrections to removal of list entries for service browser"""
  41
  42 """0.10 update - Jonathon Paisley contributed these corrections:
  43                  always multicast replies, even when query is unicast
  44                  correct a pointer encoding problem
  45                  can now write records in any order
  46                  traceback shown on failure
  47                  better TXT record parsing
  48                  server is now separate from name
  49                  can cancel a service browser
  50
  51                  modified some unit tests to accommodate these changes"""
  52
  53 """0.09 update - remove all records on service unregistration
  54                  fix DOS security problem with readName"""
  55
  56 """0.08 update - changed licensing to LGPL"""
  57
  58 """0.07 update - faster shutdown on engine
  59                  pointer encoding of outgoing names
  60                  ServiceBrowser now works
  61                  new unit tests"""
  62
  63 """0.06 update - small improvements with unit tests
  64                  added defined exception types
  65                  new style objects
  66                  fixed hostname/interface problem
  67                  fixed socket timeout problem
  68                  fixed addServiceListener() typo bug
  69                  using select() for socket reads
  70                  tested on Debian unstable with Python 2.2.2"""
  71
  72 """0.05 update - ensure case insensitivty on domain names
  73                  support for unicast DNS queries"""
  74
  75 """0.04 update - added some unit tests
  76                  added __ne__ adjuncts where required
  77                  ensure names end in '.local.'
  78                  timeout on receiving socket for clean shutdown"""
  79
  80 __author__ = "Paul Scott-Murphy"
  81 __email__ = "paul at scott dash murphy dot com"
  82 __version__ = "0.12-wmcbrine"
  83
  84 import time
  85 import struct
  86 import socket
  87 import threading
  88 import select
  89 import traceback
  90
  91 __all__ = ["Zeroconf", "ServiceInfo", "ServiceBrowser"]
  92
  93 # hook for threads
  94
  95 _GLOBAL_DONE = False
  96
  97 # Some timing constants
  98
  99 _UNREGISTER_TIME = 125
 100 _CHECK_TIME = 175
 101 _REGISTER_TIME = 225
 102 _LISTENER_TIME = 200
 103 _BROWSER_TIME = 500
 104
 105 # Some DNS constants
 106
 107 _MDNS_ADDR = '224.0.0.251'
 108 _MDNS_PORT = 5353;
 109 _DNS_PORT = 53;
 110 _DNS_TTL = 60 * 60; # one hour default TTL
 111
 112 _MAX_MSG_TYPICAL = 1460 # unused
 113 _MAX_MSG_ABSOLUTE = 8972
 114
 115 _FLAGS_QR_MASK = 0x8000 # query response mask
 116 _FLAGS_QR_QUERY = 0x0000 # query
 117 _FLAGS_QR_RESPONSE = 0x8000 # response
 118
 119 _FLAGS_AA = 0x0400 # Authorative answer
 120 _FLAGS_TC = 0x0200 # Truncated
 121 _FLAGS_RD = 0x0100 # Recursion desired
 122 _FLAGS_RA = 0x8000 # Recursion available
 123
 124 _FLAGS_Z = 0x0040 # Zero
 125 _FLAGS_AD = 0x0020 # Authentic data
 126 _FLAGS_CD = 0x0010 # Checking disabled
 127
 128 _CLASS_IN = 1
 129 _CLASS_CS = 2
 130 _CLASS_CH = 3
 131 _CLASS_HS = 4
 132 _CLASS_NONE = 254
 133 _CLASS_ANY = 255
 134 _CLASS_MASK = 0x7FFF
 135 _CLASS_UNIQUE = 0x8000
 136
 137 _TYPE_A = 1
 138 _TYPE_NS = 2
 139 _TYPE_MD = 3
 140 _TYPE_MF = 4
 141 _TYPE_CNAME = 5
 142 _TYPE_SOA = 6
 143 _TYPE_MB = 7
 144 _TYPE_MG = 8
 145 _TYPE_MR = 9
 146 _TYPE_NULL = 10
 147 _TYPE_WKS = 11
 148 _TYPE_PTR = 12
 149 _TYPE_HINFO = 13
 150 _TYPE_MINFO = 14
 151 _TYPE_MX = 15
 152 _TYPE_TXT = 16
 153 _TYPE_AAAA = 28
 154 _TYPE_SRV = 33
 155 _TYPE_ANY =  255
 156
 157 # Mapping constants to names
 158
 159 _CLASSES = { _CLASS_IN : "in",
 160              _CLASS_CS : "cs",
 161              _CLASS_CH : "ch",
 162              _CLASS_HS : "hs",
 163              _CLASS_NONE : "none",
 164              _CLASS_ANY : "any" }
 165
 166 _TYPES = { _TYPE_A : "a",
 167            _TYPE_NS : "ns",
 168            _TYPE_MD : "md",
 169            _TYPE_MF : "mf",
 170            _TYPE_CNAME : "cname",
 171            _TYPE_SOA : "soa",
 172            _TYPE_MB : "mb",
 173            _TYPE_MG : "mg",
 174            _TYPE_MR : "mr",
 175            _TYPE_NULL : "null",
 176            _TYPE_WKS : "wks",
 177            _TYPE_PTR : "ptr",
 178            _TYPE_HINFO : "hinfo",
 179            _TYPE_MINFO : "minfo",
 180            _TYPE_MX : "mx",
 181            _TYPE_TXT : "txt",
 182            _TYPE_AAAA : "quada",
 183            _TYPE_SRV : "srv",
 184            _TYPE_ANY : "any" }
 185
 186 # utility functions
 187
 188 def currentTimeMillis():
 189     """Current system time in milliseconds"""
 190     return time.time() * 1000
 191
 192 # Exceptions
 193
 194 class NonLocalNameException(Exception):
 195     pass
 196
 197 class NonUniqueNameException(Exception):
 198     pass
 199
 200 class NamePartTooLongException(Exception):
 201     pass
 202
 203 class AbstractMethodException(Exception):
 204     pass
 205
 206 class BadTypeInNameException(Exception):
 207     pass
 208
 209 # implementation classes
 210
 211 class DNSEntry(object):
 212     """A DNS entry"""
 213
 214     def __init__(self, name, type, clazz):
 215         self.key = name.lower()
 216         self.name = name
 217         self.type = type
 218         self.clazz = clazz & _CLASS_MASK
 219         self.unique = (clazz & _CLASS_UNIQUE) != 0
 220
 221     def __eq__(self, other):
 222         """Equality test on name, type, and class"""
 223         return (isinstance(other, DNSEntry) and
 224                 self.name == other.name and
 225                 self.type == other.type and
 226                 self.clazz == other.clazz)
 227
 228     def __ne__(self, other):
 229         """Non-equality test"""
 230         return not self.__eq__(other)
 231
 232     def getClazz(self, clazz):
 233         """Class accessor"""
 234         try:
 235             return _CLASSES[clazz]
 236         except:
 237             return "?(%s)" % (clazz)
 238
 239     def getType(self, type):
 240         """Type accessor"""
 241         try:
 242             return _TYPES[type]
 243         except:
 244             return "?(%s)" % (type)
 245
 246     def toString(self, hdr, other):
 247         """String representation with additional information"""
 248         result = "%s[%s,%s" % (hdr, self.getType(self.type),
 249             self.getClazz(self.clazz))
 250         if self.unique:
 251             result += "-unique,"
 252         else:
 253             result += ","
 254         result += self.name
 255         if other is not None:
 256             result += ",%s]" % (other)
 257         else:
 258             result += "]"
 259         return result
 260
 261 class DNSQuestion(DNSEntry):
 262     """A DNS question entry"""
 263
 264     def __init__(self, name, type, clazz):
 265         #if not name.endswith(".local."):
 266         #    raise NonLocalNameException
 267         DNSEntry.__init__(self, name, type, clazz)
 268
 269     def answeredBy(self, rec):
 270         """Returns true if the question is answered by the record"""
 271         return (self.clazz == rec.clazz and
 272                 (self.type == rec.type or self.type == _TYPE_ANY) and
 273                 self.name == rec.name)
 274
 275     def __repr__(self):
 276         """String representation"""
 277         return DNSEntry.toString(self, "question", None)
 278
 279
 280 class DNSRecord(DNSEntry):
 281     """A DNS record - like a DNS entry, but has a TTL"""
 282
 283     def __init__(self, name, type, clazz, ttl):
 284         DNSEntry.__init__(self, name, type, clazz)
 285         self.ttl = ttl
 286         self.created = currentTimeMillis()
 287
 288     def __eq__(self, other):
 289         """Tests equality as per DNSRecord"""
 290         return isinstance(other, DNSRecord) and DNSEntry.__eq__(self, other)
 291
 292     def suppressedBy(self, msg):
 293         """Returns true if any answer in a message can suffice for the
 294         information held in this record."""
