Store: acceptance test for proxy store (thanos-io#7084)

* Add basic acceptance tests for proxy store
* Fix bug where invalid requests got ignored because of partial response
  strategy

Signed-off-by: Michael Hoffmann <mhoffm@posteo.de>

pkg/store/acceptance_test.go

@@ -33,6 +33,7 @@ import (
 	"github.com/thanos-io/thanos/pkg/store/labelpb"
 	"github.com/thanos-io/thanos/pkg/store/storepb"
 	"github.com/thanos-io/thanos/pkg/store/storepb/prompb"
+	storetestutil "github.com/thanos-io/thanos/pkg/store/storepb/testutil"
 	"github.com/thanos-io/thanos/pkg/testutil/custom"
 	"github.com/thanos-io/thanos/pkg/testutil/e2eutil"
 )
@@ -988,3 +989,30 @@ func TestTSDBStore_Acceptance(t *testing.T) {
 	testStoreAPIsAcceptance(t, startStore)
 	testStoreAPIsSeriesSplitSamplesIntoChunksWithMaxSizeOf120(t, startStore)
 }
+
+func TestProxyStore_Acceptance(t *testing.T) {
+	t.Cleanup(func() { custom.TolerantVerifyLeak(t) })
+
+	startStore := func(tt *testing.T, extLset labels.Labels, appendFn func(app storage.Appender)) storepb.StoreServer {
+		startNestedStore := func(tt *testing.T, extLset labels.Labels, appendFn func(app storage.Appender)) storepb.StoreServer {
+			db, err := e2eutil.NewTSDB()
+			testutil.Ok(tt, err)
+			tt.Cleanup(func() { testutil.Ok(tt, db.Close()) })
+			appendFn(db.Appender(context.Background()))
+
+			return NewTSDBStore(nil, db, component.Rule, extLset)
+		}
+
+		p1 := startNestedStore(tt, extLset, appendFn)
+		p2 := startNestedStore(tt, extLset, appendFn)
+
+		clients := []Client{
+			storetestutil.TestClient{StoreClient: storepb.ServerAsClient(p1, 0)},
+			storetestutil.TestClient{StoreClient: storepb.ServerAsClient(p2, 0)},
+		}
+
+		return NewProxyStore(nil, nil, func() []Client { return clients }, component.Query, nil, 0*time.Second, RetrievalStrategy(EagerRetrieval))
+	}
+
+	testStoreAPIsAcceptance(t, startStore)
+}

pkg/store/proxy.go

@@ -540,6 +540,9 @@ func (s *ProxyStore) LabelValues(ctx context.Context, r *storepb.LabelValuesRequ
 		g, gctx        = errgroup.WithContext(ctx)
 		storeDebugMsgs []string
 	)
+	if r.Label == "" {
+		return nil, status.Error(codes.InvalidArgument, "label name parameter cannot be empty")
+	}
 
 	// We may arrive here either via the promql engine
 	// or as a result of a grpc call in layered queries