init: dec-music 项目初始化

decrypt/tm/tm.go

@@ -0,0 +1,56 @@
+package tm
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+
+	"jsuse.com/dev/dec-music/decrypt"
+	"jsuse.com/dev/dec-music/internal/sniff"
+)
+
+var replaceHeader = []byte{0x00, 0x00, 0x00, 0x20, 0x66, 0x74, 0x79, 0x70}
+var magicHeader = []byte{0x51, 0x51, 0x4D, 0x55} //0x15, 0x1D, 0x1A, 0x21
+
+type decoder struct {
+	raw io.ReadSeeker // raw is the original file reader
+
+	offset int
+	audio  io.Reader // audio is the decrypted audio data
+}
+
+func (d *decoder) Validate() error {
+	header := make([]byte, 8)
+	if _, err := io.ReadFull(d.raw, header); err != nil {
+		return fmt.Errorf("tm read header: %w", err)
+	}
+
+	if bytes.Equal(magicHeader, header[:len(magicHeader)]) { // replace m4a header
+		d.audio = io.MultiReader(bytes.NewReader(replaceHeader), d.raw)
+		return nil
+	}
+
+	if _, ok := sniff.AudioExtension(header); ok { // not encrypted
+		d.audio = io.MultiReader(bytes.NewReader(header), d.raw)
+		return nil
+	}
+
+	return errors.New("tm: valid magic header")
+}
+
+func (d *decoder) Read(buf []byte) (int, error) {
+	return d.audio.Read(buf)
+}
+
+func newTmDecoder(p *decrypt.DecoderParams) decrypt.Decoder {
+	return &decoder{raw: p.Reader}
+}
+
+func init() {
+	// QQ Music IOS M4a (replace header)
+	decrypt.RegisterDecoder("tm2", false, newTmDecoder)
+	decrypt.RegisterDecoder("tm6", false, newTmDecoder)
+	decrypt.RegisterDecoder("tm0", false, newTmDecoder)
+	decrypt.RegisterDecoder("tm3", false, newTmDecoder)
+}