Fixes a panic in the labels API when no parameters are supplied. (#4554)

* Fixes the a panic in the labels API when no parameters are supplied.

We were supporting this before.

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

* Remove bad test

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

pkg/ingester/ingester.go

@@ -97,7 +97,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
 	f.DurationVar(&cfg.RetainPeriod, "ingester.chunks-retain-period", 15*time.Minute, "")
 	f.DurationVar(&cfg.MaxChunkIdle, "ingester.chunks-idle-period", 30*time.Minute, "")
 	f.IntVar(&cfg.BlockSize, "ingester.chunks-block-size", 256*1024, "")
-	f.IntVar(&cfg.TargetChunkSize, "ingester.chunk-target-size", 1572864, "") //1.5 MB
+	f.IntVar(&cfg.TargetChunkSize, "ingester.chunk-target-size", 1572864, "") // 1.5 MB
 	f.StringVar(&cfg.ChunkEncoding, "ingester.chunk-encoding", chunkenc.EncGZIP.String(), fmt.Sprintf("The algorithm to use for compressing chunk. (%s)", chunkenc.SupportedEncoding()))
 	f.DurationVar(&cfg.SyncPeriod, "ingester.sync-period", 0, "How often to cut chunks to synchronize ingesters.")
 	f.Float64Var(&cfg.SyncMinUtilization, "ingester.sync-min-utilization", 0, "Minimum utilization of chunk when doing synchronization.")
@@ -671,6 +671,10 @@ func (i *Ingester) Label(ctx context.Context, req *logproto.LabelRequest) (*logp
 		return nil, err
 	}
 
+	if req.Start == nil {
+		return resp, nil
+	}
+
 	// Only continue if the active index type is boltdb-shipper or QueryStore flag is true.
 	boltdbShipperMaxLookBack := i.boltdbShipperMaxLookBack()
 	if boltdbShipperMaxLookBack == 0 && !i.cfg.QueryStore {

pkg/ingester/ingester_test.go

@@ -508,3 +508,54 @@ func TestValidate(t *testing.T) {
 		})
 	}
 }
+
+func Test_InMemoryLabels(t *testing.T) {
+	ingesterConfig := defaultIngesterTestConfig(t)
+	limits, err := validation.NewOverrides(defaultLimitsTestConfig(), nil)
+	require.NoError(t, err)
+
+	store := &mockStore{
+		chunks: map[string][]chunk.Chunk{},
+	}
+
+	i, err := New(ingesterConfig, client.Config{}, store, limits, runtime.DefaultTenantConfigs(), nil)
+	require.NoError(t, err)
+	defer services.StopAndAwaitTerminated(context.Background(), i) //nolint:errcheck
+
+	req := logproto.PushRequest{
+		Streams: []logproto.Stream{
+			{
+				Labels: `{foo="bar",bar="baz1"}`,
+			},
+			{
+				Labels: `{foo="bar",bar="baz2"}`,
+			},
+		},
+	}
+	for i := 0; i < 10; i++ {
+		req.Streams[0].Entries = append(req.Streams[0].Entries, logproto.Entry{
+			Timestamp: time.Unix(0, 0),
+			Line:      fmt.Sprintf("line %d", i),
+		})
+		req.Streams[1].Entries = append(req.Streams[1].Entries, logproto.Entry{
+			Timestamp: time.Unix(0, 0),
+			Line:      fmt.Sprintf("line %d", i),
+		})
+	}
+
+	ctx := user.InjectOrgID(context.Background(), "test")
+	_, err = i.Push(ctx, &req)
+	require.NoError(t, err)
+
+	res, err := i.Label(ctx, &logproto.LabelRequest{
+		Name:   "bar",
+		Values: true,
+	})
+
+	require.NoError(t, err)
+	require.Equal(t, []string{"baz1", "baz2"}, res.Values)
+
+	res, err = i.Label(ctx, &logproto.LabelRequest{})
+	require.NoError(t, err)
+	require.Equal(t, []string{"bar", "foo"}, res.Values)
+}