add bytes fetched into response header

Author: yuchen-db

internal/cortex/querier/queryrange/query_range.go

@@ -473,7 +473,11 @@ func (prometheusCodec) EncodeResponse(ctx context.Context, res Response) (*http.
 	httpHeader := http.Header{
 		"Content-Type": []string{"application/json"}}
 	if queryBytesFetchedHttpHeaderValue := QueryBytesFetchedHttpHeaderValue(res); queryBytesFetchedHttpHeaderValue != nil {
+		// M3 code path
 		httpHeader[QueryBytesFetchedHeaderName] = queryBytesFetchedHttpHeaderValue
+	} else if res.(*PrometheusResponse).Data.SeriesStatsCounter != nil {
+		// Pantheon code path
+		httpHeader[QueryBytesFetchedHeaderName] = []string{strconv.FormatInt(res.(*PrometheusResponse).Data.SeriesStatsCounter.Bytes, 10)}
 	}
 	resp := http.Response{
 		Header:        httpHeader,

pkg/queryfrontend/queryinstant_codec.go

@@ -263,11 +263,17 @@ func (c queryInstantCodec) EncodeResponse(ctx context.Context, res queryrange.Re
 
 	sp.LogFields(otlog.Int("bytes", len(b)))
 
+	httpHeader := http.Header{
+		"Content-Type": []string{"application/json"}}
+	if queryBytesFetchedHttpHeaderValue := queryrange.QueryBytesFetchedHttpHeaderValue(res); queryBytesFetchedHttpHeaderValue != nil {
+		// M3 code path
+		httpHeader[queryrange.QueryBytesFetchedHeaderName] = queryBytesFetchedHttpHeaderValue
+	} else if res.(*queryrange.PrometheusInstantQueryResponse).Data.SeriesStatsCounter != nil {
+		// Pantheon code path
+		httpHeader[queryrange.QueryBytesFetchedHeaderName] = []string{strconv.FormatInt(res.(*queryrange.PrometheusInstantQueryResponse).Data.SeriesStatsCounter.Bytes, 10)}
+	}
 	resp := http.Response{
-		Header: http.Header{
-			"Content-Type":                         []string{"application/json"},
-			queryrange.QueryBytesFetchedHeaderName: queryrange.QueryBytesFetchedHttpHeaderValue(res),
-		},
+		Header:        httpHeader,
 		Body:          io.NopCloser(bytes.NewBuffer(b)),
 		StatusCode:    http.StatusOK,
 		ContentLength: int64(len(b)),