code: func (p *Publisher) SubscribeTopicWithBuffer(topic topicFunc, buffer int) chan interface{} {
  	ch := make(chan interface{}, buffer)
  	p.m.Lock()
  	p.subscribers[ch] = topic
  	p.m.Unlock()
  	return ch
  }
docs: // SubscribeTopicWithBuffer adds a new subscriber that filters messages sent by a topic.
  // The returned channel has a buffer of the specified size.