code: func (i *Interceptor) TagRPC(ctx context.Context, info *stats.RPCTagInfo) context.Context {
  	service, method := split(info.FullMethodName)
  
  	return context.WithValue(ctx, tagRPCKey, prometheus.Labels{
  		"fail_fast": strconv.FormatBool(info.FailFast),
  		"service":   service,
  		"handler":   method,
  	})
  }
docs: // TagRPC implements stats Handler interface.