Brotli support?

[ericlaw1979]

A while back, Chromium started using Brotli compression on textual resources. It doesn't look like the unpacker handles that?

If I strip 8 bytes off the front of the file extracted from unpack.bat, I can then use brotli.exe to uncompress the resource.

[myfreeer]

References:
https://github.com/chromium/chromium/blob/c4d3c31083a2e1481253ff2d24298a1dfe19c754/tools/grit/grit/node/base.py#L657
https://github.com/chromium/chromium/blob/c4d3c31083a2e1481253ff2d24298a1dfe19c754/ui/base/resource/resource_bundle.h#L58
https://datatracker.ietf.org/doc/html/rfc7932#page-31

Format of brotli compressed resource:
2 bytes header: {0x1e, 0x9b}
6 bytes decompressed size: truncated to 6 bytes, little-endian.
compressed brotli stream

For unpacking we can detect the header bytes and truncate header and decompressed size from output, but for packing we have to parse the brotli stream, iterating all meta blocks, and restore the decompressed size, which takes time to implement.

Update: seems impossible to get uncompressed size without decompression google/brotli#861

Maybe we can make a chromium-specific brotli compression tool for this chromium-specific brotli compression format.

[myfreeer]

See experimental work at https://github.com/myfreeer/chrome-pak-customizer/tree/3.x

[0xZOne]

Why not use pak_util.py?

usage: pak_util.py [-h] {repack,extract,create,print,list-id} ...

A tool for interacting with .pak files.

For details on the pak file format, see:
https://dev.chromium.org/developers/design-documents/linuxresourcesandlocalizedstrings

positional arguments:
  {repack,extract,create,print,list-id}
    repack              Combines several .pak files into one.
    extract             Extracts pak file
    create              Creates pak file from extracted directory.
    print               Prints all pak IDs and contents. Useful for diffing.
    list-id             Outputs all resource IDs to a file.

options:
  -h, --help            show this help message and exit