lib/kv: add read-only flag in DB

lib/kv/bolt.go

@@ -33,6 +33,7 @@ type DB struct {
 	refs      int
 	bolt      *bbolt.DB
 	mu        sync.Mutex
+	readOnly  bool
 	canWrite  bool
 	queue     chan *request
 	lockTime  time.Duration
@@ -138,6 +139,10 @@ func (db *DB) open(ctx context.Context, forWrite bool) (err error) {
 	}
 	_ = db.close()
 
+	if db.readOnly && forWrite {
+		return ErrReadOnly
+	}
+
 	db.canWrite = forWrite
 	if !forWrite {
 		// mitigate https://github.com/etcd-io/bbolt/issues/98
@@ -228,6 +233,11 @@ func (db *DB) Do(write bool, op Op) error {
 	return r.err
 }
 
+// ReadOnly setter the db.readOnly
+func (db *DB) ReadOnly(b bool) {
+	db.readOnly = b
+}
+
 // request encapsulates a synchronous operation and its results
 type request struct {
 	op  Op

lib/kv/internal_test.go

@@ -66,3 +66,27 @@ func TestKvExit(t *testing.T) {
 	Exit()
 	assert.Equal(t, 0, len(dbMap))
 }
+
+func TestDbReadOnly(t *testing.T) {
+	require.Equal(t, 0, len(dbMap), "no databases can be started initially")
+	ctx := context.Background()
+
+	db, err := Start(ctx, "test", nil)
+	require.NoError(t, err)
+	require.NotNil(t, db)
+
+	assert.False(t, db.readOnly)
+
+	// set db in read only
+	db.ReadOnly(true)
+
+	assert.True(t, db.readOnly)
+
+	// write op is not allowed in read only mode, should throw error
+	err = db.Do(true, nil)
+	assert.ErrorIs(t, err, ErrReadOnly)
+
+	db.ReadOnly(false)
+	err = db.Do(true, &opStop{})
+	assert.NoError(t, err)
+}

lib/kv/types.go

@@ -10,6 +10,7 @@ var (
 	ErrEmpty       = errors.New("database empty")
 	ErrInactive    = errors.New("database stopped")
 	ErrUnsupported = errors.New("unsupported on this OS")
+	ErrReadOnly    = errors.New("database in read-only mode")
 )
 
 // Op represents a database operation