usockets: report a peer reset on a paused socket on kqueue - #39610
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…t reading On kqueue, us_socket_pause deleted the read filter and the one-shot write filter it registered was consumed by the first writable event, so a paused socket had no filter left. A peer reset was only reported once the socket resumed. epoll reports it at once (EPOLLERR and EPOLLHUP cannot be masked), and the libuv backend probes for it, so the tests added for the reset path hung on macOS. kqueue_change now keeps the EVFILT_READ knote of a socket poll in both modes: level-triggered while the socket polls for reads, EV_CLEAR while it does not. A reset or FIN still reaches the dispatcher, which masks the readable bit out, and EV_CLEAR keeps unread data from re-firing. EV_ADD on an existing knote keeps its flags, so a mode switch deletes the knote and adds a new one. This also replaces the read sentinel that three call sites armed by hand, which a later plain EV_ADD left edge-triggered, and the one-shot write filter that was added when a socket polled for nothing. us_poll_stop deletes the read knote of a socket poll in either mode. A delete of a filter that is not registered no longer counts as a failure.
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Status: fix for the darwin break of Reproduced the mechanism with kqueue probes on a macOS 14 x64 and a macOS 26 arm64 machine: with the read filter deleted and the one-shot write filter consumed, a reset produces no event. The real |
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Inline comments:
In `@packages/bun-usockets/src/eventing/epoll_kqueue.c`:
- Around line 656-659: Update the poll-adoption path around kqueue_change to
capture and propagate registration failures before replacing the existing poll;
if re-adding filters for new_p fails, restore the previous mask and keep the old
poll valid until all filters reference new_p. In us_poll_change, assign the
kqueue_change result to rc and return the failure instead of reporting success
after an unsuccessful mode switch.
In `@test/js/bun/net/socket.test.ts`:
- Line 4098: Update the transport matrix around the loop over ["tcp", "tls"] to
use describe.each() for parameterized test grouping instead of manually
iterating transports. Preserve the existing test cases and their concurrent
execution behavior within each generated transport suite.
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packages/bun-usockets/src/eventing/epoll_kqueue.cpackages/bun-usockets/src/internal/internal.hpackages/bun-usockets/src/loop.cpackages/bun-usockets/src/socket.ctest/js/bun/net/socket.test.ts
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I reviewed this PR and didn't find any bugs. Because it rewrites the core kqueue knote lifecycle in kqueue_change — a hot path every macOS socket goes through — and its correctness rests on empirically-probed kernel semantics (EV_ADD keeping flags, EV_CLEAR firing once per RST/FIN, KEVENT_FLAG_ERROR_EVENTS entry ordering), a human look would still be worthwhile, especially given the overlap with open PRs #37098/#37099.
What was reviewed:
change_list[3]bounds vs. the max 3-entry DELETE+ADD+WRITE path; return-value contract change againstus_poll_start_rccallers (!= 0checks still hold).- Traced pause/resume/raw_shutdown/half-open transitions to confirm each leaves the read knote in the intended mode and
us_poll_stopdeletes it;kqueue_is_socket_pollexcludes SEMI/UDP/CALLBACK so the removed zero-events one-shot-write fallback is not needed there. - The three removed sentinel-arm sites are subsumed by the persistent knote; the dispatcher already masks readable via
us_poll_eventsand routeseof_errto the error close.
Extended reasoning...
Overview
This PR changes packages/bun-usockets/src/eventing/epoll_kqueue.c so that on kqueue, a socket poll's EVFILT_READ knote is never deleted while the socket is alive: it is level-triggered while reading and re-registered as EV_CLEAR while not reading (paused, half-open after peer FIN, shut down with reads off, low-prio parked). kqueue_change gains a keep_read_knote parameter and now iterates KEVENT_FLAG_ERROR_EVENTS results, treating EV_DELETE+ENOENT as success. us_poll_stop now deletes the read knote even when old_events had no READABLE. The three hand-armed us_internal_kqueue_socket_arm_read_sentinel call sites (loop.c half-open, socket.c raw_shutdown and pause) and the zero-events one-shot write fallback are removed. Two new Bun.listen tcp/tls tests in test/js/bun/net/socket.test.ts pin the paused-then-RST → ECONNRESET contract.
