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The test "async generator body: client abort between yields returns the generator" gave the client abort 50 setImmediate turns to reach the server. A turn is one poll that does not wait, so 50 turns take about 0.25 ms in a release build. On macOS the loopback delivers the response and the close from a kernel thread, and both can arrive later than that. Then the generator completes and the test fails with ["completed", "finally"]. The generator now yields until the server returns it. A 3 second deadline ends it only when the server never does, and the test then fails with "completed" as before.
The probe prints how long the loopback needs to deliver a byte and a close, and how many setImmediate turns a streamed response runs before the server sees a client abort. It runs on macOS and on Linux with glibc. It is removed before this branch merges.
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Updated 4:05 AM PT - Oct 22nd, 2026
❌ @robobun, your commit ad6385a has some failures in 🧪 To try this PR locally: bunx bun-pr 45773That installs a local version of the PR into your bun-45773 --bun |
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On the darwin CI machines the server returned the generator after 129 ms at the longest. 10 s is the deadline that bun-server.test.ts uses for an abort that must reach the server, and it leaves room for a machine that stalls. A server that never returns the generator still fails the test.
The probe ran once on the darwin and the Linux machines. The pull request has its numbers.
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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 on the deadline, I also checked that the new loop costs nothing on a passing build (it exits in the turn the server calls return(), so the 10 s bound is never waited on) and that the assertion still protects the original property: a build that throws the close reason into the generator still fails with ["catch:...", "finally"], and a build that never returns it still cannot produce ["finally"].
Extended reasoning...
The diff is a four-line test-only change in test/js/bun/http/serve-direct-readable-stream.test.ts replacing a fixed 50-turn yield loop with a wall-clock-bounded loop so the client abort has as long as it needs to reach the server. It touches no runtime code and no security-sensitive surface. The one inline finding (the 10 s deadline exceeds the per-test timeout, so a regression surfaces as a timeout rather than the documented ["completed", "finally"] failure) is worth a maintainer's call on the bound, so this is not a clean approve.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughThe async-generator abort test now yields until the request signal is aborted instead of stopping after 50 iterations. ChangesAsync-generator abort test
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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| Check name | Status | Explanation |
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| Title check |  |
The title clearly identifies the main change: removing the 50-event-loop-turn limit from the generator abort test. |
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Check skipped because no linked issues were found for this pull request. |
| Out of Scope Changes check | |
Check skipped because no linked issues were found for this pull request. |
| Description check | |
The description clearly explains the intermittent Darwin failure, the signal-based loop fix, the technical rationale, and verification results. It does not use the exact template headings, but it prov… |
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Explanation
The description clearly explains the intermittent Darwin failure, the signal-based loop fix, the technical rationale, and verification results. It does not use the exact template headings, but it provides the required information in equivalent sections.
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Review comments at @test/js/bun/http/serve-direct-readable-stream.test.ts:
- Around line 2296-2297: Remove the custom deadline from the cancellation loop
near the test’s `"completed"` recording, and let the loop continue until
cancellation ends it. Rely on Bun’s test timeout if cancellation never arrives.
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test/js/bun/http/serve-direct-readable-stream.test.ts
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…adline The loop had a 10 s deadline for a server that never returns the generator. That is longer than the default 5 s test timeout, so such a server made the test time out and left the loop running. A deadline can also expire on a machine that stalls. The loop now runs while `req.signal.aborted` is false. The server fires that signal and returns the generator in the same call, so a returned generator never reaches the check again. A server that saw the abort and still resumes the body leaves the loop at once, and the test fails with ["completed", "finally"], as it does on main.
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Both reviews pointed at the deadline in the loop, from opposite sides. f4b5415 removes it. The loop now runs while
The PR body has the table with these cases. |
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LGTM — the latest push replaces the 10 s deadline with while (!req.signal.aborted), which resolves the earlier concern about a regression surfacing as a 5 s test timeout, and the loop is sound on every platform.
What was reviewed:
- Traced
on_abortin src/runtime/server/RequestContext.rs: it firesreq.signaland then calls the sink'sabort→source.abort→asyncIterableSourceCancel→iterator.return()on one stack, with microtasks drained only afterward, so nonext()can observeaborted === truebefore the return is queued;["completed", "finally"]can only appear if the server aborts the signal but never returns the generator, which is the failure the test is meant to report. - Checked the generator-executing case (abort lands while
await later()is pending): the queuedreturn()runs right after the pending yield settles, and the drive'sm_cancelledcheck keeps it from callingnext()again. req.signalis a cached getter and is first touched in the drive step immediately after "first" is written, before the client can disconnect, so the signal exists beforeon_abortruns.- Optional nit: the four-line comment at test/js/bun/http/serve-direct-readable-stream.test.ts:2293 could shrink to one line per the repo comment rule (e.g. "Turn counts cannot bound when the kernel delivers the abort; macOS loopback delivers from another thread").
