contrib/libarchive/ contains a design doc, an annotated skeleton of
archive_read_support_format_uc2(), and a CMake target that gates the
build on -DUC2_BUILD_LIBARCHIVE_PLUGIN=ON plus find_package(LibArchive).
The skeleton has the five required callbacks (bid, read_header,
read_data, read_data_skip, cleanup) with TODO markers at each
implementation point. The bid function has the magic-byte check
ready; the rest call into libuc2 for parsing and decompression.
libarchive's read-format API is internal; an out-of-tree .so cannot
be loaded into an unmodified libarchive. The integration plan in
contrib/libarchive/README.md is to upstream the file as a PR against
libarchive/libarchive. Full implementation is tracked as
git-bug b0b06a5.
Eremey Valetov
b697baef43