zlib: preserve brotli params and dictionary on reset by xia-chao · Pull Request #66157 · nodejs/node

xia-chao · 2026-09-20T12:45:28Z

reset() on a Brotli compressor or decompressor threw away the quality/params
and dictionary you set at construction. Nothing failed — the next compress just
ran with the defaults, and a dictionary decoder then rejected the frame.

Fixes: #66156

The problem

BrotliEncoderContext::ResetStream and BrotliDecoderContext::ResetStream
both did return Init(); with no arguments. Init() clears dictionary_ and
builds a brand-new Brotli instance. It never replays SetParams.

So this:

const s = zlib.createBrotliCompress({
  dictionary,
  params: { [zlib.constants.BROTLI_PARAM_QUALITY]: 0 },
});
s.reset();
s.end(input);

compressed as if you had written createBrotliCompress() with no options.
A decoder created with that same dictionary, then reset, failed with
ERR__ERROR_FORMAT_DICTIONARY.

reset() is supposed to start a new session on the same stream, not throw
the constructor options away. That is already documented for Zstd, and
test/parallel/test-zlib-zstd-reset.js already asserts it.

This is not #66087 / #66088. Those are about flush() then reset() leaving
a broken frame. Here there is no write at all — only the configuration is
dropped.

The fix

Remember each successful SetParams call. On reset(), copy the stored
dictionary and params, Init() with that dictionary, then replay the params
on the new instance. Encoder and decoder both do this.

After the change, the snippet above keeps quality 0 and the dictionary.
createBrotliDecompress({ dictionary }).reset() can still decode a
dictionary-compressed frame.

Tests

test/parallel/test-zlib-brotli-reset.js mirrors the zstd reset tests:
compress options survive reset(), and a decoder keeps its dictionary.

ResetStream currently calls Init() with no arguments, which drops the stored dictionary and never replays SetParams. Remember each successful parameter and replay both the dictionary and the params when the stream is reset. Fixes: nodejs#66156 Signed-off-by: Xia Chao <[email protected]>

The markdown linter rejects pr-url: REPLACEME. Signed-off-by: Xia Chao <[email protected]>

xia-chao · 2026-09-20T12:58:24Z

@jasnell
Please review

codecov · 2026-09-20T14:48:23Z

Codecov Report

❌ Patch coverage is 57.57576% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.27%. Comparing base (92395e7) to head (30963df).
⚠️ Report is 119 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_zlib.cc	57.57%	9 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66157      +/-   ##
==========================================
- Coverage   90.28%   90.27%   -0.02%     
==========================================
  Files         790      790              
  Lines      271974   272007      +33     
  Branches    51919    51936      +17     
==========================================
- Hits       245560   245550      -10     
- Misses      16907    16952      +45     
+ Partials     9507     9505       -2

Files with missing lines	Coverage Δ
src/node_zlib.cc	`79.53% <57.57%> (-0.26%)`	⬇️

... and 32 files with indirect coverage changes

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nodejs-github-bot · 2026-09-21T03:02:52Z

CI: https://ci.nodejs.org/job/node-test-pull-request/77695/

xia-chao · 2026-09-21T10:05:55Z

@MikeMcC399
This Jenkins has been unstable and failed again recently, it may need to be resolved

MikeMcC399 · 2026-09-21T10:25:49Z

This Jenkins has been unstable and failed again recently, it may need to be resolved

There have also been reports in Slack https://openjs-foundation.slack.com/archives/C03BJP63CH0 about this issue. Hopefully the build team will be taking a look. Unfortunately I don't have any influence on this, but if it is affecting multiple PRs, then I would assume it is going to get fixed soon.

nodejs-github-bot · 2026-09-25T07:55:39Z

CI: https://ci.nodejs.org/job/node-test-pull-request/77876/

nodejs-github-bot · 2026-09-26T18:28:07Z

Landed in 1e0167d

ResetStream currently calls Init() with no arguments, which drops the stored dictionary and never replays SetParams. Remember each successful parameter and replay both the dictionary and the params when the stream is reset. Fixes: #66156 Signed-off-by: Xia Chao <[email protected]> PR-URL: #66157 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Filip Skokan <[email protected]>

ResetStream currently calls Init() with no arguments, which drops the stored dictionary and never replays SetParams. Remember each successful parameter and replay both the dictionary and the params when the stream is reset. Fixes: nodejs#66156 Signed-off-by: Xia Chao <[email protected]> PR-URL: nodejs#66157 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Filip Skokan <[email protected]>

ResetStream currently calls Init() with no arguments, which drops the stored dictionary and never replays SetParams. Remember each successful parameter and replay both the dictionary and the params when the stream is reset. Fixes: #66156 Signed-off-by: Xia Chao <[email protected]> PR-URL: #66157 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Filip Skokan <[email protected]>

…i stream It started the new stream with the defaults, as Node did until nodejs/node#66157. The dictionaries move from the old encoder or decoder to the new one, so they are neither copied nor indexed again. Also a test through node:zlib for a stream offset with a dictionary.

ResetStream currently calls Init() with no arguments, which drops the stored dictionary and never replays SetParams. Remember each successful parameter and replay both the dictionary and the params when the stream is reset. Fixes: #66156 Signed-off-by: Xia Chao <[email protected]> PR-URL: #66157 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Filip Skokan <[email protected]>

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. needs-ci PRs that need a full CI run. zlib Issues and PRs related to the zlib module and its compression dependencies. labels Sep 20, 2026

doc: use PR URL in zlib.reset YAML

30963df

The markdown linter rejects pr-url: REPLACEME. Signed-off-by: Xia Chao <[email protected]>

jasnell approved these changes Sep 20, 2026

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robobun mentioned this pull request Sep 30, 2026

node:zlib: reset a zstd stream in place, keep its dictionary and parameters oven-sh/bun#44261

Open

github-actions Bot mentioned this pull request Oct 5, 2026

2026-10-07, Version 26.11.0 (Current) #66546

Merged

dylan-conway mentioned this pull request Oct 27, 2026

Replace the brotli C library with safe Rust oven-sh/bun#47073

Closed

leapmux-renovate Bot mentioned this pull request Nov 1, 2026

chore(deps): Update Node.js to v26 leapmux/leapmux#578

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zlib: preserve brotli params and dictionary on reset - #66157

zlib: preserve brotli params and dictionary on reset#66157
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xia-chao:zlib-brotli-reset-preserves

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