code: func (h *baseStatsHandler) TagRPC(ctx context.Context, info *stats.RPCTagInfo) context.Context {
  	service, method := split(info.FullMethodName)
  
  	return context.WithValue(ctx, tagRPCKey, prometheus.Labels{
  		labelFailFast:        strconv.FormatBool(info.FailFast),
  		labelService:         service,
  		labelMethod:          method,
  		labelClientUserAgent: userAgent(ctx),
  	})
  }
docs: // HandleRPC implements stats Handler interface.