node: pass no options to EventEmitter from OutgoingMessage and ChildProcess - #47434

Order. This is a draft because it conflicts with #46528 and #46522 in one line: the SHA-256 of the first text in the head of src/js/ahead-of-time/node/_http_outgoing.ts. The other hunks merge without a conflict. Both branches still have Stream.$call(this, options) (#46528 at 001958b: :145 and :295). On #46528 the rule for such a PR is: it stays a draft and is cut again on top.

Where it comes from. The review comment found that the two texts differ for new ServerResponse(req, { captureRejections: true }). It proposed that the second text read the option. Node does not read it, so this PR goes the other way. No issue mentions captureRejections, and node documents no options for these constructors. Stream.$call(this, options) came with #17093, where Writable.$call(this, options) became a call of Stream.

A program that relied on the option:

import http from "node:http";
const req = { method: "GET", httpVersionMajor: 1, httpVersionMinor: 1, headers: {} };
const res = new http.ServerResponse(req, { captureRejections: true });
res.on("x", async () => { throw new Error("boom"); });
res.emit("x");
setImmediate(() => console.log("destroyed:", res.destroyed));

With EventEmitter.call(res, { captureRejections: true }) after the constructor, node, main and this PR all print destroyed: true, under bun run and under --aot.

The new program, test/aot/parallel/library-modules/http-messages-hand-no-options-to-the-emitter.mjs. It makes a message in five ways. For each it prints three answers: with captureRejections: true, with captureRejections: "yes", and with no options while EventEmitter.captureRejections is true.

test/aot/run-parallel.ts on the program with a release build: main fails ("it does not exit and print as plain Bun does"), this PR passes.

ChildProcess. Node has function ChildProcess() { FunctionPrototypeCall(EventEmitter, this); (child_process.js:255). For new ChildProcess(options) and for a class that extends it, node prints false, false, true and main prints true, ERR_INVALID_ARG_TYPE, true. child_process.ts has no second text. The test is in child_process-node.test.js. Two tests of child_process.test.ts fail on a debug build in my container, with and without this change. One needs more than 1,024 descriptors, and one takes more than 5 s.

Why undefined and not a missing argument. Stream declares one parameter. In the interpreter a call with no argument costs 83 instructions more, an arity fix-up. The second text already wrote Stream.$call(this, undefined).

Measurements. Release builds of f7607a3 and of this PR, on Linux x64. Instructions in user mode per object, from perf_event_open, in a loop that makes the object and drops it. Each program imports one module. The programs of the last two rows of the second table also import node:events, node:http, node:net and node:stream. The interpreter and --aot values are the median of three readings. The JIT values are the range of six readings, and of three for ChildProcess.

A server passes options for every response, so the third row is the one a request takes.

Servers under --aot, instructions a request:

• bun test/aot/perf/compare-builds.ts --servers node,express,fastify,koa: 32 rows, 0 slower, 0 faster.
• The node server of test/aot/servers/app with createServer({ ServerResponse: class extends ServerResponse {} }, ..): all 8 routes cost less with this PR, by 0.3% to 2.0%. The text route costs 31,205 to 31,239 on main and 30,595 to 30,616 with this PR.
• A loop of http.get() against a local server calls operationAOTEnsureExtensionGranules 7 times in all. That holds for 200 and for 1,200 requests, before and after.
• In a server that uses the built-in classes, four compiled functions change size and all get smaller: OutgoingMessage (construct body) 8,922 to 5,788 bytes, EventEmitter 10,935 to 10,904, initializeProxyReceiver 5,120 to 5,092, OutgoingMessage 3,552 to 3,548.
• The bun binary has 138,270,840 bytes before and after. size reports 38 bytes more text.

