packkit/brotli

Brotli codec — pure-Gleam decoder.

Decodes RFC 7932 brotli streams, including:

• The canonical empty stream 0x3F.
• Any stream that uses uncompressed metablocks (ISUNCOMPRESSED bit set).
• Compressed metablocks with both simple-form (RFC 7932 §3.4) and complex-form (§3.5) prefix-code descriptors.
• The command loop (§4): insert-and-copy alphabet → literals from the literal prefix code → distance code → LZ77 copy from the sliding window, with the 4-entry recent-distance ring buffer.
• Static-dictionary references (§8): any command whose resolved distance exceeds the current output position falls back to the embedded 122 KiB dictionary, with the prefix / suffix / OMIT_FIRST / OMIT_LAST / UPPERCASE_FIRST / UPPERCASE_ALL transforms applied per transform_idx.
• Context-mapped literal and distance trees (§7.3) when NTREES > 1, including the RLEMAX zero-run encoding and the optional inverse move-to-front transform.
• Block switching (§6) when NBLTYPES > 1: each category tracks its own block-type prefix code, a 26-symbol block-length code, and a 2-entry recent-type ring buffer that feeds back into context-map indexing so the right tree is picked for every symbol.

Encode side:

• The encoder emits only uncompressed metablocks (one per chunk of up to 65 536 bytes), wrapped in the canonical WBITS=16 prefix. That produces a valid RFC 7932 stream that any conforming brotli decoder accepts; it does no actual compression but lets packkit.compress(..., with: codec.brotli()) round-trip end-to-end with packkit.decompress.

The SHIFT_FIRST / SHIFT_ALL transforms used by the shared-dictionary extension (RFC 8478) are deliberately omitted because the basic RFC 7932 transform set never selects them and this decoder does not accept a custom shared dictionary in the first place. Implementing them in isolation would create dead code; they will be added together with full shared-dictionary support if and when that feature lands.

pub fn codec() -> codec.Codec

pub fn decode(
  bytes bytes: BitArray,
) -> Result(BitArray, error.CodecError)

pub fn decode_with_limits(
  bytes bytes: BitArray,
  limits limits: limit.Limits,
) -> Result(BitArray, error.CodecError)

pub fn encode(
  bytes bytes: BitArray,
) -> Result(BitArray, error.CodecError)