Do not block file for writes

README.md

@@ -68,3 +68,4 @@ File is log stuctured list of commands:
 
 - [ ] Test [seekable zstd streams](https://github.com/SaveTheRbtz/zstd-seekable-format-go)
 - [ ] Implement optional separate index file to speedup store initialization
+- [ ] Add recovery previous state of store file on write error

zkv.go

@@ -15,10 +15,8 @@ import (
 type Store struct {
 	dataOffset map[string]int64
 
-	file     *os.File
 	filePath string
 	offset   int64
-	encoder  *zstd.Encoder
 
 	buffer           *bytes.Buffer
 	bufferDataOffset map[string]int64
@@ -33,24 +31,10 @@ type Store struct {
 func OpenWithOptions(filePath string, options Options) (*Store, error) {
 	options.setDefaults()
 
-	f, err := os.OpenFile(filePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
-	if err != nil {
-		f.Close()
-		return nil, fmt.Errorf("open store file: %v", err)
-	}
-
-	compressor, err := zstd.NewWriter(f)
-	if err != nil {
-		f.Close()
-		return nil, fmt.Errorf("compressor initialization: %v", err)
-	}
-
 	database := &Store{
 		dataOffset:       make(map[string]int64),
 		bufferDataOffset: make(map[string]int64),
 		offset:           0,
-		file:             f,
-		encoder:          compressor,
 		buffer:           new(bytes.Buffer),
 		filePath:         filePath,
 		options:          options,
@@ -58,15 +42,16 @@ func OpenWithOptions(filePath string, options Options) (*Store, error) {
 
 	// restore file data
 	readF, err := os.Open(filePath)
-	if err != nil {
-		f.Close()
+	if os.IsNotExist(err) {
+		// Empty datebase
+		return database, nil
+	} else if err != nil {
 		return nil, fmt.Errorf("open file for indexing: %v", err)
 	}
 	defer readF.Close()
 
 	decompressor, err := zstd.NewReader(readF)
 	if err != nil {
-		f.Close()
 		return nil, fmt.Errorf("decompressor initialization: %v", err)
 	}
 	defer decompressor.Close()
@@ -78,7 +63,6 @@ func OpenWithOptions(filePath string, options Options) (*Store, error) {
 			break
 		}
 		if err != nil {
-			f.Close()
 			return nil, fmt.Errorf("read record error: %v", err)
 		}
 
@@ -204,12 +188,7 @@ func (s *Store) Close() error {
 		return err
 	}
 
-	err = s.encoder.Close()
-	if err != nil {
-		return err
-	}
-
-	return s.file.Close()
+	return nil
 }
 
 func (s *Store) setBytes(keyHash [sha256.Size224]byte, valueBytes []byte) error {
@@ -393,7 +372,18 @@ func (s *Store) get(key, value interface{}) error {
 func (s *Store) flush() error {
 	l := int64(s.buffer.Len())
 
-	_, err := s.buffer.WriteTo(s.encoder)
+	f, err := os.OpenFile(s.filePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("open store file: %v", err)
+	}
+
+	encoder, err := zstd.NewWriter(f, zstd.WithEncoderLevel(s.options.CompressionLevel))
+	if err != nil {
+		f.Close()
+		return fmt.Errorf("open store file: %v", err)
+	}
+
+	_, err = s.buffer.WriteTo(encoder)
 	if err != nil {
 		return err
 	}
@@ -406,7 +396,13 @@ func (s *Store) flush() error {
 
 	s.offset += l
 
-	err = s.encoder.Flush()
+	err = encoder.Close()
+	if err != nil {
+		// TODO: truncate file to previous state
+		return err
+	}
+
+	err = f.Close()
 	if err != nil {
 		return err
 	}