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2275 lines (1858 loc) · 76.6 KB
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""" Multicast DNS Service Discovery for Python, v0.14-wmcbrine
Copyright 2003 Paul Scott-Murphy, 2014 William McBrine
This module provides a framework for the use of DNS Service Discovery
using IP multicast.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA
"""
import enum
import errno
import logging
import re
import select
import socket
import struct
import sys
import threading
import time
import warnings
from functools import reduce
from typing import AnyStr, Dict, List, Optional, Union, cast
from typing import Callable, Set, Tuple # noqa # used in type hints
import ifaddr
__author__ = 'Paul Scott-Murphy, William McBrine'
__maintainer__ = 'Jakub Stasiak <jakub@stasiak.at>'
__version__ = '0.23.0'
__license__ = 'LGPL'
__all__ = [
"__version__",
"Zeroconf",
"ServiceInfo",
"ServiceBrowser",
"Error",
"InterfaceChoice",
"ServiceStateChange",
]
if sys.version_info <= (3, 3):
raise ImportError(
'''
Python version > 3.3 required for python-zeroconf.
If you need support for Python 2 or Python 3.3 please use version 19.1
'''
)
log = logging.getLogger(__name__)
log.addHandler(logging.NullHandler())
if log.level == logging.NOTSET:
log.setLevel(logging.WARN)
# Some timing constants
_UNREGISTER_TIME = 125 # ms
_CHECK_TIME = 175 # ms
_REGISTER_TIME = 225 # ms
_LISTENER_TIME = 200 # ms
_BROWSER_TIME = 1000 # ms
_BROWSER_BACKOFF_LIMIT = 3600 # s
# Some DNS constants
_MDNS_ADDR = '224.0.0.251'
_MDNS_PORT = 5353
_DNS_PORT = 53
_DNS_HOST_TTL = 120 # two minute for host records (A, SRV etc) as-per RFC6762
_DNS_OTHER_TTL = 4500 # 75 minutes for non-host records (PTR, TXT etc) as-per RFC6762
_MAX_MSG_TYPICAL = 1460 # unused
_MAX_MSG_ABSOLUTE = 8966
_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",
}
_HAS_A_TO_Z = re.compile(r'[A-Za-z]')
_HAS_ONLY_A_TO_Z_NUM_HYPHEN = re.compile(r'^[A-Za-z0-9\-]+$')
_HAS_ONLY_A_TO_Z_NUM_HYPHEN_UNDERSCORE = re.compile(r'^[A-Za-z0-9\-\_]+$')
_HAS_ASCII_CONTROL_CHARS = re.compile(r'[\x00-\x1f\x7f]')
int2byte = struct.Struct(">B").pack
@enum.unique
class InterfaceChoice(enum.Enum):
Default = 1
All = 2
@enum.unique
class ServiceStateChange(enum.Enum):
Added = 1
Removed = 2
Updated = 3
# utility functions
def current_time_millis() -> float:
"""Current system time in milliseconds"""
return time.time() * 1000
def service_type_name(type_, *, allow_underscores: bool = False):
"""
Validate a fully qualified service name, instance or subtype. [rfc6763]
Returns fully qualified service name.
Domain names used by mDNS-SD take the following forms:
<sn> . <_tcp|_udp> . local.
<Instance> . <sn> . <_tcp|_udp> . local.
<sub>._sub . <sn> . <_tcp|_udp> . local.
1) must end with 'local.'
This is true because we are implementing mDNS and since the 'm' means
multi-cast, the 'local.' domain is mandatory.
2) local is preceded with either '_udp.' or '_tcp.'
3) service name <sn> precedes <_tcp|_udp>
The rules for Service Names [RFC6335] state that they may be no more
than fifteen characters long (not counting the mandatory underscore),
consisting of only letters, digits, and hyphens, must begin and end
with a letter or digit, must not contain consecutive hyphens, and
must contain at least one letter.
