[robobun]

Problem

• The seven node:http2 calls that send a header block copy the caller's headers with { ...headers } (src/js/node/http2.ts:6096), so names resolve through Object.prototype.
• With Object.prototype[":status"] = 700, stream.respond() throws ERR_HTTP2_STATUS_INVALID. With ":method" set, each session.request() fails with ERR_HTTP2_STREAM_ERROR.
• Bun hands the blocks back as plain objects (sentHeaders, sentInfoHeaders, sentTrailers, the pushStream() and statCheck() callbacks). Node v26.3.0 gives each a null prototype.

Fix

• copyHeaders() copies onto a null prototype, like node's ObjectAssign({ __proto__: null }, headers). All 15 places that build a block call it.
• The map of names that HPACK must never index gets a null prototype too: a listed header named __proto__ got no flag.
• Verified: test/js/node/http2/node-http2-header-objects.test.ts (main fails 3 of 4, node v26.3.0 passes it), the 279 vendored http2 tests, test/js/node/http2/.
• Self-reviewed: 11 concerns raised, 11 addressed.

Background

• The native HPACK encoder walks own keys only: a default read from the prototype never reached the wire.
• Considered own-key checks at each read (the object still inherits) and one merged key pass that pays for the copy (it changed which error some blocks report).

Downsides

• Each block costs 0.2k to 0.55k more instructions, up to 1.4% of a loopback round trip. Wall clock shows no difference above its noise.
• The handed-back objects have a null prototype, as in node: no hasOwnProperty or toString, and assert.deepStrictEqual() against a plain object fails.
• The respond methods now honour an inherited http2.sensitiveHeaders list, as node does.

Notes

Where this came from. A fuzz finding, not a user report. There is no issue to close. Merged changes of the same kind: #14119, #33072, #34279, and #43557 (which took over #41691).

What node does. prepareRequestHeadersObject (util.js#L712), sendTrailers, pushStream and additionalHeaders copy with ObjectAssign({ __proto__: null }, headers). prepareResponseHeadersObject (core.js#L2611-L2622) copies the own keys of a response onto { __proto__: null }. The getters sentHeaders, sentInfoHeaders and sentTrailers return those copies. Node's docs promise the null prototype only for header objects passed to callbacks. For the getters the authority is node's behaviour.

The 15 places. Seven { ...headers }, six headers = {}, this.#sentTrailers = {} for a stream with no 'wantTrailers' listener, and request() on a destroyed session, which stored the caller's own object. The raw-array forms of request() and respond() already built null-prototype objects.

The copy. Bytecode of { ...headers, __proto__: null } on a release build: one call to cloneObject, one to setPrototypeDirect, none to copyDataProperties. With __proto__: null first, JSC copies one property at a time. Structures per call: 0 (heapStats() over 20,000 retained copies). bun:jsc describe() of a copy shows no dictionary. A source with a null prototype (the compat API's header table) takes Object.assign(Object.create(null), headers), which JSC clones. A Proxy does not take that arm, so request(), additionalHeaders(), pushStream() and sendTrailers() fire the same Proxy traps as node. The three response methods fire ownKeys, one getOwnPropertyDescriptor and one get per key, and a get of the never-index symbol. Node's own-key loop there also fires getPrototypeOf and a second getOwnPropertyDescriptor.

The never-index name map. buildSensitiveNames() keeps the names in an object that the native encoder reads by name. With {}, the write map["__proto__"] = true went to the __proto__ setter, so a listed header named __proto__ was sent with no never-index flag, with no pollution at all. A read-only Object.prototype.authorization made the write throw, and an accessor took it.

The never-index list of a response. Node reads it through the caller's object in respond(), respondWithFile() and respondWithFD(). copyResponseHeaders() does the same. On main this worked only for a list on Object.prototype itself.

