brotli_neo

Pure Dart Brotli (RFC 7932) encoder and decoder.

• Pure Dart: no native assets, no FFI in the codec, works on the VM and on the web (dart2js / dart2wasm).
• Zero-copy bytes: first-class blit integration (Bytes, BytesLike, BytesMut, BytesFile).
• Implemented: RFC 7932 decoder (static dictionary, 121 transforms, large-window decode), encoder quality 0–11 with block splitting, 13-context modeling, static-dictionary matching, RLE histograms, guided parsing and large-window encoding; compound dictionary encode + decode, including a reusable BrotliPreparedDictionary; serialized shared-dictionary decode; streaming encoder and decoder; blit-native, compat and file APIs.
• Format coverage: no remaining Brotli format extensions; future work is ratio/speed tuning and ecosystem integration.
• Two API layers:
  • brotli_neo.dart: blit-native (BytesLike in, Bytes out);
  • compat.dart: Uint8List/List<int>, dart:convert codec and package:brotli-style functions.

Status: 0.1.2. The decoder is byte-exact on all 22 RFC corpus pairs; the encoder covers quality 0–11 and the public streaming/compat/file APIs are usable. CI runs the VM, browser, Wasm and Rust-oracle suites.

Getting started

dependencies:
  brotli_neo: ^0.1.0

import 'package:brotli_neo/brotli_neo.dart';

final compressed = brotliEncode(Bytes.fromList([1, 2, 3, 4]));
final raw = brotliDecode(compressed);

For a Uint8List API:

import 'package:brotli_neo/compat.dart';

final compressed = brotliCompress(Uint8List.fromList([1, 2, 3, 4]));
final raw = brotliDecompress(compressed);

A stream produced with a Rust-style compound dictionary can be decoded by attaching the same bytes, and the encoder can produce one:

final raw = brotliDecompress(
  compressed,
  options: BrotliDecodeOptions(compoundDictionary: dictionary),
);
final compressed = brotliCompress(
  raw,
  options: BrotliEncodeOptions(compoundDictionary: dictionary),
);

Serialized shared dictionaries (shared-brotli format) are attached on decode:

final raw = brotliDecompress(
  compressed,
  options: BrotliDecodeOptions(sharedDictionary: serializedDictionary),
);

Streaming in both directions:

final encoder = BrotliEncoder();
encoder.add(Bytes.fromList([1, 2, 3, 4]));
encoder.flush();          // optional: emit the pending block, keep the stream open
encoder.finish();
final compressed = encoder.takeOutput();

final decoder = BrotliDecoder();
decoder.addInput(compressed);
decoder.closeInput();
final out = Uint8List(64 * 1024);
while (decoder.decode(out) != BrotliStatus.done) {
  // consume decoder.bytesWritten bytes of `out`
}

Development

dart pub get
dart analyze
dart test

CI runs Ubuntu/Windows/macOS, Chrome browser tests, the JS/Wasm compiles and the full suite against the Rust oracle (tool/oracle_rust). For the full local suite build it and point BROTLI_ORACLE at the executable:

cargo build --release --locked --manifest-path tool/oracle_rust/Cargo.toml
BROTLI_ORACLE=tool/oracle_rust/target/release/brotli-oracle dart test

Conformance data

test/testdata contains the 22 raw/compressed pairs and 23 malformed variants from google/brotli tests/testdata (MIT). manifest.json records sizes and SHA-256 hashes. See NOTICE for attribution.

Benchmarks

Four core operations (decode/encode on 1 MiB text and binary at quality 5) are measured with benchmark_test for Dart JIT/AOT/JS/WASM and for the authoritative Rust brotli crate. The five series are normalized to bytes/second and rendered with benchcat into the card above. The single CI workflow runs the tests first, then the benchmark, then commits the changed SVG to assets/ with [skip ci].

License

MIT. The static dictionary, context table and test corpus are derived from Google's Brotli reference implementation (MIT); see LICENSE and NOTICE.