code: func (c *PCPClient) Length() int {
  	var (
  		InstanceLength = Instance1Length
  		MetricLength   = Metric1Length
  	)
  
  	if c.r.version2 {
  		InstanceLength = Instance2Length
  		MetricLength = Metric2Length
  	}
  
  	return HeaderLength +
  		(c.tocCount() * TocLength) +
  		(c.r.InstanceCount() * InstanceLength) +
  		(c.r.InstanceDomainCount() * InstanceDomainLength) +
  		(c.r.MetricCount() * MetricLength) +
  		(c.r.ValuesCount() * ValueLength) +
  		(c.r.StringCount() * StringLength)
  }
docs: // Length returns the byte length of data in the mmv file written by the current writer