build index on start

kv.go

@@ -23,12 +23,44 @@ func NewKV() (*KV, error) {
 	}
 	index := make(map[string]KeyDir)
 	kv := KV{file: file, index: index}
-	buildIndex(&kv)
+	err = buildIndex(&kv)
+	if err != nil {
+		return nil, err
+	}
 	return &kv, nil
 }
 
-func buildIndex(kv *KV) {
-
+func buildIndex(kv *KV) error {
+	_, err := kv.file.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+	offset := int64(0)
+	for {
+		keyValueSizeBytes := make([]byte, 8+8)
+		_, err = kv.file.Read(keyValueSizeBytes)
+		if err != nil {
+			if err.Error() == "EOF" {
+				return nil
+			}
+			return err
+		}
+		keySize := int64(binary.BigEndian.Uint64(keyValueSizeBytes[0:8]))
+		valueSize := int64(binary.BigEndian.Uint64(keyValueSizeBytes[0:8]))
+
+		offset += 8 + 8
+
+		keyValueBytes := make([]byte, keySize+valueSize)
+		_, err = kv.file.Read(keyValueBytes)
+		if err != nil {
+			return err
+		}
+		key := string(keyValueBytes[:keySize])
+
+		kv.index[key] = KeyDir{valueSize: valueSize, valueOffset: offset + keySize}
+
+		offset += keySize + valueSize
+	}
 }
 
 func (kv *KV) Close() error {
@@ -38,15 +70,18 @@ func (kv *KV) Close() error {
 func (kv *KV) Get(key string) (string, error) {
 	keyDir, exists := kv.index[key]
 	if !exists {
-		buildIndex(kv)
+		err := buildIndex(kv)
+		if err != nil {
+			return "", err
+		}
 	}
 	return readAt(kv.file, keyDir.valueOffset, keyDir.valueSize)
 }
 
 func readAt(file *os.File, offset int64, size int64) (string, error) {
 	_, err := file.Seek(offset, io.SeekStart)
 	if err != nil {
-		return "", nil
+		return "", err
 	}
 
 	contentBytes := make([]byte, size)