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node:http: set req.upgrade to true before shouldUpgradeCallback runs - #43413

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@robobun

@robobun robobun commented Sep 19, 2026

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Problem

  • On a node:http server, req.upgrade is null while server.shouldUpgradeCallback(req) runs. Node v26.3.0 gives true there, whether the callback accepts or declines.
  • The native request dispatcher calls the callback before it writes req.upgrade (src/js/node/_http_server.ts:882). Until then the request holds the constructor default null (src/js/node/_http_incoming.ts:110).

Fix

  • Set http_req.upgrade = true right before the shouldUpgradeCallback call. The assignment after the call still writes the final value.
  • Correct because Node's parserOnHeadersComplete copies the parser's upgrade flag onto the request before parserOnIncoming calls the callback.
  • Verified: the new test in test/js/node/http/node-http.test.ts fails on main and passes with the fix. Also that whole file and the upstream test-http-upgrade-* tests.
  • Self-reviewed: 2 concerns raised, 0 addressed. Rejected: an 'error' guard on the test's client socket, because a reset must fail the test. Rejected: the upgrade type that @types/node lacks, because four tests in this file already read it.

Background

  • shouldUpgradeCallback (Node v24.9.0) is a server option. The server calls it for each upgrade request. true routes the request to the 'upgrade' event, false to 'request'.
  • req.upgrade is the IncomingMessage flag that marks an upgrade request. Node's parser (llhttp) sets it when the request has an Upgrade header and a Connection: upgrade token.
  • The native path parses in uWebSockets and dispatches through onNodeHTTPRequest. The fallback path parses with llhttp in JS, for sockets passed through server.emit("connection", socket). It already sets the flag before the call (src/js/internal/http1_server_fallback.ts:303).
Notes

Repro:

const http = require("node:http");
const net = require("node:net");
const server = http.createServer((req, res) => { console.log("request listener:      req.upgrade =", req.upgrade); res.end(); });
server.shouldUpgradeCallback = req => { console.log("shouldUpgradeCallback: req.upgrade =", req.upgrade, "url =", req.url); return req.url === "/yes"; };
server.on("upgrade", (req, socket) => { console.log("upgrade listener:      req.upgrade =", req.upgrade); socket.end("HTTP/1.1 101 Switching Protocols\r\n\r\n"); });
server.listen(0, "127.0.0.1", async () => {
  const port = server.address().port;
  const send = text => new Promise(resolve => { const c = net.connect(port, "127.0.0.1", () => c.write(text)); c.on("data", () => {}); c.on("close", resolve); c.on("error", resolve); });
  await send("GET /yes HTTP/1.1\r\nHost: a\r\nConnection: Upgrade\r\nUpgrade: foo\r\n\r\n");
  await send("GET /no HTTP/1.1\r\nHost: a\r\nConnection: Upgrade, close\r\nUpgrade: foo\r\n\r\n");
  server.close();
});

Node v26.3.0 and this branch:

shouldUpgradeCallback: req.upgrade = true url = /yes
upgrade listener:      req.upgrade = true
shouldUpgradeCallback: req.upgrade = true url = /no
request listener:      req.upgrade = false

Bun 1.4.3-canary (367d939) prints req.upgrade = null on both shouldUpgradeCallback lines. The two listener lines already match.

Node v26.3.0 source:

// lib/_http_common.js, parserOnHeadersComplete
incoming.upgrade = upgrade;
// lib/_http_server.js, parserOnIncoming
if (req.upgrade) {
  req.upgrade = req.method === 'CONNECT' ||
                !!server.shouldUpgradeCallback(req);

Node calls the callback only inside if (req.upgrade). So req.upgrade is true in every callback call.

Other facts:

  • Three internal sites read req.upgrade: _read (src/js/node/_http_incoming.ts:368) and onDataIncomingMessage (src/js/internal/http.ts:188, :197). Only _read can run during the callback, through a synchronous req.read(). resume() and on("data") defer to the next tick. With the value true, _read resumes the native body source and leaves the raw socket alone. That is the intended path for an accepted upgrade. For a declined upgrade, later reads see false and take the normal path.
  • A probe covers that case: an upgrade request with a 5-byte body, and a callback that calls req.read(). The declined request delivers the whole body to 'request'. The accepted request delivers the body and the tunnel bytes to 'upgrade'. The output matches Node v26.3.0 line for line.
  • If the callback throws, req.upgrade stays true. Node behaves the same, because its assignment never completes.
  • The write happens only in the upgrade branch. A request without Upgrade and Connection: upgrade takes the same path as before. upgrade is already an own property from the constructor, so the write does not change the object shape.
  • The CONNECT branch already sets req.upgrade = true before it emits 'connect', and it never calls the callback, like Node.
  • The native path does not call shouldUpgradeCallback for a pipelined request (!isPipelined). This PR does not change that.
  • The test waits for the client socket to close and does not destroy it early. An early destroy resets the connection, and on Node the upgraded server socket then emits an unhandled ECONNRESET.
  • The test sits before the existing req.upgrade test so that it does not collide with the test that node:http: take the Connection and Upgrade dispatch bits from llhttp's grammar #43327 adds after it.
  • Suites run with the debug build: test/js/node/http/node-http.test.ts (163 pass, 1 skip), node-http-with-ws.test.ts, node-http-req-socket-pause.test.ts, test/js/first_party/ws/ws.test.ts, ws-upgrade-events.test.ts, and the 18 upstream files test-http-upgrade-*, test-http-connect*, test-http-parser-freed-before-upgrade.js, test-http-server-request-timeout-upgrade.js. The new test passed 30 of 30 repeated runs. A standalone copy of the test body passed 20 of 20 runs on Node v26.3.0. On the released Bun it failed the assertion 20 of 20 times, with no hang and no socket error.

@robobun

robobun commented Sep 19, 2026 •

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Status: closed. #43557 supersedes this PR and is merged (5d5f03f). It contains the same change and the same test.

How I reproduced it: I ran the script from the Notes block of the description with Node v26.3.0 and with Bun 1.4.3-canary (367d939). Node prints req.upgrade = true on both shouldUpgradeCallback lines. Bun prints req.upgrade = null on both. A debug build of main at 5d5f03f prints true on both.

The pipelined Upgrade case from the review is tracked in #43420.

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coderabbitai Bot commented Sep 19, 2026 •

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Walkthrough

The HTTP server now sets req.upgrade before shouldUpgradeCallback runs. Tests verify accepted upgrade dispatch and declined request dispatch with reset state.

Changes

HTTP upgrade state

Layer / File(s) Summary
Upgrade state and dispatch validation
src/js/node/_http_server.ts, test/js/node/http/node-http.test.ts
Upgrade requests expose req.upgrade === true during callback and upgrade handling. Declined requests dispatch through request with req.upgrade === false.

Suggested reviewers: cirospaciari

Priority: ⬇️ Low

🚥 Pre-merge checks | ✅ 4
✅ Passed checks (4 passed)
Check name Status Explanation
Title check ✅ Passed The title clearly and concisely describes the main change: setting req.upgrade before shouldUpgradeCallback runs.
Description check ✅ Passed The description explains the problem, fix, compatibility behavior, test coverage, and scope. It does not use the exact template headings, but it provides the required change summary and verification d…
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.

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

Beyond the inline finding (which is a pre-existing gate, not introduced by this diff), I also checked the sibling llhttp fallback path in src/js/internal/http1_server_fallback.ts (line 303) — it already sets req.upgrade before consulting the callback, so both dispatchers now agree. A callback that synchronously calls req.read() on a declined upgrade was also checked: _read sees true only for that one call and later reads observe the final false written at line 890, matching Node's ordering.

Extended reasoning...

The source change is a single assignment (http_req.upgrade = true) placed inside the existing non-pipelined upgrade branch of Server.prototype[kRealListen] in src/js/node/_http_server.ts, immediately before server.shouldUpgradeCallback(http_req); the unconditional http_req.upgrade = is_upgrade at line 890 still writes the final value. The fallback parser path already had the same ordering, so this brings the native dispatcher in line. The one confirmed inline finding concerns the !isPipelined gate that predates this PR and is not made worse by it. The new test lives in the existing node-http.test.ts, awaits socket close rather than sleeping, uses port: 0, and asserts a single ordered toEqual covering accept and decline; the server sends Connection: close on both paths so the client socket closes cleanly rather than resetting. No native code, security-sensitive paths, or CODEOWNER-only files are touched.

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

  • 🟣 src/js/node/_http_server.ts — Clients that pipeline an Upgrade request behind an in-flight request on the same keep-alive connection get it dispatched to 'request' with upgrade === false, and shouldUpgradeCallback never runs. Node emits 'upgrade' for that request regardless of pipelining. The gate at src/js/node/_http_server.ts:878 (!isPipelined) excludes the whole block, including the new line 884, so the callback the PR fixes still never observes these requests. Fix: cover the pipelined population too, by calling shouldUpgradeCallback for pipelined upgrade requests and routing an accepted one to 'upgrade' once the in-flight response finishes, or document the exclusion in code.

    Extended reasoning...

    A client sends GET /a then GET /ws with Upgrade: websocket and Connection: upgrade on one connection before /a's response is finished. The native dispatcher calls onNodeHTTPRequest with isPipelinedDispatch true for /ws. isPipelined is true at line 737. The condition at 878-881 is false, so lines 884-885 do not run and is_upgrade stays false. Line 890 writes upgrade = false. Line 891 queues a pipelined response and the request is emitted as a normal 'request' with a queued ServerResponse. Node's parserOnIncoming checks req.upgrade before the outgoing-queue check, calls shouldUpgradeCallback, and emits 'upgrade' with the raw socket even when a response is in flight. I confirmed the gate is unchanged at the base commit (context lines in the diff), so this is pre-existing; the PR description states it is left as-is. It is nominated because it is the sibling site of the fixed callback path: the PR's stated contract is that shouldUpgradeCallback sees req.upgrade === true on every upgrade request, and this population never reaches the callback at all. Population: HTTP clients that pipeline…

    Verification: pre-existing; acknowledged in diff: the PR description says "The native path does not call shouldUpgradeCallback for a pipelined request (!isPipelined). This PR does not change that." — the note is accurate, and the base commit has the identical gate. Triggering condition: a client sends an Upgrade + Connection: upgrade request on a keep-alive connection while an earlier response on that…

@robobun

robobun commented Sep 19, 2026 •

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Updated 3:02 AM PT - Sep 19th, 2026

❌ @robobun, your commit 094b3f6 has 1 failures in Build #118237 (All Failures):


🧪   To try this PR locally:

bunx bun-pr 43413

That installs a local version of the PR into your bun-43413 executable, so you can run:

bun-43413 --bun

@robobun

robobun commented Sep 19, 2026

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The finding about the !isPipelined gate is correct. The gate predates this PR.

Mechanism: a pipelined dispatch skips both handoff branches in onNodeHTTPRequest (src/js/node/_http_server.ts:738 for CONNECT, :878 for Upgrade). The request goes to 'request' with req.upgrade === false, and the server does not call shouldUpgradeCallback. A probe on Node v26.3.0 and on Bun confirms it.

Scope: this PR does not change that gate. It sets req.upgrade before the callback only on the path that already calls the callback. I kept the gate out of this diff for two reasons:

  • Node hands the socket to 'upgrade' while the earlier response is still pending. Its 101 then goes out before that response, so the responses leave request order. A direct copy of Node is not clearly the right behaviour.
  • A version that keeps the order needs work in the native parser, which is a larger change than this one.

Tracking: #43420 has the repro, the output of Node and of Bun, and the cause.

Comment thread src/js/node/_http_server.ts Outdated

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Code review found no issues

No high-confidence issues detected in this change.

The native request dispatcher called server.shouldUpgradeCallback(req)
while req.upgrade still held the constructor default (null). Node.js
copies llhttp's upgrade flag onto the request in parserOnHeadersComplete,
so the callback sees req.upgrade === true there. The assignment after the
call still writes the final value.
@robobun
robobun force-pushed the robobun/0cffe777/req-upgrade-in-should-upgrade-callback branch from aa51645 to 094b3f6 Compare September 19, 2026 09:38
@robobun

robobun commented Sep 19, 2026

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The red robobun/evidence status comes from the machine that runs the check, not from this diff.

  • The check runs all of test/js/node/http/node-http.test.ts (164 tests) on a shared machine.
  • On both attempts that machine was overloaded. Its load average was above 400 on 16 cores.
  • Tests that this diff does not touch timed out at the default 5 s. Two of them are https: closing a server listened from 'beforeExit' and should propagate exception in sync data handler. Both spawn a subprocess.

The new test failed without the fix and passed with the fix in every run. I ran the whole file again by hand with the same binaries. The release build passed 4 of 4 runs, and the debug build passed too (163 pass, 0 fail). CI build #118230 passed this file on every platform.

The diff is ready for review. I do not push again, because each push starts the check again on the same machine.

Jarred-Sumner added a commit that referenced this pull request Sep 26, 2026
…inish, lifecycle) (#43557)

One pull request for the open `node:http` server pull requests. Each
root cause is fixed once, and each pull request's tests are carried
over. Node is the reference: every scenario was run under Node and under
Bun from one script, and the outputs were compared.

Fixes #4733
Fixes #18613
Fixes #40350
Fixes #43155
Fixes #43297
Fixes #43513
Fixes #43527
Fixes #25632
Fixes #31301
Fixes #43027
Fixes #43163
Fixes #43342
Fixes #43344
Fixes #43370
Fixes #43490
Fixes #43512
Fixes #43519

Each of these has a repro that is wrong on Bun 1.4.3, right on this
branch, and the same as Node.

| Issue | Not closed by this PR, because |
| --- | --- |
| #30501 (msal-node keeps Bun alive at exit) | Probably fixed. The repro
copies the teardown of msal-node. The package itself was not run. |
| #14430 (yarn: "does not support SSL") | Probably fixed.
`response.hasOwnProperty("socket")` is now `true`. yarn itself was not
run. |
| #39681 (`server.setTimeout` callback after destroy) | Probably fixed.
The repro is the deterministic case of #39686. The script in the issue
depends on timing and on Windows. |
| #43455 (`req.complete`, nine flows) | Partially addressed. Flows 1, 2,
3, 5 and 7 are fixed, and flow 6 was already right. Flow 8 (a socket
timeout while the body of an Upgrade request arrives) and flow 9 (a
request that `stream.pipeline()` destroyed never reports `complete`) are
not. Flow 4 differs only in `_readableState.ended`. |

### What changes for users

| Area | Before | After (same as Node) |
| --- | --- | --- |
| `req.pause()` | The socket stops at once. `req.complete` stays `false`
for a small body. | The body is received until the buffer is full. Then
the socket stops. |
| `res.end()` before the body arrives | `req` gets `'end'` and `'close'`
at once, and the body is lost | The request completes when its body
really ends |
| `res.destroy()` in the middle of a body | `'end'` with bytes missing |
`aborted`, then `ECONNRESET` |
| `socket.destroy()` inside the `'request'` listener | The body that
came with the head is dropped | That body is still delivered |
| `'finish'` and the `end()` callback | Fire when `end()` buffers the
bytes | Fire when the last bytes have left the socket |
| A response that closes the connection | The server half-closes and
waits for the peer | The socket closes right behind the FIN |
| `'drain'` after a later write flushed the backlog | Lost. `pipe(res)`
could hang. | Emitted |
| A pipelined request whose body continues after the previous response
ends | Body dropped, no response, `server.close()` hangs | Delivered |
| CONNECT and Upgrade tunnel sockets | Keep reading when paused or full
| Stop reading. `_read()` starts them again. |
| A tunnel write that waits for a drain when the client goes away | Its
callback, the callbacks of the writes behind it and the `end()` callback
never run | They run with an error before `'close'` |
| Upgrade request with a body, paused in its listener | The body flows
away | The request keeps its body |
| `ws` on a reused keep-alive socket | Writes after the Upgrade could
stall | Sent |
| A raw `socket.write()` behind a response that still drains (the 400
for a bad pipelined request, the reply of a `'clientError'` listener) |
Lands in the middle of that response | Sent after it |
| `server.close()` | Could report closed while connections were open |
Waits for every connection. An idle tunnel does not keep the process
alive. |
| `closeAllConnections()` on a listening server | Also stops the
listener and destroys tunnels and WebSockets | Destroys only the HTTP
connections |
| `Proxy-Connection: close` (node:http only) | Ignored. The connection
stays open. | Ends the connection, like `Connection: close` |
| A response larger than 16 KB, also in `Bun.serve` and over TLS | Up to
4 `send()` calls for each chunk. Slower than Node in most cases. | One
write for the writes of one tick. 1.1x to 2.7x the requests per second
of main, and faster than Node. |
| `socket.destroy()` and then `res.end()` in a listener | (this PR,
earlier) `req` ended as if it were complete | `'aborted'`, then
`ECONNRESET` |
| `emit('connection')` or http2 `allowHTTP1`: the response ends while
the listener still reads the body | The rest of the body is dropped |
The body is complete |
| `httpValidation: "relaxed"`, `Content-Length` or `Transfer-Encoding`
in trailers | Accepted | `HPE_INVALID_CONTENT_LENGTH`,
`HPE_INVALID_TRANSFER_ENCODING` |
| `req.complete` inside `'connect'`, and inside `'upgrade'` without a
body | `false` | `true` |
| `optimizeEmptyRequests`: `socket.parser.incoming` after the response |
Keeps the request alive on an idle connection | `null` |
| A HEAD or OPTIONS request with `Content-Length` | The body is dropped,
and `req.complete` is `true` before it comes | The request has its body
|
| `res.end(chunk)` after the client went away | `finished` and
`writableEnded` stay `false`, no `'prefinish'` | The response ends |
| An HTTP/1.0 request with an `Expect` header | `100 Continue`,
`'checkContinue'`, `'checkExpectation'` or a 417 | A plain `'request'` |
| The idle sweep of `close()` and `closeIdleConnections()` | Could
destroy a connection that was still receiving a request, or whose
response was still draining | Closes only idle connections |

### Design

| Piece | What it is |
| --- | --- |
| Request body state | `None / Pending / Complete / Aborted / Upgraded /
Detached`. Only the last chunk sets `Complete`. One function,
`leave_pending`, is the only other way out of `Pending`. |
| Read flow control | One path: `push()` returning false stops the
socket, `_read()` starts it. Both native pause buffers are removed: no
read is copied and replayed. |
| "This read is parsed" signal | `notifyWhenReadParsed()` sets a uws
state bit. uws delivers a `readParsed` event after the read. It replaces
a `setImmediate`. |
| Close during a parse | One uws bit defers a close to the end of the
current message. |
| Response finish | A response is finished when it has ended and the
socket has fully drained. |
| Idle connection | One rule, `HttpResponse::closeIfIdle()`. A
connection is idle when it receives no request (head or body) and no
response is in flight, queued or undrained. The sweep of `close()` and
`closeIdleConnections()` both use it. |
| Idle tunnel | A tunnel at read EOF with nothing left to send. uws
reports it to the server through the connection filter (`-3`, `+3`,
`-4`). It still counts for `'close'`, but it does not hold the event
loop, like a libuv handle in that state. |
| Server `'close'` | One native close promise per `listen()`. `close()`
records whether its sweep left nothing open. Then a `listen()` in the
same tick cannot hold `'close'` back, as in
`net.Server._emitCloseIfDrained`. |
| Raw socket writes | While uws holds response bytes (its buffer, the
zero-copy tail of a `res.write()`, the cork buffer), a raw write goes
through `AsyncSocket::write`, the path a 1xx line takes. So the order on
the wire is the order of the calls. |
| Upgrade verdict | One scanner and one verdict, shared by the parser
and the dispatcher. |
| llhttp | Updated from 9.3.0 to 9.4.2, as Node v26.5.0 vendors it, plus
one local patch (see below). Node v26.5.1 and later vendor 9.4.3. That
update is not in this PR. |

The parser changes also tighten request framing so that it agrees with
llhttp in more cases. There is no new API surface.

### A pause holds from the next read

The copy of the rest of a read (`nodeHttpPausedSpill`), its replay from
a posted task and the nested parse are removed. Like in Node, the rest
of the read that caused a pause is still parsed, and the socket stops at
the next read. usockets reads up to 512 KB in one call. libuv reads 64
KB.

| One paused, unread request (client sends 64 MB) | Bytes held |
| --- | --- |
| Node 25.6 | 131,018 |
| This pull request | 524,234 |

The price is in one case. A client sends 512 KB of small pipelined
requests (19,418 of them) and never reads. Each handler answers with its
own 64 KB body:

| Handler | Runtime | Requests dispatched | RSS |
| --- | --- | --- | --- |
| Answers at once | Node 26.3 | 2,425 | +177 MB |
| Answers at once | main | 41 | +9 MB |
| Answers at once | This PR | 2,425 | +171 MB |
| Answers one tick later | Node 26.3 | 4,850 | +336 MB |
| Answers one tick later | main | 2,426 | +181 MB |
| Answers one tick later | This PR | 4,850 | +330 MB |

Release builds on Linux x64. This PR now does what Node does. main held
fewer responses, mostly for a handler that answers at once. On macOS one
read can return all 512 KB. There, Bun 1.4.3 already reached +951 MB for
the handler that answers one tick later, and Node reached +1,294 MB.
`server.maxRequestsPerSocket` bounds it.

### Performance

#### Responses larger than 16 KB are faster, and now faster than Node

On main, a response that did not fit the 16 KB uWS cork buffer released
the cork. After that, each piece was its own `send()`: the buffered
head, the chunk-size line, the data, the `\r\n` and the last chunk. Over
TLS, each 2-byte piece was also its own record. Two changes fix that,
for `Bun.serve` and for node:http:

| Change | Effect |
| --- | --- |
| A write that does not fit goes out with the cork buffer and its
framing in one vectored write | No copy is added. Over TLS, the records
of all the pieces share the write batch that one `SSL_write` loop
already had. |
| The cork buffer holds 128 KB, up from 16 KB. Only a write of 16 KB or
less is copied into it, as before. | Several writes in one tick go out
in one write, like in Node. A longer write still goes out without a
copy. |

The bytes on the wire are the same. The vectored write uses `sendmsg()`
with the flags that `send()` uses.

Write syscalls for one response:

| Response | Node 26.3 | main | This PR |
| --- | --- | --- | --- |
| 4 x `res.write(16 KB)` | 1 | 16 | 1 |
| 40 x `res.write(2 KB)` | 1 | 16 | 1 |
| `res.end(64 KB)` | 1 | 2 | 1 |
| 256 KB file, `.pipe(res)` | 4 | 16 | 5 |

Throughput (req/s, the mean of 2 rounds). Node v26.3.0, main
`97246d044e`, this PR `fe0ed1fbea`, with the method below:

| Case | Node | main | This PR | main / Node | PR / Node | PR / main |
| --- | --- | --- | --- | --- | --- | --- |
| http, 4 x `res.write(16 KB)` | 17,735 | 6,983 | 19,160 | 0.39x | 1.08x
| 2.74x |
| https, 4 x `res.write(16 KB)` | 11,720 | 6,110 | 15,510 | 0.52x |
1.32x | 2.54x |
| http, 40 x `res.write(2 KB)` | 9,879 | 6,140 | 14,980 | 0.62x | 1.52x
| 2.44x |
| https, 40 x `res.write(2 KB)` | 6,981 | 5,541 | 11,780 | 0.79x | 1.69x
| 2.13x |
| http, `res.end(64 KB)` | 18,535 | 16,528 | 19,889 | 0.89x | 1.07x |
1.20x |
| http, 256 KB file `.pipe(res)` | 2,684 | 2,375 | 2,719 | 0.88x | 1.01x
| 1.15x |
| https, `res.end(64 KB)` | 11,894 | 14,586 | 16,426 | 1.23x | 1.38x |
1.13x |
| http, GET hello (control) | 55,994 | 70,989 | 71,958 | 1.27x | 1.29x |
1.01x |

main was slower than Node in six of these eight cases. This PR is faster
than Node in all eight.

`Bun.serve`, measured on `a771572a8d`, before the larger cork buffer
(req/s, the mean of 2 rounds):

| Case | main | PR | Change |
| --- | --- | --- | --- |
| Direct stream, 4 x 16 KB | 6,826 | 12,479 | +83% |
| 64 KB string | 16,944 | 20,145 | +19% |
| TLS, 64 KB string | 15,045 | 16,892 | +12% |
| hello (control) | 83,957 | 83,137 | -1.0% |

These runs are on loopback, where the kernel send buffer is 2.6 MB and
the work of the receiver runs inside `send()`. That is the best case for
fewer writes. A new connection over a real network takes about 46 KB in
its first write on Linux. The rest waits in the socket buffer, as it
would after separate writes.

#### Small responses are unchanged

A small response is already one `recvfrom` and one `sendto` on both
builds. `perf` puts 66% of the time of a hello-world server in the
kernel, on both builds.

CI release builds on Linux x64: main `97246d044e` (the merge base)
against this PR `8834cd0787`. Both use the same WebKit. The server runs
on one pinned core. `oha` sends 64 connections for 5 s after a 2 s
warm-up. There are 2 rounds, and the order of the builds alternates.
"Change" compares the means of the two rounds.

Framework servers from `bun-perf-tester` (req/s):

| Server | main, round 1 | main, round 2 | PR, round 1 | PR, round 2 |
Change |
| --- | --- | --- | --- | --- | --- |
| express | 49,803 | 51,103 | 49,968 | 50,263 | -0.7% |
| fastify | 61,214 | 61,105 | 60,705 | 60,668 | -0.8% |
| node:http | 70,934 | 71,405 | 73,178 | 71,053 | +1.3% |
| elysia | 84,696 | 85,096 | 85,027 | 84,882 | +0.1% |
| `Bun.serve` | 89,020 | 89,099 | 88,168 | 88,373 | -0.9% |

node:http paths that this PR changes (req/s):

| Case | main, round 1 | main, round 2 | PR, round 1 | PR, round 2 |
Change |
| --- | --- | --- | --- | --- | --- |
| GET hello | 70,226 | 70,341 | 70,151 | 72,359 | +1.4% |
| POST, 16 KB body | 47,446 | 47,789 | 48,191 | 48,785 | +1.8% |
| 64 KB response in four writes | 6,885 | 6,894 | 6,834 | 6,868 | -0.6%
|
| Pipelined keep-alive, depth 8 | 94,063 | 93,294 | 92,909 | 93,809 |
-0.3% |

p99 latency (ms), the higher of the two rounds:

| Server | main | PR |
| --- | --- | --- |
| express | 1.94 | 1.91 |
| fastify | 1.52 | 1.55 |
| node:http | 1.11 | 1.12 |
| elysia | 0.98 | 0.96 |
| `Bun.serve` | 0.82 | 0.83 |

RSS (MB), one pass of 8 s of load:

| Server | Build | Start | Under load | 5 s idle | 15 s idle |
| --- | --- | --- | --- | --- | --- |
| express | main | 39 | 94 | 61 | 57 |
| express | PR | 40 | 92 | 60 | 57 |
| fastify | main | 41 | 91 | 58 | 55 |
| fastify | PR | 41 | 91 | 58 | 55 |
| node:http | main | 20 | 64 | 43 | 40 |
| node:http | PR | 20 | 65 | 45 | 41 |
| elysia | main | 28 | 46 | 36 | 35 |
| elysia | PR | 29 | 46 | 37 | 36 |
| `Bun.serve` | main | 14 | 30 | 22 | 22 |
| `Bun.serve` | PR | 14 | 30 | 22 | 22 |

Every change is within 2%. fastify and `Bun.serve` hello are lower in
both rounds, by about 1%. `Bun.serve` hello shows the same -1.0% in the
control row above, so a small real cost there is possible. The RSS pass
ran at the same time as the throughput runs, on other cores. The commits
after `8834cd0787` change tests and add one version check to the
node:http dispatcher. They were not measured.

### Supersedes

| Theme | Pull requests |
| --- | --- |
| Request body | #43592 #43579 #38196 #43518 #43602 #43408 #43427 #43597
#43555 #43456 #43466 |
| Tunnels | #43570 #43485. #43596 is a duplicate of #43570. |
| Parser | #43182 #43161 #43326 #43327 #40505 #43363 #42532 #42194 |
| Response write | #39386 #43371 #43548 #43499 #43496 #43464 #42008
#43549 |
| Response finish | #40351 #43021 #41822 #43473 #42068 #35207 #43425
#43503 |
| Lifecycle | #43413 #39686 #43028 #42727 #42622 #42610 #35837 #35839
#37825 #37749 #43376 #35268 |
| JS API | #41691 #41738 #38036 #42462 #36527 #39718 #37964. #42947
merged on its own. |

The close drain, `resetAndDestroy()`, the pending write callback
handling and the response `'close'` ordering come from #42622 and #42727
by @steipete. The diagnosis and the tests for the stalled `ws` writes
come from his #42610.

Not included:

| Pull request | Reason |
| --- | --- |
| #33061 | main already enforces `headersTimeout` and `requestTimeout` |
| #41672 | It makes `http.createServer({ key, cert })` stop serving TLS.
That needs a product decision. |
| #37543 | A type refactor with no tests and no user-visible change |
| #35465 | It makes `http.Server` extend `net.Server`. Only the
prototype chains were joined. The `net.Server` constructor never ran, so
`_handle` and `_connections` were `undefined`, and
`_emitCloseIfDrained()` emitted `'close'` on a listening server. The
server is backed by uWS, not `node:net`. |
| The `AutoFlusher` removal in #42622 | It makes `flushHeaders()` flush
at once. That is a performance change with no relation to the rest. |

### Tests

| Check | Result on a debug build (macOS arm64) | Head |
| --- | --- | --- |
| Every test file that this PR touches (28 files) | 1,866 pass, 2 fail.
The 2 failures are `serve.test.ts` "bounds memory when proxying ... to a
stalled client". They fail the same way on a debug build of main. |
`83af4da4a3`, run before the last commit of main came in |
| `test/js/third_party/express` (9 files) and the `body-parser` test |
299 pass, 0 fail | `83af4da4a3`, run before the last commit of main came
in |
| Node 25.6 against Bun, 32 scenarios from two scripts (event order,
framing, lifecycle) | No regression against Bun 1.4.3 | `0ff1a23f61` |
| Every vendored Node `test-http-*` and `test-https-*` file, plus the
`test-net-*` and `test-tls-*` files for pause, write, end and close |
535 of 537 exit 0. `test-http-agent-keepalive.js` and
`test-https-timeout.js` fail on that debug build. Both pass on every CI
lane. | `daee05fcfd` (before the rebase) |
| The tests that depend on what the kernel takes in one send, on Windows
Server 2019 x64 and Windows 11 arm64 | pass | `3eef223328` (x64),
`a29289bcc1` (arm64) |
| CI build 120191 (Linux, macOS and Windows, release and ASAN) | every
lane passed | `daee05fcfd` (before the rebase) |

Each new test fails on Bun 1.4.3, or on the commit before its fix for a
fault that this branch introduced.

The two tests over the limit are `node-http-connect.test.ts` ("tests
should run on bun") and `node-http-syscall-fault.test.ts` ("racing a
queued drain"). Each starts a debug subprocess that needs more than 5 s
on this machine. Both pass on CI.

### Changes in the last push

The branch is rebased on main (`daee05fcfd` was the head before). It is
now linear.

Four regressions against main, each with a test that fails without its
fix:

| Case | main | Before this push | Now (same as Node) |
| --- | --- | --- | --- |
| `emit('connection')` or http2 `allowHTTP1`: `res.end()` on a request
that nobody reads | `'end'`, `'close'` | No events | `'end'`, `'close'`
|
| The same server, an unread 32 MB body | 0 bytes held | 32 MB held | 0
bytes held |
| A NUL in a header value with `httpValidation: "relaxed"` (client,
`HTTPParser`, `emit('connection')` server) | Accepted | The process
spins forever | `HPE_INVALID_HEADER_TOKEN` |
| `Connection: close`, body in the same read as the head, a 20 KB
response before the body is read | `'end'` with an empty body | No
events on `req` | `'end'` with the body, `'close'` |
| An empty line on an idle keep-alive connection, then `server.close()`
| 0 s | About 6 s | 0 s |

| Fix | Where |
| --- | --- |
| The finish listener of a fallback connection dumps an unread request,
like Node's `resOnFinish` | `http1_server_fallback.ts` |
| llhttp patch: `llhttp__internal__c_test_lenient_flags_20` is false for
a NUL. The relaxed state does not consume a NUL, and the next state sent
it back there. 9.4.3 has the same loop. | `llhttp.c`, noted in its
`README.md` |
| A node:http socket that `onData` is parsing gets the close gate of
`onData`, also when a large write released the cork | `HttpResponse.h`
`uncorkCompletedResponse()` |
| A read that starts no message leaves an idle connection idle |
`HttpContext.h` `onData` |

The open review threads are fixed in `8834cd0787`:
`closeAllConnections()`, `Proxy-Connection: close`, five comments cut to
one line, and the test of two overlapping listeners, which now waits on
events. With the generation gate in `emitCloseServer` removed, that test
fails in both cases. `AsyncSocketData` keeps its bools together, which
takes it from 56 to 48 bytes per socket.

`http.Server` no longer extends `net.Server` (see "Not included"). The
special case for it in `Ipc.ts` is gone too. `child.send(msg,
httpServer)` still throws `ERR_INVALID_HANDLE_TYPE`, and its test stays.

<details><summary>Changes since the first revision (2988a61)</summary>

Merged with main at `c8e1f6fa5b`. The one conflict was #43708
(`req.socket` emits `'end'` and `'error'`). Its state bit
`HTTP_NODE_PEER_ENDED` moved to bit 22, because bit 19 is
`HTTP_NODE_NOTIFY_READ_PARSED` here. Its 15 tests run in
`node-http-server-abort-events.test.ts` next to the tests of this branch
(103 pass).

CI on `2988a610c` had ten red tests from four causes. They are fixed:
- `ed882e5e99`: `write()` to a response without a body (HEAD, 204) does
not wait for unsent bytes.
- `811f817704`: an idle tunnel does not hold the event loop after
`server.close()`. Four vendored Node tests timed out on every platform.
- `0697deec11`, `d428824c08`, `7aec062d14`: the write callback tests use
a body that backs up a loopback socket, and accept what Winsock does.
- `c7af1c1615`: two tests from main asserted the old `close()` contract.

Review findings, each reproduced against Node v26.3.0 and fixed with a
test that fails without the fix:
- `d4d2b783ea`, `2cc79939bb`, `45141abca9`, `9a63dbc470`, `80a23a1822`:
the idle rule. A keep-alive connection is idle again when its body ends
after its response. A connection that owes a queued pipelined response,
that still receives a request head or body, or whose response still
drains is not idle.
- `87d8904aa3`, `7eca4f7806`: `close(cb)` followed by `listen()` in the
same tick reports `'close'`, also for an https server whose only
connection was idle.
- `3fd7b25382`: a paused pipelined request behind a response that still
drains stops the connection. The first revision read 512 MiB of 512 MiB
into memory.
- `2d1a5e2d8d`, `33e4683a8a`, `539cb41eb9`, `197c7dfc29`, `0490e3540b`:
raw socket writes stay behind every unsent response byte. The cases were
a CONNECT pipelined behind a response that still drains (its `200`
landed at offset 2.6 MB of a 64 MiB body), a zero-length tunnel write
(it hung the tunnel), the 400 replies above, the zero-copy tail of a
large `res.write()`, the cork buffer, and Windows 11, where the kernel
takes the whole response and refuses the next send.
- `0abd39c133`: an upgrade from the request's `'end'` listener keeps the
body bytes out of the WebSocket. The connection closed with 1006 right
after the 101.
- `5aafc61aa6`: the callback of a small `res.write()` that the kernel
refuses at the uncork runs on the drain. Reproduced on Windows 11 only.
- `a29289bcc1`: a tunnel write that waits for a drain settles its
callbacks when the connection closes.

Known differences from Node that this PR leaves:
- A handler that calls `res.end()` and then `server.close()` closes its
keep-alive connection at once. Node waits for the `keepAliveTimeout`.
- A pipelined Upgrade behind a response that still drains is served as a
plain request.
- An `end()` on a tunnel with no write pending, while the response
before the CONNECT still drains, closes both directions after the flush.
Node half-closes.
- A raw `req.socket.write(big)` and `req.socket.end()` with no
`res.end()` sends every byte but no FIN. main loses bytes here.
- A CONNECT socket that is given back with `server.emit('connection',
socket)` answers only the first of several pipelined requests. main
answers none.
- A large write from an `'upgrade'` listener stalls while the body of
that Upgrade request is still pending. A second `listen()` on a
listening server does not throw. Both are the same on main.
- A tunnel write that fails because the client went away fails its
callbacks but emits no `'error'`. Node emits `ECONNRESET`. A new
`'error'` could end a process that has no listener for it.

</details>

<!-- robobun:evidence:begin -->

---

**no test proof** · iteration 8 · platform-specific test(s) that do not
run on this machine, deferring to CI, which covers all platforms:
test/js/web/fetch/fetch.stream.test.ts, test/js/node/url/url.test.ts,
test/js/node/tls/tls-syscall-fault.test.ts,
test/js/node/net/node-net-server.test.ts,
test/js/node/http/node-http.test.ts,
test/js/node/http/node-http-syscall-fault.test.ts,
test/js/node/http/node-http-server-close-drain.test.ts,
test/js/node/http/node-http-connect.test.ts,
test/js/node/http/node-http-backpressure.test.ts,
test/js/node/child_process/child_process_ipc_handle.test.ts,
test/js/bun/http/serve.test.ts,
test/js/bun/http/serve-syscall-fault.test.ts,
test/js/bun/http/bun-server.test.ts

<!-- robobun:evidence:end -->

---------

Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
@Jarred-Sumner

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Superseded by #43557, which is merged (5d5f03f). It fixes this once for the whole node:http server and carries the tests over.

@robobun

robobun commented Sep 26, 2026

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Confirmed on main at 5d5f03f.

  • The reproduction from this PR prints req.upgrade = true on both shouldUpgradeCallback lines, the same as Node v26.3.0.
  • The test req.upgrade is true inside shouldUpgradeCallback like Node.js is in test/js/node/http/node-http.test.ts on main. It passes on a debug build of that commit.

The pipelined Upgrade case stays open in #43420. #43441 is the open PR for it.

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