Extended reasoning...
The change is a net +6/-2 edit to one existing test in test/js/bun/http/serve-direct-readable-stream.test.ts, swapping a fixed 50-turn loop for a loop on req.signal.aborted and giving the fetch handler the req parameter; no runtime code, no security-sensitive surface. The hunt exited on dry_streak with no findings, the file is not under CODEOWNERS, and the only third-party review is a COMMENTED coderabbit note on the line the subsequent commit rewrote. Approve was decided by confirming from RequestContext.rs, streams.rs and BunAsyncIterableSource.cpp that signal fire and iterator.return() happen synchronously in one abort dispatch, so the new loop cannot spuriously push "completed" and cannot spin forever on a healthy server.
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3cd7de6 shortens the comment above the loop to one line, as suggested. The diff against main is now 3 lines added and 2 removed. |
…ake-generator-abort-test
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LGTM — the signal-bounded loop replaces the 10 s deadline from the earlier revision, so the regression path no longer collides with the 5 s per-test default.
What was reviewed:
- Checked that
req.signalis the context's own AbortSignal, created eagerly at request creation (src/runtime/server/mod.rs:849), and thaton_abortfires it (RequestContext.rs:1587) before aborting the sink that callsreturn()on the generator in the same call — so the loop cannot exit on the signal withoutreturn()following in the same tick. - Checked the ordering when the abort lands while the generator is parked in
await later(): the queuedreturn()is applied at the nextyield "more", sofinallyruns and"completed"is never pushed; a server that fires the signal but resumes the body still ends the loop and fails with"completed"as before. - The assertion
expect(events).toEqual(["finally"])is unchanged, no per-test timeout was added, and the one-line comment states only what the code cannot (why no turn count).
Extended reasoning...
The diff touches one test file, test/js/bun/http/serve-direct-readable-stream.test.ts, changing a generator body's fixed 50-iteration loop to while (!req.signal.aborted) and adding a one-line comment; it touches no production code and no security-sensitive surface. The change is three lines, the assertion is unchanged, the file is not CODEOWNERS-owned, and the only prior objection (a 10 s deadline exceeding the 5 s test timeout, raised by this bot and coderabbit on the previous revision) is removed by this revision, which has no deadline at all. I verified from the server source that the request signal exists before the body runs and is fired in the same on_abort call that cancels the stream and returns the generator, which is what makes the loop condition a correct bound.
Problem
serve-direct-readable-stream.test.ts"async generator body: client abort between yields returns the generator: finally runs, catch does not" fails on:darwin: any x64 - test-bunin 16 of 500 builds:expect(received).toEqual(expected), received["completed", "finally"].setImmediateturns to reach the server (:2293). A turn is one poll that does not wait (epoll_kqueue.c:538), so 50 turns take 0.2 ms to 0.5 ms on the darwin lanes.Fix
req.signal.abortedis false: no count, no deadline.return()in one call. A server that saw the abort and still resumes the body ends the loop, and the test fails with"completed"as before.test/js/bun/http/serve-direct-readable-stream.test.ts. With the Linux loopback delayed by 100 ms, the old test fails 20 of 20 runs with the CI message, the new test passes 20 of 20. A build whose cancel hook does nothing fails with"completed".Background
main_inputthread.AbortSignal. The server fires it when the client leaves.Notes
macOS and Linux numbers from CI
A temporary test file ran once on this branch (commit 9eae695, removed again in ed2fd42). It ran the server and the client of this test with no limit on the rounds, and counted the
await later(); yield "more"rounds until the server returned the generator. It also measured the loopback with rawlibcsockets: afterwrite(2)orclose(2)returns on one end, is the other end readable at the firstpoll(2)?return()(median / p99 / max)darwin-x64-14-8-9-1)darwin-x64-14-8-9-1)darwin-arm64-focaccia-tart-15-2)darwin-arm64-focaccia-tart-15-2)Bun.servein a loop. With no neighbors the machine is still not idle: the test runner prepares the other tests at that time (load average 6.7 on the x64 machine, 23.6 on the aarch64 machine).firstto the return was 110 ms on x64 and 129 ms on aarch64. The probe loop ended on a 3 s deadline, which no run reached.The server is not late (code path, all on one stack)
Line numbers are from main at e81a34c.
