macOS '.DS_Store' files

[SkypLabs]

Hello,

This PR aims to add a description for the macOS .DS_Store files generated by the Finder. You can test the description on these files: ds_store_samples.zip

There are two things I would like to improve though:

• The position of certain instances need to be calculated according to alignment_header but I didn't succeed to make it work. I had to manually add 4 to the result as in this example: buddy_allocator_header.ofs_bookkeeping_info_block + 4
• When I try to use _index lines 65 and 66, I get the following error: undefined TypeError: this.directoryEntries[i] is undefined. I think it is the same issue as described in Referencing _index in the pos attribute of a repeated instance produces: undefined local variable or method `i' kaitai_struct#436.

Could you please give me a hand on these two issues?

Thank you in advance.

[GreyCat]

Thanks for this PR! I haven't yet done a through review, but I've noticed that you use ofs_xxx, which follows style guide, but other IDs are not very consistent — i.e. you use xxx_size, xxx_len, length, etc, instead of len_xxx, xxx_count, counter, counter, etc, instead of num_xxxs. Could you consider using consistent names, as per style guide?

The position of certain instances need to be calculated according to alignment_header but I didn't succeed to make it work. I had to manually add 4 to the result as in this example: buddy_allocator_header.ofs_bookkeeping_info_block + 4

Um, sorry, I don't quite follow what you mean here. You want some offsets to be automatically adjusted by size of alignment_header, which is a fixed 4 bytes? If yes, probably you can benefit from kaitai-io/kaitai_struct#84, when it will be available.

When I try to use _index lines 65 and 66...

Try splitting it into separate type, i.e.:

    instances:
      directories:
        io: _root._io
        type: master_block_ref(_index)
        repeat: expr
        repeat-expr: directory_count
        doc: Master blocks of the different B-trees
types:
  master_block_ref:
    params:
      - id: idx
        type: u8
    instances:
      master_block:
        pos: (block_addresses[directory_entries[idx].block_id] >> 0x05 << 0x05) + 4
        size: 1 << block_addresses[directory_entries[idx].block_id] & 0x1f
        type: master_block

[SkypLabs]

I haven't yet done a through review, but I've noticed that you use ofs_xxx, which follows style guide, but other IDs are not very consistent — i.e. you use xxx_size, xxx_len, length, etc, instead of len_xxx, xxx_count, counter, counter, etc, instead of num_xxxs. Could you consider using consistent names, as per style guide?

Of course, thanks for catching that. Actually, I read the style guide and renamed some of the fields accordingly. For example, I searched for occurrences of length and renamed xxx_length to len_xxx. Same for offset. I missed the xxx_size ones and similar fields. It should be fixed now.

Um, sorry, I don't quite follow what you mean here. You want some offsets to be automatically adjusted by size of alignment_header, which is a fixed 4 bytes? If yes, probably you can benefit from kaitai-io/kaitai_struct#84, when it will be available.

Actually, alignment_header has a static size. This is why it is fine to use + 4 in my calculus. However, I was wondering if there is a more elegant way to explicitly refer to this field in pos.

Try splitting it into separate type

I will try and let you know. Thanks.

[GreyCat]

if there is a more elegant way

There will be, once we'll get sizeof-style things done.

[SkypLabs]

Try splitting it into separate type

It works well now 👍

[GreyCat]

Ready for to be merged?

[SkypLabs]

If you're satisfied of my work, yes ☺️

[SkypLabs]

Thanks @KOLANICH and @GreyCat for your awesome review! It was also really instructive. I've learnt a lot about your project.

[KOLANICH]

Thank you for your contribution ;)

[GreyCat]

Just merged in, thanks for this awesome work!