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resolver.py
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resolver.py
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# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
# Copyright (C) 2003-2017 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
"""DNS stub resolver."""
import contextlib
import random
import socket
import sys
import threading
import time
import warnings
from typing import Any, Dict, Iterator, List, Optional, Sequence, Tuple, Union
from urllib.parse import urlparse
import dns._ddr
import dns.edns
import dns.exception
import dns.flags
import dns.inet
import dns.ipv4
import dns.ipv6
import dns.message
import dns.name
import dns.rdata
import dns.nameserver
import dns.query
import dns.rcode
import dns.rdataclass
import dns.rdatatype
import dns.rdtypes.svcbbase
import dns.reversename
import dns.tsig
if sys.platform == "win32": # pragma: no cover
import dns.win32util
class NXDOMAIN(dns.exception.DNSException):
"""The DNS query name does not exist."""
supp_kwargs = {"qnames", "responses"}
fmt = None # we have our own __str__ implementation
# pylint: disable=arguments-differ
# We do this as otherwise mypy complains about unexpected keyword argument
# idna_exception
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def _check_kwargs(self, qnames, responses=None):
if not isinstance(qnames, (list, tuple, set)):
raise AttributeError("qnames must be a list, tuple or set")
if len(qnames) == 0:
raise AttributeError("qnames must contain at least one element")
if responses is None:
responses = {}
elif not isinstance(responses, dict):
raise AttributeError("responses must be a dict(qname=response)")
kwargs = dict(qnames=qnames, responses=responses)
return kwargs
def __str__(self) -> str:
if "qnames" not in self.kwargs:
return super().__str__()
qnames = self.kwargs["qnames"]
if len(qnames) > 1:
msg = "None of DNS query names exist"
else:
msg = "The DNS query name does not exist"
qnames = ", ".join(map(str, qnames))
return f"{msg}: {qnames}"
@property
def canonical_name(self):
"""Return the unresolved canonical name."""
if "qnames" not in self.kwargs:
raise TypeError("parametrized exception required")
for qname in self.kwargs["qnames"]:
response = self.kwargs["responses"][qname]
try:
cname = response.canonical_name()
if cname != qname:
return cname
except Exception: # pragma: no cover
# We can just eat this exception as it means there was
# something wrong with the response.
pass
return self.kwargs["qnames"][0]
def __add__(self, e_nx):
"""Augment by results from another NXDOMAIN exception."""
qnames0 = list(self.kwargs.get("qnames", []))
responses0 = dict(self.kwargs.get("responses", {}))
responses1 = e_nx.kwargs.get("responses", {})
for qname1 in e_nx.kwargs.get("qnames", []):
if qname1 not in qnames0:
qnames0.append(qname1)
if qname1 in responses1:
responses0[qname1] = responses1[qname1]
return NXDOMAIN(qnames=qnames0, responses=responses0)
def qnames(self):
"""All of the names that were tried.
Returns a list of ``dns.name.Name``.
"""
return self.kwargs["qnames"]
def responses(self):
"""A map from queried names to their NXDOMAIN responses.
Returns a dict mapping a ``dns.name.Name`` to a
``dns.message.Message``.
"""
return self.kwargs["responses"]
def response(self, qname):
"""The response for query *qname*.
Returns a ``dns.message.Message``.
"""
return self.kwargs["responses"][qname]
class YXDOMAIN(dns.exception.DNSException):
"""The DNS query name is too long after DNAME substitution."""
