# 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.
"""Asynchronous DNS stub resolver."""
import socket
import time
from typing import Any, Dict, List, Optional, Union
import dns._ddr
import dns.asyncbackend
import dns.asyncquery
import dns.exception
import dns.name
import dns.query
import dns.rdataclass
import dns.rdatatype
import dns.resolver # lgtm[py/import-and-import-from]
# import some resolver symbols for brevity
from dns.resolver import NXDOMAIN, NoAnswer, NoRootSOA, NotAbsolute
# for indentation purposes below
_udp = dns.asyncquery.udp
_tcp = dns.asyncquery.tcp
class Resolver(dns.resolver.BaseResolver):
"""Asynchronous DNS stub resolver."""
async def resolve(
self,
qname: Union[dns.name.Name, str],
rdtype: Union[dns.rdatatype.RdataType, str] = dns.rdatatype.A,
rdclass: Union[dns.rdataclass.RdataClass, str] = dns.rdataclass.IN,
tcp: bool = False,
source: Optional[str] = None,
raise_on_no_answer: bool = True,
source_port: int = 0,
lifetime: Optional[float] = None,
search: Optional[bool] = None,
backend: Optional[dns.asyncbackend.Backend] = None,
) -> dns.resolver.Answer:
"""Query nameservers asynchronously to find the answer to the question.
*backend*, a ``dns.asyncbackend.Backend``, or ``None``. If ``None``,
the default, then dnspython will use the default backend.
See :py:func:`dns.resolver.Resolver.resolve()` for the
documentation of the other parameters, exceptions, and return
type of this method.
"""
resolution = dns.resolver._Resolution(
self, qname, rdtype, rdclass, tcp, raise_on_no_answer, search
)
if not backend:
backend = dns.asyncbackend.get_default_backend()
start = time.time()
while True:
(request, answer) = resolution.next_request()
# Note we need to say "if answer is not None" and not just
# "if answer" because answer implements __len__, and python
# will call that. We want to return if we have an answer
# object, including in cases where its length is 0.
if answer is not None:
# cache hit!
return answer
assert request is not None # needed for type checking
done = False
while not done:
(nameserver, tcp, backoff) = resolution.next_nameserver()
if backoff:
await backend.sleep(backoff)
timeout = self._compute_timeout(start, lifetime, resolution.errors)
try:
response = await nameserver.async_query(
request,
timeout=timeout,
source=source,
source_port=source_port,
max_size=tcp,
backend=backend,
)
except Exception as ex:
(_, done) = resolution.query_result(None, ex)
continue
(answer, done) = resolution.query_result(response, None)
# Note we need to say "if answer is not None" and not just
# "if answer" because answer implements __len__, and python
# will call that. We want to return if we have an answer
# object, including in cases where its length is 0.
if answer is not None:
return answer
async def resolve_address(
self, ipaddr: str, *args: Any, **kwargs: Any
) -> dns.resolver.Answer:
"""Use an asynchronous resolver to run a reverse query for PTR
records.
This utilizes the resolve() method to perform a PTR lookup on the
specified IP address.
*ipaddr*, a ``str``, the IPv4 or IPv6 address you want to get
the PTR record for.
All other arguments that can be passed to the resolve() function
except for rdtype and rdclass are also supported by this
function.
"""
# We make a modified kwargs for type checking happiness, as otherwise
# we get a legit warning about possibly having rdtype and rdclass
# in the kwargs more than once.
modified_kwargs: Dict[str, Any] = {}
modified_kwargs.update(kwargs)
modified_kwargs["rdtype"] = dns.rdatatype.PTR
modified_kwargs["rdclass"] = dns.rdataclass.IN
return await self.resolve(
dns.reversename.from_address(ipaddr), *args, **modified_kwargs
)
async def resolve_name(
self,
name: Union[dns.name.Name, str],
family: int = socket.AF_UNSPEC,
**kwargs: Any,
) -> dns.resolver.HostAnswers:
"""Use an asynchronous resolver to query for address records.
This utilizes the resolve() method to perform A and/or AAAA lookups on
the specified name.
*qname*, a ``dns.name.Name`` or ``str``, the name to resolve.
*family*, an ``int``, the address family. If socket.AF_UNSPEC
(the default), both A and AAAA records will be retrieved.
All other arguments that can be passed to the resolve() function
except for rdtype and rdclass are also supported by this
function.
