terminal: release the wrapper after PTY EOF leaves input unflushed by robobun · Pull Request #42150 · oven-sh/bun

robobun · 2026-09-09T19:56:37Z

Problem

Since terminal: keep the wrapper alive while a drain dispatch is pending after PTY EOF #36962 (v1.4.0), a POSIX Bun.spawn({ terminal }) whose child exits with terminal.write() input still queued never releases the Terminal or its callbacks. It keeps three pty fds until process exit, spins on POLLHUP (2.6 s CPU per 2 s idle), and queues every later write in memory.
At reader EOF every slave fd is gone, so the queue can never drain: a pty master answers EAGAIN, not EPIPE. writer_has_buffered stayed set and maybe_downgrade_after_eof (Terminal.rs:1826 on main) never downgraded. Late echo after the EIO also re-upgraded this_value in on_read_chunk.

Fix

On POSIX on_reader_finished ends the writer and closes the reader: WRITER_DONE is set before the downgrade check, exit is the last callback, and a later write() returns without queuing.
The CONNECTED flag and its upgrade are deleted: this_value is strong until EOF, so the upgrade only fired on that late echo. The downgrade now waits for a new EXIT_DISPATCHED flag, set after the exit callback returns, instead of READER_DONE, so the wrapper stays strong through its last dispatch.
Behaviour change: no drain or data after exit. The terminal: keep the wrapper alive while a drain dispatch is pending after PTY EOF #36962 test that expected a late drain is replaced: that drain came only from the kernel discarding an unterminated line.
Verified: the new terminal.test.ts block (collection, fd count, late callbacks) fails on 1.4.3 and passes 10 of 10. Also all of test/js/bun/terminal/ and spawn.test.ts.

Background

Terminal holds its wrapper in a JsRef, strong while a callback can fire, because the wrapper's cached slots are the callbacks' only GC root.
A BufferedReader and a PosixStreamingWriter drive the pty master. The writer queues what write(2) refuses and waits for POLLOUT.
At child exit bun closes its slave fd, the master reads EIO (Linux) or EOF (macOS), and exit fires.

Notes

Reproduction on released bun (1.4.3-canary.1, Linux x64, kernel 7.0):

let proc = Bun.spawn(["sh", "-c", "exit 0"], { terminal: { data() {}, exit() {}, drain() {} } });
const big = Buffer.alloc(65536, "a\n");
for (let i = 0; i < 32; i++) proc.terminal.write(big);   // ~2 MB the child never reads
await proc.exited;

Leak: with a FinalizationRegistry on proc.terminal and a Bun.gc(true) loop, 0 of 5 wrappers are collected. Without the write() calls, 5 of 5.
Fds: /dev/fd grows by 3 per terminal (master plus the reader and writer dups) and never shrinks. With the fix it returns to the baseline once the wrappers are collected.
Spin: process.cpuUsage() over 2 s of idle after proc.exited reports 2603 ms of CPU. Without the write, 3 ms. With the fix, 39 ms.
Post-exit writes: 64 MB of terminal.write() after proc.exited grows RSS by 178 MB on 1.4.3 (256 MB grows it by 491 MB). With the fix, 3 to 4 MB.
Size: there is no clean threshold. The wrapper leaks whenever part of the input is still queued in the writer at EOF (8 KB of lines was enough here, 12 KB happened to fit) and, at any size, whenever echo arrives after the EIO (seen with 1 KB). With an unterminated line the kernel keeps discarding input, so an unfixed build drains after a few hundred ms, fires a late drain, and then releases the wrapper; with complete lines the queue is stuck for good.

Why the reader is closed too: on Linux the master read fails with EIO as soon as the last slave fd closes, but the slave's line discipline keeps processing input that was already queued and echoes it back, so later reads return data again. The reader's poll stayed armed after the error, delivered those chunks to data after exit, and the old CONNECTED branch re-rooted the wrapper on the first one. EOF (the macOS path) already closes the reader inside BufferedReader; the error path now matches it.

Why the writer is ended in Terminal and not in PosixPipeWriter::on_poll: a first version made on_poll report EndOfFile when a short write met POLLHUP, for every posix writer. With the terminal change in place the pty case no longer reaches that branch (measured: the spin is gone with the terminal change alone), and pipes and sockets fail with EPIPE or ECONNRESET there instead, so the generic change had no reachable case and was dropped.

write() after PTY EOF returns the byte length and drops the bytes. Before this change the same call also returned the byte length but queued the bytes in the writer forever (the RSS numbers above), so the return value is unchanged and the memory growth is gone. Throwing was rejected because terminal.closed is still false in that state.

Windows is unchanged: its writer already reports close when the conhost input pipe breaks, and the test is skipped there because it spawns sh.

test/js/bun/spawn/spawn-pipe-leak.test.ts fails the same way in my container on main and on this branch (three 500-process leak tests time out at 30 s on a debug ASAN build), so it is not a regression from this diff.

