Add better DNS resolver wrapper.

2 files changed, 314 insertions, 97 deletions

diff --git a/sleekxmpp/xmlstream/resolver.py b/sleekxmpp/xmlstream/resolver.py
new file mode 100644
index 00000000..ecb76519
--- /dev/null
+++ b/sleekxmpp/xmlstream/resolver.py
@@ -0,0 +1,287 @@
+# -*- encoding: utf-8 -*-
+
+"""
+    sleekxmpp.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
+USE_DNSPYTHON = False
+try:
+    import dns.resolver
+    USE_DNSPYTHON = 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 USE_DNSPYTHON:
+        return dns.resolver.get_default_resolver()
+    return None
+
+
+def resolve(host, port=None, service=None, proto='tcp', resolver=None):
+    """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.
+
+    :type     host: string
+    :type     port: int
+    :type  service: string
+    :type    proto: string
+    :type resolver: :class:`dns.resolver.Resolver`
+
+    :return: An iterable of IP address, port pairs in the order
+             dictated by SRV priorities and weights, if applicable.
+    """
+    if resolver is None 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_pton(socket.AF_INET, host)
+        yield [(host, port)]
+    except socket.error:
+        pass
+
+    try:
+        # Likewise, If `host` is an IPv6 literal, we can return it immediately.
+        ipv6 = socket.inet_pton(socket.AF_INET6, host)
+        yield [(host, port)]
+    except socket.error:
+        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)
+
+    for host, port in hosts:
+        results = []
+        for address in get_AAAA(host, resolver=resolver):
+            results.append((address, port))
+        for address in get_A(host, resolver=resolver):
+            results.append((address, port))
+
+        for address, port in results:
+            yield address, port
+
+
+def get_A(host, resolver=None):
+    """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.
+
+    :type     host: string
+    :type resolver: :class:`dns.resolver.Resolver` or ``None``
+
+    :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:
+        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):
+    """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.
+
+    :type     host: string
+    :type resolver: :class:`dns.resolver.Resolver` or ``None``
+
+    :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:
+        try:
+            recs = socket.getaddrinfo(host, None, socket.AF_INET6,
+                                                  socket.SOCK_STREAM)
+            return [rec[4][0] for rec in recs]
+        except 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):
+    """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:
+        return [(host, port)]
+
+    log.debug("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]
+                    sorted_recs.append((rec.target.to_text(), rec.port))
+                    answers[priority].remove(rec)
+                    break
+
+    return sorted_recs
diff --git a/sleekxmpp/xmlstream/xmlstream.py b/sleekxmpp/xmlstream/xmlstream.py
index 45f27929..31ca9cfe 100644
--- a/sleekxmpp/xmlstream/xmlstream.py
+++ b/sleekxmpp/xmlstream/xmlstream.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
     sleekxmpp.xmlstream.xmlstream
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -39,19 +38,13 @@ from sleekxmpp.xmlstream import Scheduler, tostring
 from sleekxmpp.xmlstream.stanzabase import StanzaBase, ET, ElementBase
 from sleekxmpp.xmlstream.handler import Waiter, XMLCallback
 from sleekxmpp.xmlstream.matcher import MatchXMLMask
+from sleekxmpp.xmlstream.resolver import resolve, default_resolver
 
 # In Python 2.x, file socket objects are broken. A patched socket
 # wrapper is provided for this case in filesocket.py.
 if sys.version_info < (3, 0):
     from sleekxmpp.xmlstream.filesocket import FileSocket, Socket26
 
-try:
-    import dns.resolver
-except ImportError:
-    DNSPYTHON = False
-else:
-    DNSPYTHON = True
-
 
 #: The time in seconds to wait before timing out waiting for response stanzas.
 RESPONSE_TIMEOUT = 30
@@ -306,6 +299,11 @@ class XMLStream(object):
         #: A list of DNS results that have not yet been tried.
         self.dns_answers = []
 
+        #: The service name to check with DNS SRV records. For
+        #: example, setting this to ``'xmpp-client'`` would query the
+        #: ``_xmpp-client._tcp`` service.
+        self.dns_service = None
+
         self.add_event_handler('connected', self._handle_connected)
         self.add_event_handler('session_start', self._start_keepalive)
         self.add_event_handler('disconnected', self._end_keepalive)
@@ -445,25 +443,10 @@ class XMLStream(object):
                 self.stop.set()
                 return False
 
