cli/algo/xiami/xm.go

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package xiami
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import (
"bytes"
"errors"
"fmt"
"io"
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"unlock-music.dev/cli/algo/common"
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)
var (
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magicHeader = []byte{'i', 'f', 'm', 't'}
magicHeader2 = []byte{0xfe, 0xfe, 0xfe, 0xfe}
typeMapping = map[string]string{
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" WAV": "wav",
"FLAC": "flac",
" MP3": "mp3",
" A4M": "m4a",
}
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ErrMagicHeader = errors.New("xm magic header not matched")
)
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type Decoder struct {
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rd io.ReadSeeker // rd is the original file reader
offset int
cipher common.StreamDecoder
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outputExt string
}
func (d *Decoder) GetAudioExt() string {
if d.outputExt != "" {
return "." + d.outputExt
}
return ""
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}
func NewDecoder(p *common.DecoderParams) common.Decoder {
return &Decoder{rd: p.Reader}
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}
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// Validate checks if the file is a valid xiami .xm file.
// rd will set to the beginning of the encrypted audio data.
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func (d *Decoder) Validate() error {
header := make([]byte, 16) // xm header is fixed to 16 bytes
if _, err := io.ReadFull(d.rd, header); err != nil {
return fmt.Errorf("xm read header: %w", err)
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}
// 0x00 - 0x03 and 0x08 - 0x0B: magic header
if !bytes.Equal(magicHeader, header[:4]) || !bytes.Equal(magicHeader2, header[8:12]) {
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return ErrMagicHeader
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}
// 0x04 - 0x07: Audio File Type
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var ok bool
d.outputExt, ok = typeMapping[string(header[4:8])]
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if !ok {
return fmt.Errorf("xm detect unknown audio type: %s", string(header[4:8]))
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}
// 0x0C - 0x0E, Encrypt Start At, LittleEndian Unit24
encStartAt := uint32(header[12]) | uint32(header[13])<<8 | uint32(header[14])<<16
// 0x0F, XOR Mask
d.cipher = newXmCipher(header[15], int(encStartAt))
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return nil
}
func (d *Decoder) Read(p []byte) (int, error) {
n, err := d.rd.Read(p)
if n > 0 {
d.cipher.Decrypt(p[:n], d.offset)
d.offset += n
}
return n, err
}
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func init() {
// Xiami Wav/M4a/Mp3/Flac
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common.RegisterDecoder("xm", false, NewDecoder)
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// Xiami Typed Format
common.RegisterDecoder("wav", false, NewDecoder)
common.RegisterDecoder("mp3", false, NewDecoder)
common.RegisterDecoder("flac", false, NewDecoder)
common.RegisterDecoder("m4a", false, NewDecoder)
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}