The three rows that rise. They rise by a decision of the slot planner. testaot print program.aot --command="plan-slots layouts fill" references=narrow shows it for the layout of OutgoingMessage:

The engine puts a field into the cell when its estimated fill is at least half of the creations. That is isLikelyFilled in AOTSlotPlanSteps.h (oven-sh/WebKit 8c6c963e). With a constant undefined in place of options, the estimate for [kShapeMode] falls below one half. Three fields then lie outside the cell. From the 502nd object on, or after a collection, each new http.OutgoingMessage() calls operationAOTEnsureExtensionGranules once.

The numbers move with the rest of the program. The program below makes 2,519 calls for 3,000 objects. Without its last block it is the loop of the table. With the block, which never runs, it makes 3 calls, as main does:

import http from "node:http";
const N = Number(process.argv[2]);
let sink = 0;
for (let i = 0; i < N; i++) sink += new http.OutgoingMessage().outputSize + 1;
if (sink <= 0) console.log("?");
if (process.argv[3] === "never") {
  for (let i = 0; i < N; i++) {
    const message = new http.OutgoingMessage();
    message._events = { __proto__: null };
    sink += message.outputSize;
  }
}

Two more release builds gave the numbers of this one. One kept the call in both arms of the if. The other also left the options interface as it was. I did not bend the second text to win a layout back.

The cost belongs to the layout on x64. A plain loop of 1,000 new http.OutgoingMessage() makes 519 calls with this PR and 1 on main, on x64. On Alpine aarch64 the same loop makes 40 calls or fewer with this PR. I saw that in CI and have no arm64 machine to look closer. An earlier commit of this PR held that count in a program with a // Todo: line. I took the program out again, because one line cannot be right for both architectures.

src/aot/CLAUDE.md asks for a fix or a revert of a row over +2%. Three rows are over it on x64, and I ask for the exception: this change is what makes the two texts agree with each other and with node.

What is left out. I gave captureRejections: true and "yes" to 68 public constructors and factories of node:* modules that make an emitter. I compared each with node v26.3.0. Besides the two classes of this PR, these differ, on main and with this PR:

• tls.TLSSocket, tls.connect and https.request. TLSSocket hands its whole options object to net.Socket (src/js/node/tls.ts:790). Node hands ten named keys (wrap.js:590). The fix there is a fixed list of keys, which changes more than this option. tls.connect({ captureRejections: true }) captures in Bun today.
• tty.ReadStream(fd, options) hands on nothing (src/js/node/tty.ts:65). Node hands the options on.
• The built-in undici module: Agent has no constructor (src/js/thirdparty/undici.ts:269), so new Agent(options) hands its options on.
• new http.ServerResponse(req, { highWaterMark: 7 }).writableHighWaterMark is 65536, and 7 in node. The option is stored as in node. The getter at src/js/node/_http_server.ts:3961 answers for the socket that it makes.
• The two texts read the keys of options in new ServerResponse(req, options) in another order, which a Proxy shows.

Within node:http, Agent, Server, IncomingMessage and ClientRequest agree with node.

Also in the diff. interface OutgoingMessageOptions no longer extends EventEmitterOptions: nothing hands these options to an emitter. tsc -p src/js prints the same 315 lines before and after. The SHA-256 in the head of the second text is that of the new first text.

Suites run.

• bun bd test on the two test files: with the src/ of main 2 tests fail, with this PR none.
• Release builds of main and of this PR, each file in a process of its own: the 87 test files of test/js/node/http, child_process, events and cluster, the two stream tests that run programs, and EventEmitterAsyncResource.test.ts. This PR: 1,649 pass. One test fails before and after (spawn still works with more than 10240 fds open, EMFILE in my container). Main differs in the two new tests only.
• 718 files of test/js/node/test/parallel (test-http-*, test-https-*, test-child-process-*, test-cluster-*, test-event-*, *capture-rejection*, *catch-rejections*): 716 exit with 0 before and after. The other two need bun test.
• test/aot/run-parallel.ts on the 50 programs of test/aot/parallel/node-http and 16 of library-modules: 66 pass.
• test/internal/source-lints (194 pass), test/internal/second-texts-of-modules.test.ts, test/aot/every-test-runs-in-ci.test.ts, bun fmt --check, bun lint.