"""
# We make a modified kwargs for type checking happiness, as otherwise
# we get a legit warning about possibly having rdtype and rdclass
# in the kwargs more than once.
modified_kwargs: Dict[str, Any] = {}
modified_kwargs.update(kwargs)
modified_kwargs.pop("rdtype", None)
modified_kwargs["rdclass"] = dns.rdataclass.IN
if family == socket.AF_INET:
v4 = await self.resolve(name, dns.rdatatype.A, **modified_kwargs)
return dns.resolver.HostAnswers.make(v4=v4)
elif family == socket.AF_INET6:
v6 = await self.resolve(name, dns.rdatatype.AAAA, **modified_kwargs)
return dns.resolver.HostAnswers.make(v6=v6)
elif family != socket.AF_UNSPEC:
raise NotImplementedError(f"unknown address family {family}")
raise_on_no_answer = modified_kwargs.pop("raise_on_no_answer", True)
lifetime = modified_kwargs.pop("lifetime", None)
start = time.time()
v6 = await self.resolve(
name,
dns.rdatatype.AAAA,
raise_on_no_answer=False,
lifetime=self._compute_timeout(start, lifetime),
**modified_kwargs,
)
# Note that setting name ensures we query the same name
# for A as we did for AAAA. (This is just in case search lists
# are active by default in the resolver configuration and
# we might be talking to a server that says NXDOMAIN when it
# wants to say NOERROR no data.
name = v6.qname
v4 = await self.resolve(
name,
dns.rdatatype.A,
raise_on_no_answer=False,
lifetime=self._compute_timeout(start, lifetime),
**modified_kwargs,
)
answers = dns.resolver.HostAnswers.make(
v6=v6, v4=v4, add_empty=not raise_on_no_answer
)
if not answers:
raise NoAnswer(response=v6.response)
return answers
# pylint: disable=redefined-outer-name
async def canonical_name(self, name: Union[dns.name.Name, str]) -> dns.name.Name:
"""Determine the canonical name of *name*.
The canonical name is the name the resolver uses for queries
after all CNAME and DNAME renamings have been applied.
*name*, a ``dns.name.Name`` or ``str``, the query name.
This method can raise any exception that ``resolve()`` can
raise, other than ``dns.resolver.NoAnswer`` and
``dns.resolver.NXDOMAIN``.
Returns a ``dns.name.Name``.
"""
try:
answer = await self.resolve(name, raise_on_no_answer=False)
canonical_name = answer.canonical_name
except dns.resolver.NXDOMAIN as e:
canonical_name = e.canonical_name
return canonical_name
async def try_ddr(self, lifetime: float = 5.0) -> None:
"""Try to update the resolver's nameservers using Discovery of Designated
Resolvers (DDR). If successful, the resolver will subsequently use
DNS-over-HTTPS or DNS-over-TLS for future queries.
*lifetime*, a float, is the maximum time to spend attempting DDR. The default
is 5 seconds.
If the SVCB query is successful and results in a non-empty list of nameservers,
then the resolver's nameservers are set to the returned servers in priority
order.
The current implementation does not use any address hints from the SVCB record,
nor does it resolve addresses for the SCVB target name, rather it assumes that
the bootstrap nameserver will always be one of the addresses and uses it.
A future revision to the code may offer fuller support. The code verifies that
the bootstrap nameserver is in the Subject Alternative Name field of the
TLS certficate.
"""
try:
expiration = time.time() + lifetime
answer = await self.resolve(
dns._ddr._local_resolver_name, "svcb", lifetime=lifetime
)
timeout = dns.query._remaining(expiration)
nameservers = await dns._ddr._get_nameservers_async(answer, timeout)
if len(nameservers) > 0:
self.nameservers = nameservers
except Exception:
pass
default_resolver = None
def get_default_resolver() -> Resolver:
"""Get the default asynchronous resolver, initializing it if necessary."""
if default_resolver is None:
reset_default_resolver()
assert default_resolver is not None
return default_resolver
def reset_default_resolver() -> None:
"""Re-initialize default asynchronous resolver.
Note that the resolver configuration (i.e. /etc/resolv.conf on UNIX
systems) will be re-read immediately.
"""
global default_resolver
default_resolver = Resolver()
async def resolve(
qname: Union[dns.name.Name, str],
rdtype: Union[dns.rdatatype.RdataType, str] = dns.rdatatype.A,
rdclass: Union[dns.rdataclass.RdataClass, str] = dns.rdataclass.IN,
tcp: bool = False,
source: Optional[str] = None,
raise_on_no_answer: bool = True,
source_port: int = 0,
lifetime: Optional[float] = None,
search: Optional[bool] = None,
backend: Optional[dns.asyncbackend.Backend] = None,
) -> dns.resolver.Answer:
"""Query nameservers asynchronously to find the answer to the question.
This is a convenience function that uses the default resolver
object to make the query.
See :py:func:`dns.asyncresolver.Resolver.resolve` for more
information on the parameters.
"""
return await get_default_resolver().resolve(
qname,
rdtype,
rdclass,
tcp,
source,
raise_on_no_answer,
source_port,
lifetime,
search,
backend,
)
async def resolve_address(
ipaddr: str, *args: Any, **kwargs: Any
) -> dns.resolver.Answer:
"""Use a resolver to run a reverse query for PTR records.
See :py:func:`dns.asyncresolver.Resolver.resolve_address` for more
information on the parameters.
"""
return await get_default_resolver().resolve_address(ipaddr, *args, **kwargs)
async def resolve_name(
name: Union[dns.name.Name, str], family: int = socket.AF_UNSPEC, **kwargs: Any
) -> dns.resolver.HostAnswers:
"""Use a resolver to asynchronously query for address records.