Security risks
None. No untrusted input parsing, auth, or crypto changes. The change is confined to how fds are registered with the kernel event queue.
Level of scrutiny
High. This is the core macOS/BSD event loop registration path — every TCP/TLS socket in Bun on darwin flows through kqueue_change. A mistake here can hang sockets (no event ever fires), busy-loop the process (a level-triggered knote on a paused socket), or use-after-free (a stale udata after resize). The correctness argument depends on XNU kqueue semantics that the author verified empirically on macOS 14 and 26 but that are not documented (EV_ADD over an existing knote keeps its flags; an EV_CLEAR knote fires once per RST with fflags=ECONNRESET; DELETE+ADD in one changelist applies both even when the DELETE errors). I traced every state transition (accept → pause → resume, pause → shutdown, half-open FIN → WRITABLE, low-prio park) against the new keep_read_knote gate and did not find one that leaves a level knote on a non-reading socket or drops the knote entirely, but I cannot execute the darwin path here — the actual proof is this PR's darwin CI lanes.
Other factors
The PR description is unusually thorough (six-scenario harness on two macs, FreeBSD changelist-stops-at-first-failure noted and shown not to bite because the DELETE always finds a knote). CodeRabbit's two comments were addressed (describe.each applied in 46036bc; the resize/change error-propagation concern is pre-existing and tracked in #37098). The return-value change to kqueue_change is safe for the two us_poll_start_rc callers, which only test != 0. The overlap with open PRs #37098 and #37099 (both touch the same kqueue functions) is a coordination concern a maintainer should weigh. Given the platform-critical nature and the reliance on kernel behavior I cannot verify locally, deferring to a human reviewer is the right call.
On Windows the close that reports the reset carries an error without a code (the WSA code is not mapped on that path), which is a separate bug.
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Updated 9:45 PM PT - Aug 18th, 2026
✅ @robobun, your commit 7fbf179358a9911a1b6d29af6aa53a13ef479db5 passed in 🧪 To try this PR locally: bunx bun-pr 39610That installs a local version of the PR into your bun-39610 --bun |
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I reviewed this PR and the bug-hunting pass found no issues. Because it reworks kqueue's read-knote lifecycle in the core socket polling path — with correctness resting on empirically-probed macOS kevent semantics (EV_ADD flag retention, KEVENT_FLAG_ERROR_EVENTS entry shape, EV_CLEAR re-fire behavior) — a maintainer look is still worthwhile before merge.
What was reviewed:
kqueue_changechangelist sizing (now 3 entries), the delete+re-add mode switch, and the new per-entry error loop that ignores ENOENT on EV_DELETE.us_poll_stopdeleting the read knote for a paused socket poll, andus_poll_start_rc/us_poll_resizestill passingkeep_read_knote=0so non-socket polls and initial registration are unchanged.- Removal of the three
us_internal_kqueue_socket_arm_read_sentinelsites and the zero-events one-shot write filter — traced against the dispatcher's existing eof/error masking inloop.c. - The new
socket.test.tstcp/tls matrix: failure paths wired to reject, greeting round-trip guarantees the one-shot write is consumed beforeterminate(), Windows code check gated on POSIX.
Extended reasoning...
Overview
This PR fixes a darwin-only hang introduced when #39600 added tests asserting that a peer RST on a paused socket is reported as ECONNRESET. On kqueue, us_socket_pause deleted the read filter and left only a one-shot write filter that the kernel consumes immediately, so a subsequent RST produced no event. The fix moves the previously hand-armed "read sentinel" (an EV_CLEAR EVFILT_READ knote) into kqueue_change itself: for socket polls, the read knote is always registered — level-triggered while reading, EV_CLEAR while not — and a mode switch is a delete+re-add because EV_ADD on an existing knote keeps its flags. Three ad-hoc sentinel call sites (raw_shutdown, socket_pause, and the half-open branch in loop.c) are removed, along with the zero-events one-shot write filter. us_poll_stop now deletes the read knote even when the socket wasn't polling for reads. The error-event loop in kqueue_change now iterates all returned entries and treats ENOENT-on-DELETE as benign.
