UC2 for Python

Read UltraCompressor II archives using the native UC2 decoder. The package also includes the UC2 command-line program for listing, extraction, archive creation, and stream ingestion. Wheels contain the native code; no separate UC2 install or compiler is needed when a wheel is available.

This is an alpha release. It supports the implemented legacy Huffman methods, master dictionaries, directories, stored versions, and UC2 v3 rANS entries. Turbo/method 80 and multi-volume archives remain unsupported. The Python API is read-only; use the bundled CLI to create archives.

Install and read

python -m pip install --pre uc2
uc2 -l archive.uc2
python -m uc2 -t archive.uc2

Wheels support CPython 3.10-3.14 on Linux x86-64 (glibc), Windows x86-64, and Intel/Apple Silicon macOS.

from uc2 import UC2File

with UC2File("archive.uc2") as archive:
    for info in archive.infolist():
        print(info.filename, info.file_size, info.version)
    contents = archive.read("notes.txt")
    archive.verify()
    archive.extractall("restored")

The constructor accepts a path or a seekable binary file, including BytesIO. Caller-owned files stay open; their seek position changes. Keep the source unchanged while the archive is open. Each thread should use its own UC2File.

infolist() and namelist() return the newest version of each path by default. Use infolist(all_versions=True) to include older entries. A literal semicolon in a filename remains part of the name:

with UC2File("archive.uc2") as archive:
    newest = archive.read("notes.txt")
    older = archive.read("notes.txt", version=1)
    literal_name = archive.read("notes.txt;1")

UC2Info records the name, uncompressed and compressed sizes, DOS timestamp (a naive datetime, or None if invalid), attributes, method, version, and is_dir(). Metadata objects can be passed directly to read, extract, and copy_to. They belong to the archive that produced them.

Limits and extraction

Defaults are 100,000 entries, 64 MiB of decoder allocations, 64 MiB per read, 1 GiB per streamed file, and 1 GiB total per extractall or verify call. Constructor keywords are max_entries, max_decoder_memory, max_read_size, max_extract_size, and max_total_size. They must be positive integers. The decoder limit excludes Python metadata and caller-owned buffers. Archive offsets and this reader are limited to 32 bits. These limits are not a CPU-time sandbox for hostile input.

copy_to(member, binary_file) decodes without collecting the file in memory. Its output may be partial if decoding or writing fails. extract and extractall instead stage each file and install it after its UC2 checksum passes. Existing files are preserved unless overwrite=True is supplied. Earlier successfully extracted files remain if a later member fails.

Extraction rejects absolute paths, traversal, reserved Windows names, control characters, ambiguous case-folded names, and links below the destination. It uses file-descriptor-relative operations without following links on POSIX. Windows checks links and reparse points; use a destination that other processes cannot modify during extraction. The explicitly chosen destination itself may be a symlink. POSIX files use mode 0600 and directories use 0755, both masked by the process umask. Archived permissions and timestamps are exposed as metadata but not applied.

Errors include BadArchiveError, ResourceLimitError, UnsafePathError, and ordinary Python I/O exceptions. Verification uses the archive's legacy checksums, which are not cryptographic authentication. A missing entry or version raises KeyError.

Read-only Linux mount

python -m pip install --pre 'uc2[mount]'
mkdir archived
uc2-mount archive.uc2 archived --cache-mib 512

The mount runs in the foreground. Use another terminal to browse archived/files and archived/versions/1, then unmount with fusermount -u archived. Linux libfuse2 and /dev/fuse are required. Files decode on first access into a checksum-verified disk cache; an entry larger than its budget fails with EFBIG. The default cache holds up to 512 MiB and 128 files. Decoder allocations are limited to 64 MiB and released after every decode. Python metadata is outside that budget and has separate entry and node limits. See the mount documentation for options, stored versions, and error behavior.

Build from source

Requires Python 3.10+, CMake, and a C99 compiler. The build backend obtains CMake when necessary.

python -m pip install .
python -m build

Source, releases, and the project roadmap are at github.com/evvaletov/uc2.

The distribution contains GPL-3.0-or-later and LGPL-3.0-only code. Independently written Python integration code also has a BSD-2-Clause option. This does not change the licenses of the bundled core or third-party code. License texts, credits, and the per-file audit are included in the distribution.