 295         for record in msg.answers:
 296             if self.suppressedByAnswer(record):
 297                 return True
 298         return False
 299
 300     def suppressedByAnswer(self, other):
 301         """Returns true if another record has same name, type and class,
 302         and if its TTL is at least half of this record's."""
 303         return self == other and other.ttl > (self.ttl / 2)
 304
 305     def getExpirationTime(self, percent):
 306         """Returns the time at which this record will have expired
 307         by a certain percentage."""
 308         return self.created + (percent * self.ttl * 10)
 309
 310     def getRemainingTTL(self, now):
 311         """Returns the remaining TTL in seconds."""
 312         return max(0, (self.getExpirationTime(100) - now) / 1000)
 313
 314     def isExpired(self, now):
 315         """Returns true if this record has expired."""
 316         return self.getExpirationTime(100) <= now
 317
 318     def isStale(self, now):
 319         """Returns true if this record is at least half way expired."""
 320         return self.getExpirationTime(50) <= now
 321
 322     def resetTTL(self, other):
 323         """Sets this record's TTL and created time to that of
 324         another record."""
 325         self.created = other.created
 326         self.ttl = other.ttl
 327
 328     def write(self, out):
 329         """Abstract method"""
 330         raise AbstractMethodException
 331
 332     def toString(self, other):
 333         """String representation with addtional information"""
 334         arg = "%s/%s,%s" % (self.ttl,
 335             self.getRemainingTTL(currentTimeMillis()), other)
 336         return DNSEntry.toString(self, "record", arg)
 337
 338 class DNSAddress(DNSRecord):
 339     """A DNS address record"""
 340
 341     def __init__(self, name, type, clazz, ttl, address):
 342         DNSRecord.__init__(self, name, type, clazz, ttl)
 343         self.address = address
 344
 345     def write(self, out):
 346         """Used in constructing an outgoing packet"""
 347         out.writeString(self.address)
 348
 349     def __eq__(self, other):
 350         """Tests equality on address"""
 351         return isinstance(other, DNSAddress) and self.address == other.address
 352
 353     def __repr__(self):
 354         """String representation"""
 355         try:
 356             return socket.inet_ntoa(self.address)
 357         except:
 358             return self.address
 359
 360 class DNSHinfo(DNSRecord):
 361     """A DNS host information record"""
 362
 363     def __init__(self, name, type, clazz, ttl, cpu, os):
 364         DNSRecord.__init__(self, name, type, clazz, ttl)
 365         self.cpu = cpu
 366         self.os = os
 367
 368     def write(self, out):
 369         """Used in constructing an outgoing packet"""
 370         out.writeString(self.cpu)
 371         out.writeString(self.oso)
 372
 373     def __eq__(self, other):
 374         """Tests equality on cpu and os"""
 375         return (isinstance(other, DNSHinfo) and
 376                 self.cpu == other.cpu and self.os == other.os)
 377
 378     def __repr__(self):
 379         """String representation"""
 380         return self.cpu + " " + self.os
 381
 382 class DNSPointer(DNSRecord):
 383     """A DNS pointer record"""
 384
 385     def __init__(self, name, type, clazz, ttl, alias):
 386         DNSRecord.__init__(self, name, type, clazz, ttl)
 387         self.alias = alias
 388
 389     def write(self, out):
 390         """Used in constructing an outgoing packet"""
 391         out.writeName(self.alias)
 392
 393     def __eq__(self, other):
 394         """Tests equality on alias"""
 395         return isinstance(other, DNSPointer) and self.alias == other.alias
 396
 397     def __repr__(self):
 398         """String representation"""
 399         return self.toString(self.alias)
 400
 401 class DNSText(DNSRecord):
 402     """A DNS text record"""
 403
 404     def __init__(self, name, type, clazz, ttl, text):
 405         DNSRecord.__init__(self, name, type, clazz, ttl)
 406         self.text = text
 407
 408     def write(self, out):
 409         """Used in constructing an outgoing packet"""
 410         out.writeString(self.text)
 411
 412     def __eq__(self, other):
 413         """Tests equality on text"""
 414         return isinstance(other, DNSText) and self.text == other.text
 415
 416     def __repr__(self):
 417         """String representation"""
 418         if len(self.text) > 10:
 419             return self.toString(self.text[:7] + "...")