ErrorTuple = Tuple[
Optional[str],
bool,
int,
Union[Exception, str],
Optional[dns.message.Message],
]
def _errors_to_text(errors: List[ErrorTuple]) -> List[str]:
"""Turn a resolution errors trace into a list of text."""
texts = []
for err in errors:
texts.append(f"Server {err[0]} answered {err[3]}")
return texts
class LifetimeTimeout(dns.exception.Timeout):
"""The resolution lifetime expired."""
msg = "The resolution lifetime expired."
fmt = f"{msg[:-1]} after {{timeout:.3f}} seconds: {{errors}}"
supp_kwargs = {"timeout", "errors"}
# We do this as otherwise mypy complains about unexpected keyword argument
# idna_exception
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def _fmt_kwargs(self, **kwargs):
srv_msgs = _errors_to_text(kwargs["errors"])
return super()._fmt_kwargs(
timeout=kwargs["timeout"], errors="; ".join(srv_msgs)
)
# We added more detail to resolution timeouts, but they are still
# subclasses of dns.exception.Timeout for backwards compatibility. We also
# keep dns.resolver.Timeout defined for backwards compatibility.
Timeout = LifetimeTimeout
class NoAnswer(dns.exception.DNSException):
"""The DNS response does not contain an answer to the question."""
fmt = "The DNS response does not contain an answer to the question: {query}"
supp_kwargs = {"response"}
# We do this as otherwise mypy complains about unexpected keyword argument
# idna_exception
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def _fmt_kwargs(self, **kwargs):
return super()._fmt_kwargs(query=kwargs["response"].question)
def response(self):
return self.kwargs["response"]
class NoNameservers(dns.exception.DNSException):
"""All nameservers failed to answer the query.
errors: list of servers and respective errors
The type of errors is
[(server IP address, any object convertible to string)].
Non-empty errors list will add explanatory message ()
"""
msg = "All nameservers failed to answer the query."
fmt = f"{msg[:-1]} {{query}}: {{errors}}"
supp_kwargs = {"request", "errors"}
# We do this as otherwise mypy complains about unexpected keyword argument
# idna_exception
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def _fmt_kwargs(self, **kwargs):
srv_msgs = _errors_to_text(kwargs["errors"])
return super()._fmt_kwargs(
query=kwargs["request"].question, errors="; ".join(srv_msgs)
)
class NotAbsolute(dns.exception.DNSException):
"""An absolute domain name is required but a relative name was provided."""
class NoRootSOA(dns.exception.DNSException):
"""There is no SOA RR at the DNS root name. This should never happen!"""
class NoMetaqueries(dns.exception.DNSException):
"""DNS metaqueries are not allowed."""
class NoResolverConfiguration(dns.exception.DNSException):
"""Resolver configuration could not be read or specified no nameservers."""
class Answer:
"""DNS stub resolver answer.
Instances of this class bundle up the result of a successful DNS
resolution.
For convenience, the answer object implements much of the sequence
protocol, forwarding to its ``rrset`` attribute. E.g.
``for a in answer`` is equivalent to ``for a in answer.rrset``.
``answer[i]`` is equivalent to ``answer.rrset[i]``, and
``answer[i:j]`` is equivalent to ``answer.rrset[i:j]``.
Note that CNAMEs or DNAMEs in the response may mean that answer
RRset's name might not be the query name.
"""
def __init__(
self,
qname: dns.name.Name,
rdtype: dns.rdatatype.RdataType,
rdclass: dns.rdataclass.RdataClass,
response: dns.message.QueryMessage,
nameserver: Optional[str] = None,
port: Optional[int] = None,
) -> None:
self.qname = qname
self.rdtype = rdtype
self.rdclass = rdclass
self.response = response
self.nameserver = nameserver
self.port = port
self.chaining_result = response.resolve_chaining()
