[ronag]

SSL_read() returns at most one TLS record per call, and TLSWrap::ClearOut() emits a separate read for each one. Records can be up to 16 KiB, but plenty of servers send smaller ones: nginx defaults ssl_buffer_size to 4 KiB, and servers that do dynamic record sizing start out at around 1 KiB. Every record then pays for its own buffer allocation and call into JS.

With this change ClearOut() keeps calling SSL_read() into the same 16 KiB buffer while the next record in enc_in_ is application data. It never waits for more input, it only merges records that have already arrived, and reads never get bigger than one full record already makes them.

Some notes:

• Batching stops in front of any other record type, and in front of application data records that are short enough to be empty, since SSL_read() skips empty records and goes straight on to the next one. In TLS 1.2 that means handshake and alert records are still processed after the preceding data has been emitted, so a 'data' handler can e.g. still call disableRenegotiation() before a renegotiation that arrived in the same read. test-tls-coalesce-renegotiation covers that, and fails if the record type check is removed.
• When SSL_read() fails in the middle of a batch, SSL_get_error() and the error are still read right away, as before. The batched data is emitted next, then the error or EOF.
• TLS 1.3 encrypts post-handshake messages, so a NewSessionTicket or KeyUpdate can't be told apart from data by its record header. If one arrives together with data, 'session' or 'keylog' can now be emitted before the 'data' that came before it. There is no documented ordering between those events and 'data'. Keeping it would mean emitting data from inside OpenSSL callbacks, with the reentrancy problems that brings, so I didn't.
• 'data' chunks no longer line up with records, so test-tls-max-send-fragment now checks the record sizes on the wire through a small proxy.
• I also tried a 64 KiB buffer, which lets full 16 KiB records merge too. It was only 2-5 points faster than 16 KiB in the runs below, and a paused stream then buffers up to one extra 64 KiB chunk past its high water mark (pummel/test-https-no-reader fails), so I kept 16 KiB.

benchmark/tls/throughput-s2c.js gets a recordlen option, which sets the server's setMaxSendFragment().

Results on an AMD EPYC 9355P (Linux, Docker, 16 CPUs on one NUMA node, benchmark pinned to one CPU), 10 runs each, MiB/s:

recordlen	recvbuflen	before	after
1024	0	667 ± 10	945 ± 7	+41.6% ***
4096	0	1456 ± 41	1833 ± 17	+25.9% ***
16384	0	2271 ± 63	2235 ± 66	-1.6%
1024	65536	913 ± 14	1083 ± 15	+18.6% ***
4096	65536	2011 ± 16	2127 ± 13	+5.8% ***
16384	65536	2826 ± 10	2816 ± 11	-0.4%

$ node benchmark/compare.js --old ./node-base --new ./node-new --runs 10 \
    --filter throughput-s2c --set CPUSET=21 --set dur=3 --set type=buf \
    --set sendchunklen=16777216 --set recvbufgenfn=false \
    --set recvbuflen=0 --set recvbuflen=65536 --analyze tls

[nodejs-github-bot]

Review requested:

• @nodejs/crypto

[Copilot]

🟡 Changes recommended

Additional SSL reads can let renegotiation callbacks overtake preceding application data.

1 open finding

• TLS renegotiation callback can overtake buffered application data · New

What changed in this PR

Coalesces buffered TLS records into 16 KiB reads to reduce per-record overhead.

Changes:

• Batches decrypted records while preserving EOF and TLS error handling.
• Adds coalescing, small-buffer, EOF, and corruption tests.
• Updates fragment-size validation to inspect wire records.

File	Description
src/​crypto/​crypto_tls.cc	Implements record coalescing and deferred error emission.
src/​crypto/​crypto_tls.h	Declares extracted TLS error helpers.
test/​parallel/​test-tls-coalesce-records.js	Adds coalescing regressions.
test/​parallel/​test-tls-max-send-fragment.js	Validates fragment sizes on the wire.

🧠 Review effort: Balanced

---

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[Copilot]

🟡 Changes recommended

TLS 1.3 protocol records can trigger callbacks before preceding application data is emitted.