Security risks
None. This is event-loop plumbing with no user-controlled input reaching the changed code paths; the only external data is kernel-reported kevent flags/errno.
Level of scrutiny
High. epoll_kqueue.c is the core polling backend for every macOS/BSD socket in Bun. A regression here (a leaked knote firing on a freed poll, a busy-spin from a level-triggered knote that should be EV_CLEAR, or a lost event) would affect every TCP/TLS connection. The correctness argument leans on kernel behavior the author verified with C probes on macOS 14 x64 and macOS 26 arm64, but those claims (EV_ADD preserves an existing knote's flags; KEVENT_FLAG_ERROR_EVENTS entries carry EV_DELETE in flags and ENOENT in data; an EV_CLEAR knote fires once per RST/FIN arrival) are not something I can independently verify from source. The PR description is unusually thorough and the design is cleaner than the sentinel approach it replaces, but this is exactly the class of change a maintainer with kqueue experience should sign off on.
Other factors
- The PR notes it interacts with two open PRs (#37098 rewrites
us_poll_resize's kqueue branch; #37099 touches the same pause code) — a human should confirm the merge order. - The FreeBSD note ("stops a changelist at the first failing entry") is relevant because the delete+add is submitted as one changelist; the author argues the delete always finds a knote so the add is never skipped, but FreeBSD is shimmed and not CI-tested.
- The CodeRabbit thread on
us_poll_resize/us_poll_changeerror propagation was correctly scoped out as pre-existing behavior. - Verification depends on this PR's darwin CI lanes going green (build #101037 was still running per the timeline); Linux lanes cannot show a before/after for this diff by design.
…nstead of a code-less error (#39615) ### Problem - On Windows, `close(socket, error)` after a peer reset gets an error with no `code` (`errno: -10054`, message `Unknown Error, read`). Linux and macOS report `ECONNRESET`. - Cause: usockets reports the close error in the platform's numbering, a WSA code on Windows (`WSAECONNRESET` = 10054). `on_close` in `src/runtime/socket/socket_body.rs` stores it unmapped with `sys::Error::from_code_int`, which on Windows holds `SystemErrno` discriminants. 10054 is not one. - The poll-error fallback in `loop.c` is the CRT's `ECONNRESET`, 108 on Windows. Discriminant 108 is `ESHUTDOWN`. ### Fix - On Windows, `on_close` maps the code through the WSA table, as the connect error path does. `WSAECONNABORTED` becomes `ECONNRESET`, as in libuv's read path (`uv__process_tcp_read_req`), so the code matches node. An unknown code becomes `ECONNRESET` too: the connection is gone either way. - The fallbacks in `loop.c` and `us_socket_resume` use the new `LIBUS_ECONNRESET` (`WSAECONNRESET` on Windows), and the libuv `us_socket_get_error` returns `LIBUS_ERR` when `getsockopt` fails. All close codes now share one numbering per platform. - POSIX does not change: the code is already an errno there, and the macro expands to the same constant. - Verified: 3 new tests in `test/js/bun/net/socket.test.ts`, plus the two paused-reset tests from #39610, which now check the code on Windows too. A Windows x64 debug build fails them without the `src` and `packages` diff and passes with it. Linux passes both ways. The net and tls reset suites pass on both platforms (notes). ### Background - usockets closes a socket from the event loop when `recv()` fails or the poll reports an error, and the close code is then the error (`LIBUS_ERR`, `SO_ERROR`, or a fallback). Codes 0 to 2 are closes that Bun started. `NewSocket::on_close` passes a larger code to the JS `close` handler as `error`. - On Windows, `SystemErrno` uses Linux numbering. `SystemErrno::init` maps a Win32 or WSA code onto it, and `sys::Error` stores the mapped value. <details><summary>Notes</summary> Test design: the peer is a child process killed while it has unread data, so the kernel sends an RST with nothing queued ahead of it. An in-process TLS `terminate()` sends a close_notify first, which a reading POSIX peer consumes as a clean end, so