usockets: skip the poll-error close for a socket a handler already closed - #39621
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…osed Since #39600 an error event whose data handler closes the socket reaches the poll-error close. That read SO_ERROR from the closed socket's fd number. A socket opened by the handler (a reconnect from close()) owns that number by then, so the read consumed its pending error and a refused connect reported ECONNRESET. The same read happened before when on_end closed the socket on an error event. Nothing is left to close for a closed socket, so skip the block.
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Status: fix pushed, waiting for CI. How it was reproduced: Review state: the one review thread (Windows skip) was withdrawn by its author after e1948bd. The merge-risk line in the generated summary above still mentions a null-device path. That path is gone since e1948bd: the fixture reserves the fd with its own file, and the outcome it asserts holds on Windows too. |
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LGTM — one-condition guard matching the existing is_closed checks in the same dispatch, with a deterministic regression test.
What was reviewed:
- The added
!us_socket_is_closed(s)mirrors the eof block's guard at loop.c:888 and the read-loop guards; closed-socket memory stays valid untilus_internal_free_closed_socketsin loop_post, so the read is safe. - Confirmed the on_end branch (
allow_half_open && !hangup) falls through without returning, so a socket closed byon_endnow correctly skips the staleSO_ERRORread too. - Test follows harness conventions (subprocess isolation for fd numbering, concurrent pipe drain, combined-object assertion). Checked Windows:
openSync("/dev/null")is mapped to\\.\NULin node_fs.rs, and the fd-reuse trick is a POSIX-only accelerant — the assertedECONNREFUSEDoutcome holds regardless.
Extended reasoning...
Overview
Single-line change to packages/bun-usockets/src/loop.c: adds && !us_socket_is_closed(s) to the poll-error close guard in us_internal_dispatch_ready_poll. This is a follow-up to #39600, which routed error events past the eof block's early-return-on-closed. The eof block already has this exact check (line 888); this restores it for the error block. Plus a ~70-line regression test in test/js/bun/net/socket.test.ts that reproduces the fd-reuse race deterministically in a subprocess.
Security risks
None. The change narrows a code path (skip work on an already-closed socket). No new user-controlled input reaches native code.
Level of scrutiny
Medium — this is core event-loop dispatch C code, but the change is a one-condition guard identical in shape to six other us_socket_is_closed(s) checks already in the same function. The memory-safety claim (closed socket stays on loop->data.closed_head until loop_post) is verified by reading us_internal_free_closed_sockets and its call site. us_internal_socket_close_raw was already a no-op for a closed socket, so the only behavior removed is the destructive getsockopt(SO_ERROR) on a stale fd number — which is exactly the bug.
Other factors
- The PR description traces the mechanism precisely (fd reuse + destructive SO_ERROR read) and reports 25/25 passes plus a full sweep of related reset/half-open tests.
- The test uses a subprocess so fd numbering is controlled, drains stdout/stderr/exited concurrently, asserts a combined
{stdout, stderr}object beforeexitCode, and usestempDir/bunEnv/bunExeper harness conventions. - Two finder-raised concerns about Windows (
/dev/null, POSIX fd-reuse) were verified: node_fs.rs maps/dev/null→\\.\NULon Windows, and on Windows SOCKET handles don't share the CRT fd space so the reserve trick is inert but harmless — the connect to a bound-but-unlistened port still reportsECONNREFUSED.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Path: .coderabbit.yaml Review profile: ASSERTIVE Plan: Pro Run ID: 📒 Files selected for processing (1)
Included review availability: Your plan provides up to 5 included reviews per hour; 0 remain after this review. WalkthroughThe poll-error close path now checks whether a socket remains open before reading ChangesSocket error handling
Possibly related PRs
Suggested reviewers: Merge Risk: 🔵 Low · up to The PR corrects stale socket-error handling and is otherwise mergeable, but the regression test assumes POSIX file-descriptor allocation and a POSIX null-device path without a Windows guard, so explicit owner follow-up is needed to keep the test portable. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Actionable comments posted: 1
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Inline comments:
In `@test/js/bun/net/socket.test.ts`:
- Around line 4320-4326: Guard this descriptor-order test with the existing
isWindows platform check so it is skipped on Windows, while preserving the
current POSIX setup using reserved, connecting, and closeSync. Do not alter the
test’s behavior on non-Windows platforms.
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Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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packages/bun-usockets/src/loop.ctest/js/bun/net/socket.test.ts
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LGTM — the added !us_socket_is_closed(s) guard mirrors the eof block just above it, and us_internal_socket_close_raw was already a no-op for a closed socket, so the only behavior removed is the stale SO_ERROR read that consumed a reused fd's error.
