[coordinator] Add WriteNamespaces API to rules store

src/metrics/rules/store.go

@@ -31,6 +31,9 @@ type Store interface {
 	// WriteRuleSet saves the given ruleset to the backing store.
 	WriteRuleSet(rs MutableRuleSet) error
 
+	// WriteNamespaces saves the given namespaces to the backing store.
+	WriteNamespaces(nss *Namespaces) error
+
 	// WriteAll saves both the given ruleset and namespace to the backing store.
 	WriteAll(nss *Namespaces, rs MutableRuleSet) error
 

src/metrics/rules/store/kv/store.go

@@ -99,6 +99,16 @@ func (s *store) WriteRuleSet(rs rules.MutableRuleSet) error {
 	return wrapWriteError(err)
 }
 
+func (s *store) WriteNamespaces(nss *rules.Namespaces) error {
+	namespacesCond, namespacesOp, err := s.namespacesTransaction(nss)
+	if err != nil {
+		return err
+	}
+	conditions, ops := []kv.Condition{namespacesCond}, []kv.Op{namespacesOp}
+	_, err = s.kvStore.Commit(conditions, ops)
+	return wrapWriteError(err)
+}
+
 func (s *store) WriteAll(nss *rules.Namespaces, rs rules.MutableRuleSet) error {
 	if s.opts.Validator != nil {
 		if err := s.opts.Validator.Validate(rs); err != nil {

src/metrics/rules/store/kv/store_test.go

@@ -596,6 +596,56 @@ func TestWriteRuleSetStaleDataError(t *testing.T) {
 	require.IsType(t, merrors.NewStaleDataError(""), err)
 }
 
+func TestWriteNamespace(t *testing.T) {
+	s := testStore()
+	defer s.Close()
+
+	nss, err := rules.NewNamespaces(0, testNamespaces)
+	require.NoError(t, err)
+
+	err = s.WriteNamespaces(&nss)
+	require.NoError(t, err)
+
+	existing, err := s.ReadNamespaces()
+	require.NoError(t, err)
+
+	revived, err := existing.AddNamespace(
+		"new",
+		rules.NewRuleSetUpdateHelper(0).NewUpdateMetadata(time.Now().UnixNano(), "test"),
+	)
+	require.NoError(t, err)
+	require.False(t, revived)
+
+	// Update should succeed
+	err = s.WriteNamespaces(existing)
+	require.NoError(t, err)
+}
+
+func TestWriteNamespaceError(t *testing.T) {
+	s := testStore()
+	defer s.Close()
+
+	err := s.WriteNamespaces(nil)
+	require.Error(t, err)
+}
+
+func TestWriteNamespacesStaleDataError(t *testing.T) {
+	s := testStore()
+	defer s.Close()
+
+	nss, err := rules.NewNamespaces(0, testNamespaces)
+	require.NoError(t, err)
+
+	// First write should succeed
+	err = s.WriteNamespaces(&nss)
+	require.NoError(t, err)
+
+	// writing again will encounter stale version
+	err = s.WriteNamespaces(&nss)
+	require.Error(t, err)
+	require.IsType(t, merrors.NewStaleDataError(""), err)
+}
+
 func TestWriteAllNoNamespace(t *testing.T) {
 	s := testStore()
 	defer s.Close()