Pollution rows. The last test puts one name on Object.prototype for the time of one call that builds a header block, and notes what the other end of the session receives: 29 rows. For a file response the name stays until the stream closes, because those headers go out after the file is open. The test also checks that nothing stays on Object.prototype, and an after hook takes the names off if the test times out. Node v26.3.0 and this branch note the same 29 lines. Main differs on 28. A few of them (- node and this branch, + main):

- request({ ":path": "/x" }) | ":method" enumerable: GET http peer /x
+ request({ ":path": "/x" }) | ":method" enumerable: error ERR_HTTP2_STREAM_ERROR
- request({ authorization }) | "authorization" read-only: GET http peer /, never indexed: authorization
+ request({ authorization }) | "authorization" read-only: throws TypeError
- request({ cookie }) | "cookie" accessor: GET http peer /, never indexed: cookie
+ request({ cookie }) | "cookie" accessor: GET http peer /, setter calls: 1
- respond() | ":status" enumerable: status 200
+ respond() | ":status" enumerable: status 302
- respond() | ":status" out of range: status 200
+ respond() | ":status" out of range: throws ERR_HTTP2_STATUS_INVALID, status 200
- respondWithFD(fd) | ":status" enumerable: status 200
+ respondWithFD(fd) | ":status" enumerable: status 302
- respond({ ":status": 200 }) | "date" read-only: status 200, with a date
+ respond({ ":status": 200 }) | "date" read-only: status 200, date undefined
- pushStream({ ":path": "/p" }) | "te" enumerable: status 200, push /p
+ pushStream({ ":path": "/p" }) | "te" enumerable: throws ERR_HTTP2_INVALID_CONNECTION_HEADERS, status 200

One line is the same everywhere on purpose: respond({ ":status": 200 }) with a never-index list on Object.prototype that is not an array throws ERR_INVALID_ARG_VALUE in node, on main and here.

The ten calls of the fuzz note ran as a script of their own too, with the name on Object.prototype for the life of one process and the peer in another process. This branch gives the same result as node v26.3.0 for all ten, with an enumerable and with a non-enumerable property. Main differs on 10 and on 7 of them.

Tests. The test file uses node:test and node:assert, so node --test runs the same file: 5 pass under node v26.3.0. With this build 4 pass and 1 is todo (below). On main 3 fail. The one that passes on main checks that each entry point reads the caller's object once and does not write to it.

No test starts a process or sets a timeout. In a debug build the slowest test takes 1.5 to 2.6 s, and a release build runs the file in about 0.2 s. The first push ran the pollution rows in a fixture with a process of its own. A debug build needs about 2.4 s to start a process, load node:http2, connect and make a first request, so that test took 9 to 15 s there and had a timeout of its own.

Not done here.

• request() on a destroyed session copies only the object form. The raw-array form still stores the caller's array and the bare form stores undefined. Node prepares the block before it looks at the session. node:http2: validate request() headers and options before the session state #43536 moves that return. The todo test holds the two forms.
• http2.getDefaultSettings() returns an object on Object.prototype where node's has a null prototype.
• A file response prepares its block twice: statCheck() gets the first copy, and sentHeaders returns the second, which respond() makes after statCheck() ran. Node hands one object to both. Main does the same. node:http2: prepare the final response headers like node #43526 lists it and node:http2: port node's respondWithFD() and respondWithFile() response paths #43564 rewrites these functions.
• null and a function pass as headers in all seven calls, and pushStream() has no type check for headers. Node throws ERR_INVALID_ARG_TYPE. Main does the same. node:http2: validate the headers and options arguments like node #43491 is open for it.
• Options (endStream, sendDate, waitForTrailers, offset, length, statCheck, signal) are read through Object.prototype, as in node.
• A response with a caller's Date next to the default date makes the native encoder throw after it changed the HPACK table, and the session ends. node:http2: encode each header block in one call, all fields or none #41520 owns the encoder side.
• The three if (sensitives !== undefined) headers[sensitiveHeaders] = sensitives; lines now write a value that is already there. They stay, because taking them out adds conflicts with three open PRs.

Cost. The unit is user instructions of the whole process (perf_event_open, instructions:u, threads included), with BUN_JSC_useConcurrentJIT=0 BUN_JSC_useConcurrentGC=0 BUN_JSC_numberOfGCMarkers=1. Per call is (I(N2) - I(N1)) / (N2 - N1) for two loop counts. The binaries are the release build of main 91e7e3b and the same binary with its node:http2 module text built from that commit plus this diff. That text is the only part of the binary that this PR changes. The same method gave the same numbers as a full release build of an earlier shape of this branch. Valgrind and perf are not installed in the build container, so the counter is a 40-line C program around perf_event_open.

