Loki: Adds a suggestions resource call that inject scopes for finding label/labelvalues (#96025)

Signed-off-by: bergquist <carl.bergquist@gmail.com>
Co-authored-by: Sven Grossmann <sven.grossmann@grafana.com>

pkg/tsdb/loki/loki.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"regexp"
+	"strings"
 	"sync"
 	"time"
 
@@ -131,13 +132,30 @@ func callResource(ctx context.Context, req *backend.CallResourceRequest, sender
 
 	api := newLokiAPI(dsInfo.HTTPClient, dsInfo.URL, plog, tracer, false)
 
-	rawLokiResponse, err := api.RawQuery(ctx, lokiURL)
-	if err != nil {
-		span.RecordError(err)
-		span.SetStatus(codes.Error, err.Error())
-		plog.Error("Failed resource call from loki", "err", err, "url", lokiURL)
-		return err
+	var rawLokiResponse RawLokiResponse
+	var err error
+
+	// suggestions is a resource endpoint that will return label and label value suggestions based
+	// on queries and the existing scope. By moving this to the backend we can use the logql parser to
+	// rewrite queries safely.
+	if req.Method == http.MethodPost && strings.EqualFold(req.Path, "suggestions") {
+		rawLokiResponse, err = GetSuggestions(ctx, api, req)
+		if err != nil {
+			span.RecordError(err)
+			span.SetStatus(codes.Error, err.Error())
+			plog.FromContext(ctx).Error("Failed to get suggestions from loki", "err", err)
+			return err
+		}
+	} else {
+		rawLokiResponse, err = api.RawQuery(ctx, lokiURL)
+		if err != nil {
+			span.RecordError(err)
+			span.SetStatus(codes.Error, err.Error())
+			plog.Error("Failed resource call from loki", "err", err, "url", lokiURL)
+			return err
+		}
 	}
+
 	respHeaders := map[string][]string{
 		"content-type": {"application/json"},
 	}