it cannot stand in for the reset in the tls case. The third test resets a plain tcp connection from the server side in-process and checks the `Bun.connect` socket, which shares `on_close`. Error shape on Windows x64 (`Bun.listen` socket, client `terminate()`), tcp and tls give the same result: - unfixed release build: `{ code: undefined, errno: -10054, syscall: "read", message: "Unknown Error, read" }` - this branch: `{ code: "ECONNRESET", errno: -4077, syscall: "read", message: "ECONNRESET: connection reset by peer, read" }` - node v26.3.0 on the same machine, `net` server socket: `{ code: 'ECONNRESET', errno: -4077, syscall: 'read' }` The `ESHUTDOWN` flavor: the poll-error close in `loop.c` is reached on Windows when libuv reports an error status for the poll. Windows does not reliably latch a received RST in `SO_ERROR` (see `us_internal_libuv_peer_reset_probe`), so the fallback is taken there. #37104 observed it as `error=ESHUTDOWN` in its test matrix. From JS, a reset on a reading or paused socket goes through the `recv()` close on Windows (the paused probe in `poll_cb` adds READABLE, and Windows discards the receive queue on a reset), so the new tests cover the `recv()` flavor and the fallback is fixed by inspection. A reset that arrives after the accepted socket consumed the peer's FIN (half open, polling nothing) is not reported at all on Windows, with or without this change. That is a separate defect and is not touched here. `src/js/node/net.ts` keeps its `code === undefined` branches. With this change it takes the `code === "ECONNRESET"` branch on Windows and reports `errno: -4077` like node, instead of `-10054`. Other consumers of the close code were checked: the HTTP client, WebSocket client, Postgres, MySQL, Valkey, IPC and uWS ignore the value (uWS WebSocket uses it as a reason length for its own closes). `NewSocket::on_close` is the only consumer that reads it as an error. Related PRs: #39579 adds `LIBUS_ECONNABORTED` and `LIBUS_ECONNREFUSED` to the same block of `internal.h` for the connect path, and `LIBUS_ECONNRESET` follows that shape. Whichever lands second has a small merge in `internal.h`. #39610 landed first. Its paused-reset tests in `socket.test.ts` checked the code on POSIX only because of this bug, and the rebase removes that guard, so they are part of the proof now (they observed `code: undefined` on both Windows lanes in that PR's CI). Suites run on the Windows x64 debug build: `test/js/bun/net/socket.test.ts` (82 pass, 9 skip), `test/js/node/net/node-net.test.ts` (78 pass, 1 fail: "should allow reconnecting after end()" is a 3 ms timer race with no reset in it, and it passes in 2 of 4 runs on this build), the 4 reset tests in `test/js/node/tls/node-tls-server.test.ts`, and the 17 files in `test/js/node/test/parallel` whose names match reset, econnreset or error-twice. On the Linux debug build: `socket.test.ts` (the same 9 failures as the released binary in this container: `localhost` resolution and external network), the `node-tls-server` reset tests, `test-net-error-twice`, `test-net-server-reset`, `test-net-socket-reset-send`, `test-net-socket-reset-twice`, `test-tls-econnreset`, `test-tls-wrap-econnreset`, `test-tls-wrap-econnreset-socket` and `test-http-conn-reset`. The new tests passed 25 of 25 repeated runs on Linux with the released binary. </details>
Bun.Socket pins the opposite contract: a pause() the app may never resume must still close with read ECONNRESET when the peer resets, unread data discarded (socket.test.ts, #39610). Gate the deferral on a new defer_reset_while_paused socket flag, set only by the HTTP client when it pauses for fetch() receive backpressure, where a JS pull or an abort always resumes the socket. Also defer when the reset was collected while paused but an earlier dispatch in the same epoll batch resumed the socket: the captured events still lack READABLE, so the read loop could not drain. Reads are armed again, so the next poll re-reports the level-triggered error together with READABLE, the same shape as the deferred-eof arm. The test releases its server and connection in a finally block.
