Fix panic caused by nil pointer dereference in Query Frontend

CHANGELOG.md

@@ -15,6 +15,7 @@
 * [BUGFIX] Compactor: Cleaner would delete bucket index when there is no block in bucket store. #6577
 * [BUGFIX] Querier: Fix marshal native histogram with empty bucket when protobuf codec is enabled. #6595
 * [BUGFIX] Query Frontend: Fix samples scanned and peak samples query stats when query hits results cache. #6591
+* [BUGFIX] Query Frontend: Fix panic caused by nil pointer dereference. #6609
 
 ## 1.19.0 in progress
 

pkg/frontend/v2/frontend_scheduler_worker.go

@@ -291,7 +291,7 @@ func (w *frontendSchedulerWorker) schedulerLoop(loop schedulerpb.SchedulerForFro
 				req.response <- &frontendv2pb.QueryResultRequest{
 					HttpResponse: &httpgrpc.HTTPResponse{
 						Code: http.StatusInternalServerError,
-						Body: []byte(err.Error()),
+						Body: []byte(resp.GetError()),
 					},
 				}
 

pkg/frontend/v2/frontend_test.go

@@ -3,6 +3,7 @@ package v2
 import (
 	"context"
 	"net"
+	"net/http"
 	"strconv"
 	"strings"
 	"sync"
@@ -182,6 +183,18 @@ func TestFrontendEnqueueFailure(t *testing.T) {
 	require.True(t, strings.Contains(err.Error(), "failed to enqueue request"))
 }
 
+func TestFrontendEnqueueInternalError(t *testing.T) {
+	errorMsg := "Some error"
+	f, _ := setupFrontend(t, func(f *Frontend, msg *schedulerpb.FrontendToScheduler) *schedulerpb.SchedulerToFrontend {
+		return &schedulerpb.SchedulerToFrontend{Status: schedulerpb.ERROR, Error: errorMsg}
+	}, 0)
+
+	resp, err := f.RoundTripGRPC(user.InjectOrgID(context.Background(), "test"), &httpgrpc.HTTPRequest{})
+	require.NoError(t, err)
+	require.Equal(t, []byte(errorMsg), resp.Body)
+	require.Equal(t, int32(http.StatusInternalServerError), resp.Code)
+}
+
 func TestFrontendCancellation(t *testing.T) {
 	f, ms := setupFrontend(t, nil, 0)