1 open finding

• TLS 1.3 control records can overtake buffered application data · New

1 resolved since last review

• TLS renegotiation callback can overtake buffered application data

🧠 Review effort: Balanced

[Copilot]

🟡 Changes recommended

The implementation raises the read cap to 64 KiB despite the stated requirement to preserve 16 KiB behavior.

1 open finding

• Restore the 16 KiB chunk limit or justify the 64 KiB increase · New

2 resolved since last review

• TLS 1.3 control records can overtake buffered application data
• TLS renegotiation callback can overtake buffered application data

🧠 Review effort: Balanced

[Copilot]

🟡 Changes recommended

A data callback can synchronously destroy the SSL object while an OpenSSL callback is still using it.

2 open findings

• Defer SSL destruction during callbacks to prevent use-after-free · New
• Restore the 16 KiB chunk limit or justify the 64 KiB increase

🧠 Review effort: Balanced

[Copilot]

🔵 Needs a closer look

Native TLS callback and lifetime changes require human review and completion of the stated runtime validation.

1 open finding

• Restore the 16 KiB chunk limit or justify the 64 KiB increase

1 resolved since last review

• Defer SSL destruction during callbacks to prevent use-after-free

🧠 Review effort: Balanced

[codecov]

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.50%. Comparing base (c883ccf) to head (6f8a340).
⚠️ Report is 134 commits behind head on main.

Files with missing lines	Patch %	Lines
src/crypto/crypto_tls.cc	85.18%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66698      +/-   ##
==========================================
- Coverage   92.82%   90.50%   -2.33%     
==========================================
  Files         422      797     +375     
  Lines      194189   278211   +84022     
  Branches    30039    53450   +23411     
==========================================
+ Hits       180257   251787   +71530     
- Misses      13607    16797    +3190     
- Partials      325     9627    +9302     

Files with missing lines	Coverage Δ
src/crypto/crypto_tls.cc	78.40% <85.18%> (ø)

... and 533 files with indirect coverage changes

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• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

🔵 Needs a closer look

An unresolved empty-record ordering issue and changes to TLS callback behavior require human review and CI validation.

1 open issue

• Empty TLS record bypasses renegotiation guard before payload handler · New

1 resolved since last review

• Restore the 16 KiB chunk limit or justify the 64 KiB increase

_{Review effort: Balanced}

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78468/

[Copilot]

🔵 Needs a closer look

Native TLS read-loop and callback-ordering changes require final human review and CI verification.

No open issues 🎉

_{Review effort: Balanced}

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78485/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78504/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78506/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78507/

[nodejs-github-bot]

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----------------------------------- PR info ------------------------------------
Title      tls: coalesce buffered records into one read (#66698)
Author     Robert Nagy <ronagy@icloud.com> (@ronag)
Branch     ronag:codex/tls-coalesce-buffered-records -> nodejs:main
Labels     crypto, c++, needs-ci, commit-queue
Commits    3
 - tls: coalesce buffered records into one read
 - test: fix TLS tests for coalesced records
 - tls: retain debug output when buffered reads destroy SSL
Committers 1
 - Robert Nagy <ronagy@icloud.com>
PR-URL: https://github.com/nodejs/node/pull/66698
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/66698
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Tue, 13 Oct 2026 07:29:15 GMT
   ✔  Approvals: 2
   ✔  - Yagiz Nizipli (@anonrig) (TSC): https://github.com/nodejs/node/pull/66698#pullrequestreview-5572396658
   ✔  - Ben Noordhuis (@bnoordhuis): https://github.com/nodejs/node/pull/66698#pullrequestreview-5590395478
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 * branch                  main       -> FETCH_HEAD
   b85dd8021c..8c345413c1  main       -> origin/main
✔  origin/main is now up-to-date
main is out of sync with origin/main. Mismatched commits:
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 - 9731991b3c tls: fix ip normalization regression
 - 9ccbc81ece tls: reject non-canonical IP addresses
 - c5f5cb5b96 zlib: avoid caching invalid ZIP local headers
 - 5faa1497e0 src: fix the fs permission tree node on wildcard nodes
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--------------------------------------------------------------------------------
Auto-merging src/crypto/crypto_tls.cc
[main 878632c789] tls: coalesce buffered records into one read
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Sat Oct 17 09:16:36 2026 +0200
 5 files changed, 302 insertions(+), 29 deletions(-)
 create mode 100644 test/parallel/test-tls-coalesce-records.js
 create mode 100644 test/parallel/test-tls-coalesce-renegotiation.js
[main e8571570cb] test: fix TLS tests for coalesced records
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Sun Oct 18 09:23:59 2026 +0200
 2 files changed, 13 insertions(+), 4 deletions(-)
Auto-merging src/crypto/crypto_tls.cc
[main 9420023c17] tls: retain debug output when buffered reads destroy SSL
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Mon Oct 19 15:30:21 2026 +0200
 1 file changed, 7 insertions(+), 1 deletion(-)
   ✔  Patches applied
There are 3 commits in the PR. Attempting autorebase.
(node:488) [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 ----------------------------------
tls: coalesce buffered records into one read

