code: func (l *Listener) closeSession(remote net.Addr) (ret bool) {
  	l.sessionLock.Lock()
  	defer l.sessionLock.Unlock()
  	if _, ok := l.sessions[remote.String()]; ok {
  		delete(l.sessions, remote.String())
  		return true
  	}
  	return false
  }
docs: // closeSession notify the listener that a session has closed