code: def start(self, xmlstream):
          
  
          if self.running:
              raise RuntimeError("already started")
  
          self._start_prepare(xmlstream, self.recv_stanza)
          self._closed = False
          self._start_commit(xmlstream)
docs: Start or resume the stanza stream on the given
          :class:`aioxmpp.protocol.XMLStream` `xmlstream`.
  
          This starts the main broker task, registers stanza classes at the
          `xmlstream` .