package xm import ( "bytes" "errors" "fmt" "io" "github.com/unlock-music/cli/algo/common" ) var ( magicHeader = []byte{'i', 'f', 'm', 't'} magicHeader2 = []byte{0xfe, 0xfe, 0xfe, 0xfe} typeMapping = map[string]string{ " WAV": "wav", "FLAC": "flac", " MP3": "mp3", " A4M": "m4a", } ErrMagicHeader = errors.New("xm magic header not matched") ) type Decoder struct { rd io.ReadSeeker offset int cipher common.StreamDecoder outputExt string mask byte audio []byte } func (d *Decoder) GetAudioExt() string { if d.outputExt != "" { return "." + d.outputExt } return "" } func NewDecoder(rd io.ReadSeeker) common.Decoder { return &Decoder{rd: rd} } 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) } // 0x00 - 0x03 and 0x08 - 0x0B: magic header if !bytes.Equal(magicHeader, header[:4]) || !bytes.Equal(magicHeader2, header[8:12]) { return ErrMagicHeader } // 0x04 - 0x07: Audio File Type var ok bool d.outputExt, ok = typeMapping[string(header[4:8])] if !ok { return fmt.Errorf("xm detect unknown audio type: %s", string(header[4:8])) } // 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)) 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 } func init() { // Xiami Wav/M4a/Mp3/Flac common.RegisterDecoder("xm", false, NewDecoder) // Xiami Typed Format common.RegisterDecoder("wav", false, NewDecoder) common.RegisterDecoder("mp3", false, NewDecoder) common.RegisterDecoder("flac", false, NewDecoder) common.RegisterDecoder("m4a", false, NewDecoder) }