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What it’s for

brotli binds libbrotli, the reference Brotli library, through a small C shim it loads at run time. BROTLI is one of Parquet’s page codecs, and parquet-full uses this to read and write it. It is a binding, not an implementation: the speed is libbrotli’s.

Install

A new project needs Modular’s channel, pixi’s build preview and the compiler before the tin:

pixi init app -c https://conda.modular.com/max -c conda-forge && cd app
sed -i.bak 's/^\[workspace\]/[workspace]\npreview = ["pixi-build"]/' pixi.toml
pixi add "mojo-compiler==1.2.0"
pixi shelf add brotli-mojo     # no shelf dependencies; builds the shim against conda-forge libbrotli

pixi builds the shim, libbrotlimojo.dylib on macOS and libbrotlimojo.so on Linux, into the environment’s lib. You need no link flags.

Quick start

Compress a page at a Parquet-friendly quality, then decode it with and without its size:

from brotli import compress, decoder_version, decompress, decompress_unsized


def main() raises:
    var page = List[UInt8]()
    for i in range(100_000):
        page.append(UInt8(i % 7))

    var stream = compress(page, quality=5)   # the default, 11, is slow
    # Parquet: the page header carries the size, so decode in one pass.
    var back = decompress(stream, len(page))
    # Anything else: the decoder grows its buffer until the stream fits.
    var again = decompress_unsized(stream)
    print("libbrotli", decoder_version())
    print(len(stream), "bytes,", back == page, again == page)

API

Everything is exported from brotli.

• compress(data: Span[UInt8, _], quality: Int = DEFAULT_QUALITY, lgwin: Int = DEFAULT_WINDOW_BITS, mode: Int = MODE_GENERIC) raises -> List[UInt8]: one stream. quality is 0 to 11, lgwin the window in bits, 10 to 24, and mode a hint: MODE_GENERIC, MODE_TEXT or MODE_FONT.
• decompress(data: Span[UInt8, _], uncompressed_size: Int) raises -> List[UInt8]: one pass into a buffer of exactly that size, the Parquet path.
• decompress_into(data: Span[UInt8, _], dst: Span[mut=True, UInt8, _]) raises -> Int: into a buffer you own; returns the bytes written.
• decompress_unsized(data: Span[UInt8, _]) raises -> List[UInt8]: when you don’t know the size. It starts at 8 times the input and doubles, decoding from the start each time.
• encoder_version() raises -> String and decoder_version() raises -> String: the libbrotli versions loaded, such as 1.2.1.

The constants are MIN_QUALITY (0), MAX_QUALITY (11), DEFAULT_QUALITY (11), MIN_WINDOW_BITS (10), MAX_WINDOW_BITS (24) and DEFAULT_WINDOW_BITS (22).

Errors and limits

• A Brotli stream records no decoded size anywhere, which is why sized and unsized decoding are separate calls. Prefer the sized one whenever you know the size.
• decompress treats a stream that decodes to a different length as corrupt: brotli.decompress: size mismatch (got <n>, expected <m>), or stream decodes to more than the <m> bytes it was said to hold. A cut-off stream raises brotli.decompress: input ended mid-stream, other decoder failures carry libbrotli’s own error string, and decompress_into raises destination too small rather than growing.
• quality 11, the default, runs at single-digit MB/s on large inputs; 4 or 5 is the usual choice for Parquet pages.
• The shim is looked for in $CONDA_PREFIX/lib, then next to the executable and in its ../lib, then on the binary’s rpath. If none has it, the first call raises brotli.mojo: cannot load libbrotlimojo.dylib; looked in: ... and says to set CONDA_PREFIX.
• The shim is opened once per process and never closed, so page-sized calls stay cheap.

Tests

pixi run test round-trips sizes from 0 B to 1 MiB across qualities, window sizes and all three modes, and checks every error path. Three streams produced by CPython’s brotli package are baked in as constants and decoded: a stored block, a quality-5 stream that uses the static dictionary and a quality-9 stream of back-references. It runs again with CONDA_PREFIX unset to test the library search. CI runs it on Linux and macOS with Mojo 1.2.0 and nightly.

The full reference is the README on GitHub.