-        try:
-            # Look for IPv6 addresses, in addition to IPv4
-            for res in Socket.getaddrinfo(self.address[0],
-                                          int(self.address[1]),
-                                          0,
-                                          Socket.SOCK_STREAM):
-                log.debug("Trying: %s", res[-1])
-                af, sock_type, proto, canonical, sock_addr = res
-                try:
-                    self.socket = self.socket_class(af, sock_type, proto)
-                    break
-                except Socket.error:
-                    log.debug("Could not open IPv%s socket." % proto)
-        except Socket.gaierror:
-            log.warning("Socket could not be opened: no connectivity" + \
-                        " or wrong IP versions.")
-            if reattempt:
-                self.reconnect_delay = delay
-            return False
+        af = Socket.AF_INET
+        if ':' in self.address[0]:
+            af = Socket.AF_INET6
+        self.socket = self.socket_class(af, Socket.SOCK_STREAM)
 
         self.configure_socket()
 
@@ -511,7 +494,10 @@ class XMLStream(object):
         except Socket.error as serr:
             error_msg = "Could not connect to %s:%s. Socket Error #%s: %s"
             self.event('socket_error', serr, direct=True)
-            log.error(error_msg, self.address[0], self.address[1],
+            domain = self.address[0]
+            if ':' in domain:
+                domain = '[%s]' % domain
+            log.error(error_msg, domain, self.address[1],
                                  serr.errno, serr.strerror)
             if reattempt:
                 self.reconnect_delay = delay
@@ -915,50 +901,11 @@ class XMLStream(object):
         """
         if port is None:
             port = self.default_port
-        if DNSPYTHON:
-            resolver = dns.resolver.get_default_resolver()
-            self.configure_dns(resolver, domain=domain, port=port)
-
-            v4_answers = []
-            v6_answers = []
-            answers = []
-
-            try:
-                log.debug("Querying A records for %s" % domain)
-                v4_answers = resolver.query(domain, dns.rdatatype.A)
-            except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
-                log.warning("No A records for %s", domain)
-                v4_answers = [((domain, port), 0, 0)]
-            except dns.exception.Timeout:
-                log.warning("DNS resolution timed out " + \
-                            "for A record of %s", domain)
-                v4_answers = [((domain, port), 0, 0)]
-            else:
-                for ans in v4_answers:
-                    log.debug("Found A record: %s", ans.address)
-                    answers.append(((ans.address, port), 0, 0))
-
-            try:
-                log.debug("Querying AAAA records for %s" % domain)
-                v6_answers = resolver.query(domain, dns.rdatatype.AAAA)
-            except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
-                log.warning("No AAAA records for %s", domain)
-                v6_answers = [((domain, port), 0, 0)]
-            except dns.exception.Timeout:
-                log.warning("DNS resolution timed out " + \
-                            "for AAAA record of %s", domain)
-                v6_answers = [((domain, port), 0, 0)]
-            else:
-                for ans in v6_answers:
-                    log.debug("Found AAAA record: %s", ans.address)
-                    answers.append(((ans.address, port), 0, 0))
+            
+        resolver = default_resolver()
+        self.configure_dns(resolver, domain=domain, port=port)
 
-            return answers
-        else:
-            log.warning("dnspython is not installed -- " + \
-                        "relying on OS A/AAAA record resolution")
-            self.configure_dns(None, domain=domain, port=port)
-            return [((domain, port), 0, 0)]
+        return resolve(domain, port, service=self.dns_service, resolver=resolver)
 
     def pick_dns_answer(self, domain, port=None):
         """Pick a server and port from DNS answers.
@@ -971,33 +918,16 @@ class XMLStream(object):
         """
         if not self.dns_answers:
             self.dns_answers = self.get_dns_records(domain, port)
-        addresses = {}
-        intmax = 0
-        topprio = 65535
-        for answer in self.dns_answers:
-            topprio = min(topprio, answer[1])
-        for answer in self.dns_answers:
-            if answer[1] == topprio:
-                intmax += answer[2]
-                addresses[intmax] = answer[0]
-
-        #python3 returns a generator for dictionary keys
-        items = [x for x in addresses.keys()]
-        items.sort()
-
-        address = (domain, port)
-        picked = random.randint(0, intmax)
-        for item in items:
-            if picked <= item:
-                address = addresses[item]
-                break
-        for idx, answer in enumerate(self.dns_answers):
-            if self.dns_answers[0] == address:
-                self.dns_answers.pop(idx)
-                break
-        log.debug("Trying to connect to %s:%s", *address)
-        return address
 
+        try:
+            if sys.version_info < (3, 0):
+                return self.dns_answers.next()
+            else:
+                return next(self.dns_answers)
+        except StopIteration:
+            self.dns_answers = None
+            return (domain, port)
+            
     def add_event_handler(self, name, pointer,
                           threaded=False, disposable=False):
         """Add a custom event handler that will be executed whenever