GeezerVison

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 <[email protected]>

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 <[email protected]>

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