datasources: querier: better handling of timestamps (#108973)

* query: support query-local timestamps

* make it configurable

* lint fix

* corrected unit test

* fixed unit test

pkg/expr/query_convert.go

@@ -0,0 +1,51 @@
+package expr
+
+import (
+	"encoding/json"
+	"strconv"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	data "github.com/grafana/grafana-plugin-sdk-go/experimental/apis/data/v0alpha1"
+)
+
+func convertBackendQueryToDataQuery(q backend.DataQuery) (data.DataQuery, error) {
+	// we first restore it from the raw json data,
+	// this should take care of all datasource-specific (for example, specific
+	// for prometheus or loki) fields
+	var dataQuery data.DataQuery
+	err := json.Unmarshal(q.JSON, &dataQuery)
+	if err != nil {
+		return data.DataQuery{}, err
+	}
+
+	// then we override the result with values that are available as fields in backend.DataQuery
+	dataQuery.RefID = q.RefID
+	dataQuery.QueryType = q.QueryType
+	dataQuery.MaxDataPoints = q.MaxDataPoints
+	dataQuery.IntervalMS = float64(q.Interval.Nanoseconds()) / 1000000.0
+	dataQuery.TimeRange = &data.TimeRange{
+		From: strconv.FormatInt(q.TimeRange.From.UnixMilli(), 10),
+		To:   strconv.FormatInt(q.TimeRange.To.UnixMilli(), 10),
+	}
+
+	return dataQuery, nil
+}
+
+func ConvertBackendRequestToDataRequest(req *backend.QueryDataRequest) (*data.QueryDataRequest, error) {
+	k8sReq := &data.QueryDataRequest{
+		// `backend.QueryDataRequest` does not have a concept of a top-level global from/to.
+		// timeRanges are always inside the queries,
+		// so we leave them empty here too.
+	}
+
+	for _, q := range req.Queries {
+		dataQuery, err := convertBackendQueryToDataQuery(q)
+		if err != nil {
+			return nil, err
+		}
+
+		k8sReq.Queries = append(k8sReq.Queries, dataQuery)
+	}
+
+	return k8sReq, nil
+}