The instance name <Instance> and sub type <sub> may be up to 63 bytes.
The portion of the Service Instance Name is a user-
friendly name consisting of arbitrary Net-Unicode text [RFC5198]. It
MUST NOT contain ASCII control characters (byte values 0x00-0x1F and
0x7F) [RFC20] but otherwise is allowed to contain any characters,
without restriction, including spaces, uppercase, lowercase,
punctuation -- including dots -- accented characters, non-Roman text,
and anything else that may be represented using Net-Unicode.
:param type_: Type, SubType or service name to validate
:return: fully qualified service name (eg: _http._tcp.local.)
"""
if not (type_.endswith('._tcp.local.') or type_.endswith('._udp.local.')):
raise BadTypeInNameException("Type '%s' must end with '._tcp.local.' or '._udp.local.'" % type_)
remaining = type_[: -len('._tcp.local.')].split('.')
name = remaining.pop()
if not name:
raise BadTypeInNameException("No Service name found")
if len(remaining) == 1 and len(remaining[0]) == 0:
raise BadTypeInNameException("Type '%s' must not start with '.'" % type_)
if name[0] != '_':
raise BadTypeInNameException("Service name (%s) must start with '_'" % name)
# remove leading underscore
name = name[1:]
if len(name) > 15:
raise BadTypeInNameException("Service name (%s) must be <= 15 bytes" % name)
if '--' in name:
raise BadTypeInNameException("Service name (%s) must not contain '--'" % name)
if '-' in (name[0], name[-1]):
raise BadTypeInNameException("Service name (%s) may not start or end with '-'" % name)
if not _HAS_A_TO_Z.search(name):
raise BadTypeInNameException("Service name (%s) must contain at least one letter (eg: 'A-Z')" % name)
allowed_characters_re = (
_HAS_ONLY_A_TO_Z_NUM_HYPHEN_UNDERSCORE if allow_underscores else _HAS_ONLY_A_TO_Z_NUM_HYPHEN
)
if not allowed_characters_re.search(name):
raise BadTypeInNameException(
"Service name (%s) must contain only these characters: "
"A-Z, a-z, 0-9, hyphen ('-')%s" % (name, ", underscore ('_')" if allow_underscores else "")
)
if remaining and remaining[-1] == '_sub':
remaining.pop()
if len(remaining) == 0 or len(remaining[0]) == 0:
raise BadTypeInNameException("_sub requires a subtype name")
if len(remaining) > 1:
remaining = ['.'.join(remaining)]
if remaining:
length = len(remaining[0].encode('utf-8'))
if length > 63:
raise BadTypeInNameException("Too long: '%s'" % remaining[0])
if _HAS_ASCII_CONTROL_CHARS.search(remaining[0]):
raise BadTypeInNameException(
"Ascii control character 0x00-0x1F and 0x7F illegal in '%s'" % remaining[0]
)
return '_' + name + type_[-len('._tcp.local.') :]
# Exceptions
class Error(Exception):
pass
class IncomingDecodeError(Error):
pass
class NonUniqueNameException(Error):
pass
class NamePartTooLongException(Error):
pass
class AbstractMethodException(Error):
pass
class BadTypeInNameException(Error):
pass
# implementation classes
class QuietLogger:
_seen_logs = {} # type: Dict[str, tuple]
@classmethod
def log_exception_warning(cls, logger_data=None):
exc_info = sys.exc_info()
exc_str = str(exc_info[1])
if exc_str not in cls._seen_logs:
# log at warning level the first time this is seen
cls._seen_logs[exc_str] = exc_info
logger = log.warning
else:
logger = log.debug
if logger_data is not None:
logger(*logger_data)
logger('Exception occurred:', exc_info=True)
@classmethod
def log_warning_once(cls, *args):
msg_str = args[0]
if msg_str not in cls._seen_logs:
cls._seen_logs[msg_str] = 0
logger = log.warning
else:
logger = log.debug
cls._seen_logs[msg_str] += 1
logger(*args)
class DNSEntry:
"""A DNS entry"""
def __init__(self, name: str, type_: int, class_):
self.key = name.lower()
self.name = name
self.type = type_
self.class_ = class_ & _CLASS_MASK
self.unique = (class_ & _CLASS_UNIQUE) != 0
def __eq__(self, other):
"""Equality test on name, type, and class"""
return (
isinstance(other, DNSEntry)
and self.name == other.name