# Copy some attributes out of chaining_result for backwards
# compatibility and convenience.
self.canonical_name = self.chaining_result.canonical_name
self.rrset = self.chaining_result.answer
self.expiration = time.time() + self.chaining_result.minimum_ttl
def __getattr__(self, attr): # pragma: no cover
if attr == "name":
return self.rrset.name
elif attr == "ttl":
return self.rrset.ttl
elif attr == "covers":
return self.rrset.covers
elif attr == "rdclass":
return self.rrset.rdclass
elif attr == "rdtype":
return self.rrset.rdtype
else:
raise AttributeError(attr)
def __len__(self) -> int:
return self.rrset and len(self.rrset) or 0
def __iter__(self) -> Iterator[dns.rdata.Rdata]:
return self.rrset and iter(self.rrset) or iter(tuple())
def __getitem__(self, i):
if self.rrset is None:
raise IndexError
return self.rrset[i]
def __delitem__(self, i):
if self.rrset is None:
raise IndexError
del self.rrset[i]
class Answers(dict):
"""A dict of DNS stub resolver answers, indexed by type."""
class HostAnswers(Answers):
"""A dict of DNS stub resolver answers to a host name lookup, indexed by
type.
"""
@classmethod
def make(
cls,
v6: Optional[Answer] = None,
v4: Optional[Answer] = None,
add_empty: bool = True,
) -> "HostAnswers":
answers = HostAnswers()
if v6 is not None and (add_empty or v6.rrset):
answers[dns.rdatatype.AAAA] = v6
if v4 is not None and (add_empty or v4.rrset):
answers[dns.rdatatype.A] = v4
return answers
# Returns pairs of (address, family) from this result, potentially
# filtering by address family.
def addresses_and_families(
self, family: int = socket.AF_UNSPEC
) -> Iterator[Tuple[str, int]]:
if family == socket.AF_UNSPEC:
yield from self.addresses_and_families(socket.AF_INET6)
yield from self.addresses_and_families(socket.AF_INET)
return
elif family == socket.AF_INET6:
answer = self.get(dns.rdatatype.AAAA)
elif family == socket.AF_INET:
answer = self.get(dns.rdatatype.A)
else: # pragma: no cover
raise NotImplementedError(f"unknown address family {family}")
if answer:
for rdata in answer:
yield (rdata.address, family)
# Returns addresses from this result, potentially filtering by
# address family.
def addresses(self, family: int = socket.AF_UNSPEC) -> Iterator[str]:
return (pair[0] for pair in self.addresses_and_families(family))
# Returns the canonical name from this result.
def canonical_name(self) -> dns.name.Name:
answer = self.get(dns.rdatatype.AAAA, self.get(dns.rdatatype.A))
return answer.canonical_name
class CacheStatistics:
"""Cache Statistics"""
def __init__(self, hits: int = 0, misses: int = 0) -> None:
self.hits = hits
self.misses = misses
def reset(self) -> None:
self.hits = 0
self.misses = 0
def clone(self) -> "CacheStatistics":
return CacheStatistics(self.hits, self.misses)
class CacheBase:
def __init__(self) -> None:
self.lock = threading.Lock()
self.statistics = CacheStatistics()
def reset_statistics(self) -> None:
"""Reset all statistics to zero."""
with self.lock:
self.statistics.reset()
def hits(self) -> int:
"""How many hits has the cache had?"""
with self.lock:
return self.statistics.hits
def misses(self) -> int:
"""How many misses has the cache had?"""
with self.lock:
return self.statistics.misses
def get_statistics_snapshot(self) -> CacheStatistics:
"""Return a consistent snapshot of all the statistics.
If running with multiple threads, it's better to take a
snapshot than to call statistics methods such as hits() and
misses() individually.
"""
with self.lock:
return self.statistics.clone()
CacheKey = Tuple[dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass]
class Cache(CacheBase):
"""Simple thread-safe DNS answer cache."""
def __init__(self, cleaning_interval: float = 300.0) -> None:
"""*cleaning_interval*, a ``float`` is the number of seconds between
periodic cleanings.
