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Diffstat (limited to 'slixmpp/xmlstream/resolver.py')
| -rw-r--r-- | slixmpp/xmlstream/resolver.py | 333 |
1 files changed, 333 insertions, 0 deletions
diff --git a/slixmpp/xmlstream/resolver.py b/slixmpp/xmlstream/resolver.py new file mode 100644 index 00000000..ed899569 --- /dev/null +++ b/slixmpp/xmlstream/resolver.py @@ -0,0 +1,333 @@ +# -*- encoding: utf-8 -*- + +""" + slixmpp.xmlstream.dns + ~~~~~~~~~~~~~~~~~~~~~~~ + + :copyright: (c) 2012 Nathanael C. Fritz + :license: MIT, see LICENSE for more details +""" + +import socket +import logging +import random + + +log = logging.getLogger(__name__) + + +#: Global flag indicating the availability of the ``dnspython`` package. +#: Installing ``dnspython`` can be done via: +#: +#: .. code-block:: sh +#: +#: pip install dnspython +#: +#: For Python3, installation may require installing from source using +#: the ``python3`` branch: +#: +#: .. code-block:: sh +#: +#: git clone http://github.com/rthalley/dnspython +#: cd dnspython +#: git checkout python3 +#: python3 setup.py install +DNSPYTHON_AVAILABLE = False +try: + import dns.resolver + DNSPYTHON_AVAILABLE = True +except ImportError as e: + log.debug("Could not find dnspython package. " + \ + "Not all features will be available") + + +def default_resolver(): + """Return a basic DNS resolver object. + + :returns: A :class:`dns.resolver.Resolver` object if dnspython + is available. Otherwise, ``None``. + """ + if DNSPYTHON_AVAILABLE: + return dns.resolver.get_default_resolver() + return None + + +def resolve(host, port=None, service=None, proto='tcp', + resolver=None, use_ipv6=True, use_dnspython=True): + """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 dnspython 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_dnspython: Optionally control if dnspython 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:`dns.resolver.Resolver` + :type use_ipv6: bool + :type use_dnspython: bool + + :return: An iterable of IP address, port pairs in the order + dictated by SRV priorities and weights, if applicable. + """ + + if not use_dnspython: + if DNSPYTHON_AVAILABLE: + log.debug("DNS: Not using dnspython, but dnspython is installed.") + else: + log.debug("DNS: Not using dnspython.") + + if not use_ipv6: + log.debug("DNS: Use of IPv6 has been disabled.") + + if resolver is None and DNSPYTHON_AVAILABLE and use_dnspython: + resolver = dns.resolver.get_default_resolver() + + # 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. + ipv4 = socket.inet_aton(host) + yield (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'): + ipv6 = socket.inet_pton(socket.AF_INET6, host) + yield (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 = get_SRV(host, port, service, proto, + resolver=resolver, + use_dnspython=use_dnspython) + + for host, port in hosts: + results = [] + if host == 'localhost': + if use_ipv6: + results.append((host, '::1', port)) + results.append((host, '127.0.0.1', port)) + if use_ipv6: + for address in get_AAAA(host, resolver=resolver, + use_dnspython=use_dnspython): + results.append((host, address, port)) + for address in get_A(host, resolver=resolver, + use_dnspython=use_dnspython): + results.append((host, address, port)) + + for host, address, port in results: + yield host, address, port + + +def get_A(host, resolver=None, use_dnspython=True): + """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_dnspython: Optionally control if dnspython is used to make + the DNS queries instead of the built-in DNS + library. + + :type host: string + :type resolver: :class:`dns.resolver.Resolver` or ``None`` + :type use_dnspython: bool + + :return: A list of IPv4 literals. + """ + log.debug("DNS: Querying %s for A records." % host) + + # If not using dnspython, attempt lookup using the OS level + # getaddrinfo() method. + if resolver is None or not use_dnspython: + try: + recs = socket.getaddrinfo(host, None, socket.AF_INET, + socket.SOCK_STREAM) + return [rec[4][0] for rec in recs] + except socket.gaierror: + log.debug("DNS: Error retreiving A address info for %s." % host) + return [] + + # Using dnspython: + try: + recs = resolver.query(host, dns.rdatatype.A) + return [rec.to_text() for rec in recs] + except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer): + log.debug("DNS: No A records for %s" % host) + return [] + except dns.exception.Timeout: + log.debug("DNS: A record resolution timed out for %s" % host) + return [] + except dns.exception.DNSException as e: + log.debug("DNS: Error querying A records for %s" % host) + log.exception(e) + return [] + + +def get_AAAA(host, resolver=None, use_dnspython=True): + """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_dnspython: Optionally control if dnspython is used to make + the DNS queries instead of the built-in DNS + library. + + :type host: string + :type resolver: :class:`dns.resolver.Resolver` or ``None`` + :type use_dnspython: bool + + :return: A list of IPv6 literals. + """ + log.debug("DNS: Querying %s for AAAA records." % host) + + # If not using dnspython, attempt lookup using the OS level + # getaddrinfo() method. + if resolver is None or not use_dnspython: + if not socket.has_ipv6: + log.debug("Unable to query %s for AAAA records: IPv6 is not supported", host) + return [] + try: + recs = socket.getaddrinfo(host, None, socket.AF_INET6, + socket.SOCK_STREAM) + return [rec[4][0] for rec in recs] + except (OSError, socket.gaierror): + log.debug("DNS: Error retreiving AAAA address " + \ + "info for %s." % host) + return [] + + # Using dnspython: + try: + recs = resolver.query(host, dns.rdatatype.AAAA) + return [rec.to_text() for rec in recs] + except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer): + log.debug("DNS: No AAAA records for %s" % host) + return [] + except dns.exception.Timeout: + log.debug("DNS: AAAA record resolution timed out for %s" % host) + return [] + except dns.exception.DNSException as e: + log.debug("DNS: Error querying AAAA records for %s" % host) + log.exception(e) + return [] + + +def get_SRV(host, port, service, proto='tcp', resolver=None, use_dnspython=True): + """Perform SRV record resolution for a given host. + + .. note:: + + This function requires the use of the ``dnspython`` package. Calling + :func:`get_SRV` without ``dnspython`` 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:`dns.resolver.Resolver` + + :return: A list of hostname, port pairs in the order dictacted + by SRV priorities and weights. + """ + if resolver is None or not use_dnspython: + log.warning("DNS: dnspython not found. Can not use SRV lookup.") + return [(host, port)] + + log.debug("DNS: Querying SRV records for %s" % host) + try: + recs = resolver.query('_%s._%s.%s' % (service, proto, host), + dns.rdatatype.SRV) + except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer): + log.debug("DNS: No SRV records for %s." % host) + return [(host, port)] + except dns.exception.Timeout: + log.debug("DNS: SRV record resolution timed out for %s." % host) + return [(host, port)] + except dns.exception.DNSException as e: + log.debug("DNS: Error querying SRV records for %s." % host) + log.exception(e) + return [(host, port)] + + if len(recs) == 1 and recs[0].target == '.': + return [(host, port)] + + answers = {} + 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.target.to_text() + if host.endswith('.'): + host = host[:-1] + sorted_recs.append((host, rec.port)) + answers[priority].remove(rec) + break + + return sorted_recs |