DNS is now properly checked and different answers are tried for each reconnect until exhausted

sleekxmpp/xmlstream/xmlstream.py

@@ -36,6 +36,13 @@ from sleekxmpp.xmlstream.matcher import MatchXMLMask
 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 = 10
@@ -51,7 +58,6 @@ SSL_SUPPORT = True
 # Maximum time to delay between connection attempts is one hour.
 RECONNECT_MAX_DELAY = 600
 
-
 log = logging.getLogger(__name__)
 
 
@@ -92,6 +98,7 @@ class XMLStream(object):
                          events to be processed.
         filesocket    -- A filesocket created from the main connection socket.
                          Required for ElementTree.iterparse.
+        default_port  -- Default port to connect to.
         namespace_map -- Optional mapping of namespaces to namespace prefixes.
         scheduler     -- A scheduler object for triggering events
                          after a given period of time.
@@ -121,6 +128,7 @@ class XMLStream(object):
         reconnect_max_delay -- Maximum time to delay between connection
                                attempts. Defaults to RECONNECT_MAX_DELAY,
                                which is one hour.
+        dns_answers     -- List of dns answers not yet used to connect.
 
     Methods:
         add_event_handler    -- Add a handler for a custom event.
@@ -177,6 +185,8 @@ class XMLStream(object):
         self.state = StateMachine(('disconnected', 'connected'))
         self.state._set_state('disconnected')
 
+        self.default_port = int(port)
+        self.default_domain = ''
         self.address = (host, int(port))
         self.filesocket = None
         self.set_socket(socket)
@@ -219,6 +229,7 @@ class XMLStream(object):
 
         self.auto_reconnect = True
         self.is_client = False
+        self.dns_answers = []
 
     def use_signals(self, signals=None):
         """
@@ -303,6 +314,10 @@ class XMLStream(object):
         """
         if host and port:
             self.address = (host, int(port))
+        try:
+            Socket.inet_aton(self.address[0])
+        except Socket.error:
+            self.default_domain = self.address[0]
 
         self.is_client = True
         # Respect previous SSL and TLS usage directives.
@@ -322,6 +337,8 @@ class XMLStream(object):
 
     def _connect(self):
         self.stop.clear()
+        if self.default_domain:
+            self.address = self.pick_dns_answer(self.default_domain, self.address[1])
         self.socket = self.socket_class(Socket.AF_INET, Socket.SOCK_STREAM)
         self.socket.settimeout(None)
 
@@ -639,6 +656,51 @@ class XMLStream(object):
             idx += 1
         return False
 
+    def get_dns_records(self, domain, port=None):
+        if port is None:
+            port = self.default_port
+        if DNSPYTHON:
+            try:
+                answers = dns.resolver.query(domain, dns.rdatatype.A)
+            except dns.resolver.NXDOMAIN, dns.resolver.NoAnswer:
+                log.warning("No A records for %s" % domain)
+            except dns.exception.Timeout:
+                log.warning("DNS resolution timed out for A record of %s" % domain)
+            answers = [((answer.address, port), 0, 0) for answer in answers]
+            return answers
+        else:
+            log.warning("dnspython is not installed -- relying on OS A record resolution")
+            return [((domain, port), 0, 0)]
+
+    def pick_dns_answer(self, domain, port=None):
+        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()
+
+        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:
+                break
+        self.dns_answers.pop(idx)
+        log.debug("Trying to connect to %s:%s" % address)
+        return address
+
     def add_event_handler(self, name, pointer,
                           threaded=False, disposable=False):
         """