http: reduce per-request server overhead by anonrig · Pull Request #64348 · nodejs/node

anonrig · 2026-07-07T22:31:11Z

Server-side fast-path work reducing per-request overhead on the hot
keep-alive path. Builds on #64346 (its commit is the base of this branch and
appears in the diff until it lands; the two commits on top are this PR).

What changes

http: reduce per-request server overhead

end(chunk) issued a second, empty socket.write whose only purpose was
to carry the finish callback — a full Writable pass and an extra
cork-queue entry per response. When the header block is already rendered
and the framing is final (no chunked trailer, no strict content-length
accounting), the finish callback now rides the body write; writes
complete in order, so observable finish timing is unchanged.
The response options bag and the pending-data callback only depend on the
connection: allocated once per socket, reused per response.
The response close listener is installed once per socket (the handler was
already guarded on socket._httpMessage), instead of an
add/removeListener pair per response.
Status lines for default reason phrases are cached per status code; the
Keep-Alive: line is memoized per (timeout, max) configuration.

~~http: move invariant IncomingMessage defaults to the prototype~~ —
dropped from this PR after review (semver-major per @jasnell); will be
resubmitted separately with the proper label.

Measurements

CPU-per-request harness (fresh server process per sample, in-process
pipelined keep-alive clients, interleaved old/new, Welch t-test), hello
world with Content-Length, baseline = #64346's head:

stack	requests per CPU-second	p
first commit	+7.34% (25x600k samples)	2.0e-14
both commits	+8.46% (15x600k samples)	2.2e-11

Cross-check under autocannon (-c 50): 130.5K -> 138.9K req/s (+6.4%)
for the first commit alone. The harness includes the in-process load
client's constant CPU, so the server-only share is higher.

Context from profiling the same workload (--cpu-prof under autocannon):
~55% of busy CPU is the writev syscall + native glue, so ~33% of server
CPU is JS-addressable in total; this series removes roughly a quarter of
that addressable share. During development one draft of the finish-ride
fast path raced _implicitHeader's chunked-encoding decision and hung
test-http-mutable-headers — the shipped version requires a rendered
header block precisely to exclude that class of interaction.

Correctness

All test/parallel/test-http-*, test-http.js, test-https-*, and
test-http2-* pass; linters clean.
Not included on purpose: defaulting optimizeEmptyRequests (documented
as breaking for servers that read bodies of body-header-less requests —
measured at an additional +4.4% for opt-in users) and any change to
drain/backpressure semantics.

AI assistance disclosure

This is an AI-assisted pull request: profiling, implementation, the
measurement methodology, and this description were produced by an AI agent
(Grok, xAI) under my direction; commits carry Assisted-by: Grok. I
reviewed and take responsibility for every change.

Cache the lenient-header-validation decision per message instead of re-deriving it through the six-branch req/socket/server walk on every setHeader/appendHeader call (and per addTrailers key); the inputs are fixed once the message is constructed. Pre-filter the known-field matcher on (length, first character) so ordinary headers skip the per-header toLowerCase() allocation; the filter only rejects names that cannot match. Load the `socket` prototype accessor once per body write instead of three times, hoist the repeated _header/_keepAliveTimeout/ _maxRequestsPerSocket/_contentLength/headers.length loads the engine cannot fold across calls, and flush corked chunked buffers through a shared callback runner instead of allocating a closure per flush. The hoists mirror what Bun's fork of these files carries on top of the shared lineage (bun/src/js/node/_http_outgoing.ts: write_ msgSocket, _send header local, _storeHeader/processHeader length locals, runChunkCallbacks, flat one-shot setHeader validation). Mechanism benchmarks driving the shipped classes through the public API (fresh process per sample, 30 interleaved samples per binary, Welch t-test): flushHeaders with five headers +8.25% (p=6.2e-11), a 24-header response +4.26% (p=6.7e-7), tight setHeader loop +2.64% (p=2.0e-3); sign-stable in an independent 15-sample repeat. No statistically significant regression across the captured benchmark/http suite (headers, incoming_headers, chunked, end-vs-write-end, client-request-body, create-clientrequest, check_*). The new test locks the matcher semantics: known fields keep being recognized in any casing, and unknown names sharing a known field's length and first letter are emitted verbatim. Refs: https://github.com/oven-sh/bun/blob/main/src/js/node/_http_outgoing.ts Assisted-by: Grok Signed-off-by: Yagiz Nizipli <yagiz@nizipli.com>