 420         else:
 421             return self.toString(self.text)
 422
 423 class DNSService(DNSRecord):
 424     """A DNS service record"""
 425
 426     def __init__(self, name, type, clazz, ttl, priority, weight, port, server):
 427         DNSRecord.__init__(self, name, type, clazz, ttl)
 428         self.priority = priority
 429         self.weight = weight
 430         self.port = port
 431         self.server = server
 432
 433     def write(self, out):
 434         """Used in constructing an outgoing packet"""
 435         out.writeShort(self.priority)
 436         out.writeShort(self.weight)
 437         out.writeShort(self.port)
 438         out.writeName(self.server)
 439
 440     def __eq__(self, other):
 441         """Tests equality on priority, weight, port and server"""
 442         return (isinstance(other, DNSService) and
 443                 self.priority == other.priority and
 444                 self.weight == other.weight and
 445                 self.port == other.port and
 446                 self.server == other.server)
 447
 448     def __repr__(self):
 449         """String representation"""
 450         return self.toString("%s:%s" % (self.server, self.port))
 451
 452 class DNSIncoming(object):
 453     """Object representation of an incoming DNS packet"""
 454
 455     def __init__(self, data):
 456         """Constructor from string holding bytes of packet"""
 457         self.offset = 0
 458         self.data = data
 459         self.questions = []
 460         self.answers = []
 461         self.numQuestions = 0
 462         self.numAnswers = 0
 463         self.numAuthorities = 0
 464         self.numAdditionals = 0
 465
 466         self.readHeader()
 467         self.readQuestions()
 468         self.readOthers()
 469
 470     def unpack(self, format):
 471         length = struct.calcsize(format)
 472         info = struct.unpack(format, self.data[self.offset:self.offset+length])
 473         self.offset += length
 474         return info
 475
 476     def readHeader(self):
 477         """Reads header portion of packet"""
 478         (self.id, self.flags, self.numQuestions, self.numAnswers,
 479          self.numAuthorities, self.numAdditionals) = self.unpack('!6H')
 480
 481     def readQuestions(self):
 482         """Reads questions section of packet"""
 483         for i in xrange(self.numQuestions):
 484             name = self.readName()
 485             type, clazz = self.unpack('!HH')
 486
 487             question = DNSQuestion(name, type, clazz)
 488             self.questions.append(question)
 489
 490     def readInt(self):
 491         """Reads an integer from the packet"""
 492         return self.unpack('!I')[0]
 493
 494     def readCharacterString(self):
 495         """Reads a character string from the packet"""
 496         length = ord(self.data[self.offset])
 497         self.offset += 1
 498         return self.readString(length)
 499
 500     def readString(self, length):
 501         """Reads a string of a given length from the packet"""
 502         info = self.data[self.offset:self.offset+length]
 503         self.offset += length
 504         return info
 505
 506     def readUnsignedShort(self):
 507         """Reads an unsigned short from the packet"""
 508         return self.unpack('!H')[0]
 509
 510     def readOthers(self):
 511         """Reads the answers, authorities and additionals section of the
 512         packet"""
 513         n = self.numAnswers + self.numAuthorities + self.numAdditionals
 514         for i in xrange(n):
 515             domain = self.readName()
 516             type, clazz, ttl, length = self.unpack('!HHiH')
 517
 518             rec = None
 519             if type == _TYPE_A:
 520                 rec = DNSAddress(domain, type, clazz, ttl, self.readString(4))
 521             elif type == _TYPE_CNAME or type == _TYPE_PTR:
 522                 rec = DNSPointer(domain, type, clazz, ttl, self.readName())
 523             elif type == _TYPE_TXT:
 524                 rec = DNSText(domain, type, clazz, ttl, self.readString(length))
 525             elif type == _TYPE_SRV:
 526                 rec = DNSService(domain, type, clazz, ttl,
 527                     self.readUnsignedShort(), self.readUnsignedShort(),
 528                     self.readUnsignedShort(), self.readName())
 529             elif type == _TYPE_HINFO:
 530                 rec = DNSHinfo(domain, type, clazz, ttl,
 531                     self.readCharacterString(), self.readCharacterString())
 532             elif type == _TYPE_AAAA:
 533                 rec = DNSAddress(domain, type, clazz, ttl, self.readString(16))
 534             else:
 535                 # Try to ignore types we don't know about
 536                 # Skip the payload for the resource record so the next
 537                 # records can be parsed correctly
 538                 self.offset += length
 539
 540             if rec is not None:
 541                 self.answers.append(rec)
 542
 543     def isQuery(self):
 544         """Returns true if this is a query"""
 545         return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_QUERY
 546
 547     def isResponse(self):
 548         """Returns true if this is a response"""
 549         return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_RESPONSE
 550
 551     def readUTF(self, offset, len):
 552         """Reads a UTF-8 string of a given length from the packet"""
 553         return unicode(self.data[offset:offset+len], 'utf-8', 'replace')
 554
 555     def readName(self):
 556         """Reads a domain name from the packet"""
 557         result = ''
 558         off = self.offset
 559         next = -1
 560         first = off
 561
 562         while True:
 563             len = ord(self.data[off])
 564             off += 1
 565             if len == 0:
 566                 break
 567             t = len & 0xC0
 568             if t == 0x00:
 569                 result = ''.join((result, self.readUTF(off, len) + '.'))
 570                 off += len
 571             elif t == 0xC0:
 572                 if next < 0:
 573                     next = off + 1
 574                 off = ((len & 0x3F) << 8) | ord(self.data[off])
 575                 if off >= first:
 576                     raise "Bad domain name (circular) at " + str(off)
 577                 first = off
 578             else:
 579                 raise "Bad domain name at " + str(off)
 580
 581         if next >= 0:
 582             self.offset = next
 583         else:
 584             self.offset = off
 585
 586         return result
 587
 588
 589 class DNSOutgoing(object):
 590     """Object representation of an outgoing packet"""
 591
 592     def __init__(self, flags, multicast=True):
 593         self.finished = False
 594         self.id = 0
 595         self.multicast = multicast
 596         self.flags = flags
 597         self.names = {}
 598         self.data = []
 599         self.size = 12
 600
 601         self.questions = []
 602         self.answers = []
 603         self.authorities = []
 604         self.additionals = []
 605
 606     def addQuestion(self, record):
 607         """Adds a question"""
 608         self.questions.append(record)
 609
 610     def addAnswer(self, inp, record):
 611         """Adds an answer"""
 612         if not record.suppressedBy(inp):
 613             self.addAnswerAtTime(record, 0)
 614
 615     def addAnswerAtTime(self, record, now):
 616         """Adds an answer if if does not expire by a certain time"""
 617         if record is not None:
 618             if now == 0 or not record.isExpired(now):
 619                 self.answers.append((record, now))
 620
 621     def addAuthorativeAnswer(self, record):
 622         """Adds an authoritative answer"""
 623         self.authorities.append(record)
 624
 625     def addAdditionalAnswer(self, record):
 626         """Adds an additional answer"""
 627         self.additionals.append(record)
 628
 629     def pack(self, format, value):
 630         self.data.append(struct.pack(format, value))
 631         self.size += struct.calcsize(format)
 632
 633     def writeByte(self, value):
 634         """Writes a single byte to the packet"""
 635         self.pack('!c', chr(value))
 636
 637     def insertShort(self, index, value):
 638         """Inserts an unsigned short in a certain position in the packet"""
 639         self.data.insert(index, struct.pack('!H', value))
 640         self.size += 2
 641
 642     def writeShort(self, value):
 643         """Writes an unsigned short to the packet"""
 644         self.pack('!H', value)
 645
 646     def writeInt(self, value):
 647         """Writes an unsigned integer to the packet"""
 648         self.pack('!I', int(value))
 649
 650     def writeString(self, value):
 651         """Writes a string to the packet"""
 652         self.data.append(value)
 653         self.size += len(value)
 654
 655     def writeUTF(self, s):
 656         """Writes a UTF-8 string of a given length to the packet"""
 657         utfstr = s.encode('utf-8')
 658         length = len(utfstr)
 659         if length > 64:
 660             raise NamePartTooLongException
 661         self.writeByte(length)
 662         self.writeString(utfstr)
 663
 664     def writeName(self, name):
 665         """Writes a domain name to the packet"""
 666
 667         try:
 668             # Find existing instance of this name in packet
 669             #
 670             index = self.names[name]
 671         except KeyError:
 672             # No record of this name already, so write it
 673             # out as normal, recording the location of the name
 674             # for future pointers to it.
