Method init

reader.go:384–582

nolint:cyclop,funlen,gocognit,gocyclo,maintidx

(r io.ReaderAt, size int64)

//nolint:cyclop,funlen,gocognit,gocyclo,maintidx
func (z *Reader) init(r io.ReaderAt, size int64) (err error) {
	h := crc32.NewIEEE()
	tra := plumbing.TeeReaderAt(r, h)

	var (
		signature = []byte{'7', 'z', 0xbc, 0xaf, 0x27, 0x1c}
		offsets   []int64
	)

	offsets, err = findSignature(r, signature)
	if err != nil {
		return err
	}

	if len(offsets) == 0 {
		return errFormat
	}

	var (
		sr    *io.SectionReader
		off   int64
		start startHeader
	)

	for _, off = range offsets {
		sr = io.NewSectionReader(tra, off, size-off) // Will only read first 32 bytes

		var sh signatureHeader
		if err = binary.Read(sr, binary.LittleEndian, &sh); err != nil {
			return fmt.Errorf("sevenzip: error reading signature header: %w", err)
		}

		z.r = r

		h.Reset()

		if err = binary.Read(sr, binary.LittleEndian, &start); err != nil {
			return fmt.Errorf("sevenzip: error reading start header: %w", err)
		}

		// CRC of the start header should match
		if util.CRC32Equal(h.Sum(nil), sh.CRC) {
			break
		}

		err = errChecksum
	}

	if err != nil {
		return err
	}

	// Work out where we are in the file (32, avoiding magic numbers)
	if z.start, err = sr.Seek(0, io.SeekCurrent); err != nil {
		return fmt.Errorf("sevenzip: error seeking current position: %w", err)
	}

	// Seek over the streams