The header preparation alone, where a run repeats within 0.1%:

call	keys	main	this PR	delta
request() while the session connects	none / 1 / 5 / 12	9,712 / 12,591 / 18,101 / 27,500	9,883 / 13,137 / 18,651 / 27,900	+171 / +546 / +551 / +400
respond() up to its status check	1 / 5 / 12	6,447 / 10,766 / 15,336	6,854 / 11,180 / 15,766	+407 / +414 / +430
additionalHeaders() up to its status check	1 / 5 / 12	6,478 / 8,891 / 12,219	6,850 / 9,250 / 12,574	+372 / +360 / +355
sendTrailers() up to the encoder	1 / 5 / 12	14,031 / 15,749 / 20,303	14,498 / 16,263 / 20,723	+467 / +513 / +420

The last three rows include a thrown error per call, so only the delta is the cost of the block.

One loopback round trip (one session, one request after the other, rounds 30,000 to 150,000). A window of 30,000 rounds moves by 2% to 5% between the two binaries in both directions, so only the whole span is given:

the server answers with	main	this PR	delta
respond()	89,191	90,314	+1.3%
respond() with 1 / 5 / 12 keys	90,325 / 115,588 / 149,668	91,258 / 116,446 / 150,187	+1.0% / +0.7% / +0.35%
respond() and sendTrailers() with 1 / 5 keys	105,379 / 122,831	106,846 / 124,246	+1.4% / +1.15%
additionalHeaders() with 1 / 5 keys, then respond()	102,038 / 123,816	103,486 / 125,092	+1.4% / +1.0%
pushStream(), 1 key (rounds 20,000 to 80,000)	170,593	171,810	+0.7%
compat res.end() after 1 / 5 / 12 res.setHeader()	116,673 / 154,710 / 220,044	117,050 / 154,464 / 217,695	+0.3% / -0.2% / -1.1%

The compat API keeps its headers on a null-prototype object, which takes the Object.assign arm of the copy, and that arm is cheaper than the spread of main. File responses were too noisy to give a number: they copy the block twice, once in respondWithFile() or respondWithFD() and once in respond().

Wall clock: mitata p50 of 19 loopback round-trip benchmarks, 6 interleaved runs per binary. The deltas range from -8.8% to +11.5%, and the spread between runs of one binary from 4% to 79%. This machine cannot show a wall-clock difference of this size.

The design history. The first shape of this change was larger: this copy plus one merged key pass per entry point, which removes two to three Object.keys passes and made each call cheaper than main (a loopback round trip was up to 3.2% below main in instructions). A review of that diff found blocks where the merged pass reported another error than node and main, for example respond({ ":Status": 200, ":method": "POST" }), and it conflicted with many more open node:http2 PRs. So this PR is the copy alone, with its cost stated. The pass merge can follow as its own change.

Overlap with open PRs. Of 25 open node:http2 PR heads checked with git merge-tree, this branch adds a conflict in http2.ts to two that merge cleanly with main today: #45992 and #37722. Both touch a line next to a copy.

Found while measuring, not part of this PR. A session stalls after 100,823 rounds of request plus pushStream(). Node completes 120,000. #38082 and #43419 are open for the two halves.

[robobun]

^{Updated 6:27 AM PT - Oct 22nd, 2026}

❌ @robobun, your commit c7b96b4 has some failures in Build #130898 (All Failures)

---

🧪   To try this PR locally:

bunx bun-pr 46261

That installs a local version of the PR into your bun-46261 executable, so you can run:

bun-46261 --bun

[robobun]

How to reproduce (Bun 1.4.2 and main, node v26.3.0 for comparison).

With no pollution, the objects that node:http2 hands back:

const http2 = require("node:http2");
const server = http2.createServer();
server.on("stream", stream => {
  stream.respond({ ":status": 200 });
  console.log("server sentHeaders:", Object.getPrototypeOf(stream.sentHeaders) === null);
  stream.end();
});
server.listen(0, () => {
  const client = http2.connect(`http://127.0.0.1:${server.address().port}`);
  const req = client.request({ ":path": "/" });
  console.log("client sentHeaders:", Object.getPrototypeOf(req.sentHeaders) === null);
  req.resume();
  req.on("close", () => (client.close(), server.close()));
  req.end();
});

node prints true twice. Bun 1.4.2 and main print false twice. This branch prints true twice.

With one header name on Object.prototype while the call runs:

const http2 = require("node:http2");
const server = http2.createServer();
server.on("stream", stream => {
  Object.prototype[":status"] = 302;
  stream.respond();
  delete Object.prototype[":status"];
  stream.end();
});
server.listen(0, () => {
  const client = http2.connect(`http://127.0.0.1:${server.address().port}`);
  const req = client.request({ ":path": "/" });
  req.on("response", headers => console.log("status:", headers[":status"]));
  req.resume();
  req.on("close", () => (client.close(), server.close()));
  req.end();
});

node prints status: 200. Bun 1.4.2 and main print status: 302. This branch prints status: 200.

The last test of test/js/node/http2/node-http2-header-objects.test.ts has 29 rows of this kind. Node and this branch give the same 29 lines. Bun main differs on 28.

PR: #46261

[coderabbitai]

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• src/js/node/http2.ts
• test/js/node/http2/node-http2-header-objects.test.ts

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Walkthrough

HTTP/2 header handling now copies headers into null-prototype objects across request, response, trailer, push, and file-response paths. Tests cover header access patterns, sensitive-header metadata, and properties inherited from Object.prototype.

Changes

HTTP/2 Header Copying

Layer / File(s)	Summary
Header-copy helpers and requests src/js/node/http2.ts, test/js/node/http2/node-http2-header-objects.test.ts	Added shared null-prototype header-copy helpers. Applied them to request headers, including requests on destroyed sessions. Tests cover copying behavior, proxy access, caller immutability, and request paths.
Response and auxiliary header paths src/js/node/http2.ts, test/js/node/http2/node-http2-header-objects.test.ts	Applied null-prototype copies to response, trailer, push, file-response, and informational-header paths. Preserved inherited sensitive-header metadata and changed sensitive-header maps to null-prototype objects.
Header metadata and prototype-pollution tests test/js/node/http2/node-http2-header-objects.test.ts	Added coverage for explicit and implicit never-index names, special property names, inherited sensitive-header lists, and polluted Object.prototype properties.

Suggested reviewers: dylan-conway

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to c7b96

This change makes outbound HTTP/2 header objects null-prototype copies. That prevents inherited Object.prototype properties from altering header blocks, in line with Node. The reported tests pass and I found no remaining merge-blocking risk.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the primary change: copying outbound HTTP/2 headers onto null-prototype objects.
Description check		The description provides detailed problem context, implementation details, verification results, performance data, and known limitations. It does not use the template headings exactly, but it covers t…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description provides detailed problem context, implementation details, verification results, performance data, and known limitations. It does not use the template headings exactly, but it covers the required content for what the PR does and how it was verified.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @test/js/node/http2/node-http2-header-objects.test.ts:
- Around line 633-636: Remove the per-test timeout options object from the test
named “a header name on Object.prototype does not reach a header block,” while
preserving its asynchronous callback and assertions. If the test exceeds the
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• test/js/node/http2/node-http2-header-objects.test.ts

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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline findings, I also checked two things in copyHeaders/copyResponseHeaders and ruled them out: a source object with an own __proto__ key (e.g. from JSON.parse) keeps it as an own data property through the spread, same as node's ObjectAssign({ __proto__: null }, headers) onto a null-prototype target; and the helpers only use load-time captured Object.create/getPrototypeOf/assign plus the $isProxyObject intrinsic, so a polluted or replaced global cannot redirect the copy.

Extended reasoning...

The change is confined to src/js/node/http2.ts (two new header-copy helpers replacing fifteen {} / { ...headers } sites plus a null-prototype sensitive-name map) and two new test files; it hardens the outbound header path against Object.prototype pollution and touches no auth or crypto surface. Inline findings are posted, so this note only records the two extra concerns examined and ruled out.

Additional findings (outside the current diff — GitHub can't attach inline comments there):

• 🟣 src/js/node/http2.ts — Users of respondWithFile()/respondWithFD() with a statCheck callback get a headers object that is not stream.sentHeaders, and pay two header copies per file response. doSendFileFD hands the first copy to statCheck at src/js/node/http2.ts:3098, then respond() at src/js/node/http2.ts:3131 runs copyResponseHeaders again (src/js/node/http2.ts:3660), so the stored block is a second object. Node keeps the single prepared object for statCheck and sentHeaders. Fix: make respond() accept an already-prepared null-prototype block from the file paths without re-copying (or copy once in respondWithFile/respondWithFD and pass through), so statCheck's object is the one that backs sentHeaders.

  Why this was flagged

  Trigger: any server calling respondWithFile() or respondWithFD() with options.statCheck, the normal static-file path. respondWithFile copies at src/js/node/http2.ts:3480 (copyResponseHeaders), statCheck receives that copy at src/js/node/http2.ts:3098, then this.respond(headers) at src/js/node/http2.ts:3131 copies again at src/js/node/http2.ts:3660. A statCheck that keeps a reference and later compares or mutates expecting stream.sentHeaders === headers (node semantics: doSendFileFD passes the same prepared object that becomes kSentHeaders) sees a different object. The PR description claims the statCheck copy is what 'comes back as sentHeaders'; the code does not do that. On the base the identity also differed, but the base was not claiming node parity for these objects and did not add the null-prototype copy twice. Each file response also allocates and walks the header block twice. Remedy: prepare once in the file paths and let respond() skip the copy for an already-prepared block.

  Verification: pre-existing. Trigger: any respondWithFile()/respondWithFD() call. doSendFileFD hands the copied block to statCheck at src/js/node/http2.ts:3098, then calls respond() at :3131, which copies again at :3660, so sentHeaders is a second, distinct object from the one statCheck received. The base branch at 9b4284f already does exactly this (base :3401, :3461, :3637); the diff only swaps the copy expression.

[robobun]

On the finding outside the diff in the review above (the object that statCheck() gets is not stream.sentHeaders):

Confirmed, and main does the same. respondWithFile() and respondWithFD() copy the block, statCheck() gets that copy, and respond() copies it again after statCheck() ran. So what a statCheck() writes still reaches the wire and sentHeaders, but the two objects are not the same one. Node v26.3.0 hands one object to both.

This PR changes only how each copy is made, so it leaves the double preparation as it is. #43526 lists it under "Not changed here", and #43564 rewrites the same functions. The Problem section read as if the two objects were one, so I reworded it, and the Notes now list this under "Not done here".

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

[claude]

I re-reviewed the latest push and found no bugs; the after() hook now takes the pollution rows off Object.prototype even when a row stalls, which settles the one nit left open from the previous round. Because this changes the observable shape of every object node:http2 hands back (sentHeaders, sentInfoHeaders, sentTrailers, the pushStream()/statCheck() callbacks now have a null prototype) on a hot path, a human look at that API-surface trade-off would still be worthwhile.

What was reviewed:

• copyHeaders/copyResponseHeaders in src/js/node/http2.ts: captured Object.create/Object.getPrototypeOf/Object.assign primordials, $isProxyObject is a declared intrinsic, and the null-prototype fast path cannot be reached by a Proxy.
• All 15 call sites (sendTrailers, auto-trailers, pushStream, respond/respondWithFD/respondWithFile, additionalHeaders, request live and destroyed-session forms, buildSensitiveNames) now go through the helpers; checked the inherited sensitiveHeaders read in copyResponseHeaders against node's own-keys loop and it matches for the response paths only.
• The test file wires error/sessionError/stream error to reject the awaited promises, uses port 0, releases the fd and server in finally, and checks nothing is left on Object.prototype.

Extended reasoning...

The diff touches src/js/node/http2.ts (two new helpers plus 15 header-block build sites switched to null-prototype copies) and adds a 915-line test file; no CODEOWNERS entry covers either path. The surface is prototype-pollution hardening of outbound HTTP/2 header blocks, which is security-relevant but not auth or crypto. The bug-hunting rounds reported nothing, the prior-round nit about cleanup on a timed-out row was addressed by the last commit, and no third-party objection is outstanding. Deferral rather than approval because the change alters the prototype of every header object the module returns to users and adds a copy on a hot path, which is a design trade-off a maintainer should confirm.