# slixmpp.xmlstream.dns # ~~~~~~~~~~~~~~~~~~~~~~~ # :copyright: (c) 2012 Nathanael C. Fritz # :license: MIT, see LICENSE for more details import socket import sys import logging import random from asyncio import Future, AbstractEventLoop from typing import Optional, Tuple, Dict, List, Iterable, cast from slixmpp.types import Protocol log = logging.getLogger(__name__) class AnswerProtocol(Protocol): host: str priority: int weight: int port: int class ResolverProtocol(Protocol): def query(self, query: str, querytype: str) -> Future: ... #: Global flag indicating the availability of the ``aiodns`` package. #: Installing ``aiodns`` can be done via: #: #: .. code-block:: sh #: #: pip install aiodns AIODNS_AVAILABLE = False try: import aiodns AIODNS_AVAILABLE = True except ImportError: log.debug("Could not find aiodns package. " "Not all features will be available") def default_resolver(loop: AbstractEventLoop) -> Optional[ResolverProtocol]: """Return a basic DNS resolver object. :returns: A :class:`aiodns.DNSResolver` object if aiodns is available. Otherwise, ``None``. """ if AIODNS_AVAILABLE: return aiodns.DNSResolver(loop=loop, tries=1, timeout=1.0) return None async def resolve(host: str, port: int, *, loop: AbstractEventLoop, service: Optional[str] = None, proto: str = 'tcp', resolver: Optional[ResolverProtocol] = None, use_ipv6: bool = True, use_aiodns: bool = True) -> List[Tuple[str, str, int]]: """Peform DNS resolution for a given hostname. Resolution may perform SRV record lookups if a service and protocol are specified. The returned addresses will be sorted according to the SRV priorities and weights. If no resolver is provided, the aiodns resolver will be used if available. Otherwise the built-in socket facilities will be used, but those do not provide SRV support. If SRV records were used, queries to resolve alternative hosts will be made as needed instead of all at once. :param host: The hostname to resolve. :param port: A default port to connect with. SRV records may dictate use of a different port. :param service: Optional SRV service name without leading underscore. :param proto: Optional SRV protocol name without leading underscore. :param resolver: Optionally provide a DNS resolver object that has been custom configured. :param use_ipv6: Optionally control the use of IPv6 in situations where it is either not available, or performance is degraded. Defaults to ``True``. :param use_aiodns: Optionally control if aiodns is used to make the DNS queries instead of the built-in DNS library. :type host: string :type port: int :type service: string :type proto: string :type resolver: :class:`aiodns.DNSResolver` :type use_ipv6: bool :type use_aiodns: bool :return: An iterable of IP address, port pairs in the order dictated by SRV priorities and weights, if applicable. """ if not use_aiodns: if AIODNS_AVAILABLE: log.debug("DNS: Not using aiodns, but aiodns is installed.") else: log.debug("DNS: Not using aiodns.") if not use_ipv6: log.debug("DNS: Use of IPv6 has been disabled.") if resolver is None and use_aiodns: resolver = default_resolver(loop=loop) # An IPv6 literal is allowed to be enclosed in square brackets, but # the brackets must be stripped in order to process the literal; # otherwise, things break. host = host.strip('[]') try: # If `host` is an IPv4 literal, we can return it immediately. socket.inet_aton(host) return [(host, host, port)] except socket.error: pass if use_ipv6: try: # Likewise, If `host` is an IPv6 literal, we can return # it immediately. if hasattr(socket, 'inet_pton'): socket.inet_pton(socket.AF_INET6, host) return [(host, host, port)] except (socket.error, ValueError): pass # If no service was provided, then we can just do A/AAAA lookups on the # provided host. Otherwise we need to get an ordered list of hosts to # resolve based on SRV records. if not service: hosts = [(host, port)] else: hosts = await get_SRV(host, port, service, proto, resolver=resolver, use_aiodns=use_aiodns) if not hosts: hosts = [(host, port)] results = [] for host, port in hosts: if host == 'localhost': if use_ipv6: results.append((host, '::1', port)) results.append((host, '127.0.0.1', port)) if use_ipv6: aaaa = await get_AAAA(host, resolver=resolver, use_aiodns=use_aiodns, loop=loop) for address in aaaa: results.append((host, address, port)) a = await get_A(host, resolver=resolver, use_aiodns=use_aiodns, loop=loop) for address in a: results.append((host, address, port)) return results async def get_A(host: str, *, loop: AbstractEventLoop, resolver: Optional[ResolverProtocol] = None, use_aiodns: bool = True) -> List[str]: """Lookup DNS A records for a given host. If ``resolver`` is not provided, or is ``None``, then