and self.type == other.type
and self.class_ == other.class_
)
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
@staticmethod
def get_class_(class_):
"""Class accessor"""
return _CLASSES.get(class_, "?(%s)" % class_)
@staticmethod
def get_type(t):
"""Type accessor"""
return _TYPES.get(t, "?(%s)" % t)
def to_string(self, hdr, other) -> str:
"""String representation with additional information"""
result = "%s[%s,%s" % (hdr, self.get_type(self.type), self.get_class_(self.class_))
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: str, type_: int, class_: int) -> None:
DNSEntry.__init__(self, name, type_, class_)
def answered_by(self, rec: 'DNSRecord') -> bool:
"""Returns true if the question is answered by the record"""
return (
self.class_ == rec.class_
and (self.type == rec.type or self.type == _TYPE_ANY)
and self.name == rec.name
)
def __repr__(self) -> str:
"""String representation"""
return DNSEntry.to_string(self, "question", None)
class DNSRecord(DNSEntry):
"""A DNS record - like a DNS entry, but has a TTL"""
def __init__(self, name, type_, class_, ttl: float):
DNSEntry.__init__(self, name, type_, class_)
self.ttl = ttl
self.created = current_time_millis()
def __eq__(self, other):
"""Abstract method"""
raise AbstractMethodException
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def suppressed_by(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.suppressed_by_answer(record):
return True
return False
def suppressed_by_answer(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."""
return self == other and other.ttl > (self.ttl / 2)
def get_expiration_time(self, percent: float) -> float:
"""Returns the time at which this record will have expired
by a certain percentage."""
return self.created + (percent * self.ttl * 10)
def get_remaining_ttl(self, now):
"""Returns the remaining TTL in seconds."""
return max(0, (self.get_expiration_time(100) - now) / 1000.0)
def is_expired(self, now: float) -> bool:
"""Returns true if this record has expired."""
return self.get_expiration_time(100) <= now
def is_stale(self, now):
"""Returns true if this record is at least half way expired."""
return self.get_expiration_time(50) <= now
def reset_ttl(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 to_string(self, other):
"""String representation with additional information"""
arg = "%s/%s,%s" % (self.ttl, self.get_remaining_ttl(current_time_millis()), other)
return DNSEntry.to_string(self, "record", arg)
class DNSAddress(DNSRecord):
"""A DNS address record"""
def __init__(self, name, type_, class_, ttl, address):
DNSRecord.__init__(self, name, type_, class_, ttl)
self.address = address
def write(self, out):
"""Used in constructing an outgoing packet"""
out.write_string(self.address)
def __eq__(self, other):
"""Tests equality on address"""
return (
isinstance(other, DNSAddress) and DNSEntry.__eq__(self, other) and self.address == other.address
)
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def __repr__(self):
"""String representation"""
try:
return str(socket.inet_ntoa(self.address))
except Exception: # TODO stop catching all Exceptions
return str(self.address)
class DNSHinfo(DNSRecord):
"""A DNS host information record"""
def __init__(self, name, type_, class_, ttl, cpu, os):
DNSRecord.__init__(self, name, type_, class_, ttl)
try:
self.cpu = cpu.decode('utf-8')
except AttributeError:
self.cpu = cpu
try:
self.os = os.decode('utf-8')
except AttributeError:
self.os = os
def write(self, out):
"""Used in constructing an outgoing packet"""
out.write_character_string(self.cpu.encode('utf-8'))
out.write_character_string(self.os.encode('utf-8'))
def __eq__(self, other):
"""Tests equality on cpu and os"""
return (
isinstance(other, DNSHinfo)
and DNSEntry.__eq__(self, other)
and self.cpu == other.cpu
and self.os == other.os
)
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def __repr__(self):