See :py:func:`dns.asyncresolver.Resolver.resolve_name` for more
information on the parameters.
"""
return await get_default_resolver().resolve_name(name, family, **kwargs)
async def canonical_name(name: Union[dns.name.Name, str]) -> dns.name.Name:
"""Determine the canonical name of *name*.
See :py:func:`dns.resolver.Resolver.canonical_name` for more
information on the parameters and possible exceptions.
"""
return await get_default_resolver().canonical_name(name)
async def try_ddr(timeout: float = 5.0) -> None:
"""Try to update the default resolver's nameservers using Discovery of Designated
Resolvers (DDR). If successful, the resolver will subsequently use
DNS-over-HTTPS or DNS-over-TLS for future queries.
See :py:func:`dns.resolver.Resolver.try_ddr` for more information.
"""
return await get_default_resolver().try_ddr(timeout)
async def zone_for_name(
name: Union[dns.name.Name, str],
rdclass: dns.rdataclass.RdataClass = dns.rdataclass.IN,
tcp: bool = False,
resolver: Optional[Resolver] = None,
backend: Optional[dns.asyncbackend.Backend] = None,
) -> dns.name.Name:
"""Find the name of the zone which contains the specified name.
See :py:func:`dns.resolver.Resolver.zone_for_name` for more
information on the parameters and possible exceptions.
"""
if isinstance(name, str):
name = dns.name.from_text(name, dns.name.root)
if resolver is None:
resolver = get_default_resolver()
if not name.is_absolute():
raise NotAbsolute(name)
while True:
try:
answer = await resolver.resolve(
name, dns.rdatatype.SOA, rdclass, tcp, backend=backend
)
assert answer.rrset is not None
if answer.rrset.name == name:
return name
# otherwise we were CNAMEd or DNAMEd and need to look higher
except (NXDOMAIN, NoAnswer):
pass
try:
name = name.parent()
except dns.name.NoParent: # pragma: no cover
raise NoRootSOA
async def make_resolver_at(
where: Union[dns.name.Name, str],
port: int = 53,
family: int = socket.AF_UNSPEC,
resolver: Optional[Resolver] = None,
) -> Resolver:
"""Make a stub resolver using the specified destination as the full resolver.
*where*, a ``dns.name.Name`` or ``str`` the domain name or IP address of the
full resolver.
*port*, an ``int``, the port to use. If not specified, the default is 53.
*family*, an ``int``, the address family to use. This parameter is used if
*where* is not an address. The default is ``socket.AF_UNSPEC`` in which case
the first address returned by ``resolve_name()`` will be used, otherwise the
first address of the specified family will be used.
*resolver*, a ``dns.asyncresolver.Resolver`` or ``None``, the resolver to use for
resolution of hostnames. If not specified, the default resolver will be used.
Returns a ``dns.resolver.Resolver`` or raises an exception.
"""
if resolver is None:
resolver = get_default_resolver()
nameservers: List[Union[str, dns.nameserver.Nameserver]] = []
if isinstance(where, str) and dns.inet.is_address(where):
nameservers.append(dns.nameserver.Do53Nameserver(where, port))
else:
answers = await resolver.resolve_name(where, family)
for address in answers.addresses():
nameservers.append(dns.nameserver.Do53Nameserver(address, port))
res = dns.asyncresolver.Resolver(configure=False)
res.nameservers = nameservers
return res
async def resolve_at(
where: Union[dns.name.Name, str],
qname: Union[dns.name.Name, str],
rdtype: Union[dns.rdatatype.RdataType, str] = dns.rdatatype.A,
rdclass: Union[dns.rdataclass.RdataClass, str] = dns.rdataclass.IN,
tcp: bool = False,
source: Optional[str] = None,
raise_on_no_answer: bool = True,
source_port: int = 0,
lifetime: Optional[float] = None,
search: Optional[bool] = None,
backend: Optional[dns.asyncbackend.Backend] = None,
port: int = 53,
family: int = socket.AF_UNSPEC,
resolver: Optional[Resolver] = None,
) -> dns.resolver.Answer:
"""Query nameservers to find the answer to the question.
This is a convenience function that calls ``dns.asyncresolver.make_resolver_at()``
to make a resolver, and then uses it to resolve the query.
See ``dns.asyncresolver.Resolver.resolve`` for more information on the resolution
parameters, and ``dns.asyncresolver.make_resolver_at`` for information about the
resolver parameters *where*, *port*, *family*, and *resolver*.
If making more than one query, it is more efficient to call
``dns.asyncresolver.make_resolver_at()`` and then use that resolver for the queries
instead of calling ``resolve_at()`` multiple times.
"""
res = await make_resolver_at(where, port, family, resolver)
return await res.resolve(
qname,
rdtype,
rdclass,
tcp,
source,
raise_on_no_answer,
source_port,
lifetime,
search,
backend,
)
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