Read value on a given offset and return pointer back.

[Zekfad]

Hi, thank you for the great package!

It would be nice to have a flag for offset options to be able to restore offset after reading referenced chunk.

I have an archive structure that have sparsely referenced buffers. I'm using the following reader method:

type File struct {
	Offset uint64
	Size uint32
	
	InlineBuffer []byte `bin:"FileReadInlineBuffer"`
	// desired
	// InlineBuffer []byte `bin:"offsetStart:Offset, len:Size, restoreOffsetOrSomeBetterNameForThisFlag:true"`
}

func (file *File) FileReadInlineBuffer(r binstruct.Reader) error {
	oldPos, err := r.Seek(0, io.SeekCurrent)
	if err != nil {
		return err
	}

	_, err = r.Seek(int64(file.Offset), io.SeekStart)
	if err != nil {
		return err
	}

	size := int(file.Size)
	file.InlineBuffer = make([]byte, size)
	n, err := r.Read(file.InlineBuffer)
	if err != nil {
		return err
	}
	if n != size {
		return fmt.Errorf("failed to read inline buffer: expected %d bytes, got: %d", size, n)
	}

	_, err = r.Seek(oldPos, io.SeekStart)
	if err != nil {
		return err
	}
	return nil
}

[ghostiam]

Hi, check out the new version.

func Test_OffsetRestore(t *testing.T) {
	var v struct {
		Offset uint8
		Size   uint8
		Data   []byte `bin:"offsetStart:Offset,len:Size,offsetRestore"`
		Other  []byte `bin:"len:3"`
	}

	err := UnmarshalBE([]byte{0x05, 0x02, 0x01, 0x02, 0x03, 0x04, 0x05}, &v)
	require.NoError(t, err)
	require.Equal(t, uint8(5), v.Offset)
	require.Equal(t, uint8(2), v.Size)
	require.Equal(t, []byte{0x04, 0x05}, v.Data)
	require.Equal(t, []byte{0x01, 0x02, 0x03}, v.Other)
}

[Zekfad]

Thank you very much, works like a charm!