zlib: fix zstd reset

[jasnell]

Handful of additional bits I noticed while poking around zstd..

• Preserve dictionaries and params when zstd is reset.
• Update missing documentation.
• Reject invalid dictionaries (they would previously no-op)

The rejection is technically a behavior change but zstd is still experimental.

[codecov]

Codecov Report

❌ Patch coverage is 59.45946% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.16%. Comparing base (0de4fcc) to head (aa7a2fe).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_zlib.cc	53.12%	11 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65867      +/-   ##
==========================================
- Coverage   90.17%   90.16%   -0.01%     
==========================================
  Files         771      771              
  Lines      265470   265506      +36     
  Branches    50463    50455       -8     
==========================================
+ Hits       239383   239404      +21     
+ Misses      17055    17048       -7     
- Partials     9032     9054      +22     

Files with missing lines	Coverage Δ
lib/zlib.js	98.42% <100.00%> (+0.26%)	⬆️
src/node_zlib.cc	80.11% <53.12%> (+0.19%)	⬆️

... and 29 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77222/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77338/

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- Loading data for nodejs/node/pull/65867
✔  Done loading data for nodejs/node/pull/65867
----------------------------------- PR info ------------------------------------
Title      zlib: fix zstd reset (#65867)
Author     James M Snell <jasnell@gmail.com> (@jasnell)
Branch     jasnell:jasnell/zstd-reset -> nodejs:main
Labels     c++, zlib, author ready, needs-ci, commit-queue
Commits    3
 - zlib: fix zstd reset
 - doc: fill in missing zstd docs
 - zlib: reject invalid zstd dictionaries
Committers 1
 - James M Snell <jasnell@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/65867
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/65867
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Sun, 06 Sep 2026 22:38:20 GMT
   ✔  Approvals: 3
   ✔  - Trivikram Kamat (@trivikr): https://github.com/nodejs/node/pull/65867#pullrequestreview-5175385386
   ✔  - Filip Skokan (@panva) (TSC): https://github.com/nodejs/node/pull/65867#pullrequestreview-5142709758
   ✔  - Robert Nagy (@ronag) (TSC): https://github.com/nodejs/node/pull/65867#pullrequestreview-5175283787
   ✔  Last GitHub CI successful
   ℹ  Last Full PR CI on 2026-09-11T05:48:47Z: https://ci.nodejs.org/job/node-test-pull-request/77338/
- Querying data for job/node-test-pull-request/77338/
✔  Build data downloaded
   ✔  Last Jenkins CI successful
--------------------------------------------------------------------------------
   ✔  No git cherry-pick in progress
   ✔  No git am in progress
   ✔  No git rebase in progress
--------------------------------------------------------------------------------
- Bringing origin/main up to date...
From https://github.com/nodejs/node
 * branch                  main       -> FETCH_HEAD
✔  origin/main is now up-to-date
- Downloading patch for 65867
From https://github.com/nodejs/node
 * branch                  refs/pull/65867/merge -> FETCH_HEAD
✔  Fetched commits as 0de4fcceb937..aa7a2fea5e5d
--------------------------------------------------------------------------------
[main 5fca60480f] zlib: fix zstd reset
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:27:21 2026 -0700
 3 files changed, 116 insertions(+), 6 deletions(-)
 create mode 100644 test/parallel/test-zlib-zstd-reset.js
[main a1489f96f2] doc: fill in missing zstd docs
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:34:06 2026 -0700
 1 file changed, 7 insertions(+), 1 deletion(-)
[main 0102bb6978] zlib: reject invalid zstd dictionaries
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:35:23 2026 -0700
 3 files changed, 27 insertions(+), 3 deletions(-)
   ✔  Patches applied
There are 3 commits in the PR. Attempting autorebase.
(node:435) [DEP0190] DeprecationWarning: Passing args to a child process with shell option true can lead to security vulnerabilities, as the arguments are not escaped, only concatenated.
(Use `node --trace-deprecation ...` to show where the warning was created)
Rebasing (2/6)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
zlib: fix zstd reset

Preserve dictionaries and params when zstd is reset.

Update missing documentation.

Signed-off-by: James M Snell <jasnell@gmail.com>
Assisted-by: Opencode
PR-URL: https://github.com/nodejs/node/pull/65867
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
--------------------------------------------------------------------------------
[detached HEAD 1ac6b06900] zlib: fix zstd reset
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:27:21 2026 -0700
 3 files changed, 116 insertions(+), 6 deletions(-)
 create mode 100644 test/parallel/test-zlib-zstd-reset.js
Rebasing (3/6)
Rebasing (4/6)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
doc: fill in missing zstd docs

Signed-off-by: James M Snell <jasnell@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/65867
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
--------------------------------------------------------------------------------
[detached HEAD cbfcbfd8f8] doc: fill in missing zstd docs
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:34:06 2026 -0700
 1 file changed, 7 insertions(+), 1 deletion(-)
Rebasing (5/6)
Rebasing (6/6)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
zlib: reject invalid zstd dictionaries

Signed-off-by: James M Snell <jsnell@cloudflare.com>
PR-URL: https://github.com/nodejs/node/pull/65867
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
--------------------------------------------------------------------------------
[detached HEAD c12bd90915] zlib: reject invalid zstd dictionaries
 Author: James M Snell <jsnell@cloudflare.com>
 Date: Sun Sep 6 15:35:23 2026 -0700
 3 files changed, 27 insertions(+), 3 deletions(-)
Successfully rebased and updated refs/heads/main.
--------------------------------------------------------------------------------
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[jasnell]

Landed in 9e7f67f...c143041