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