Bun.Socket pins the opposite contract: a pause() the app may never resume must still close with read ECONNRESET when the peer resets, unread data discarded (socket.test.ts, #39610). Gate the deferral on a new defer_reset_while_paused socket flag, set only by the HTTP client when it pauses for fetch() receive backpressure, where a JS pull or an abort always resumes the socket. Also defer when the reset was collected while paused but an earlier dispatch in the same epoll batch resumed the socket: the captured events still lack READABLE, so the read loop could not drain. Reads are armed again, so the next poll re-reports the level-triggered error together with READABLE, the same shape as the deferred-eof arm. The test releases its server and connection in a finally block.
…the loop on data (#39949) ### Problem On kqueue, a socket that is not polling readable (paused, half-open after the peer's FIN, shut down with reads off) keeps an `EV_CLEAR` read knote registered so the peer's FIN or reset still reaches the dispatcher (#39610). That knote also activates for every segment that arrives while reads are off, so a paused socket receiving a stream — e.g. a `fetch()` body under receive backpressure, or a `net.Socket` that is `pause()`d — wakes the event loop once per packet just to have the readable bit masked out. ### Fix Register the not-reading knote with `NOTE_LOWAT` and an unreachable low-water mark (`INT_MAX`). Both xnu's and FreeBSD's socket read filter test `SS_CANTRCVMORE` / `so_error` before the low-water mark, so FIN and RST are still reported (once, `EV_CLEAR`), while data never activates it. xnu clamps the mark to `so_rcv.sb_hiwat`, so on macOS it can fire one extra time when the receive buffer is full — at which point the window is closed and nothing more arrives anyway. `us_poll_resize` re-creates the read knote in its current mode (delete + add) instead of relying on `EV_ADD` keeping an existing knote's flags, because `EV_ADD` does overwrite `fflags`/`data` and would drop the mark; it also now re-registers only the filters that are actually polled. No dispatcher change; no new state. ### Verification (FreeBSD 14.3 / kqueue, cross-built `--os=freebsd`, QEMU) Kernel probes (small C programs): - plain `EV_CLEAR` knote, 5 segments while not reading → **5 wakeups**; with `NOTE_LOWAT=INT_MAX` → **0 wakeups**, then FIN → 1 event (`EV_EOF`, no re-fire), RST → 1 event (`EV_EOF`, `fflags=ECONNRESET`); after delete+add (resume) the level filter reports the data, and `recv()` returns it followed by 0 / `ECONNRESET`. Same with our side already `SHUT_WR`. - `EV_ADD` over an `EV_CLEAR` knote stays edge-triggered on FreeBSD too (the quirk #39610 found on macOS), so delete+add is the portable mode switch. Through Bun: `Bun.listen` socket paused in `open()`, peer writes 300 × 1 byte with `Bun.sleep(2)` between; `ktrace -t c | grep -c 'RET.*kevent'`: **598 → 313** (the ~300 floor is the peer's timer in the same process). `socket.test.ts`, `tcp-server.test.ts`, `node-net.test.ts`, `node-net-allowHalfOpen.test.js`, `node-tls-server.test.ts`, `fetch-backpressure.test.ts` and the `test-net-half-open-peer-reset-*` / `test-net-*reset*` fixtures give the same pass/fail set on FreeBSD before and after (the failures there are FreeBSD-environment ones: 48 KiB default socket buffers making 64 KiB writes short, and `close()` with unread data sending FIN rather than RST). darwin lanes in CI are the real target. --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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Problem
test/js/node/tls/node-tls-server.test.tsis red on every darwin lane since usockets: report a peer reset behind unread data as ECONNRESET, not 'end' #39600: "reports the reset that arrives while the socket is paused as ECONNRESET, not 'end'" hangs to the timeout. Linux passes.us_socket_pause(socket.c:864) deletes the read filter, and the one-shot write filter it adds is consumed at once. The peer's RST is reported only afterresume().EV_ADDon an existing knote keeps its flags (macOS 14 and 26). The read sentinel from usockets: stop spinning on a half-open socket whose peer resets behind pending writes (kqueue) #37077 stayed edge-triggered after the re-add on resume.Fix
kqueue_change(epoll_kqueue.c) keeps the read knote of a socket poll in both modes: level-triggered while the socket reads,EV_CLEARwhile it does not. A mode switch deletes the knote and adds a new one.us_poll_stopdeletes it in either mode.kqueue_changeon both macs (notes), the related suites on Linux, and newBun.listentcp/tls tests intest/js/bun/net/socket.test.ts. Linux behavior does not change, so this PR's darwin lanes prove the red test.Background
EV_CLEARknote fires once per activation (data, FIN, RST). The dispatcher sees a FIN as eof and a reset as error (fflags == ECONNRESET).us_poll_resizere-adds both filters only to move the udata.EV_ADDkeeps the mode of an existing knote, so that still works.Notes
Culprit: #39600 added the tests. The kqueue gap predates it: the write filter became one-shot in #25475, and the sentinel from #37077 covered shutdown and half-open but not pause. The rare darwin pass in CI was the RST landing before the one-shot write filter was consumed.
