code: func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
  	_, span := trace.StartSpan(req.Context(), "elastic:PerformRequest")
  	attrs := append([]trace.Attribute(nil), t.defaultAttributes...)
  	attrs = append(attrs,
  		trace.StringAttribute("Component", "github.com/olivere/elastic/v7"),
  		trace.StringAttribute("Method", req.Method),
  		trace.StringAttribute("URL", req.URL.String()),
  		trace.StringAttribute("Hostname", req.URL.Hostname()),
  		trace.Int64Attribute("Port", atoi64(req.URL.Port())),
  	)
  	span.AddAttributes(attrs...)
  
  	var (
  		resp *http.Response
  		err  error
  	)
  	defer func() {
  		setSpanStatus(span, err)
  		span.End()
  	}()
  	if t.rt != nil {
  		resp, err = t.rt.RoundTrip(req)
  	} else {
  		resp, err = http.DefaultTransport.RoundTrip(req)
  	}
  	return resp, err
  }
docs: // RoundTrip captures the request and starts an OpenTracing span
  // for Elastic PerformRequest operation.