fix: incorrect metadata returned per source (#1599)

This PR fixes an issue where the wrong metadata is returned when a
selector is used.

This bug is easy to fix, but was also easy to write. We eventually need
to refactor the flag memory store (`flags.go`) to store all flags per
source. This was retrofitted in to support selectors, from a
single-flagSet model.

To test, do the manual test specified in
https://github.com/open-feature/flagd/issues/1597.

Fixes: https://github.com/open-feature/flagd/issues/1597

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

core/pkg/store/flags.go

@@ -70,7 +70,7 @@ func (f *State) Get(_ context.Context, key string) (model.Flag, model.Metadata,
 	metadata := f.getMetadata()
 	flag, ok := f.Flags[key]
 	if ok {
-		metadata = f.getMetadataForSource(flag.Source)
+		metadata = f.GetMetadataForSource(flag.Source)
 	}
 
 	return flag, metadata, ok
@@ -319,7 +319,7 @@ func (f *State) Merge(
 	return notifications, resyncRequired
 }
 
-func (f *State) getMetadataForSource(source string) model.Metadata {
+func (f *State) GetMetadataForSource(source string) model.Metadata {
 	perSource, ok := f.MetadataPerSource[source]
 	if ok && perSource != nil {
 		return maps.Clone(perSource)

flagd/pkg/service/flag-sync/sync-multiplexer.go

@@ -199,6 +199,8 @@ func (r *Multiplexer) reFill() error {
 
 	// for all flags, sort them into their correct selector
 	for source, flags := range collector {
+		// store the corresponding metadata
+		metadata := r.store.GetMetadataForSource(source)
 		bytes, err := json.Marshal(map[string]interface{}{"flags": flags, "metadata": metadata})
 		if err != nil {
 			return fmt.Errorf("unable to marshal flags: %w", err)

flagd/pkg/service/flag-sync/sync-multiplexer_test.go

@@ -168,35 +168,94 @@ func TestGetAllFlags(t *testing.T) {
 	}
 
 	// when - get all with open scope
-	flags, err := mux.GetAllFlags("")
+	flagConfig, err := mux.GetAllFlags("")
 	if err != nil {
 		t.Fatal("error when retrieving all flags")
 		return
 	}
 
-	if len(flags) == 0 {
+	if len(flagConfig) == 0 {
 		t.Fatal("expected no empty flags")
 		return
 	}
 
 	// when - get all with a scope
-	flags, err = mux.GetAllFlags("A")
+	flagConfig, err = mux.GetAllFlags("A")
 	if err != nil {
 		t.Fatal("error when retrieving all flags")
 		return
 	}
 
-	if len(flags) == 0 || !strings.Contains(flags, fmt.Sprintf("\"source\":\"%s\"", "A")) {
+	if len(flagConfig) == 0 || !strings.Contains(flagConfig, fmt.Sprintf("\"source\":\"%s\"", "A")) {
 		t.Fatal("expected flags to be scoped")
 		return
 	}
 
 	// when - get all for a flagless-scope
-	flags, err = mux.GetAllFlags("C")
+	flagConfig, err = mux.GetAllFlags("C")
 	if err != nil {
 		t.Fatal("error when retrieving all flags")
 		return
 	}
 
-	assert.Equal(t, flags, emptyConfigString)
+	assert.Equal(t, flagConfig, emptyConfigString)
+}
+
+func TestGetAllFlagsMetadata(t *testing.T) {
+	// given
+	mux, err := NewMux(getSimpleFlagStore())
+	if err != nil {
+		t.Fatal("error during flag extraction")
+		return
+	}
+
+	// when - get all with open scope
+	flagConfig, err := mux.GetAllFlags("")
+	if err != nil {
+		t.Fatal("error when retrieving all flags")
+		return
+	}
+
+	if len(flagConfig) == 0 {
+		t.Fatal("expected no empty flags")
+		return
+	}
+
+	if !strings.Contains(flagConfig, "\"keyA\":\"valueA\"") {
+		t.Fatal("expected unique metadata key for A to be present")
+		return
+	}
+
+	if !strings.Contains(flagConfig, "\"keyB\":\"valueB\"") {
+		t.Fatal("expected unique metadata key for B to be present")
+		return
+	}
+
+	// duplicated keys are removed
+	if strings.Contains(flagConfig, "\"keyDuped\":\"value\"") {
+		t.Fatal("expected duplicated metadata key NOT to be present")
+		return
+	}
+
+	// when - get all with a scope
+	flagConfig, err = mux.GetAllFlags("A")
+	if err != nil {
+		t.Fatal("error when retrieving all flags")
+		return
+	}
+
+	if len(flagConfig) == 0 {
+		t.Fatal("expected no empty flags")
+		return
+	}
+
+	if !strings.Contains(flagConfig, "\"keyA\":\"valueA\"") {
+		t.Fatal("expected unique metadata key to be present")
+		return
+	}
+
+	if !strings.Contains(flagConfig, "\"keyDuped\":\"value\"") {
+		t.Fatal("expected duplicated metadata key to be present")
+		return
+	}
 }

flagd/pkg/service/flag-sync/util_test.go

@@ -34,6 +34,16 @@ func getSimpleFlagStore() (*store.State, []string) {
 		Source:         "B",
 	})
 
+	flagStore.MetadataPerSource["A"] = model.Metadata{
+		"keyDuped": "value",
+		"keyA":     "valueA",
+	}
+
+	flagStore.MetadataPerSource["B"] = model.Metadata{
+		"keyDuped": "value",
+		"keyB":     "valueB",
+	}
+
 	return flagStore, []string{"A", "B", "C"}
 }