Current File : //proc/self/root/lib/python3/dist-packages/zeroconf/_protocol/incoming.py
""" 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 struct
from typing import Callable, Dict, List, Optional, Set, Tuple, cast
from . import DNSMessage
from .._dns import DNSAddress, DNSHinfo, DNSNsec, DNSPointer, DNSQuestion, DNSRecord, DNSService, DNSText
from .._exceptions import IncomingDecodeError
from .._logger import QuietLogger, log
from .._utils.time import current_time_millis
from ..const import (
_TYPES,
_TYPE_A,
_TYPE_AAAA,
_TYPE_CNAME,
_TYPE_HINFO,
_TYPE_NSEC,
_TYPE_PTR,
_TYPE_SRV,
_TYPE_TXT,
)
DNS_COMPRESSION_HEADER_LEN = 1
DNS_COMPRESSION_POINTER_LEN = 2
MAX_DNS_LABELS = 128
MAX_NAME_LENGTH = 253
DECODE_EXCEPTIONS = (IndexError, struct.error, IncomingDecodeError)
class DNSIncoming(DNSMessage, QuietLogger):
"""Object representation of an incoming DNS packet"""
__slots__ = (
'offset',
'data',
'data_len',
'name_cache',
'questions',
'_answers',
'id',
'num_questions',
'num_answers',
'num_authorities',
'num_additionals',
'valid',
'now',
'scope_id',
'source',
)
def __init__(
self,
data: bytes,
source: Optional[Tuple[str, int]] = None,
scope_id: Optional[int] = None,
now: Optional[float] = None,
) -> None:
"""Constructor from string holding bytes of packet"""
super().__init__(0)
self.offset = 0
self.data = data
self.data_len = len(data)
self.name_cache: Dict[int, List[str]] = {}
self.questions: List[DNSQuestion] = []
self._answers: List[DNSRecord] = []
self.id = 0
self.num_questions = 0
self.num_answers = 0
self.num_authorities = 0
self.num_additionals = 0
self.valid = False
self._read_others = False
self.now = now or current_time_millis()
self.source = source
self.scope_id = scope_id
self._parse_data(self._initial_parse)
def _initial_parse(self) -> None:
"""Parse the data needed to initalize the packet object."""
self.read_header()
self.read_questions()
if not self.num_questions:
self.read_others()
self.valid = True
def _parse_data(self, parser_call: Callable) -> None:
"""Parse part of the packet and catch exceptions."""
try:
parser_call()
except DECODE_EXCEPTIONS:
self.log_exception_debug(
'Received invalid packet from %s at offset %d while unpacking %r',
self.source,
self.offset,
self.data,
)
@property
def answers(self) -> List[DNSRecord]:
"""Answers in the packet."""
if not self._read_others:
self._parse_data(self.read_others)
return self._answers
def __repr__(self) -> str:
return '<DNSIncoming:{%s}>' % ', '.join(
[
'id=%s' % self.id,
'flags=%s' % self.flags,
'truncated=%s' % self.truncated,
'n_q=%s' % self.num_questions,
'n_ans=%s' % self.num_answers,
'n_auth=%s' % self.num_authorities,
'n_add=%s' % self.num_additionals,
'questions=%s' % self.questions,
'answers=%s' % self.answers,
]
)
def unpack(self, format_: bytes, length: int) -> tuple:
self.offset += length
return struct.unpack(format_, self.data[self.offset - length : self.offset])
def read_header(self) -> None:
"""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', 12)
def read_questions(self) -> None:
"""Reads questions section of packet"""
self.questions = [
DNSQuestion(self.read_name(), *self.unpack(b'!HH', 4)) for _ in range(self.num_questions)
]
def read_character_string(self) -> bytes:
"""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: int) -> bytes:
"""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) -> int:
"""Reads an unsigned short from the packet"""
return cast(int, self.unpack(b'!H', 2)[0])
def read_others(self) -> None:
"""Reads the answers, authorities and additionals section of the
packet"""
self._read_others = True
n = self.num_answers + self.num_authorities + self.num_additionals
for _ in range(n):
domain = self.read_name()
type_, class_, ttl, length = self.unpack(b'!HHiH', 10)
end = self.offset + length
rec = None
try:
rec = self.read_record(domain, type_, class_, ttl, length)
except DECODE_EXCEPTIONS:
# Skip records that fail to decode if we know the length
# If the packet is really corrupt read_name and the unpack
# above would fail and hit the exception catch in read_others
self.offset = end
log.debug(
'Unable to parse; skipping record for %s with type %s at offset %d while unpacking %r',
domain,
_TYPES.get(type_, type_),
self.offset,
self.data,
exc_info=True,
)
if rec is not None:
self._answers.append(rec)
def read_record(self, domain: str, type_: int, class_: int, ttl: int, length: int) -> Optional[DNSRecord]:
"""Read known records types and skip unknown ones."""
