refactor: use io.Reader instead of custom method

algo/kgm/kgm.go

@@ -1,7 +1,6 @@
 package kgm
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 
@@ -9,64 +8,48 @@ import (
 )
 
 type Decoder struct {
-	header      Header
-	initializer kgmCryptoInitializer
+	header header
+	cipher common.StreamDecoder
 
-	file  []byte
-	audio []byte
+	rd     io.ReadSeeker
+	offset int
 }
 
-type kgmCryptoInitializer func(header *Header, body io.Reader) (io.Reader, error)
+func NewDecoder(rd io.ReadSeeker) common.Decoder {
+	return &Decoder{rd: rd}
+}
 
-var kgmCryptoInitializers = map[uint32]kgmCryptoInitializer{
+var kgmCryptoInitializers = map[uint32]func(header *header) (common.StreamDecoder, error){
 	3: newKgmCryptoV3,
 }
 
-func NewDecoder(file []byte) common.Decoder {
-	return &Decoder{
-		file: file,
-	}
-}
-
-func (d *Decoder) GetAudioData() []byte {
-	return d.audio
-}
-
-func (d *Decoder) GetAudioExt() string {
-	return "" // use sniffer
-}
-
-func (d *Decoder) GetMeta() common.Meta {
-	return nil
-}
-
 func (d *Decoder) Validate() error {
-	if err := d.header.FromBytes(d.file); err != nil {
+	if err := d.header.FromFile(d.rd); err != nil {
 		return err
 	}
 	// TODO; validate crypto version
 
-	var ok bool
-	d.initializer, ok = kgmCryptoInitializers[d.header.CryptoVersion]
+	initializer, ok := kgmCryptoInitializers[d.header.CryptoVersion]
 	if !ok {
 		return fmt.Errorf("kgm: unsupported crypto version %d", d.header.CryptoVersion)
 	}
 
+	var err error
+	d.cipher, err = initializer(&d.header)
+	if err != nil {
+		return fmt.Errorf("kgm: failed to initialize crypto: %w", err)
+	}
+
 	return nil
 }
 
-func (d *Decoder) Decode() error {
-	d.audio = d.file[d.header.AudioOffset:]
-
-	r, err := d.initializer(&d.header, bytes.NewReader(d.audio))
-	if err != nil {
-		return fmt.Errorf("kgm: failed to initialize crypto: %w", err)
+func (d *Decoder) Read(buf []byte) (int, error) {
+	n, err := d.rd.Read(buf)
+	if n > 0 {
+		d.cipher.Decrypt(buf[:n], d.offset)
+		d.offset += n
 	}
-	d.audio, err = io.ReadAll(r)
-	if err != nil {
-		return fmt.Errorf("kgm: failed to decrypt audio: %w", err)
-	}
-	return nil
+	return n, err
 }
 
 func init() {