init: dec-music 项目初始化

decrypt/kgm/kgm.go

@@ -0,0 +1,67 @@
+package kgm
+
+import (
+	"fmt"
+	"io"
+
+	"jsuse.com/dev/dec-music/decrypt"
+)
+
+type decoder struct {
+	rd io.ReadSeeker
+
+	cipher decrypt.StreamDecoder
+	offset int
+
+	header header
+}
+
+func newDecoder(p *decrypt.DecoderParams) decrypt.Decoder {
+	return &decoder{rd: p.Reader}
+}
+
+// Validate checks if the file is a valid Kugou (.kgm, .vpr, .kgma) file.
+// rd will be seeked to the beginning of the encrypted audio.
+func (d *decoder) Validate() (err error) {
+	if err := d.header.FromFile(d.rd); err != nil {
+		return err
+	}
+	// TODO; validate crypto version
+
+	switch d.header.CryptoVersion {
+	case 3:
+		d.cipher, err = newKgmCryptoV3(&d.header)
+		if err != nil {
+			return fmt.Errorf("kgm init crypto v3: %w", err)
+		}
+	default:
+		return fmt.Errorf("kgm: unsupported crypto version %d", d.header.CryptoVersion)
+	}
+
+	// prepare for read
+	if _, err := d.rd.Seek(int64(d.header.AudioOffset), io.SeekStart); err != nil {
+		return fmt.Errorf("kgm seek to audio: %w", err)
+	}
+
+	return nil
+}
+
+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
+	}
+	return n, err
+}
+
+func init() {
+	// Kugou
+	decrypt.RegisterDecoder("kgm", false , newDecoder)
+	decrypt.RegisterDecoder("kgma", false , newDecoder)
+	// Viper
+	decrypt.RegisterDecoder("vpr", false , newDecoder)
+	// Kugou Android
+	decrypt.RegisterDecoder("kgm.flac", false , newDecoder)
+	decrypt.RegisterDecoder("vpr.flac", false , newDecoder)
+}