code: func (c *client) shutdown() {
  	c.closeLock.Lock()
  	defer c.closeLock.Unlock()
  
  	if c.closed {
  		return
  	}
  	c.closed = true
  	close(c.closedCh)
  
  	if c.ipv4conn != nil {
  		c.ipv4conn.Close()
  	}
  	if c.ipv6conn != nil {
  		c.ipv6conn.Close()
  	}
  }
docs: // Shutdown client will close currently open connections & channel