code: func newMeteredMsgWriter(rw p2p.MsgReadWriter) p2p.MsgReadWriter {
  	if !metrics.Enabled {
  		return rw
  	}
  	return &meteredMsgReadWriter{MsgReadWriter: rw}
  }
docs: // newMeteredMsgWriter wraps a p2p MsgReadWriter with metering support. If the
  // metrics system is disabled, this function returns the original object.