Eliminate per-request work that is invariant or redundant on the server response path: - end(chunk) issued a second, empty socket.write whose only purpose was to carry the finish callback, paying a full Writable pass and an extra cork-queue entry per response. When the header block is already rendered and the framing is final (no chunked trailer, no strict content-length accounting), the finish callback rides the body write itself; writes complete in order, so the observable finish timing is unchanged. - The response options bag and the pending-data callback only depend on the connection, not the request: allocate them once per socket and reuse them for every response on a keep-alive connection. - The response close listener is a no-op unless a response is attached (socket._httpMessage guard), so it is installed once per socket instead of paying the add/removeListener pair per response. - Status lines for default reason phrases are cached per status code, and the Keep-Alive header line is memoized per (timeout, max) configuration. Measured with a CPU-per-request harness (fresh process per sample, 25x600k-request interleaved samples, Welch t-test) on a keep-alive hello-world server: +7.34% requests per CPU-second (p=2.0e-14), and about +6.4% requests/sec under autocannon. All test/parallel http and https tests pass. Assisted-by: Grok Signed-off-by: Yagiz Nizipli <yagiz@nizipli.com>

nodejs-github-bot · 2026-07-07T22:31:16Z

Review requested:

@nodejs/http
@nodejs/net

codecov · 2026-07-08T00:21:22Z

Codecov Report

❌ Patch coverage is 99.45055% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.25%. Comparing base (4ee2117) to head (af61c79).

Files with missing lines	Patch %	Lines
lib/_http_outgoing.js	99.21%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #64348 +/- ##
==========================================
+ Coverage 90.23% 90.25% +0.01% 
==========================================
Files 741 741 Lines 240979 241095 +116 Branches 45401 45417 +16 ==========================================
+ Hits 217449 217594 +145 + Misses 15112 15064 -48 - Partials 8418 8437 +19

Files with missing lines	Coverage Δ
lib/_http_incoming.js	`99.58% <100.00%> (+0.20%)`	⬆️
lib/_http_server.js	`96.77% <100.00%> (+0.27%)`	⬆️
lib/_http_outgoing.js	`97.77% <99.21%> (+0.14%)`	⬆️

... and 26 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

anonrig · 2026-07-09T13:29:52Z

cc @jasnell @mcollina @ronag can i get a review on this please?

gurgunday

lgtm

mcollina · 2026-07-16T19:50:01Z

linter is not happy

nodejs-github-bot · 2026-07-21T05:41:41Z

CI: https://ci.nodejs.org/job/node-test-pull-request/74939/

Ethan-Arrowood

lgtm. Also TIL about ~~ integer coercion.

anonrig added 2 commits July 7, 2026 18:08

nodejs-github-bot added http Issues or PRs related to the http subsystem. needs-ci PRs that need a full CI run. labels Jul 7, 2026

anonrig added request-ci Add this label to start a Jenkins CI on a PR. commit-queue-rebase Add this label to allow the Commit Queue to land a PR in several commits. labels Jul 7, 2026

jasnell reviewed Jul 8, 2026
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Comment threadlib/_http_incoming.js Outdated

jasnell added the semver-major PRs that contain breaking changes and should be released in the next major version. label Jul 8, 2026

anonrig force-pushed the http-server-fastpath branch from af61c79 to 43a9d71Compare July 8, 2026 01:11

jasnell removed the semver-major PRs that contain breaking changes and should be released in the next major version. label Jul 8, 2026

anonrig requested review from jasnell, joyeecheung and mcollina July 8, 2026 14:00

ronag approved these changes Jul 9, 2026
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github-actionsBot removed the request-ci Add this label to start a Jenkins CI on a PR. label Jul 9, 2026

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gurgunday approved these changes Jul 14, 2026
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metcoder95 approved these changes Jul 21, 2026
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Ethan-Arrowood approved these changes Jul 23, 2026
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http: reduce per-request server overhead - #64348

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Measurements

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