 675             #
 676             self.names[name] = self.size
 677             parts = name.split('.')
 678             if parts[-1] == '':
 679                 parts = parts[:-1]
 680             for part in parts:
 681                 self.writeUTF(part)
 682             self.writeByte(0)
 683             return
 684
 685         # An index was found, so write a pointer to it
 686         #
 687         self.writeByte((index >> 8) | 0xC0)
 688         self.writeByte(index)
 689
 690     def writeQuestion(self, question):
 691         """Writes a question to the packet"""
 692         self.writeName(question.name)
 693         self.writeShort(question.type)
 694         self.writeShort(question.clazz)
 695
 696     def writeRecord(self, record, now):
 697         """Writes a record (answer, authoritative answer, additional) to
 698         the packet"""
 699         self.writeName(record.name)
 700         self.writeShort(record.type)
 701         if record.unique and self.multicast:
 702             self.writeShort(record.clazz | _CLASS_UNIQUE)
 703         else:
 704             self.writeShort(record.clazz)
 705         if now == 0:
 706             self.writeInt(record.ttl)
 707         else:
 708             self.writeInt(record.getRemainingTTL(now))
 709         index = len(self.data)
 710         # Adjust size for the short we will write before this record
 711         #
 712         self.size += 2
 713         record.write(self)
 714         self.size -= 2
 715
 716         length = len(''.join(self.data[index:]))
 717         self.insertShort(index, length) # Here is the short we adjusted for
 718
 719     def packet(self):
 720         """Returns a string containing the packet's bytes
 721
 722         No further parts should be added to the packet once this
 723         is done."""
 724         if not self.finished:
 725             self.finished = True
 726             for question in self.questions:
 727                 self.writeQuestion(question)
 728             for answer, time in self.answers:
 729                 self.writeRecord(answer, time)
 730             for authority in self.authorities:
 731                 self.writeRecord(authority, 0)
 732             for additional in self.additionals:
 733                 self.writeRecord(additional, 0)
 734
 735             self.insertShort(0, len(self.additionals))
 736             self.insertShort(0, len(self.authorities))
 737             self.insertShort(0, len(self.answers))
 738             self.insertShort(0, len(self.questions))
 739             self.insertShort(0, self.flags)
 740             if self.multicast:
 741                 self.insertShort(0, 0)
 742             else:
 743                 self.insertShort(0, self.id)
 744         return ''.join(self.data)
 745
 746
 747 class DNSCache(object):
 748     """A cache of DNS entries"""
 749
 750     def __init__(self):
 751         self.cache = {}
 752
 753     def add(self, entry):
 754         """Adds an entry"""
 755         try:
 756             list = self.cache[entry.key]
 757         except:
 758             list = self.cache[entry.key] = []
 759         list.append(entry)
 760
 761     def remove(self, entry):
 762         """Removes an entry"""
 763         try:
 764             list = self.cache[entry.key]
 765             list.remove(entry)
 766         except:
 767             pass
 768
 769     def get(self, entry):
 770         """Gets an entry by key.  Will return None if there is no
 771         matching entry."""
 772         try:
 773             list = self.cache[entry.key]
 774             return list[list.index(entry)]
 775         except:
 776             return None
 777
 778     def getByDetails(self, name, type, clazz):
 779         """Gets an entry by details.  Will return None if there is
 780         no matching entry."""
 781         entry = DNSEntry(name, type, clazz)
 782         return self.get(entry)
 783
 784     def entriesWithName(self, name):
 785         """Returns a list of entries whose key matches the name."""
 786         try:
 787             return self.cache[name]
 788         except:
 789             return []
 790
 791     def entries(self):
 792         """Returns a list of all entries"""
 793         def add(x, y): return x+y
 794         try:
 795             return reduce(add, self.cache.values())
 796         except:
 797             return []
 798
 799
 800 class Engine(threading.Thread):
 801     """An engine wraps read access to sockets, allowing objects that
 802     need to receive data from sockets to be called back when the
 803     sockets are ready.
 804
 805     A reader needs a handle_read() method, which is called when the socket
 806     it is interested in is ready for reading.
 807
 808     Writers are not implemented here, because we only send short
 809     packets.
 810     """
 811
 812     def __init__(self, zc):
 813         threading.Thread.__init__(self)
 814         self.zc = zc
 815         self.readers = {} # maps socket to reader
 816         self.timeout = 5
 817         self.condition = threading.Condition()
 818         self.start()
 819
 820     def run(self):
 821         while not _GLOBAL_DONE:
 822             rs = self.getReaders()
 823             if len(rs) == 0:
 824                 # No sockets to manage, but we wait for the timeout
 825                 # or addition of a socket
 826                 #
 827                 self.condition.acquire()
 828                 self.condition.wait(self.timeout)
 829                 self.condition.release()
 830             else:
 831                 try:
 832                     rr, wr, er = select.select(rs, [], [], self.timeout)
 833                     for socket in rr:
 834                         try:
 835                             self.readers[socket].handle_read()
 836                         except:
 837                             traceback.print_exc()
 838                 except:
 839                     pass
 840
 841     def getReaders(self):
 842         result = []
 843         self.condition.acquire()
 844         result = self.readers.keys()
 845         self.condition.release()
 846         return result
 847
 848     def addReader(self, reader, socket):
 849         self.condition.acquire()
 850         self.readers[socket] = reader
 851         self.condition.notify()
 852         self.condition.release()
 853
 854     def delReader(self, socket):
 855         self.condition.acquire()
 856         del(self.readers[socket])
 857         self.condition.notify()
 858         self.condition.release()
 859
 860     def notify(self):
 861         self.condition.acquire()
 862         self.condition.notify()
 863         self.condition.release()
 864
 865 class Listener(object):
 866     """A Listener is used by this module to listen on the multicast
 867     group to which DNS messages are sent, allowing the implementation
 868     to cache information as it arrives.