SSL_read() returns at most one TLS record, and ClearOut() emitted a
separate read for each one. Peers that use small records, such as
nginx with its default 4 KiB ssl_buffer_size or servers doing dynamic
record sizing, made every record pay for its own buffer allocation
and call into JavaScript.

While the next buffered record is application data, keep reading into
the same 16 KiB buffer before emitting it, so reads never get larger
than one full record already makes them. Batching stops before any
other record type, so that e.g. a TLS 1.2 renegotiation is still
processed after the data in front of it has been emitted. It also
stops before records short enough to be empty, because SSL_read()
skips empty records and carries on with the next one. If SSL_read()
fails in the middle of a batch, the error is captured first and
reported after the data.

test-tls-max-send-fragment relied on 'data' chunks matching records,
so it now checks the record sizes on the wire.

Signed-off-by: Robert Nagy <ronagy@icloud.com>
Assisted-by: claude:opus-5.5
PR-URL: https://github.com/nodejs/node/pull/66698
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
--------------------------------------------------------------------------------
[detached HEAD 7b3ecb9362] tls: coalesce buffered records into one read
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Sat Oct 17 09:16:36 2026 +0200
 5 files changed, 302 insertions(+), 29 deletions(-)
 create mode 100644 test/parallel/test-tls-coalesce-records.js
 create mode 100644 test/parallel/test-tls-coalesce-renegotiation.js
Rebasing (3/6)
Rebasing (4/6)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
test: fix TLS tests for coalesced records

test-double-tls-client expected the head and the inner ClientHello in
separate 'data' chunks. Now that buffered records are read together,
both can arrive in one chunk, so put back whatever follows the head
before handing the socket to the inner server.

BoringSSL reports the corrupted record in test-tls-coalesce-records as
ERR_SSL_BAD_DECRYPT.

Signed-off-by: Robert Nagy <ronagy@icloud.com>
Assisted-by: claude:opus-5.5
PR-URL: https://github.com/nodejs/node/pull/66698
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
--------------------------------------------------------------------------------
[detached HEAD 13470cde60] test: fix TLS tests for coalesced records
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Sun Oct 18 09:23:59 2026 +0200
 2 files changed, 13 insertions(+), 4 deletions(-)
Rebasing (5/6)
Rebasing (6/6)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
tls: retain debug output when buffered reads destroy SSL

Log the captured SSL error when emitting buffered plaintext destroys the
SSL context before onerror can run. Clarify that an incomplete next
record can return WANT_READ and still flush the accumulated plaintext.

Signed-off-by: Robert Nagy <ronagy@icloud.com>
Assisted-by: Codex
PR-URL: https://github.com/nodejs/node/pull/66698
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
--------------------------------------------------------------------------------
[detached HEAD 2455658738] tls: retain debug output when buffered reads destroy SSL
 Author: Robert Nagy <ronagy@icloud.com>
 Date: Mon Oct 19 15:30:21 2026 +0200
 1 file changed, 7 insertions(+), 1 deletion(-)
Successfully rebased and updated refs/heads/main.
--------------------------------------------------------------------------------
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[nodejs-github-bot]

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