if type_ == _TYPE_A:
return DNSAddress(domain, type_, class_, ttl, self.read_string(4), created=self.now)
if type_ in (_TYPE_CNAME, _TYPE_PTR):
return DNSPointer(domain, type_, class_, ttl, self.read_name(), self.now)
if type_ == _TYPE_TXT:
return DNSText(domain, type_, class_, ttl, self.read_string(length), self.now)
if type_ == _TYPE_SRV:
return DNSService(
domain,
type_,
class_,
ttl,
self.read_unsigned_short(),
self.read_unsigned_short(),
self.read_unsigned_short(),
self.read_name(),
self.now,
)
if type_ == _TYPE_HINFO:
return DNSHinfo(
domain,
type_,
class_,
ttl,
self.read_character_string().decode('utf-8'),
self.read_character_string().decode('utf-8'),
self.now,
)
if type_ == _TYPE_AAAA:
return DNSAddress(
domain, type_, class_, ttl, self.read_string(16), created=self.now, scope_id=self.scope_id
)
if type_ == _TYPE_NSEC:
name_start = self.offset
return DNSNsec(
domain,
type_,
class_,
ttl,
self.read_name(),
self.read_bitmap(name_start + length),
self.now,
)
# 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
return None
def read_bitmap(self, end: int) -> List[int]:
"""Reads an NSEC bitmap from the packet."""
rdtypes = []
while self.offset < end:
window = self.data[self.offset]
bitmap_length = self.data[self.offset + 1]
for i, byte in enumerate(self.data[self.offset + 2 : self.offset + 2 + bitmap_length]):
for bit in range(0, 8):
if byte & (0x80 >> bit):
rdtypes.append(bit + window * 256 + i * 8)
self.offset += 2 + bitmap_length
return rdtypes
def read_name(self) -> str:
"""Reads a domain name from the packet."""
labels: List[str] = []
seen_pointers: Set[int] = set()
self.offset = self._decode_labels_at_offset(self.offset, labels, seen_pointers)
name = ".".join(labels) + "."
if len(name) > MAX_NAME_LENGTH:
raise IncomingDecodeError(
f"DNS name {name} exceeds maximum length of {MAX_NAME_LENGTH} from {self.source}"
)
return name
def _decode_labels_at_offset(self, off: int, labels: List[str], seen_pointers: Set[int]) -> int:
# This is a tight loop that is called frequently, small optimizations can make a difference.
while off < self.data_len:
length = self.data[off]
if length == 0:
return off + DNS_COMPRESSION_HEADER_LEN
if length < 0x40:
label_idx = off + DNS_COMPRESSION_HEADER_LEN
labels.append(self.data[label_idx : label_idx + length].decode('utf-8', 'replace'))
off += DNS_COMPRESSION_HEADER_LEN + length
continue
if length < 0xC0:
raise IncomingDecodeError(
f"DNS compression type {length} is unknown at {off} from {self.source}"
)
# We have a DNS compression pointer
link = (length & 0x3F) * 256 + self.data[off + 1]
if link > self.data_len:
raise IncomingDecodeError(
f"DNS compression pointer at {off} points to {link} beyond packet from {self.source}"
)
if link == off:
raise IncomingDecodeError(
f"DNS compression pointer at {off} points to itself from {self.source}"
)
if link in seen_pointers:
raise IncomingDecodeError(
f"DNS compression pointer at {off} was seen again from {self.source}"
)
linked_labels = self.name_cache.get(link, [])
if not linked_labels:
seen_pointers.add(link)
self._decode_labels_at_offset(link, linked_labels, seen_pointers)
self.name_cache[link] = linked_labels
labels.extend(linked_labels)
if len(labels) > MAX_DNS_LABELS:
raise IncomingDecodeError(
f"Maximum dns labels reached while processing pointer at {off} from {self.source}"
)
return off + DNS_COMPRESSION_POINTER_LEN
raise IncomingDecodeError("Corrupt packet received while decoding name from {self.source}")
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