packages/bun-usockets/src/eventing/epoll_kqueue.c:538,:558recv()returns 0, the socket getson_endpackages/bun-usockets/src/loop.c:886,:1003packages/bun-uws/src/HttpContext.h:1134onClosecallsonAbortedpackages/bun-uws/src/HttpContext.h:301RequestContext::on_abortaborts the sinksrc/runtime/server/RequestContext.rs:1593,:1666src/runtime/webcore/streams.rs:2018cancelsrc/jsc/bindings/webcore/streams/BunStreamSource.cpp:717cancelcallsiterator.return()src/jsc/bindings/webcore/streams/BunAsyncIterableSource.cpp:461,:85The client is a
node:netsocket in the same process. It reads untilfirst, then callsdestroy(). It has no deferral either: thedataevent, theawait,sock.destroy()andclose(2)run inside the oneon_datadispatch (src/js/node/net.ts:4525,packages/bun-usockets/src/socket.c:329).What a turn costs
With an immediate pending,
timer::All::get_timeoutreturns a zero timeout (src/runtime/timer/mod.rs:932).us_loop_run_bun_tickthen callskevent64withKEVENT_FLAG_IMMEDIATE(epoll_kqueue.c:545), which returns without a wait. On Linux x64, release build, 50 rounds ofawait later(); yield "more"take 0.22 ms at best and 1.7 ms at the median.Linux: synchronous loopback, then the same run through a proxy
lodelivers a packet in the softirq of the sending syscall. So the client seesfirstat the next poll and the server sees the close one poll later.The proxy runs in a private network namespace.
iptables -t nat ... -j REDIRECTsends each connection to127.0.0.1through it, and the test file and bun are not changed. With 100 ms for each direction and the debug build, the old test fails 20 of 20 runs with["completed", "finally"]. 168 of the 169 tests in the file pass under that delay: no other test in the file has this race.macOS: asynchronous loopback
lo_outputhands each packet toifnet_input_extended(bsd/net/if_loop.c:329). Forlo0that isdlil_input_async: it appends the packet tolo_rcvq_pktsand wakes the main input thread (bsd/net/dlil_input.c:417,:484). The comment on that thread says "handles all inbound packets for lo0" (dlil_input.c:1359). Line numbers are from xnu-12377.1.9. The test needs two such deliveries, the response to the client and the close to the server, and every process on the machine shares that one thread.The 16 sightings
All are on the agent
darwin-x64-14-8-9-1, all in the parallel batch, and the file passed when it ran alone. The failing test took 5.9 ms to 16.4 ms. Builds: 125725, 125739, 125889, 126068, 126148, 126188, 126217, 126256, 126295, 126336, 126378, 126413, 126444, 126453, 126475, 126526.What the test reports for a broken server
Debug build on Linux. The two broken servers are temporary patches to the cancel hook,
jsWebStreamsHandler_asyncIterableSourceCancel.["completed", "finally"]["completed", "finally"]1.4.3-canary.1+367d939d9, which throws the close reason into the generator["catch:The connection was closed.", "finally"]["catch:The connection was closed.", "finally"]In the second row the generator stays at its
yield, because nothing callsnext()again. No loop condition can report that case.Why the loop ends on the request signal
The first version of this PR ended the loop on a deadline (3 s, then 10 s). Review found the flaw on each side. A deadline longer than the default 5 s test timeout turns the first row above into "timed out after 5000ms" and leaves the loop running. A shorter one can expire on a machine that stalls.
on_abortfires the request signal and then aborts the sink, which returns the generator, in one call (src/runtime/server/RequestContext.rs:1646,:1666). So a returned generator never evaluates the condition again, and a healthy server cannot produce"completed".Build 125907, "write, flush() not awaited, task, write, close()"
This is a different failure. The response that the client got has
x-powered-by: hidden,content-security-policy: connect-src 'self'andkeep-alive: timeout=5: it is the web page of a Verdaccio registry. That build ran on a branch from 2026-10-07. At that commit the install tests started Verdaccio on127.0.0.1with a port fromrandomPort()(test/harness.ts), which does not check that the port is free. #44055 replaced Verdaccio with a registry onBun.serve({ port: 0 }).no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/http/serve-direct-readable-stream.test.ts