docs: def send(self, message):
          """
          Sends a MESSAGE frame to an eligible subscriber connection.
  
          Note that this method will modify the incoming message object to 
          add a message-id header (if not present) and to change the command
          to 'MESSAGE' (if it is not).
  
          @param message: The message frame.
          @type message: C{stompclient.frame.Frame}
          """
          dest = message.headers.get('destination')
          if not dest:
              raise ValueError(
                  "Cannot send frame with no destination: %s" % message)
  
          message.cmd = 'message'
  
          message.headers.setdefault('message-id', str(uuid.uuid4()))
  
          # Grab all subscribers for this destination that do not have pending
          # frames
          subscribers = [s for s in self._queues[dest]
                         if s not in self._pending]
  
          if not subscribers:
              self.log.debug(
                  "No eligible subscribers; adding message %s to queue %s" % (message, dest))
              self.store.enqueue(dest, message)
          else:
              selected = self.subscriber_scheduler.choice(subscribers, message)
              self.log.debug("Delivering message %s to subscriber %s" %
                             (message, selected))
              self._send_frame(selected, message)