 869
 870     It requires registration with an Engine object in order to have
 871     the read() method called when a socket is availble for reading."""
 872
 873     def __init__(self, zc):
 874         self.zc = zc
 875         self.zc.engine.addReader(self, self.zc.socket)
 876
 877     def handle_read(self):
 878         try:
 879             data, (addr, port) = self.zc.socket.recvfrom(_MAX_MSG_ABSOLUTE)
 880         except socket.error, e:
 881             # If the socket was closed by another thread -- which happens
 882             # regularly on shutdown -- an EBADF exception is thrown here.
 883             # Ignore it.
 884             if e[0] == socket.EBADF:
 885                 return
 886             else:
 887                 raise e
 888         self.data = data
 889         msg = DNSIncoming(data)
 890         if msg.isQuery():
 891             # Always multicast responses
 892             #
 893             if port == _MDNS_PORT:
 894                 self.zc.handleQuery(msg, _MDNS_ADDR, _MDNS_PORT)
 895             # If it's not a multicast query, reply via unicast
 896             # and multicast
 897             #
 898             elif port == _DNS_PORT:
 899                 self.zc.handleQuery(msg, addr, port)
 900                 self.zc.handleQuery(msg, _MDNS_ADDR, _MDNS_PORT)
 901         else:
 902             self.zc.handleResponse(msg)
 903
 904
 905 class Reaper(threading.Thread):
 906     """A Reaper is used by this module to remove cache entries that
 907     have expired."""
 908
 909     def __init__(self, zc):
 910         threading.Thread.__init__(self)
 911         self.zc = zc
 912         self.start()
 913
 914     def run(self):
 915         while True:
 916             self.zc.wait(10 * 1000)
 917             if _GLOBAL_DONE:
 918                 return
 919             now = currentTimeMillis()
 920             for record in self.zc.cache.entries():
 921                 if record.isExpired(now):
 922                     self.zc.updateRecord(now, record)
 923                     self.zc.cache.remove(record)
 924
 925
 926 class ServiceBrowser(threading.Thread):
 927     """Used to browse for a service of a specific type.
 928
 929     The listener object will have its addService() and
 930     removeService() methods called when this browser
 931     discovers changes in the services availability."""
 932
 933     def __init__(self, zc, type, listener):
 934         """Creates a browser for a specific type"""
 935         threading.Thread.__init__(self)
 936         self.zc = zc
 937         self.type = type
 938         self.listener = listener
 939         self.services = {}
 940         self.nextTime = currentTimeMillis()
 941         self.delay = _BROWSER_TIME
 942         self.list = []
 943
 944         self.done = False
 945
 946         self.zc.addListener(self, DNSQuestion(self.type, _TYPE_PTR, _CLASS_IN))
 947         self.start()
 948
 949     def updateRecord(self, zc, now, record):
 950         """Callback invoked by Zeroconf when new information arrives.
 951
 952         Updates information required by browser in the Zeroconf cache."""
 953         if record.type == _TYPE_PTR and record.name == self.type:
 954             expired = record.isExpired(now)
 955             try:
 956                 oldrecord = self.services[record.alias.lower()]
 957                 if not expired:
 958                     oldrecord.resetTTL(record)
 959                 else:
 960                     del(self.services[record.alias.lower()])
 961                     callback = lambda x: self.listener.removeService(x,
 962                         self.type, record.alias)
 963                     self.list.append(callback)
 964                     return
 965             except:
 966                 if not expired:
 967                     self.services[record.alias.lower()] = record
 968                     callback = lambda x: self.listener.addService(x,
 969                         self.type, record.alias)
 970                     self.list.append(callback)
 971
 972             expires = record.getExpirationTime(75)
 973             if expires < self.nextTime:
 974                 self.nextTime = expires
 975
 976     def cancel(self):
 977         self.done = True
 978         self.zc.notifyAll()
 979
 980     def run(self):
 981         while True:
 982             event = None
 983             now = currentTimeMillis()
 984             if len(self.list) == 0 and self.nextTime > now:
 985                 self.zc.wait(self.nextTime - now)
 986             if _GLOBAL_DONE or self.done:
 987                 return
 988             now = currentTimeMillis()
 989
 990             if self.nextTime <= now:
 991                 out = DNSOutgoing(_FLAGS_QR_QUERY)
 992                 out.addQuestion(DNSQuestion(self.type, _TYPE_PTR, _CLASS_IN))
 993                 for record in self.services.values():
 994                     if not record.isExpired(now):
 995                         out.addAnswerAtTime(record, now)
 996                 self.zc.send(out)
 997                 self.nextTime = now + self.delay
 998                 self.delay = min(20 * 1000, self.delay * 2)
 999
1000             if len(self.list) > 0:
1001                 event = self.list.pop(0)
1002
1003             if event is not None:
1004                 event(self.zc)
1005
1006
1007 class ServiceInfo(object):
1008     """Service information"""
1009
1010     def __init__(self, type, name, address=None, port=None, weight=0,
1011                  priority=0, properties=None, server=None):
1012         """Create a service description.