kqueue probes, run as small C programs on darwin-arm64 (macOS 26.6, xnu 12377) and darwin-x64 (macOS 14.8, xnu 10063), identical results:
EVFILT_WRITEwithEV_EOF fflags=54(the flaky pass).EV_ADD|EV_CLEARknote, then plainEV_ADD: still edge-triggered, udata updated.EV_ADD|EV_CLEARover a level knote: still level.EV_DELETE+EV_ADDin one changelist: level again.EV_CLEARknote, RST behind 10 unread bytes: one event,EV_EOF fflags=ECONNRESET,SO_ERROR=ECONNRESET, no re-fire. FIN behind data: one event,fflags=0, no re-fire. More data while not reading: one wakeup per arrival.EV_CLEARknote registered before our ownSHUT_WRstill reports the peer's later FIN and RST, fresh or already cleared once. So dropping the post-shutdown re-arm inraw_shutdownis safe.KEVENT_FLAG_ERROR_EVENTSwith a failing delete first: the error entry keepsEV_DELETEin flags andENOENTin data, and the following add still applies.The real
kqueue_changebody, compiled into a harness on both machines: pause then RST (reported, no spin), pause then FIN then resume (FIN deferred once, level-triggered after resume), stop on a paused socket (nothing left), resize touch (udata moved, mode kept), plain changes on a reading socket, EBADF still reported. The changed files also compile with-fsyntax-onlyin the kqueue configuration.Linux, debug build:
node-tls-server.test.ts(73 pass, the SNICallback failure is pre-existing in this container),node-net.test.ts,node-net-allowHalfOpen.test.js,fetch-backpressure.test.ts,node-http-backpressure.test.ts(the same 15 pre-existing failures as unmodified main: localhost resolution and h3),socket.test.ts(the same 9 pre-existing failures as main, the 2 new tests pass), the ninetest-net-half-open-peer-reset-*.mjsfixtures,node-http-server-socket-end-drain,node-http-connect,tls-syscall-fault,net-syscall-fault.The new
socket.test.tsvariants also fail on a release binary from before #39600 (the close carried no error), so they pin that contract for the Bun socket API on Linux as well. On macOS without this diff they hang like the node ones.Node itself does not report a reset while a socket is paused. libuv removes the fd from the poll set, and node v26.3.0 reports
ECONNRESETafter the resume (checked with the same server logic). Bun's epoll and libuv backends have reported it at once for a long time, and #39600 made that the tested contract. This PR only brings kqueue to the same contract.Related open PRs: #37098 rewrites the kqueue branch of
us_poll_resizeand would delete the read knote of a non-reading socket, which this rule keeps. #37099 touches the same pause code against an older base.JSNodeHTTPServerSocketPrototype.cpp:226pauses and resumes around a shutdown to work around the same gap. It still works and is left alone here.kqueue on FreeBSD (shimmed, not a CI target) stops a changelist at the first failing entry. The delete in a mode switch always finds a knote, because every socket poll starts with a level read filter, so the add after it is not affected.
Windows lanes on the first CI run: the new tests reached the close with
syscall: "read"but nocode. The libuv backend reports the reset on a paused socket as intended, but on Windows the close carries the raw WSA code, whichon_closestores unmapped (node:net acceptscode === undefinedas a reset, which is why the node tests pass there). That is a pre-existing bug in a different layer and is handed off separately. The tests check the code on POSIX only until it is fixed.