"""
super().__init__()
self.data: Dict[CacheKey, Answer] = {}
self.cleaning_interval = cleaning_interval
self.next_cleaning: float = time.time() + self.cleaning_interval
def _maybe_clean(self) -> None:
"""Clean the cache if it's time to do so."""
now = time.time()
if self.next_cleaning <= now:
keys_to_delete = []
for k, v in self.data.items():
if v.expiration <= now:
keys_to_delete.append(k)
for k in keys_to_delete:
del self.data[k]
now = time.time()
self.next_cleaning = now + self.cleaning_interval
def get(self, key: CacheKey) -> Optional[Answer]:
"""Get the answer associated with *key*.
Returns None if no answer is cached for the key.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
Returns a ``dns.resolver.Answer`` or ``None``.
"""
with self.lock:
self._maybe_clean()
v = self.data.get(key)
if v is None or v.expiration <= time.time():
self.statistics.misses += 1
return None
self.statistics.hits += 1
return v
def put(self, key: CacheKey, value: Answer) -> None:
"""Associate key and value in the cache.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
*value*, a ``dns.resolver.Answer``, the answer.
"""
with self.lock:
self._maybe_clean()
self.data[key] = value
def flush(self, key: Optional[CacheKey] = None) -> None:
"""Flush the cache.
If *key* is not ``None``, only that item is flushed. Otherwise the entire cache
is flushed.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
"""
with self.lock:
if key is not None:
if key in self.data:
del self.data[key]
else:
self.data = {}
self.next_cleaning = time.time() + self.cleaning_interval
class LRUCacheNode:
"""LRUCache node."""
def __init__(self, key, value):
self.key = key
self.value = value
self.hits = 0
self.prev = self
self.next = self
def link_after(self, node: "LRUCacheNode") -> None:
self.prev = node
self.next = node.next
node.next.prev = self
node.next = self
def unlink(self) -> None:
self.next.prev = self.prev
self.prev.next = self.next
class LRUCache(CacheBase):
"""Thread-safe, bounded, least-recently-used DNS answer cache.
This cache is better than the simple cache (above) if you're
running a web crawler or other process that does a lot of
resolutions. The LRUCache has a maximum number of nodes, and when
it is full, the least-recently used node is removed to make space
for a new one.
"""
def __init__(self, max_size: int = 100000) -> None:
"""*max_size*, an ``int``, is the maximum number of nodes to cache;
it must be greater than 0.
"""
super().__init__()
self.data: Dict[CacheKey, LRUCacheNode] = {}
self.set_max_size(max_size)
self.sentinel: LRUCacheNode = LRUCacheNode(None, None)
self.sentinel.prev = self.sentinel
self.sentinel.next = self.sentinel
def set_max_size(self, max_size: int) -> None:
if max_size < 1:
max_size = 1
self.max_size = max_size
def get(self, key: CacheKey) -> Optional[Answer]:
"""Get the answer associated with *key*.
Returns None if no answer is cached for the key.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
Returns a ``dns.resolver.Answer`` or ``None``.
"""
with self.lock:
node = self.data.get(key)
if node is None:
self.statistics.misses += 1
return None
# Unlink because we're either going to move the node to the front
# of the LRU list or we're going to free it.
node.unlink()
if node.value.expiration <= time.time():
del self.data[node.key]
self.statistics.misses += 1
return None
node.link_after(self.sentinel)
self.statistics.hits += 1
node.hits += 1
return node.value
def get_hits_for_key(self, key: CacheKey) -> int:
"""Return the number of cache hits associated with the specified key."""
with self.lock:
node = self.data.get(key)
if node is None or node.value.expiration <= time.time():
return 0
else:
return node.hits
def put(self, key: CacheKey, value: Answer) -> None:
"""Associate key and value in the cache.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
*value*, a ``dns.resolver.Answer``, the answer.
"""
with self.lock:
node = self.data.get(key)
if node is not None:
node.unlink()
del self.data[node.key]
while len(self.data) >= self.max_size:
gnode = self.sentinel.prev
gnode.unlink()
del self.data[gnode.key]
node = LRUCacheNode(key, value)
node.link_after(self.sentinel)
self.data[key] = node
def flush(self, key: Optional[CacheKey] = None) -> None:
"""Flush the cache.