1013
1014         type: fully qualified service type name
1015         name: fully qualified service name
1016         address: IP address as unsigned short, network byte order
1017         port: port that the service runs on
1018         weight: weight of the service
1019         priority: priority of the service
1020         properties: dictionary of properties (or a string holding the
1021                     bytes for the text field)
1022         server: fully qualified name for service host (defaults to name)"""
1023
1024         if not name.endswith(type):
1025             raise BadTypeInNameException
1026         self.type = type
1027         self.name = name
1028         self.address = address
1029         self.port = port
1030         self.weight = weight
1031         self.priority = priority
1032         if server:
1033             self.server = server
1034         else:
1035             self.server = name
1036         self.setProperties(properties)
1037
1038     def setProperties(self, properties):
1039         """Sets properties and text of this info from a dictionary"""
1040         if isinstance(properties, dict):
1041             self.properties = properties
1042             list = []
1043             result = ''
1044             for key in properties:
1045                 value = properties[key]
1046                 if value is None:
1047                     suffix = ''.encode('utf-8')
1048                 elif isinstance(value, str):
1049                     suffix = value.encode('utf-8')
1050                 elif isinstance(value, int):
1051                     if value:
1052                         suffix = 'true'
1053                     else:
1054                         suffix = 'false'
1055                 else:
1056                     suffix = ''.encode('utf-8')
1057                 list.append('='.join((key, suffix)))
1058             for item in list:
1059                 result = ''.join((result, chr(len(item)), item))
1060             self.text = result
1061         else:
1062             self.text = properties
1063
1064     def setText(self, text):
1065         """Sets properties and text given a text field"""
1066         self.text = text
1067         try:
1068             result = {}
1069             end = len(text)
1070             index = 0
1071             strs = []
1072             while index < end:
1073                 length = ord(text[index])
1074                 index += 1
1075                 strs.append(text[index:index+length])
1076                 index += length
1077
1078             for s in strs:
1079                 try:
1080                     key, value = s.split('=', 1)
1081                     if value == 'true':
1082                         value = True
1083                     elif value == 'false' or not value:
1084                         value = False
1085                 except:
1086                     # No equals sign at all
1087                     key = s
1088                     value = False
1089
1090                 # Only update non-existent properties
1091                 if key and result.get(key) == None:
1092                     result[key] = value
1093
1094             self.properties = result
1095         except:
1096             traceback.print_exc()
1097             self.properties = None
1098
1099     def getType(self):
1100         """Type accessor"""
1101         return self.type
1102
1103     def getName(self):
1104         """Name accessor"""
1105         if self.type is not None and self.name.endswith("." + self.type):
1106             return self.name[:len(self.name) - len(self.type) - 1]
1107         return self.name
1108
1109     def getAddress(self):
1110         """Address accessor"""
1111         return self.address
1112
1113     def getPort(self):
1114         """Port accessor"""
1115         return self.port
1116
1117     def getPriority(self):
1118         """Pirority accessor"""
1119         return self.priority
1120
1121     def getWeight(self):
1122         """Weight accessor"""
1123         return self.weight
1124
1125     def getProperties(self):
1126         """Properties accessor"""
1127         return self.properties
1128
1129     def getText(self):
1130         """Text accessor"""
1131         return self.text
1132
1133     def getServer(self):
1134         """Server accessor"""
1135         return self.server
1136
1137     def updateRecord(self, zc, now, record):
1138         """Updates service information from a DNS record"""
1139         if record is not None and not record.isExpired(now):
1140             if record.type == _TYPE_A:
1141                 #if record.name == self.name:
1142                 if record.name == self.server:
1143                     self.address = record.address
1144             elif record.type == _TYPE_SRV:
1145                 if record.name == self.name:
1146                     self.server = record.server
1147                     self.port = record.port
1148                     self.weight = record.weight
1149                     self.priority = record.priority
1150                     #self.address = None
1151                     self.updateRecord(zc, now,
1152                         zc.cache.getByDetails(self.server, _TYPE_A, _CLASS_IN))
1153             elif record.type == _TYPE_TXT:
1154                 if record.name == self.name:
1155                     self.setText(record.text)
1156
1157     def request(self, zc, timeout):
1158         """Returns true if the service could be discovered on the
1159         network, and updates this object with details discovered.
1160         """
1161         now = currentTimeMillis()
1162         delay = _LISTENER_TIME
1163         next = now + delay
1164         last = now + timeout
1165         result = False
1166         try:
1167             zc.addListener(self, DNSQuestion(self.name, _TYPE_ANY, _CLASS_IN))
1168             while (self.server is None or self.address is None or
1169                    self.text is None):
1170                 if last <= now:
1171                     return False
1172                 if next <= now:
1173                     out = DNSOutgoing(_FLAGS_QR_QUERY)
1174                     out.addQuestion(DNSQuestion(self.name, _TYPE_SRV,
1175                         _CLASS_IN))
1176                     out.addAnswerAtTime(zc.cache.getByDetails(self.name,
1177                         _TYPE_SRV, _CLASS_IN), now)
1178                     out.addQuestion(DNSQuestion(self.name, _TYPE_TXT,
1179                         _CLASS_IN))
1180                     out.addAnswerAtTime(zc.cache.getByDetails(self.name,
1181                         _TYPE_TXT, _CLASS_IN), now)
1182                     if self.server is not None:
1183                         out.addQuestion(DNSQuestion(self.server,
1184                             _TYPE_A, _CLASS_IN))
1185                         out.addAnswerAtTime(zc.cache.getByDetails(self.server,
1186                             _TYPE_A, _CLASS_IN), now)
1187                     zc.send(out)
1188                     next = now + delay
1189                     delay = delay * 2
1190
1191                 zc.wait(min(next, last) - now)
1192                 now = currentTimeMillis()
1193             result = True
1194         finally:
1195             zc.removeListener(self)
1196
1197         return result
1198
1199     def __eq__(self, other):
1200         """Tests equality of service name"""
1201         if isinstance(other, ServiceInfo):
1202             return other.name == self.name
1203         return False
1204
1205     def __ne__(self, other):
1206         """Non-equality test"""
1207         return not self.__eq__(other)
1208
1209     def __repr__(self):
1210         """String representation"""
1211         result = "service[%s,%s:%s," % (self.name,
1212             socket.inet_ntoa(self.getAddress()), self.port)
1213         if self.text is None:
1214             result += "None"
1215         else:
1216             if len(self.text) < 20:
1217                 result += self.text
1218             else:
1219                 result += self.text[:17] + "..."
1220         result += "]"
1221         return result
1222
1223
1224 class Zeroconf(object):
1225     """Implementation of Zeroconf Multicast DNS Service Discovery
1226
1227     Supports registration, unregistration, queries and browsing.
1228     """
1229     def __init__(self, bindaddress=None):
1230         """Creates an instance of the Zeroconf class, establishing
1231         multicast communications, listening and reaping threads."""
1232         global _GLOBAL_DONE
1233         _GLOBAL_DONE = False
1234         if bindaddress is None:
1235             try:
1236                 s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
1237                 s.connect(('4.2.2.1', 123))
1238                 self.intf = s.getsockname()[0]
1239             except:
1240                 self.intf = socket.gethostbyname(socket.gethostname())
1241         else:
1242             self.intf = bindaddress
1243         self.group = ('', _MDNS_PORT)
1244         self.socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
1245         try:
1246             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
1247             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
1248         except:
1249             # SO_REUSEADDR should be equivalent to SO_REUSEPORT for
1250             # multicast UDP sockets (p 731, "TCP/IP Illustrated,
1251             # Volume 2"), but some BSD-derived systems require
1252             # SO_REUSEPORT to be specified explicity.  Also, not all
1253             # versions of Python have SO_REUSEPORT available.  So
1254             # if you're on a BSD-based system, and haven't upgraded
1255             # to Python 2.3 yet, you may find this library doesn't
1256             # work as expected.
1257             #
1258             pass
1259         self.socket.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_TTL, 255)
1260         self.socket.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_LOOP, 1)
1261         try:
1262             self.socket.bind(self.group)
1263         except:
1264             # Some versions of linux raise an exception even though
1265             # the SO_REUSE* options have been set, so ignore it
1266             #
1267             pass
1268         #self.socket.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_IF,
1269         #    socket.inet_aton(self.intf) + socket.inet_aton('0.0.0.0'))
1270         self.socket.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP,
1271             socket.inet_aton(_MDNS_ADDR) + socket.inet_aton('0.0.0.0'))
1272
1273         self.listeners = []
1274         self.browsers = []
1275         self.services = {}
1276         self.servicetypes = {}
1277
1278         self.cache = DNSCache()
1279
1280         self.condition = threading.Condition()
1281
1282         self.engine = Engine(self)
1283         self.listener = Listener(self)
1284         self.reaper = Reaper(self)
1285
1286     def isLoopback(self):
1287         return self.intf.startswith("127.0.0.1")
1288
1289     def isLinklocal(self):
1290         return self.intf.startswith("169.254.")