"""String representation"""
return self.cpu + " " + self.os
class DNSPointer(DNSRecord):
"""A DNS pointer record"""
def __init__(self, name, type_, class_, ttl, alias):
DNSRecord.__init__(self, name, type_, class_, ttl)
self.alias = alias
def write(self, out):
"""Used in constructing an outgoing packet"""
out.write_name(self.alias)
def __eq__(self, other):
"""Tests equality on alias"""
return isinstance(other, DNSPointer) and DNSEntry.__eq__(self, other) and self.alias == other.alias
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def __repr__(self):
"""String representation"""
return self.to_string(self.alias)
class DNSText(DNSRecord):
"""A DNS text record"""
def __init__(self, name, type_, class_, ttl, text):
assert isinstance(text, (bytes, type(None)))
DNSRecord.__init__(self, name, type_, class_, ttl)
self.text = text
def write(self, out):
"""Used in constructing an outgoing packet"""
out.write_string(self.text)
def __eq__(self, other):
"""Tests equality on text"""
return isinstance(other, DNSText) and DNSEntry.__eq__(self, other) and self.text == other.text
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def __repr__(self):
"""String representation"""
if len(self.text) > 10:
return self.to_string(self.text[:7]) + "..."
else:
return self.to_string(self.text)
class DNSService(DNSRecord):
"""A DNS service record"""
def __init__(self, name, type_, class_, ttl, priority, weight, port, server):
DNSRecord.__init__(self, name, type_, class_, ttl)
self.priority = priority
self.weight = weight
self.port = port
self.server = server
def write(self, out):
"""Used in constructing an outgoing packet"""
out.write_short(self.priority)
out.write_short(self.weight)
out.write_short(self.port)
out.write_name(self.server)
def __eq__(self, other):
"""Tests equality on priority, weight, port and server"""
return (
isinstance(other, DNSService)
and DNSEntry.__eq__(self, other)
and self.priority == other.priority
and self.weight == other.weight
and self.port == other.port
and self.server == other.server
)
def __ne__(self, other):
"""Non-equality test"""
return not self.__eq__(other)
def __repr__(self):
"""String representation"""
return self.to_string("%s:%s" % (self.server, self.port))
class DNSIncoming(QuietLogger):
"""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 = [] # type: List[DNSQuestion]
self.answers = [] # type: List[DNSRecord]
self.id = 0
self.flags = 0 # type: int
self.num_questions = 0
self.num_answers = 0
self.num_authorities = 0
self.num_additionals = 0
self.valid = False
try:
self.read_header()
self.read_questions()
self.read_others()
self.valid = True
except (IndexError, struct.error, IncomingDecodeError):
self.log_exception_warning(('Choked at offset %d while unpacking %r', self.offset, data))
def unpack(self, format_):
length = struct.calcsize(format_)
info = struct.unpack(format_, self.data[self.offset : self.offset + length])
self.offset += length
return info
def read_header(self):
"""Reads header portion of packet"""
(
self.id,
self.flags,
self.num_questions,
self.num_answers,
self.num_authorities,
self.num_additionals,
) = self.unpack(b'!6H')
def read_questions(self):
"""Reads questions section of packet"""
for i in range(self.num_questions):
name = self.read_name()
type_, class_ = self.unpack(b'!HH')
question = DNSQuestion(name, type_, class_)
self.questions.append(question)
# def read_int(self):
# """Reads an integer from the packet"""
# return self.unpack(b'!I')[0]
def read_character_string(self):
"""Reads a character string from the packet"""
length = self.data[self.offset]
self.offset += 1
return self.read_string(length)
def read_string(self, length):
"""Reads a string of a given length from the packet"""
info = self.data[self.offset : self.offset + length]
self.offset += length
return info
def read_unsigned_short(self):
"""Reads an unsigned short from the packet"""
return self.unpack(b'!H')[0]
