Use a set to track negotiated features.

Added guards to prevent renegotiating STARTTLS or SASL in cases where
servers don't behave properly.

sleekxmpp/clientxmpp.py

@@ -83,7 +83,7 @@ class ClientXMPP(BaseXMPP):
                 "xmlns='%s'" % self.default_ns)
         self.stream_footer = "</stream:stream>"
 
-        self.features = []
+        self.features = set()
         self._stream_feature_handlers = {}
         self._stream_feature_order = []
 
@@ -273,7 +273,7 @@ class ClientXMPP(BaseXMPP):
         self.sessionstarted = False
         self.bound = False
         self.bindfail = False
-        self.features = []
+        self.features = set()
 
         def session_timeout():
             if not self.session_started_event.isSet():

sleekxmpp/features/feature_bind/bind.py

@@ -53,6 +53,8 @@ class feature_bind(base_plugin):
         self.xmpp.set_jid(response['bind']['jid'])
         self.xmpp.bound = True
 
+        self.features.add('bind')
+
         log.info("Node set to: %s" % self.xmpp.boundjid.full)
 
         if 'session' not in features['features']:

sleekxmpp/features/feature_mechanisms/mechanisms.py

@@ -90,6 +90,11 @@ class feature_mechanisms(base_plugin):
         Arguments:
             features -- The stream features stanza.
         """
+        if 'mechanisms' in self.xmpp.features:
+            # SASL authentication has already succeeded, but the
+            # server has incorrectly offered it again.
+            return False
+
         for priority, mech in self._mechanism_priorities:
             if mech in features['mechanisms']:
                 log.debug('Attempt to use SASL %s' % mech)
@@ -105,7 +110,7 @@ class feature_mechanisms(base_plugin):
     def _handle_success(self, stanza):
         """SASL authentication succeeded. Restart the stream."""
         self.xmpp.authenticated = True
-        self.xmpp.features.append('mechanisms')
+        self.xmpp.features.add('mechanisms')
         raise RestartStream()
 
     def _handle_fail(self, stanza):

sleekxmpp/features/feature_session/session.py

@@ -48,6 +48,8 @@ class feature_session(base_plugin):
         iq.enable('session')
         response = iq.send(now=True)
 
+        self.xmpp.features.add('session')
+
         log.debug("Established Session")
         self.xmpp.sessionstarted = True
         self.xmpp.session_started_event.set()

sleekxmpp/features/feature_starttls/starttls.py

@@ -48,7 +48,11 @@ class feature_starttls(base_plugin):
         Arguments:
             features -- The stream:features element.
         """
-        if not self.xmpp.use_tls:
+        if 'starttls' in self.xmpp.features:
+            # We have already negotiated TLS, but the server is
+            # offering it again, against spec.
+            return False
+        elif not self.xmpp.use_tls:
             return False
         elif self.xmpp.ssl_support:
             self.xmpp.send(features['starttls'], now=True)
@@ -62,5 +66,5 @@ class feature_starttls(base_plugin):
         """Restart the XML stream when TLS is accepted."""
         log.debug("Starting TLS")
         if self.xmpp.start_tls():
-            self.xmpp.features.append('starttls')
+            self.xmpp.features.add('starttls')
             raise RestartStream()