If *key* is not ``None``, only that item is flushed. Otherwise the entire cache
is flushed.
*key*, a ``(dns.name.Name, dns.rdatatype.RdataType, dns.rdataclass.RdataClass)``
tuple whose values are the query name, rdtype, and rdclass respectively.
"""
with self.lock:
if key is not None:
node = self.data.get(key)
if node is not None:
node.unlink()
del self.data[node.key]
else:
gnode = self.sentinel.next
while gnode != self.sentinel:
next = gnode.next
gnode.unlink()
gnode = next
self.data = {}
class _Resolution:
"""Helper class for dns.resolver.Resolver.resolve().
All of the "business logic" of resolution is encapsulated in this
class, allowing us to have multiple resolve() implementations
using different I/O schemes without copying all of the
complicated logic.
This class is a "friend" to dns.resolver.Resolver and manipulates
resolver data structures directly.
"""
def __init__(
self,
resolver: "BaseResolver",
qname: Union[dns.name.Name, str],
rdtype: Union[dns.rdatatype.RdataType, str],
rdclass: Union[dns.rdataclass.RdataClass, str],
tcp: bool,
raise_on_no_answer: bool,
search: Optional[bool],
) -> None:
if isinstance(qname, str):
qname = dns.name.from_text(qname, None)
rdtype = dns.rdatatype.RdataType.make(rdtype)
if dns.rdatatype.is_metatype(rdtype):
raise NoMetaqueries
rdclass = dns.rdataclass.RdataClass.make(rdclass)
if dns.rdataclass.is_metaclass(rdclass):
raise NoMetaqueries
self.resolver = resolver
self.qnames_to_try = resolver._get_qnames_to_try(qname, search)
self.qnames = self.qnames_to_try[:]
self.rdtype = rdtype
self.rdclass = rdclass
self.tcp = tcp
self.raise_on_no_answer = raise_on_no_answer
self.nxdomain_responses: Dict[dns.name.Name, dns.message.QueryMessage] = {}
# Initialize other things to help analysis tools
self.qname = dns.name.empty
self.nameservers: List[dns.nameserver.Nameserver] = []
self.current_nameservers: List[dns.nameserver.Nameserver] = []
self.errors: List[ErrorTuple] = []
self.nameserver: Optional[dns.nameserver.Nameserver] = None
self.tcp_attempt = False
self.retry_with_tcp = False
self.request: Optional[dns.message.QueryMessage] = None
self.backoff = 0.0
def next_request(
self,
) -> Tuple[Optional[dns.message.QueryMessage], Optional[Answer]]:
"""Get the next request to send, and check the cache.
Returns a (request, answer) tuple. At most one of request or
answer will not be None.
"""
# We return a tuple instead of Union[Message,Answer] as it lets
# the caller avoid isinstance().
while len(self.qnames) > 0:
self.qname = self.qnames.pop(0)
# Do we know the answer?
if self.resolver.cache:
answer = self.resolver.cache.get(
(self.qname, self.rdtype, self.rdclass)
)
if answer is not None:
if answer.rrset is None and self.raise_on_no_answer:
raise NoAnswer(response=answer.response)
else:
return (None, answer)
answer = self.resolver.cache.get(
(self.qname, dns.rdatatype.ANY, self.rdclass)
)
if answer is not None and answer.response.rcode() == dns.rcode.NXDOMAIN:
# cached NXDOMAIN; record it and continue to next
# name.
self.nxdomain_responses[self.qname] = answer.response
continue
# Build the request
request = dns.message.make_query(self.qname, self.rdtype, self.rdclass)
if self.resolver.keyname is not None:
request.use_tsig(
self.resolver.keyring,
self.resolver.keyname,
algorithm=self.resolver.keyalgorithm,
)
request.use_edns(
self.resolver.edns,
self.resolver.ednsflags,
self.resolver.payload,
options=self.resolver.ednsoptions,
)
if self.resolver.flags is not None:
request.flags = self.resolver.flags
self.nameservers = self.resolver._enrich_nameservers(
self.resolver._nameservers,
self.resolver.nameserver_ports,
self.resolver.port,
)
if self.resolver.rotate:
random.shuffle(self.nameservers)
self.current_nameservers = self.nameservers[:]
self.errors = []
self.nameserver = None
self.tcp_attempt = False
self.retry_with_tcp = False
self.request = request
self.backoff = 0.10
return (request, None)
#
# We've tried everything and only gotten NXDOMAINs. (We know
# it's only NXDOMAINs as anything else would have returned
# before now.)
#
raise NXDOMAIN(qnames=self.qnames_to_try, responses=self.nxdomain_responses)
def next_nameserver(self) -> Tuple[dns.nameserver.Nameserver, bool, float]:
if self.retry_with_tcp:
assert self.nameserver is not None
assert not self.nameserver.is_always_max_size()
self.tcp_attempt = True
self.retry_with_tcp = False
return (self.nameserver, True, 0)
backoff = 0.0
if not self.current_nameservers:
if len(self.nameservers) == 0:
# Out of things to try!
raise NoNameservers(request=self.request, errors=self.errors)
self.current_nameservers = self.nameservers[:]
backoff = self.backoff
self.backoff = min(self.backoff * 2, 2)
self.nameserver = self.current_nameservers.pop(0)
self.tcp_attempt = self.tcp or self.nameserver.is_always_max_size()
return (self.nameserver, self.tcp_attempt, backoff)
def query_result(
self, response: Optional[dns.message.Message], ex: Optional[Exception]
) -> Tuple[Optional[Answer], bool]:
#
# returns an (answer: Answer, end_loop: bool) tuple.
#
assert self.nameserver is not None
if ex:
# Exception during I/O or from_wire()
assert response is None
self.errors.append(
(
str(self.nameserver),
self.tcp_attempt,
self.nameserver.answer_port(),
ex,
response,
)
)
if (
isinstance(ex, dns.exception.FormError)
or isinstance(ex, EOFError)
or isinstance(ex, OSError)
or isinstance(ex, NotImplementedError)
):
# This nameserver is no good, take it out of the mix.
self.nameservers.remove(self.nameserver)
elif isinstance(ex, dns.message.Truncated):
if self.tcp_attempt:
# Truncation with TCP is no good!
self.nameservers.remove(self.nameserver)
else:
self.retry_with_tcp = True
return (None, False)
# We got an answer!
assert response is not None
assert isinstance(response, dns.message.QueryMessage)
rcode = response.rcode()
if rcode == dns.rcode.NOERROR:
try:
answer = Answer(
self.qname,
self.rdtype,
self.rdclass,
response,
self.nameserver.answer_nameserver(),
self.nameserver.answer_port(),
)
except Exception as e:
self.errors.append(
(
str(self.nameserver),
self.tcp_attempt,
self.nameserver.answer_port(),
e,
response,
)
)
# The nameserver is no good, take it out of the mix.
self.nameservers.remove(self.nameserver)
return (None, False)
if self.resolver.cache:
self.resolver.cache.put((self.qname, self.rdtype, self.rdclass), answer)
if answer.rrset is None and self.raise_on_no_answer:
raise NoAnswer(response=answer.response)
return (answer, True)
elif rcode == dns.rcode.NXDOMAIN:
# Further validate the response by making an Answer, even
# if we aren't going to cache it.
try:
answer = Answer(
self.qname, dns.rdatatype.ANY, dns.rdataclass.IN, response
)
except Exception as e:
self.errors.append(
(
str(self.nameserver),
self.tcp_attempt,
self.nameserver.answer_port(),
e,
response,
)
)
