code: func (c *meteredConn) Write(b []byte) (n int, err error) {
  	n, err = c.Conn.Write(b)
  	egressTrafficMeter.Mark(int64(n))
  	c.lock.RLock()
  	if c.trafficMetered {
  		c.egressMeter.Mark(int64(n))
  	}
  	c.lock.RUnlock()
  	return n, err
  }
docs: // Write delegates a network write to the underlying connection, bumping the common
  // and the peer egress traffic meters along the way.