code: func (c *rawConnection) ClusterConfig(config ClusterConfig) {
  	select {
  	case <-c.sentClusterConfig:
  		return
  	case <-c.closed:
  		return
  	default:
  	}
  	if err := c.writeMessage(&config); err != nil {
  		c.internalClose(err)
  	}
  	close(c.sentClusterConfig)
  }
docs: // ClusterConfig sends the cluster configuration message to the peer.
  // It must be called just once (as per BEP).