1291
1292     def wait(self, timeout):
1293         """Calling thread waits for a given number of milliseconds or
1294         until notified."""
1295         self.condition.acquire()
1296         self.condition.wait(timeout/1000)
1297         self.condition.release()
1298
1299     def notifyAll(self):
1300         """Notifies all waiting threads"""
1301         self.condition.acquire()
1302         self.condition.notifyAll()
1303         self.condition.release()
1304
1305     def getServiceInfo(self, type, name, timeout=3000):
1306         """Returns network's service information for a particular
1307         name and type, or None if no service matches by the timeout,
1308         which defaults to 3 seconds."""
1309         info = ServiceInfo(type, name)
1310         if info.request(self, timeout):
1311             return info
1312         return None
1313
1314     def addServiceListener(self, type, listener):
1315         """Adds a listener for a particular service type.  This object
1316         will then have its updateRecord method called when information
1317         arrives for that type."""
1318         self.removeServiceListener(listener)
1319         self.browsers.append(ServiceBrowser(self, type, listener))
1320
1321     def removeServiceListener(self, listener):
1322         """Removes a listener from the set that is currently listening."""
1323         for browser in self.browsers:
1324             if browser.listener == listener:
1325                 browser.cancel()
1326                 del(browser)
1327
1328     def registerService(self, info, ttl=_DNS_TTL):
1329         """Registers service information to the network with a default TTL
1330         of 60 seconds.  Zeroconf will then respond to requests for
1331         information for that service.  The name of the service may be
1332         changed if needed to make it unique on the network."""
1333         self.checkService(info)
1334         self.services[info.name.lower()] = info
1335         if info.type in self.servicetypes:
1336             self.servicetypes[info.type]+=1
1337         else:
1338             self.servicetypes[info.type]=1
1339         now = currentTimeMillis()
1340         nextTime = now
1341         i = 0
1342         while i < 3:
1343             if now < nextTime:
1344                 self.wait(nextTime - now)
1345                 now = currentTimeMillis()
1346                 continue
1347             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1348             out.addAnswerAtTime(DNSPointer(info.type, _TYPE_PTR,
1349                 _CLASS_IN, ttl, info.name), 0)
1350             out.addAnswerAtTime(DNSService(info.name, _TYPE_SRV,
1351                 _CLASS_IN, ttl, info.priority, info.weight, info.port,
1352                 info.server), 0)
1353             out.addAnswerAtTime(DNSText(info.name, _TYPE_TXT, _CLASS_IN,
1354                 ttl, info.text), 0)
1355             if info.address:
1356                 out.addAnswerAtTime(DNSAddress(info.server, _TYPE_A,
1357                     _CLASS_IN, ttl, info.address), 0)
1358             self.send(out)
1359             i += 1
1360             nextTime += _REGISTER_TIME
1361
1362     def unregisterService(self, info):
1363         """Unregister a service."""
1364         try:
1365             del(self.services[info.name.lower()])
1366             if self.servicetypes[info.type]>1:
1367                 self.servicetypes[info.type]-=1
1368             else:
1369                 del self.servicetypes[info.type]
1370         except:
1371             pass
1372         now = currentTimeMillis()
1373         nextTime = now
1374         i = 0
1375         while i < 3:
1376             if now < nextTime:
1377                 self.wait(nextTime - now)
1378                 now = currentTimeMillis()
1379                 continue
1380             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1381             out.addAnswerAtTime(DNSPointer(info.type, _TYPE_PTR,
1382                 _CLASS_IN, 0, info.name), 0)
1383             out.addAnswerAtTime(DNSService(info.name, _TYPE_SRV,
1384                 _CLASS_IN, 0, info.priority, info.weight, info.port,
1385                 info.name), 0)
1386             out.addAnswerAtTime(DNSText(info.name, _TYPE_TXT, _CLASS_IN,
1387                 0, info.text), 0)
1388             if info.address:
1389                 out.addAnswerAtTime(DNSAddress(info.server, _TYPE_A,
1390                     _CLASS_IN, 0, info.address), 0)
1391             self.send(out)
1392             i += 1
1393             nextTime += _UNREGISTER_TIME
1394
1395     def unregisterAllServices(self):
1396         """Unregister all registered services."""
1397         if len(self.services) > 0:
1398             now = currentTimeMillis()
1399             nextTime = now
1400             i = 0
1401             while i < 3:
1402                 if now < nextTime:
1403                     self.wait(nextTime - now)
1404                     now = currentTimeMillis()
1405                     continue
1406                 out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1407                 for info in self.services.values():
1408                     out.addAnswerAtTime(DNSPointer(info.type, _TYPE_PTR,
1409                         _CLASS_IN, 0, info.name), 0)
1410                     out.addAnswerAtTime(DNSService(info.name, _TYPE_SRV,
1411                         _CLASS_IN, 0, info.priority, info.weight,
1412                         info.port, info.server), 0)
1413                     out.addAnswerAtTime(DNSText(info.name, _TYPE_TXT,
1414                         _CLASS_IN, 0, info.text), 0)
1415                     if info.address:
1416                         out.addAnswerAtTime(DNSAddress(info.server,
1417                             _TYPE_A, _CLASS_IN, 0, info.address), 0)
1418                 self.send(out)
1419                 i += 1
1420                 nextTime += _UNREGISTER_TIME
1421
1422     def checkService(self, info):
1423         """Checks the network for a unique service name, modifying the
1424         ServiceInfo passed in if it is not unique."""
1425         now = currentTimeMillis()
1426         nextTime = now
1427         i = 0
1428         while i < 3:
1429             for record in self.cache.entriesWithName(info.type):
1430                 if (record.type == _TYPE_PTR and
1431                     not record.isExpired(now) and
1432                     record.alias == info.name):
1433                     if info.name.find('.') < 0:
1434                         info.name = '%s.[%s:%s].%s' % (info.name,
1435                             info.address, info.port, info.type)
1436
1437                         self.checkService(info)
1438                         return
1439                     raise NonUniqueNameException
1440             if now < nextTime:
1441                 self.wait(nextTime - now)
1442                 now = currentTimeMillis()
1443                 continue
1444             out = DNSOutgoing(_FLAGS_QR_QUERY | _FLAGS_AA)
1445             self.debug = out
1446             out.addQuestion(DNSQuestion(info.type, _TYPE_PTR, _CLASS_IN))
1447             out.addAuthorativeAnswer(DNSPointer(info.type, _TYPE_PTR,
1448                                                 _CLASS_IN, _DNS_TTL, info.name))
1449             self.send(out)
1450             i += 1
1451             nextTime += _CHECK_TIME
1452
1453     def addListener(self, listener, question):
1454         """Adds a listener for a given question.  The listener will have
1455         its updateRecord method called when information is available to
1456         answer the question."""
