package kgm import ( "fmt" "io" "unlock-music.dev/cli/algo/common" ) type Decoder struct { rd io.ReadSeeker cipher common.StreamDecoder offset int header header } func NewDecoder(p *common.DecoderParams) common.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 common.RegisterDecoder("kgm", false, NewDecoder) common.RegisterDecoder("kgma", false, NewDecoder) // Viper common.RegisterDecoder("vpr", false, NewDecoder) }