def read_others(self):
"""Reads the answers, authorities and additionals section of the
packet"""
n = self.num_answers + self.num_authorities + self.num_additionals
for i in range(n):
domain = self.read_name()
type_, class_, ttl, length = self.unpack(b'!HHiH')
rec = None # type: Optional[DNSRecord]
if type_ == _TYPE_A:
rec = DNSAddress(domain, type_, class_, ttl, self.read_string(4))
elif type_ == _TYPE_CNAME or type_ == _TYPE_PTR:
rec = DNSPointer(domain, type_, class_, ttl, self.read_name())
elif type_ == _TYPE_TXT:
rec = DNSText(domain, type_, class_, ttl, self.read_string(length))
elif type_ == _TYPE_SRV:
rec = DNSService(
domain,
type_,
class_,
ttl,
self.read_unsigned_short(),
self.read_unsigned_short(),
self.read_unsigned_short(),
self.read_name(),
)
elif type_ == _TYPE_HINFO:
rec = DNSHinfo(
domain, type_, class_, ttl, self.read_character_string(), self.read_character_string()
)
elif type_ == _TYPE_AAAA:
rec = DNSAddress(domain, type_, class_, ttl, self.read_string(16))
else:
# Try to ignore types we don't know about
# Skip the payload for the resource record so the next
# records can be parsed correctly
self.offset += length
if rec is not None:
self.answers.append(rec)
def is_query(self) -> bool:
"""Returns true if this is a query"""
return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_QUERY
def is_response(self):
"""Returns true if this is a response"""
return (self.flags & _FLAGS_QR_MASK) == _FLAGS_QR_RESPONSE
def read_utf(self, offset, length):
"""Reads a UTF-8 string of a given length from the packet"""
return str(self.data[offset : offset + length], 'utf-8', 'replace')
def read_name(self):
"""Reads a domain name from the packet"""
result = ''
off = self.offset
next_ = -1
first = off
while True:
length = self.data[off]
off += 1
if length == 0:
break
t = length & 0xC0
if t == 0x00:
result = ''.join((result, self.read_utf(off, length) + '.'))
off += length
elif t == 0xC0:
if next_ < 0:
next_ = off + 1
off = ((length & 0x3F) << 8) | self.data[off]
if off >= first:
raise IncomingDecodeError("Bad domain name (circular) at %s" % (off,))
first = off
else:
raise IncomingDecodeError("Bad domain name at %s" % (off,))
if next_ >= 0:
self.offset = next_
else:
self.offset = off
return result
class DNSOutgoing:
"""Object representation of an outgoing packet"""
def __init__(self, flags, multicast=True):
self.finished = False
self.id = 0
self.multicast = multicast
self.flags = flags
self.names = {} # type: Dict[str, int]
self.data = [] # type: List[bytes]
self.size = 12
self.state = self.State.init
self.questions = [] # type: List[DNSQuestion]
self.answers = [] # type: List[Tuple[DNSEntry, float]]
self.authorities = [] # type: List[DNSPointer]
self.additionals = [] # type: List[DNSAddress]
def __repr__(self):
return '<DNSOutgoing:{%s}>' % ', '.join(
[
'multicast=%s' % self.multicast,
'flags=%s' % self.flags,
'questions=%s' % self.questions,
'answers=%s' % self.answers,
'authorities=%s' % self.authorities,
'additionals=%s' % self.additionals,
]
)
class State(enum.Enum):
init = 0
finished = 1
def add_question(self, record):
"""Adds a question"""
self.questions.append(record)
def add_answer(self, inp, record):
"""Adds an answer"""
if not record.suppressed_by(inp):
self.add_answer_at_time(record, 0)
def add_answer_at_time(self, record, now):
"""Adds an answer if it does not expire by a certain time"""
if record is not None:
if now == 0 or not record.is_expired(now):
self.answers.append((record, now))
def add_authorative_answer(self, record):
"""Adds an authoritative answer"""
self.authorities.append(record)
def add_additional_answer(self, record):
""" Adds an additional answer
From: RFC 6763, DNS-Based Service Discovery, February 2013
12. DNS Additional Record Generation
DNS has an efficiency feature whereby a DNS server may place
additional records in the additional section of the DNS message.