# The nameserver is no good, take it out of the mix.
self.nameservers.remove(self.nameserver)
return (None, False)
self.nxdomain_responses[self.qname] = response
if self.resolver.cache:
self.resolver.cache.put(
(self.qname, dns.rdatatype.ANY, self.rdclass), answer
)
# Make next_nameserver() return None, so caller breaks its
# inner loop and calls next_request().
return (None, True)
elif rcode == dns.rcode.YXDOMAIN:
yex = YXDOMAIN()
self.errors.append(
(
str(self.nameserver),
self.tcp_attempt,
self.nameserver.answer_port(),
yex,
response,
)
)
raise yex
else:
#
# We got a response, but we're not happy with the
# rcode in it.
#
if rcode != dns.rcode.SERVFAIL or not self.resolver.retry_servfail:
self.nameservers.remove(self.nameserver)
self.errors.append(
(
str(self.nameserver),
self.tcp_attempt,
self.nameserver.answer_port(),
dns.rcode.to_text(rcode),
response,
)
)
return (None, False)
class BaseResolver:
"""DNS stub resolver."""
# We initialize in reset()
#
# pylint: disable=attribute-defined-outside-init
domain: dns.name.Name
nameserver_ports: Dict[str, int]
port: int
search: List[dns.name.Name]
use_search_by_default: bool
timeout: float
lifetime: float
keyring: Optional[Any]
keyname: Optional[Union[dns.name.Name, str]]
keyalgorithm: Union[dns.name.Name, str]
edns: int
ednsflags: int
ednsoptions: Optional[List[dns.edns.Option]]
payload: int
cache: Any
flags: Optional[int]
retry_servfail: bool
rotate: bool
ndots: Optional[int]
_nameservers: Sequence[Union[str, dns.nameserver.Nameserver]]
def __init__(
self, filename: str = "/etc/resolv.conf", configure: bool = True
) -> None:
"""*filename*, a ``str`` or file object, specifying a file
in standard /etc/resolv.conf format. This parameter is meaningful
only when *configure* is true and the platform is POSIX.
*configure*, a ``bool``. If True (the default), the resolver
instance is configured in the normal fashion for the operating
system the resolver is running on. (I.e. by reading a
/etc/resolv.conf file on POSIX systems and from the registry
on Windows systems.)
"""
self.reset()
if configure:
if sys.platform == "win32": # pragma: no cover
self.read_registry()
elif filename:
self.read_resolv_conf(filename)
def reset(self) -> None:
"""Reset all resolver configuration to the defaults."""
self.domain = dns.name.Name(dns.name.from_text(socket.gethostname())[1:])
if len(self.domain) == 0: # pragma: no cover
self.domain = dns.name.root
self._nameservers = []
self.nameserver_ports = {}
self.port = 53
self.search = []
self.use_search_by_default = False
self.timeout = 2.0
self.lifetime = 5.0
self.keyring = None
self.keyname = None
self.keyalgorithm = dns.tsig.default_algorithm
self.edns = -1
self.ednsflags = 0
self.ednsoptions = None
self.payload = 0
self.cache = None
self.flags = None
self.retry_servfail = False
self.rotate = False
self.ndots = None
def read_resolv_conf(self, f: Any) -> None:
"""Process *f* as a file in the /etc/resolv.conf format. If f is
a ``str``, it is used as the name of the file to open; otherwise it
is treated as the file itself.
Interprets the following items:
- nameserver - name server IP address
- domain - local domain name
- search - search list for host-name lookup
- options - supported options are rotate, timeout, edns0, and ndots
"""
nameservers = []
if isinstance(f, str):
try:
cm: contextlib.AbstractContextManager = open(f)
except OSError:
# /etc/resolv.conf doesn't exist, can't be read, etc.
raise NoResolverConfiguration(f"cannot open {f}")
else:
cm = contextlib.nullcontext(f)
with cm as f:
for l in f: