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fetch: do not reuse a pooled connection the origin already wrote to - #41987
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The keep-alive pool hands a parked connection to the next request from HTTPThread::drain_events, which runs before the event loop polls. Input the origin wrote after its last response is then still unread in the kernel, and is_closed/is_shutdown/get_error cannot see it. Writing the request onto that connection makes bun answer it with bytes that were already on the wire: an unsolicited response, or the 408 Request Timeout plus Connection: close that servers and load balancers use to retire an idle keep-alive connection. HTTPContext::find_in now peeks the read side before it hands a socket out and reaches the same verdict the idle-socket handlers reach after a poll: queued data or a read error retires the connection with a reset, a FIN retires it with a FIN. HTTP/2 sessions keep their own idle-frame handling. us_socket_queued_input is the new uSockets entry point; it peeks, so the normal read path still sees whatever it found.
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Included review availability: Your plan provides up to 10 included reviews per hour; 0 remain after this review. WalkthroughAdds non-consuming socket queued-input APIs across C and Rust. HTTP keep-alive pooling checks queued input before reusing non-HTTP/2 sockets. Tests cover responses, malformed bytes, timeout, CRLF, and FIN events during checkout. ChangesQueued input detection and HTTP reuse
Suggested reviewers: Priority: ➖ Normal — Schedule the fetch keep-alive change because it prevents origin-written or malformed queued data from being attributed to a later request. Merge Risk: ⚪ Minimal · up to Fetch keep-alive reuse now avoids assigning stale origin data or closed connections to a subsequent request. The implementation and targeted regression coverage indicate no remaining actionable merge risk. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Updated 9:30 AM PT - Sep 8th, 2026
✅ @robobun, your commit 41e53c95af838a25e1d2a279c726e90ea43561c9 passed in 🧪 To try this PR locally: bunx bun-pr 41987That installs a local version of the PR into your bun-41987 --bun |
…quest The first version timed the origin's injected write against one fetch() round trip. That window is tens of microseconds on a release build, so on the CI lanes the injected event landed after bun had already written request 2, which no readability check can cover, and the test failed. Each round now writes the injected event before it queues request 2, so the bytes are in bun's kernel buffer before bun can write that request anywhere. Two requests to an origin that never answers are queued first to take the HTTP thread out of poll(). Stock bun misattributes 12 of 12 rounds on each of the four leaking events; this branch misattributes none. Also mirror the LIBUS_QUEUED_INPUT_* codes by name in Rust and give QueuedInput explicit discriminants, so the two sides of the FFI cannot renumber independently.
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Status What breaks. A pooled keep-alive connection is handed to the next request before the event loop polls it, so bytes the origin already wrote are unread in the kernel and invisible to the checks at checkout. The next How I reproduced it. A raw origin answers request 1 honestly, then writes one unsolicited event on the now idle connection. The client reads response 1 and issues request 2 at once.
With the injected event at least 1 ms old, stock bun has already retired the connection. The fault is the checkout window only. Fix. #41987. The regression test is in |
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In `@test/js/web/fetch/fetch-keepalive.test.ts`:
- Line 753: Update the tests around the injections iteration to use
describe.each() with idleInjections entries as independent named test
parameters, and keep the existing 12-round loop inside each generated case.
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packages/bun-usockets/src/bsd.cpackages/bun-usockets/src/internal/networking/bsd.hpackages/bun-usockets/src/libusockets.hpackages/bun-usockets/src/socket.csrc/http/HTTPContext.rssrc/uws/lib.rssrc/uws_sys/lib.rssrc/uws_sys/socket.rssrc/uws_sys/us_socket_t.rstest/js/web/fetch/fetch-keepalive.test.ts
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I re-reviewed after the follow-up commits and found no bugs — the earlier nits (named FFI constants with #[repr(i32)], Buffer.alloc over .repeat, using-scoped listeners) are all addressed. Because this adds a new uSockets C entry point with a Windows-specific branch, threads it across the FFI boundary, and changes the HTTP client's keep-alive checkout hot path, a human look would still be worthwhile.
What was reviewed: bsd_queued_input — MSG_PEEK consumes nothing and the EINTR loop / bsd_would_block() mapping matches the sibling bsd_recv; the Windows branch's non-blocking assumption is the same one bsd_recv already relies on. Rust LIBUS_QUEUED_INPUT_* constants and the #[repr(i32)] QueuedInput discriminants match libusockets.h exactly, and the extern signature matches the C definition. find_in verdicts mirror the existing idle on_data/on_end handlers, HTTP/2 is correctly exempted, and duplex/pipe transports fall through unchanged. The test orders the injected write before the fetch via the shared JS thread (no sleep/timing race) and drains stdout/stderr/exited concurrently.
Extended reasoning...
Overview
This PR stops fetch() from reusing a pooled keep-alive connection that the origin has already written to or closed while it was parked. It adds bsd_queued_input() (a non-consuming recv(MSG_PEEK | MSG_DONTWAIT) peek) and us_socket_queued_input() in bun-usockets, mirrors the four LIBUS_QUEUED_INPUT_* return codes as a #[repr(i32)] QueuedInput enum on the Rust side with named constants, exposes it through bun_uws_sys → bun_uws, and calls it in HTTPContext::find_in before handing an HTTP/1.x socket out of the pool. On Eof the socket is closed, on Data/Error it is terminated, and only on None is it reused — the same verdicts the idle on_data/on_end handlers already reach once the loop polls. A test.concurrent.each in fetch-keepalive.test.ts covers five injected events (408+close, unsolicited 200, stray CRLF, garbage, FIN) over 12 rounds each in a subprocess.
Since my prior review, three follow-up commits addressed all three inline nits I raised: the FFI mapping now uses named LIBUS_QUEUED_INPUT_* constants and QueuedInput is #[repr(i32)] with explicit discriminants (matching the CloseCode neighbour); the test uses Buffer.alloc(64, "!").toString(); and the listeners are now using-scoped inside a subprocess so nothing leaks on failure.
Security risks
Low. The peek is read-only on a socket the process already owns, consumes nothing, and only tightens reuse (fails closed toward "dial fresh" on anything but a clean would-block). Misclassification in the worst case costs one extra connection, not a security exposure. No user-controlled input reaches the new C path beyond the fd already in the pool. The test is hermetic (local Bun.listen({ port: 0 }), subprocess-isolated pool).
Level of scrutiny
Medium-high. The change is small and focused, but it spans a C→Rust FFI boundary with a new extern, has a Windows-specific #ifdef branch that relies on all uSockets-owned fds being non-blocking (the same assumption bsd_recv already makes), and sits in the HTTP client's keep-alive checkout hot path where every pooled request now pays one extra recv() syscall. REVIEW.md's cross-platform/FFI rules apply directly, and .claude/docs/landing-prs.md calls out both Cross-platform and Performance as sections warranting a human read. None of that is a defect I can point to — it is why a maintainer should sign off rather than an automated approval.
Other factors
The bug hunt ran to a dry streak with zero findings and zero ruled-out candidates. The FFI constants now match by name on both sides (verified against libusockets.h), the us_socket_queued_input guard returns NONE for closed/semi sockets (fail-open only to "reuse when provably idle"), and the find_in verdicts mirror the existing idle handlers so the fix lives at the layer owning the invariant. The test orders the injected write before the queued fetch on a shared JS thread and uses ballast requests to a never-answering listener to keep the HTTP thread out of poll(), so it awaits conditions rather than sleeping. No CODEOWNERS entries cover the changed paths. The one coderabbitai inline thread was resolved by a non-author.
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Same fix, found in parallel. I am standing down in favour of this PR. My branch is Two test cells from that branch cover doors this PR's set does not, if you want them (all three live in
One measurement that may matter for your CI. On Windows the loopback hands a local write over a moment after |
…usly The darwin lane showed the injected bytes landing after the checkout in 4 of 60 rounds: macOS hands a TCP loopback segment to the dlil input thread before the peer can read it, so writing it before fetch() is called does not put it in bun's receive buffer before the checkout. No client-side check can cover bytes that are not there yet. An AF_UNIX write, and a TCP loopback write on Linux and Windows, is in the peer's buffer when write() returns. So the test now runs over the unix-socket pool everywhere fetch() has one (not Windows) and over TCP on Linux and Windows. Both pools check a socket out through find_in. Stock bun misattributes 12 of 12 rounds on every leaking event over both transports; this branch misattributes none.
…olicited data (#42128) ### Problem - A socket parked in `agent.freeSockets` (`keepAlive: true`) keeps reading while idle, and unsolicited bytes do not retire it. A whole response written there is attributed to the next request. - The cause is the Agent's `'free'` handler (`src/js/node/_http_agent.ts:123`). It pools the socket with nothing watching the read side, where the parser is already detached. Node fixed the same hole as CVE-2026-48931 (https://hackerone.com/reports/3582376). This ports that one fix only. ### Fix - The Agent marks a pooled socket with `kDestroyOnRead`, and `reuseSocket` clears it. A freed socket that already holds buffered readable data is destroyed before it can be pooled or handed to a queued request. - In `node:net`, `pushDataToSocket` (the one function through which all three handler tables feed the stream, from #35347) destroys a marked socket instead of pushing the bytes. - Like node's guard, it adds no public stream listener (Notes). - Verified: `test/js/node/http/node-http-agent-free-socket.test.ts`, 8 `node:test` cases that Bun runs in-process, plus one that runs the same file under Node.js. 6 fail on released bun. On Node they pass from v26.4.0, where the upstream fix shipped (Notes). Also `test/js/node/http/`, `test/js/node/net/`, and the vendored http, https, net, tls suites. Self-reviewed: 4 concerns, 3 addressed, 1 declined (Notes, "Scope"). ### Background - `Agent.freeSockets` holds idle keep-alive sockets per origin. `addRequest` takes one out and calls `reuseSocket`. - A pooled socket has no parser and no `'data'` listener: what it receives goes nowhere, or reaches the next response's parser. - A bun `net.Socket` reads through a native handler table passed at dial time. One table serves every socket that used it, so a per-socket hook must live on the socket. <details><summary>Notes</summary> **Reproduction** (bun 1.4.3, linux x64). A raw origin answers each request with its own path, then writes a complete unsolicited response on the idle pooled connection. | when the stray response arrives | stock bun | this branch | | --- | --- | --- | | the event loop polls before the next request | socket stays pooled, bytes discarded | socket destroyed, next request dials a fresh connection | | the next request is issued in the same tick | next request reads `poison` | next request reads `poison` | Node v26.3.0 (before the guard shipped) behaves like stock bun in both rows. **Node versions.** The upstream fix first shipped in Node v26.4.0 (`lib/_http_agent.js` at the v26.3.0 tag has no `installFreeSocketDataGuard`). Forced to run everywhere: Node v26.3.0 passes 2 of 8 (the reuse cases) and fails the 6 guard cases, like stock Bun; Node v26.4.0 passes 6 and fails the 2 queued-request cases (Node checks buffered bytes only on the pool path); this branch passes 8. In the file the guard cases skip on Node < 26.4.0 and the queued-request case skips on Node, each with the reason. **No public listener.** Node's first version of this guard used a `'data'` listener plus `resume()`. node-fetch@2 reads `socket.listenerCount('data')` while a response closes and started reporting false `ERR_STREAM_PREMATURE_CLOSE` errors (nodejs/node#63989), so node reworked the guard onto the stream handle's internal `onread` hook. Bun has no per-socket equivalent of that hook: the handler table given to `Bun.connect` is one shared cell, and `socket.reload()` mutates it for every socket that shares it. Hence the per-socket flag, read in `pushDataToSocket`. The test asserts `listenerCount('data')` and `listenerCount('readable')` are still 0 on a free socket, as node's does. The handler table built for the `onread` socket option keeps its own `data` callback: it bypasses the stream, and `node:http` cannot use such a socket. **The same-tick row is the residual race, and node has it too.** The stray bytes are still unread in the kernel when `addRequest` hands the socket out, so no check in JS can see them. Node's own test says as much ("in a real attack, there is always time between the poison arriving and the next client request"). Closing it needs a peek of the read side at checkout, which is what #41987 does for `fetch()`'s pool in Rust. Unrelated to this change: when bytes that win that race are not a valid response, the client's parse error surfaces as an uncaught exception instead of an `'error'` event on the request, on stock bun and on this branch alike. **The upstream test is not vendored yet.** `test/parallel/test-http-agent-free-socket-data-guard.js` injects the stray bytes with `req.socket.write()` on a `node:http` server. Bun's server leaves that socket corked after the request (`socket.writableCorked === 1`, the bytes sit in the writable buffer), which is #35664. Once that lands, the upstream file can be vendored as is and the bespoke cases trimmed. The new cases drive a raw `net`/`tls` server instead, which is also how they cover `https.Agent`. **Scope.** CVE-2026-48931 shipped in a Node security release together with other advisories. This PR does not examine or claim anything about the others. The self-review asked for a public tracking issue that lists them against bun; I left that to the maintainers, since it amounts to publishing an unverified vulnerability list. **Already-buffered bytes.** Node's `installFreeSocketDataGuard` destroys a socket whose `readableLength > 0`, but the caller still pushes it into `freeSockets`, where `'close'` prunes it a tick later (and `addRequest` can pop it first under `lifo`), and the check does not run at all when the freed socket goes straight to a request queued in `agent.requests`. Here the check runs right after the `writable` check in the `'free'` handler, so both hand-off paths share it and a destroyed socket is never pooled. For the queued path, the destroyed socket's `'close'` reaches `removeSocket`, which dials a new connection for the waiting request. The "holds unsolicited data" cases cover both paths: they `push()` the stray bytes in the response's `'end'` handler, which is after the parser detached and one tick before `'free'`. **Disarm point.** `reuseSocket` clears the flag, as in Node, where `Agent.prototype.reuseSocket` is the only caller of `removeFreeSocketDataGuard` and nothing else restores `_handle.onread` (`initSocketHandle` runs only for a new or reconnected socket). A subclass that replaces `reuseSocket` without calling the parent loses reused sockets on both runtimes. **TLS.** The guard sees decrypted application data only, so a post-handshake `NewSessionTicket` on an idle pooled socket does not trip it. The `https` cases cover a parked TLS socket that is poisoned, one freed with buffered bytes (pooled and queued paths), and one that is reused. **Cost.** One symbol-property load per received chunk. The `src/` diff is 28 lines. `kDestroyOnRead` is initialized in the `Socket` constructor so the read path stays monomorphic. **Pre-existing failures in this container, with and without this diff** (each one rechecked against main's `src/js` on the same build): `test-http-agent-keepalive.js` (`agent.sockets[name]` is not cleaned up after the server closes the socket), `test-http-client-timeout-option.js`, the `test-http(s)-proxy-request*` family, one subprocess case of `node-http-syscall-fault.test.ts`, 10 `node-net.test.ts` cases that fail here with `ECONNREFUSED`, `test-net-server-async-dispose.mjs`, `test-net-connect-custom-lookup-non-string-address.mjs`, `test-tls-client-allow-partial-trust-chain.js`. </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 2 · 4 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 6 FAILED $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/node/http/node-http-agent-free-socket.test.ts bun test v1.4.3 (4ff9193) test/js/node/http/node-http-agent-free-socket.test.ts: 157 | assert.strictEqual(freeSocket.listenerCount("readable"), 0); 158 | 159 | serverSockets[0].write(poisonedResponse); 160 | 161 | await pollUntil(() => freeSocket.destroyed && agent.freeSockets[name] === undefined); 162 | assert.strictEqual(freeSocket.destroyed, true); ^ AssertionError: Expected values to be strictly equal: false !== true generatedMessage: true, actual: false, expected: true, operator: "strictEqual", diff: "simple", code: "ERR_ASSERTION" at /workspace/bun/test/js/node/http/node-http-agent-free-socket.test.ts:162:16 at withAgent (/workspace/bun/test/js/node/http/node-http-agent-free-socket.test.ts:118:11) at /workspace/bun/test/js/node/http/node-http-agent-free-socket.test.ts:150:13 at node:test:1781:26 at executeTestNode (node:test:1785:63) at processTicksAndRejec ... (truncated) release without fix: all passed bun test v1.4.3-canary.1 (9f655b7) test/js/node/http/node-http-agent-free-socket.test.ts: (pass) http.Agent free keep-alive socket over http > destroys a free socket that receives unsolicited data [22.64ms] (pass) http.Agent free keep-alive socket over http > does not pool a socket that holds unsolicited data when it is freed [3.12ms] (pass) http.Agent free keep-alive socket over http > does not hand a freed socket that holds unsolicited data to a queued request [2.17ms] (pass) http.Agent free keep-alive socket over http > reuses a free socket that received nothing [1.64ms] (pass) http.Agent free keep-alive socket over https > destroys a free socket that receives unsolicited data [41.32ms] (pass) http.Agent free keep-alive socket over https > does not pool a socket that holds unsolicited data when it is freed [5.10ms] (pass) http.Agent free keep-alive socket over https > does not hand a freed socket that holds unsolicited data to a queued request [4.67ms] (pass) http.Agent free keep-alive socket over https > reuses a free socket that received nothing [3.29ms] (pass) Node.js compatibility > all tests pass in Node.js [156.92ms] 9 pass 0 fail Ran 9 tests across 1 ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/node/http/node-http-agent-free-socket.test.ts bun test v1.4.3 (4ff9193) test/js/node/http/node-http-agent-free-socket.test.ts: (pass) http.Agent free keep-alive socket over http > destroys a free socket that receives unsolicited data [1158.89ms] (pass) http.Agent free keep-alive socket over http > does not pool a socket that holds unsolicited data when it is freed [172.89ms] (pass) http.Agent free keep-alive socket over http > does not hand a freed socket that holds unsolicited data to a queued request [115.53ms] (pass) http.Agent free keep-alive socket over http > reuses a free socket that received nothing [100.60ms] (pass) http.Agent free keep-alive socket over https > destroys a free socket that receives unsolicited data [474.62ms] (pass) http.Agent free keep-alive socket over https > does not pool a socket that holds unsolicited data when it is freed [200.09ms] (pass) http.Agent free keep-alive socket over https > does not hand a freed socket that holds unsolicited data to a queued request [147.77ms] (pass) http.Agent fre ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision 400b9a9 features baseline 23 deps, 131 codegen, 1172 objects in 697ms ninja: Entering directory `/workspace/bun/build/release' [1/146] fetch picohttpparser [picohttpparser] up to date [2/146] fetch WebKit (prebuilt) [WebKit] up to date [3/146] gen ZigGeneratedClasses.{cpp,h,rs} Found 2 classes from /workspace/bun/src/jsc/resolve_message.classes.ts - ResolveMessage (15 fields) - BuildMessage (10 fields) Found 1 classes from /workspace/bun/src/runtime/api/Archive.classes.ts - Archive (4 fields, 1 class fields) Found 2 classes from /workspace/bun/src/runtime/api/BunObject.classes.ts - ResourceUsage (8 fields) - Subprocess (20 fields) Found 1 classes from /workspace/bun/src/runtime/api/cron.classes.ts - CronJob (5 fields) Found 3 classes from /workspace/bun/src/runtime/api/filesystem_router.classes.ts - FileSystemRouter (5 fields) - FrameworkFileSystemRouter (2 fields) - MatchedRoute (8 fields) Found 1 classes from /workspace/bun/src/runtime/api/Glob.classes.ts ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` src/js/internal/net/symbols.ts | 3 + src/js/node/_http_agent.ts | 12 + src/js/node/net.ts | 14 +- .../node/http/node-http-agent-free-socket.test.ts | 251 +++++++++++++++++++++ 4 files changed, 279 insertions(+), 1 deletion(-) ``` </details> **gate history** · 3 passed · 2 rejected · iteration 2 <details><summary>evidence per changed file</summary> ``` file reads edits tests src/js/internal/net/symbols.ts 3 4 6 src/js/node/_http_agent.ts 5 10 8 src/js/node/net.ts 13 15 7 test/js/node/http/node-http-agent-free-socket.test.ts 0 0 2 ``` </details> <!-- robobun:evidence:end -->
2 participants
Problem
fetch()can resolve with bytes that were on the wire before its request. An origin that retires an idle keep-alive connection withHTTP/1.1 408 Request TimeoutandConnection: close, or that sends an unsolicited response, has that answer attributed to the next request: 99 of 100 rounds here, GET and POST alike. undici, curl and Chromium dial a fresh connection instead.HTTPContext::find_in(src/http/HTTPContext.rs:869). The pool hands a parked socket out fromHTTPThread::drain_events, which runs beforeuws_loop.tick()(src/http/HTTPThread.rs:1272). Input the origin already wrote is still unread in the kernel, andis_closed,is_shutdownandget_errorcannot see it.Fix
find_inpeeks the read side before it hands a socket out. Queued data or a read error retires the connection with a reset. A FIN retires it with a FIN. An HTTP/2 session keeps its own idle-frame handling.Handler::on_dataterminates,Handler::on_endcloses). A zero gap now behaves like a 5 ms gap.us_socket_queued_inputis the new uSockets call.recv(MSG_PEEK | MSG_DONTWAIT)consumes nothing, so the normal read path still sees what it found.test/js/web/fetch/fetch-keepalive.test.ts, one case per injected event and pool (TCP, unix), 12 rounds each. Stock bun misattributes 12 of 12 rounds on each event that leaks. Also all oftest/js/web/fetch/,test/js/node/http/node-http.test.ts, and keep-alive reuse over plain, TLS and unix (30 requests, 1 connection).Background
pending_socketsand hands it to the next request for the same origin.release_socketparks it,find_inchecks it out.drain_events()and thenuws_loop.tick(), so the queue of new requests is drained before the loop polls the sockets. A checkout can happen with no poll since the socket was parked.MSG_PEEKreports what the kernel holds on a socket without removing it.Notes
Reproduction. A raw origin answers request 1 with
200 ... REAL1, waits, then writes one unsolicited event on the now idle connection. The client reads response 1 and issues request 2 at once.HTTP/1.1 408 Request Timeout+Connection: close408/T-OUT200responseMalformed_HTTP_ResponseMalformed_HTTP_ResponseNode v26 answers 0/50 on the unsolicited-response origin. With the injected event at least 1 ms old, stock bun already retires the socket (0/100), because the loop has polled by then.
Sweep of the origin's delay between response 1 and the injected event (40 rounds each,
408event):The residual from 1 ms on is the other half of the race: the injected bytes reach the client after it has already written request 2. No readability check can see those, and no client can tell them from an answer (node answers 7/100 there, curl 3/30). Browsers treat a
408on a reused connection that answered no byte as a stale socket and replay an idempotent request. That is a separate behaviour change and is not in this PR. bun's existing stale-socket retry (src/http/lib.rs:2141) already covers the FIN and reset flavours the same way.The test does not race. Each round writes the injected event before it queues request 2, so the bytes are in bun's kernel buffer before bun can write that request anywhere. Two requests to an origin that never answers are queued first, which takes the HTTP thread out of
poll(): without them the loop reads the injected bytes on the idle connection and retires it throughHandler::on_data, which is the behaviour this change extends to the checkout window. Whichever of the two wins, request 2 has to be answered on a later connection, so the test has no timing tolerance to spend.That ordering only holds when
write()returns with the bytes already in the peer's receive buffer. An AF_UNIX stream does that everywhere, and TCP loopback does it on Linux and Windows. macOS hands a loopback segment to the dlil input thread first: the darwin lane saw it land after the checkout in 4 of 60 rounds, which no client can tell from an answer. So the cases run over the unix-socket pool wherever fetch() has one (not Windows) and over TCP on Linux and Windows. Both pools check a socket out throughfind_in. An earlier version timed the origin's write against one fetch() round trip and was flaky everywhere.Keep-alive reuse is unchanged. 30 sequential requests still ride one connection over plain HTTP, TLS and a unix socket. A TLS 1.3
NewSessionTicketwas the main worry: a ticket queued at checkout time would retire a healthy connection. It never is, because the client consumes the ticket while it reads the first response. Checked against an OpenSSL origin that sends tickets: 30 requests, 1 connection.Conservative by design. The peek reports that input is queued, not what it is, which is all a TLS socket can report without decrypting. So a pooled HTTP/1 socket carrying a trailing
0\r\n\r\n(whichHandler::on_dataignores by name) is retired when the race window hits it, instead of reused. That costs one connection, and only in the window.Cost. One
recv(MSG_PEEK | MSG_DONTWAIT)per pooled checkout, on a socket the kernel has cached. Transports the loop does not read withrecv()(an upgraded duplex, a Windows named pipe) report nothing queued and behave as before.Related. #35817 makes bun honour a server's
Keep-Alive: timeout=Nhint, which shortens how long bun holds a connection the origin is about to time out. This PR is the other side: what to do with a connection the origin has already written to.