1457         now = currentTimeMillis()
1458         self.listeners.append(listener)
1459         if question is not None:
1460             for record in self.cache.entriesWithName(question.name):
1461                 if question.answeredBy(record) and not record.isExpired(now):
1462                     listener.updateRecord(self, now, record)
1463         self.notifyAll()
1464
1465     def removeListener(self, listener):
1466         """Removes a listener."""
1467         try:
1468             self.listeners.remove(listener)
1469             self.notifyAll()
1470         except:
1471             pass
1472
1473     def updateRecord(self, now, rec):
1474         """Used to notify listeners of new information that has updated
1475         a record."""
1476         for listener in self.listeners:
1477             listener.updateRecord(self, now, rec)
1478         self.notifyAll()
1479
1480     def handleResponse(self, msg):
1481         """Deal with incoming response packets.  All answers
1482         are held in the cache, and listeners are notified."""
1483         now = currentTimeMillis()
1484         for record in msg.answers:
1485             expired = record.isExpired(now)
1486             if record in self.cache.entries():
1487                 if expired:
1488                     self.cache.remove(record)
1489                 else:
1490                     entry = self.cache.get(record)
1491                     if entry is not None:
1492                         entry.resetTTL(record)
1493                         record = entry
1494             else:
1495                 self.cache.add(record)
1496
1497             self.updateRecord(now, record)
1498
1499     def handleQuery(self, msg, addr, port):
1500         """Deal with incoming query packets.  Provides a response if
1501         possible."""
1502         out = None
1503
1504         # Support unicast client responses
1505         #
1506         if port != _MDNS_PORT:
1507             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA, False)
1508             for question in msg.questions:
1509                 out.addQuestion(question)
1510
1511         for question in msg.questions:
1512             if question.type == _TYPE_PTR:
1513                 if question.name == "_services._dns-sd._udp.local.":
1514                     for stype in self.servicetypes.keys():
1515                         if out is None:
1516                             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1517                         out.addAnswer(msg,
1518                             DNSPointer("_services._dns-sd._udp.local.",
1519                                        _TYPE_PTR, _CLASS_IN, _DNS_TTL, stype))
1520                 for service in self.services.values():
1521                     if question.name == service.type:
1522                         if out is None:
1523                             out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1524                         out.addAnswer(msg,
1525                             DNSPointer(service.type, _TYPE_PTR,
1526                                        _CLASS_IN, _DNS_TTL, service.name))
1527             else:
1528                 try:
1529                     if out is None:
1530                         out = DNSOutgoing(_FLAGS_QR_RESPONSE | _FLAGS_AA)
1531
1532                     # Answer A record queries for any service addresses we know
1533                     if question.type in (_TYPE_A, _TYPE_ANY):
1534                         for service in self.services.values():
1535                             if service.server == question.name.lower():
1536                                 out.addAnswer(msg, DNSAddress(question.name,
1537                                     _TYPE_A, _CLASS_IN | _CLASS_UNIQUE,
1538                                     _DNS_TTL, service.address))
1539
1540                     service = self.services.get(question.name.lower(), None)
1541                     if not service: continue
1542
1543                     if question.type in (_TYPE_SRV, _TYPE_ANY):
1544                         out.addAnswer(msg, DNSService(question.name,
1545                             _TYPE_SRV, _CLASS_IN | _CLASS_UNIQUE,
1546                             _DNS_TTL, service.priority, service.weight,
1547                             service.port, service.server))
1548                     if question.type in (_TYPE_TXT, _TYPE_ANY):
1549                         out.addAnswer(msg, DNSText(question.name,
1550                             _TYPE_TXT, _CLASS_IN | _CLASS_UNIQUE,
1551                             _DNS_TTL, service.text))
1552                     if question.type == _TYPE_SRV:
1553                         out.addAdditionalAnswer(DNSAddress(service.server,
1554                             _TYPE_A, _CLASS_IN | _CLASS_UNIQUE,
1555                             _DNS_TTL, service.address))
1556                 except:
1557                     traceback.print_exc()
1558
1559         if out is not None and out.answers:
1560             out.id = msg.id
1561             self.send(out, addr, port)
1562
1563     def send(self, out, addr = _MDNS_ADDR, port = _MDNS_PORT):
1564         """Sends an outgoing packet."""
1565         packet = out.packet()
1566         try:
1567             while packet:
1568                 bytes_sent = self.socket.sendto(packet, 0, (addr, port))
1569                 if bytes_sent < 0:
1570                     break
1571                 packet = packet[bytes_sent:]
1572         except:
1573             # Ignore this, it may be a temporary loss of network connection
1574             pass
1575
1576     def close(self):
1577         """Ends the background threads, and prevent this instance from
1578         servicing further queries."""
1579         global _GLOBAL_DONE
1580         if not _GLOBAL_DONE:
1581             _GLOBAL_DONE = True
1582             self.notifyAll()
1583             self.engine.notify()
1584             self.unregisterAllServices()
1585             self.socket.setsockopt(socket.SOL_IP,
1586                                    socket.IP_DROP_MEMBERSHIP,
1587                                    socket.inet_aton(_MDNS_ADDR) +
1588                                    socket.inet_aton('0.0.0.0'))
1589             self.socket.close()
1590
1591 # Test a few module features, including service registration, service
1592 # query (for Zoe), and service unregistration.
1593
1594 if __name__ == '__main__':
1595     print "Multicast DNS Service Discovery for Python, version", __version__
1596     r = Zeroconf()
1597     print "1. Testing registration of a service..."
1598     desc = {'version':'0.10','a':'test value', 'b':'another value'}
1599     info = ServiceInfo("_http._tcp.local.",
1600                        "My Service Name._http._tcp.local.",
1601                        socket.inet_aton("127.0.0.1"), 1234, 0, 0, desc)
1602     print "   Registering service..."
1603     r.registerService(info)
1604     print "   Registration done."
1605     print "2. Testing query of service information..."
1606     print "   Getting ZOE service:",
1607     print str(r.getServiceInfo("_http._tcp.local.", "ZOE._http._tcp.local."))
1608     print "   Query done."
1609     print "3. Testing query of own service..."
1610     print "   Getting self:",
1611     print str(r.getServiceInfo("_http._tcp.local.",
1612                                "My Service Name._http._tcp.local."))
1613     print "   Query done."
1614     print "4. Testing unregister of service information..."
1615     r.unregisterService(info)
1616     print "   Unregister done."
1617     r.close()