dec-music/decrypt/qmc/qmc.go

package qmc

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"runtime"
	"strings"

	"jsuse.com/dev/dec-music/decrypt"
	"jsuse.com/dev/dec-music/internal/sniff"
	"jsuse.com/dev/dec-music/log"
)

type decoder struct {
	raw    io.ReadSeeker
	params *decrypt.DecoderParams

	audio    io.Reader
	audioLen int
	offset   int

	decodedKey []byte
	cipher     decrypt.StreamDecoder

	logger *log.Logger
}

func newDecoder(p *decrypt.DecoderParams) decrypt.Decoder {
	return &decoder{raw: p.Reader, params: p, logger: p.Logger}
}

func (d *decoder) Read(p []byte) (int, error) {
	n, err := d.audio.Read(p)
	if n > 0 {
		d.cipher.Decrypt(p[:n], d.offset)
		d.offset += n
	}
	return n, err
}

func (d *decoder) Validate() error {
	if err := d.searchKey(); err != nil {
		return err
	}

	var err error
	if len(d.decodedKey) > 300 {
		d.cipher, err = newRC4Cipher(d.decodedKey)
	} else if len(d.decodedKey) != 0 {
		d.cipher, err = newMapCipher(d.decodedKey)
	} else {
		d.cipher = newStaticCipher()
	}
	if err != nil {
		return err
	}

	if err := d.validateDecode(); err != nil {
		return err
	}

	if _, err := d.raw.Seek(0, io.SeekStart); err != nil {
		return err
	}
	d.audio = io.LimitReader(d.raw, int64(d.audioLen))
	return nil
}

func (d *decoder) validateDecode() error {
	if _, err := d.raw.Seek(0, io.SeekStart); err != nil {
		return fmt.Errorf("qmc seek to start: %w", err)
	}

	buf := make([]byte, 64)
	if _, err := io.ReadFull(d.raw, buf); err != nil {
		return fmt.Errorf("qmc read header: %w", err)
	}

	d.cipher.Decrypt(buf, 0)
	if _, ok := sniff.AudioExtension(buf); !ok {
		return errors.New("qmc: detect file type failed")
	}
	return nil
}

func (d *decoder) searchKey() (err error) {
	fileSizeM4, err := d.raw.Seek(-4, io.SeekEnd)
	if err != nil {
		return err
	}
	fileSize := int(fileSizeM4) + 4

	if runtime.GOOS == "darwin" && !strings.HasPrefix(d.params.Extension, ".qmc") {
		d.decodedKey, err = readKeyFromMMKV(d.params.FilePath, d.logger)
		if err == nil {
			d.audioLen = fileSize
			return nil
		}
		if d.logger != nil {
			d.logger.Warn("read key from mmkv failed:", err)
		}
	}

	suffixBuf := make([]byte, 4)
	if _, err := io.ReadFull(d.raw, suffixBuf); err != nil {
		return err
	}

	switch string(suffixBuf) {
	case "QTag":
		return d.readRawMetaQTag()
	case "STag":
		return errors.New("qmc: file with 'STag' suffix doesn't contains media key")
	case "cex\x00":
		footer, err := newMusicExTag(d.raw)
		if err != nil {
			return err
		}
		d.audioLen = fileSize - int(footer.tagSize)
		d.decodedKey, err = readKeyFromMMKVCustom(footer.mediaFileName)
		return err
	default:
		size := binary.LittleEndian.Uint32(suffixBuf)
		if size <= 0xFFFF && size != 0 {
			return d.readRawKey(int64(size))
		}
		d.audioLen = fileSize
		return nil
	}
}

func (d *decoder) readRawKey(rawKeyLen int64) error {
	audioLen, err := d.raw.Seek(-(4 + rawKeyLen), io.SeekEnd)
	if err != nil {
		return err
	}
	d.audioLen = int(audioLen)

	rawKeyData, err := io.ReadAll(io.LimitReader(d.raw, rawKeyLen))
	if err != nil {
		return err
	}
	rawKeyData = bytes.TrimRight(rawKeyData, "\x00")

	d.decodedKey, err = deriveKey(rawKeyData)
	return err
}

func (d *decoder) readRawMetaQTag() error {
	if _, err := d.raw.Seek(-8, io.SeekEnd); err != nil {
		return err
	}
	buf, err := io.ReadAll(io.LimitReader(d.raw, 4))
	if err != nil {
		return err
	}
	rawMetaLen := int64(binary.BigEndian.Uint32(buf))

	audioLen, err := d.raw.Seek(-(8 + rawMetaLen), io.SeekEnd)
	if err != nil {
		return err
	}
	d.audioLen = int(audioLen)
	rawMetaData, err := io.ReadAll(io.LimitReader(d.raw, rawMetaLen))
	if err != nil {
		return err
	}

	items := strings.Split(string(rawMetaData), ",")
	if len(items) != 3 {
		return errors.New("invalid raw meta data")
	}

	d.decodedKey, err = deriveKey([]byte(items[0]))
	return err
}

func init() {
	supportedExts := []string{
		"qmc0", "qmc3", "qmc2", "qmc4", "qmc6", "qmc8",
		"qmcflac", "qmcogg", "tkm",
		"bkcmp3", "bkcm4a", "bkcflac", "bkcwav", "bkcape", "bkcogg", "bkcwma",
		"666c6163", "6d7033", "6f6767", "6d3461", "776176", "mmp4",
	}
	for _, ext := range supportedExts {
		decrypt.RegisterDecoder(ext, false , newDecoder)
	}

	for _, ext := range []string{"mgg", "mflac"} {
		decrypt.RegisterDecoder(ext, false , newDecoder)
		for _, suffix := range []string{"0", "1", "a", "h", "l"} {
			decrypt.RegisterDecoder(ext+suffix, false , newDecoder)
		}
	}
}