resolution will be performed using the built-in :mod:`socket` module. :param host: The hostname to resolve for A record IPv4 addresses. :param resolver: Optional DNS resolver object to use for the query. :param use_aiodns: Optionally control if aiodns is used to make the DNS queries instead of the built-in DNS library. :type host: string :type resolver: :class:`aiodns.DNSResolver` or ``None`` :type use_aiodns: bool :return: A list of IPv4 literals. """ log.debug("DNS: Querying %s for A records." % host) # If not using aiodns, attempt lookup using the OS level # getaddrinfo() method. if resolver is None or not use_aiodns: try: inet_recs = await loop.getaddrinfo(host, None, family=socket.AF_INET, type=socket.SOCK_STREAM) return [rec[4][0] for rec in inet_recs] except socket.gaierror: log.debug("DNS: Error retrieving A address info for %s." % host) return [] # Using aiodns: future = resolver.query(host, 'A') try: recs = cast(Iterable[AnswerProtocol], await future) except Exception as e: log.debug('DNS: Exception while querying for %s A records: %s', host, e) recs = [] return [rec.host for rec in recs] async def get_AAAA(host: str, *, loop: AbstractEventLoop, resolver: Optional[ResolverProtocol] = None, use_aiodns: bool = True) -> List[str]: """Lookup DNS AAAA records for a given host. If ``resolver`` is not provided, or is ``None``, then resolution will be performed using the built-in :mod:`socket` module. :param host: The hostname to resolve for AAAA record IPv6 addresses. :param resolver: Optional DNS resolver object to use for the query. :param use_aiodns: Optionally control if aiodns is used to make the DNS queries instead of the built-in DNS library. :type host: string :type resolver: :class:`aiodns.DNSResolver` or ``None`` :type use_aiodns: bool :return: A list of IPv6 literals. """ log.debug("DNS: Querying %s for AAAA records." % host) # If not using aiodns, attempt lookup using the OS level # getaddrinfo() method. if resolver is None or not use_aiodns: if not socket.has_ipv6: log.debug("DNS: Unable to query %s for AAAA records: IPv6 is not supported", host) return [] try: inet_recs = await loop.getaddrinfo(host, None, family=socket.AF_INET6, type=socket.SOCK_STREAM) return [rec[4][0] for rec in inet_recs] except (OSError, socket.gaierror): log.debug("DNS: Error retrieving AAAA address " + \ "info for %s." % host) return [] # Using aiodns: future = resolver.query(host, 'AAAA') try: recs = cast(Iterable[AnswerProtocol], await future) except Exception as e: log.debug('DNS: Exception while querying for %s AAAA records: %s', host, e) recs = [] return [rec.host for rec in recs] async def get_SRV(host: str, port: int, service: str, proto: str = 'tcp', resolver: Optional[ResolverProtocol] = None, use_aiodns: bool = True) -> List[Tuple[str, int]]: """Perform SRV record resolution for a given host. .. note:: This function requires the use of the ``aiodns`` package. Calling :func:`get_SRV` without ``aiodns`` will return the provided host and port without performing any DNS queries. :param host: The hostname to resolve. :param port: A default port to connect with. SRV records may dictate use of a different port. :param service: Optional SRV service name without leading underscore. :param proto: Optional SRV protocol name without leading underscore. :param resolver: Optionally provide a DNS resolver object that has been custom configured. :type host: string :type port: int :type service: string :type proto: string :type resolver: :class:`aiodns.DNSResolver` :return: A list of hostname, port pairs in the order dictacted by SRV priorities and weights. """ if resolver is None or not use_aiodns: log.warning("DNS: aiodns not found. Can not use SRV lookup.") return [(host, port)] log.debug("DNS: Querying SRV records for %s" % host) try: future = resolver.query('_%s._%s.%s' % (service, proto, host), 'SRV') recs = cast(Iterable[AnswerProtocol], await future) except Exception as e: log.debug('DNS: Exception while querying for %s SRV records: %s', host, e) return [] answers: Dict[int, List[AnswerProtocol]] = {} for rec in recs: if rec.priority not in answers: answers[rec.priority] = [] if rec.weight == 0: answers[rec.priority].insert(0, rec) else: answers[rec.priority].append(rec) sorted_recs = [] for priority in sorted(answers.keys()): while answers[priority]: running_sum = 0 sums = {} for rec in answers[priority]: running_sum += rec.weight sums[running_sum] = rec selected = random.randint(0, running_sum + 1) for running_sum in sums: if running_sum >= selected: rec = sums[running_sum] host = rec.host if host.endswith('.'): host = host[:-1] sorted_recs.append((host, rec.port)) answers[priority].remove(rec) break return sorted_recs