code: func (a *HistoricalApi) processMetricNamesRequest(key core.HistoricalKey, response *restful.Response) {
  	if resp, err := a.historicalSource.GetMetricNames(key); err != nil {
  		response.WriteError(http.StatusInternalServerError, err)
  	} else {
  		response.WriteEntity(resp)
  	}
  }
docs: // processMetricNamesRequest retrieves the available metrics for the object at the specified key.