Checked that closed sockets stay on loop->data.closed_head until us_internal_free_closed_sockets in loop_post, so s->flags.is_closed is a valid read here. Also checked the sibling exit points in this dispatch (writable, recv-error, eof) — each already returns or guards on is_closed, so this was the one remaining unguarded path. The test follows harness conventions (subprocess, port: 0, concurrent pipe drain, tempDir), and the fixture's Windows note is sound: the fd-ordering trick is inert there but the asserted outcome still holds.
Extended reasoning...
Overview
One-line logic change in packages/bun-usockets/src/loop.c: the poll-error close block gains a !us_socket_is_closed(s) guard, plus an explanatory comment. A subprocess regression test is added to test/js/bun/net/socket.test.ts that arranges fd reuse so a stale SO_ERROR read on a closed socket's fd number would consume a new connect's ECONNREFUSED.
Security risks
None. This is error-code reporting on a socket the runtime already closed; no auth, crypto, or untrusted-input parsing is touched.
Level of scrutiny
The dispatch loop is a hot, critical path, but the change strictly narrows behavior: it only skips a block for sockets that are already closed. I verified in socket.c:287 that us_internal_socket_close_raw already no-ops on is_closed, so the sole effect being removed is the us_socket_get_error() call — exactly the stale getsockopt the PR describes. The guard cannot change behavior for any open socket. Memory safety holds because closed sockets sit on closed_head until loop_post frees them (guarded by tick_depth <= 1), and the eof block a few lines up already reads s->flags.is_closed on the same object under the same assumption.
Other factors
The test is well-constructed per REVIEW.md: it awaits the actual condition (the connect's connectError), drains stdout/stderr/exited concurrently, asserts the combined {stdout, stderr} before exitCode, uses port: 0 throughout, and runs in its own process so fd numbering is deterministic. The refused-port trick (an ephemeral local port held bound by a live connection) avoids hardcoding and race with other listeners. CodeRabbit's Windows concern is answered in the fixture comment — the fd-reuse arrangement is POSIX-specific but the asserted outcome (ECONNREFUSED for a refused connect) is platform-independent, so no skip is needed. The PR description states it was verified against main (fails) and pre-#39600 (passes), and the broader reset/half-open suites were re-run.
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Problem
data()handler closes the socket (terminate()), aBun.connect()opened from that socket'sclose()handler to a port nothing listens on reportsECONNRESETinstead ofECONNREFUSED. Deterministic on Linux with the fd layout in the new test. Before usockets: report a peer reset behind unread data as ECONNRESET, not 'end' #39600 it reportedECONNREFUSED.us_internal_dispatch_ready_poll(packages/bun-usockets/src/loop.c:925) runs for a socket that a handler closed earlier in the same dispatch.us_socket_get_error()then readsSO_ERRORfrom the closed socket's fd number. The connect opened fromclose()owns that number by then (it takes the lowest free fd), andSO_ERRORis cleared by the read. The connect's own dispatch later finds no error and falls back toECONNRESET(loop.c:495).on_endclosed the socket during an error event, or on an error event without an eof hint.Fix
if (error && s && !us_socket_is_closed(s)). Nothing is left to close for such a socket, andus_internal_socket_close_rawwas already a no-op for it. The only effect of the block was the staleSO_ERRORread.close_rawputs it on the loop's closed list, which is freed after the dispatch. The eof block readsis_closedthe same way.test/js/bun/net/socket.test.ts, "a socket closed by data() while its peer's reset is being dispatched". It fails on a build of main (stdoutECONNRESET), passes with this change (25 of 25 runs), and passes on a build from before usockets: report a peer reset behind unread data as ECONNRESET, not 'end' #39600. Also run: the rest ofsocket.test.ts(the same 9 failures as main in this container:localhostresolution and external network), the 4 reset tests innode-tls-server.test.ts, the ninetest-net-half-open-peer-reset-*fixtures,test-net-error-twice,test-net-socket-reset-send,test-net-socket-reset-twice,test-net-server-reset,test-net-connect-reset,test-tls-econnreset.Background
data()for eachrecv(), then the eof block handles a FIN, then the error block closes the socket withSO_ERRORwhen the event carried the error flag. A handler can close the socket at any point in between.close()handlers run synchronously inside that close, so code in them runs in the middle of the dispatch.SO_ERRORis a destructive read:getsockopt(SO_ERROR)returns the pending error and clears it. Reading it through a stale fd number acts on whatever socket owns the number now.socket()call if it is the lowest free one. The test reserves a number so that the accepted socket gets a lower number than the peer, becausepeer.terminate()frees the peer's number first. It runs in a child process so that nothing else in the process interferes with the numbering.