zeroconf.py

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""" 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, write to the Free Software
    Foundation, Inc., 51 Franklin Steet, Fifth Floor, Boston, MA 02110-1301 USA
	
"""

""" patch for meta-service (_services._dns-sd._udp) publishing """

"""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. on 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 insensitivty 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 string
import time
import struct
import socket
import threading
import select
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 # Authorative 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

# 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:
			return "?(%s)" % (clazz)

	def getType(self, type):
		"""Type accessor"""
		try:
			return _TYPES[type]
		except:
			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
		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 addtional 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:
			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):