memory (disco): added findServiceEntity helper method to get first service of a kind

src/memory/disco.py

@@ -230,6 +230,16 @@ class Discovery(object):
         log.warning(_(u"Error while requesting [%(jid)s]: %(error)s") % {'jid': entity_jid.full(),
                                                                     'error': failure_.getErrorMessage()})
 
+    def findServiceEntity(self, client, category, type_, jid_=None):
+        """Helper method to find first available entity from findServiceEntities
+
+        args are the same as for [findServiceEntities]
+        @return (jid.JID, None): found entity
+        """
+        d = self.host.findServiceEntities(client, "pubsub", "service")
+        d.addCallback(lambda entities: entities.pop() if entities else None)
+        return d
+
     def findServiceEntities(self, client, category, type_, jid_=None):
         """Return all available items of an entity which correspond to (category, type_)