fix: No data for format=dot queries, should not result in a 500

pkg/querier/http.go

@@ -171,6 +171,12 @@ func (q *QueryHandlers) Render(w http.ResponseWriter, req *http.Request) {
 			httputil.Error(w, connect.NewError(connect.CodeInternal, err))
 			return
 		}
+		// Check if profile has any data - return empty string if no data
+		if resp.Msg == nil || len(resp.Msg.Sample) == 0 {
+			w.Header().Set("Content-Type", "text/plain")
+			w.WriteHeader(http.StatusOK)
+			return
+		}
 		if err = pprofToDotProfile(w, resp.Msg, int(dotProfileMaxNodes)); err != nil {
 			httputil.Error(w, connect.NewError(connect.CodeInternal, err))
 		}

pkg/querier/http_test.go

@@ -1,15 +1,20 @@
 package querier
 
 import (
+	"context"
 	"fmt"
 	"net/http"
+	"net/http/httptest"
 	"net/url"
 	"testing"
 	"time"
 
+	"connectrpc.com/connect"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 
+	profilev1 "github.com/grafana/pyroscope/api/gen/proto/go/google/v1"
+	querierv1 "github.com/grafana/pyroscope/api/gen/proto/go/querier/v1"
 	typesv1 "github.com/grafana/pyroscope/api/gen/proto/go/types/v1"
 )
 
@@ -40,3 +45,91 @@ func Test_ParseQuery(t *testing.T) {
 
 	require.Equal(t, `{foo="bar",bar=~"buzz"}`, queryRequest.LabelSelector)
 }
+
+// mockQuerierClient is a mock implementation of QuerierServiceClient
+type mockQuerierClient struct {
+	selectMergeProfileFunc func(context.Context, *connect.Request[querierv1.SelectMergeProfileRequest]) (*connect.Response[profilev1.Profile], error)
+}
+
+func (m *mockQuerierClient) ProfileTypes(context.Context, *connect.Request[querierv1.ProfileTypesRequest]) (*connect.Response[querierv1.ProfileTypesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) LabelValues(context.Context, *connect.Request[typesv1.LabelValuesRequest]) (*connect.Response[typesv1.LabelValuesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) LabelNames(context.Context, *connect.Request[typesv1.LabelNamesRequest]) (*connect.Response[typesv1.LabelNamesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) Series(context.Context, *connect.Request[querierv1.SeriesRequest]) (*connect.Response[querierv1.SeriesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) SelectMergeStacktraces(context.Context, *connect.Request[querierv1.SelectMergeStacktracesRequest]) (*connect.Response[querierv1.SelectMergeStacktracesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) SelectMergeSpanProfile(context.Context, *connect.Request[querierv1.SelectMergeSpanProfileRequest]) (*connect.Response[querierv1.SelectMergeSpanProfileResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) SelectMergeProfile(ctx context.Context, req *connect.Request[querierv1.SelectMergeProfileRequest]) (*connect.Response[profilev1.Profile], error) {
+	if m.selectMergeProfileFunc != nil {
+		return m.selectMergeProfileFunc(ctx, req)
+	}
+	return nil, nil
+}
+
+func (m *mockQuerierClient) SelectSeries(context.Context, *connect.Request[querierv1.SelectSeriesRequest]) (*connect.Response[querierv1.SelectSeriesResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) Diff(context.Context, *connect.Request[querierv1.DiffRequest]) (*connect.Response[querierv1.DiffResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) GetProfileStats(context.Context, *connect.Request[typesv1.GetProfileStatsRequest]) (*connect.Response[typesv1.GetProfileStatsResponse], error) {
+	return nil, nil
+}
+
+func (m *mockQuerierClient) AnalyzeQuery(context.Context, *connect.Request[querierv1.AnalyzeQueryRequest]) (*connect.Response[querierv1.AnalyzeQueryResponse], error) {
+	return nil, nil
+}
+
+func Test_RenderDotFormatEmptyProfile(t *testing.T) {
+	// Create a mock client that returns an empty profile
+	mockClient := &mockQuerierClient{
+		selectMergeProfileFunc: func(ctx context.Context, req *connect.Request[querierv1.SelectMergeProfileRequest]) (*connect.Response[profilev1.Profile], error) {
+			// Return an empty profile (no samples)
+			return connect.NewResponse(&profilev1.Profile{
+				Sample: []*profilev1.Sample{}, // Empty samples
+			}), nil
+		},
+	}
+
+	handlers := NewHTTPHandlers(mockClient)
+
+	// Create a request with format=dot
+	q := url.Values{
+		"query":  []string{`memory:alloc_space:bytes:space:bytes{}`},
+		"from":   []string{"now-1h"},
+		"until":  []string{"now"},
+		"format": []string{"dot"},
+	}
+
+	req, err := http.NewRequest("GET", fmt.Sprintf("http://localhost/render?%s", q.Encode()), nil)
+	require.NoError(t, err)
+
+	// Create a response recorder
+	rr := httptest.NewRecorder()
+
+	// Call the handler
+	handlers.Render(rr, req)
+
+	// Verify we get a 200 OK with empty body instead of 500 (Internal Server Error)
+	require.Equal(t, http.StatusOK, rr.Code, "Expected 200 OK for empty profile, got %d", rr.Code)
+	require.Equal(t, "", rr.Body.String(), "Expected empty body for empty profile")
+	require.Equal(t, "text/plain", rr.Header().Get("Content-Type"), "Expected text/plain content type")
+}