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() {

algo/kgm/kgm_header.go

@@ -21,8 +21,8 @@ var (
 	ErrKgmMagicHeader = errors.New("kgm magic header not matched")
 )
 
-// Header is the header of a KGM file.
-type Header struct {
+// header is the header of a KGM file.
+type header struct {
 	MagicHeader    []byte // 0x00-0x0f: magic header
 	AudioOffset    uint32 // 0x10-0x13: offset of audio data
 	CryptoVersion  uint32 // 0x14-0x17: crypto version
@@ -31,7 +31,7 @@ type Header struct {
 	CryptoKey      []byte // 0x2c-0x3b: crypto key
 }
 
-func (h *Header) FromFile(rd io.ReadSeeker) error {
+func (h *header) FromFile(rd io.ReadSeeker) error {
 	if _, err := rd.Seek(0, io.SeekStart); err != nil {
 		return fmt.Errorf("kgm seek start: %w", err)
 	}
@@ -44,7 +44,7 @@ func (h *Header) FromFile(rd io.ReadSeeker) error {
 	return h.FromBytes(buf)
 }
 
-func (h *Header) FromBytes(buf []byte) error {
+func (h *header) FromBytes(buf []byte) error {
 	if len(buf) < 0x3c {
 		return errors.New("invalid kgm header length")
 	}

algo/kgm/kgm_v3.go

@@ -3,24 +3,22 @@ package kgm
 import (
 	"crypto/md5"
 	"fmt"
-	"io"
+
+	"github.com/unlock-music/cli/algo/common"
 )
 
 // kgmCryptoV3 is kgm file crypto v3
 type kgmCryptoV3 struct {
 	slotBox []byte
 	fileBox []byte
-
-	rd     io.Reader
-	offset int
 }
 
 var kgmV3Slot2Key = map[uint32][]byte{
 	1: {0x6C, 0x2C, 0x2F, 0x27},
 }
 
-func newKgmCryptoV3(header *Header, body io.Reader) (io.Reader, error) {
-	c := &kgmCryptoV3{rd: body}
+func newKgmCryptoV3(header *header) (common.StreamDecoder, error) {
+	c := &kgmCryptoV3{}
 
 	slotKey, ok := kgmV3Slot2Key[header.CryptoSlot]
 	if !ok {
@@ -33,16 +31,7 @@ func newKgmCryptoV3(header *Header, body io.Reader) (io.Reader, error) {
 	return c, nil
 }
 
-func (d *kgmCryptoV3) Read(buf []byte) (int, error) {
-	n, err := d.rd.Read(buf)
-	if n > 0 {
-		d.decrypt(buf[:n], d.offset)
-		d.offset += n
-	}
-	return n, err
-}
-
-func (d *kgmCryptoV3) decrypt(b []byte, offset int) {
+func (d *kgmCryptoV3) Decrypt(b []byte, offset int) {
 	for i := 0; i < len(b); i++ {
 		b[i] ^= d.fileBox[(offset+i)%len(d.fileBox)]
 		b[i] ^= b[i] << 4