These additional records are records that the client did not
explicitly request, but the server has reasonable grounds to expect
that the client might request them shortly, so including them can
save the client from having to issue additional queries.
This section recommends which additional records SHOULD be generated
to improve network efficiency, for both Unicast and Multicast DNS-SD
responses.
12.1. PTR Records
When including a DNS-SD Service Instance Enumeration or Selective
Instance Enumeration (subtype) PTR record in a response packet, the
server/responder SHOULD include the following additional records:
o The SRV record(s) named in the PTR rdata.
o The TXT record(s) named in the PTR rdata.
o All address records (type "A" and "AAAA") named in the SRV rdata.
12.2. SRV Records
When including an SRV record in a response packet, the
server/responder SHOULD include the following additional records:
o All address records (type "A" and "AAAA") named in the SRV rdata.
"""
self.additionals.append(record)
def pack(self, format_, value):
self.data.append(struct.pack(format_, value))
self.size += struct.calcsize(format_)
def write_byte(self, value):
"""Writes a single byte to the packet"""
self.pack(b'!c', int2byte(value))
def insert_short(self, index, value):
"""Inserts an unsigned short in a certain position in the packet"""
self.data.insert(index, struct.pack(b'!H', value))
self.size += 2
def write_short(self, value):
"""Writes an unsigned short to the packet"""
self.pack(b'!H', value)
def write_int(self, value):
"""Writes an unsigned integer to the packet"""
self.pack(b'!I', int(value))
def write_string(self, value):
"""Writes a string to the packet"""
assert isinstance(value, bytes)
self.data.append(value)
self.size += len(value)
def write_utf(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.write_byte(length)
self.write_string(utfstr)
def write_character_string(self, value):
assert isinstance(value, bytes)
length = len(value)
if length > 256:
raise NamePartTooLongException
self.write_byte(length)
self.write_string(value)
def write_name(self, name):
"""
Write names to packet
18.14. Name Compression
When generating Multicast DNS messages, implementations SHOULD use
name compression wherever possible to compress the names of resource
records, by replacing some or all of the resource record name with a
compact two-byte reference to an appearance of that data somewhere
earlier in the message [RFC1035].
"""
# split name into each label
parts = name.split('.')
if not parts[-1]:
parts.pop()
# construct each suffix
name_suffices = ['.'.join(parts[i:]) for i in range(len(parts))]
# look for an existing name or suffix
for count, sub_name in enumerate(name_suffices):
if sub_name in self.names:
break
else:
count = len(name_suffices)
# note the new names we are saving into the packet
name_length = len(name.encode('utf-8'))
for suffix in name_suffices[:count]:
self.names[suffix] = self.size + name_length - len(suffix.encode('utf-8')) - 1
# write the new names out.
for part in parts[:count]:
self.write_utf(part)
# if we wrote part of the name, create a pointer to the rest
if count != len(name_suffices):
# Found substring in packet, create pointer
index = self.names[name_suffices[count]]
self.write_byte((index >> 8) | 0xC0)
self.write_byte(index & 0xFF)
else:
# this is the end of a name
self.write_byte(0)
def write_question(self, question):
"""Writes a question to the packet"""
self.write_name(question.name)
self.write_short(question.type)
self.write_short(question.class_)
def write_record(self, record, now):
"""Writes a record (answer, authoritative answer, additional) to
the packet"""
if self.state == self.State.finished:
return 1
start_data_length, start_size = len(self.data), self.size
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