Self-reviewed: the review asked for the fd assertion, the post-exit write coverage, the regression origin and the measured consequences in this body, and deletion of the dead CONNECTED state instead of a guard. All done. An RSS assertion was not added: the post-exit writes in the test already fail the collection and fd checks on a build without the write() guard (verified by removing it), and RSS bounds are noisy under ASAN.

cargo check -p bun_runtime is clean for x86_64-pc-windows-msvc and aarch64-apple-darwin.

no test proof · iteration 1 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/terminal/terminal.test.ts

On POSIX, reader EOF means every slave fd is gone, so input the child never read can never drain. A pty master answers EAGAIN instead of EPIPE, so the writer kept waiting for a drain that cannot arrive: its poll re-armed on a permanent POLLHUP and writer_has_buffered blocked maybe_downgrade_after_eof, which kept the JS wrapper and its data, exit and drain callbacks alive for the rest of the process. End the writer in on_reader_finished. Clear writer_has_buffered and re-check the downgrade when on_write reports EndOfFile. Drop a write() that arrives after WRITER_DONE so it cannot re-root the wrapper. Skip the CONNECTED upgrade once the reader is done, because a chunk the poll delivers after EOF re-rooted the wrapper with nothing left to downgrade it.

Linux reports the last slave close as EIO, which leaves the reader open with its poll armed; echo of input the slave's line discipline was still processing then reached the data callback after exit, and the CONNECTED branch re-rooted the wrapper on the first such chunk. Close the reader in on_reader_finished (EOF already closes it inside BufferedReader) so exit is the last callback, and delete CONNECTED: this_value is strong from creation until EOF, so its upgrade could only ever fire on that late echo. The test now also writes after exit, counts data and drain callbacks after exit, and checks that /dev/fd returns to its baseline.

robobun · 2026-09-09T19:57:05Z

Status

Reproduced on bun 1.4.3-canary.1 (Linux x64) before writing the fix:

let proc = Bun.spawn(["sh", "-c", "exit 0"], { terminal: { data() {}, exit() {}, drain() {} } });
const big = Buffer.alloc(65536, "a\n");
for (let i = 0; i < 32; i++) proc.terminal.write(big);
await proc.exited;
// drop `proc`, loop Bun.gc(true): a FinalizationRegistry on proc.terminal never fires,
// /dev/fd keeps 3 extra fds per terminal, process.cpuUsage() shows ~100% CPU while idle.

The new block in test/js/bun/terminal/terminal.test.ts ("terminal is released after the child exits with input it never read") fails on 1.4.3 and on a debug build of main (collected: 0, leakedFds: 12, callbacksAfterExit: 3), and passes with this branch.

Head 413c7b1: Buildkite #113605 green (182/182), both automated reviews clean, all review threads resolved. Ready for maintainer review.

coderabbitai · 2026-09-09T20:02:27Z

No actionable comments were generated in the recent review. 🎉

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src/runtime/api/bun/Terminal.rs

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Walkthrough

Terminal lifecycle handling now treats PTY reader completion as shutdown. POSIX resources and pending writer data are closed or ended, late callbacks are suppressed, and post-EOF writes are accepted without dispatch. Tests cover unread input, exit callback ordering, wrapper finalization, and file descriptor cleanup.

Changes

Terminal lifecycle cleanup

Layer / File(s)	Summary
Status and write handling `src/runtime/api/bun/Terminal.rs`	Terminal flags and writer status handling now distinguish pending, drained, and EOF states. Writes after writer completion return the accepted input length without dispatching data.
Reader completion cleanup `src/runtime/api/bun/Terminal.rs`	PTY reader completion closes active POSIX resources, ends pending writer data, invalidates descriptors, suppresses late callbacks, and removes the first-data wrapper upgrade path.
Cross-platform cleanup validation `test/js/bun/terminal/terminal.test.ts`	The test covers complete and unterminated unread input queues, final exit callbacks, post-EOF writes, wrapper finalization, and file descriptor cleanup on POSIX platforms.

Suggested reviewers: dylan-conway, jarred-sumner

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 413c7

POSIX terminal teardown now releases PTY resources at EOF, suppresses late callbacks, and drops post-exit writes without queuing them. The supplied regression coverage and readiness assessment indicate no remaining merge-blocking risk.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly summarizes the primary change: releasing the terminal wrapper after PTY EOF when input remains unflushed.
Description check	✅ Passed	The description provides a detailed problem statement, fix, behavior changes, verification results, platform scope, and background. It does not use the template headings exactly, but it covers the req…

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robobun · 2026-09-09T20:04:21Z

The automated review pass on 39855a5 reported no actionable findings, so nothing changes on the branch for it. Buildkite build #113598 is still running. I will follow up on its result.

macOS fails a master write with no slave with EIO. The writer reports that as an error, which closes the terminal, so the queue never gets stuck there and a write after EOF throws instead of being dropped.

Move the reader-close and writer-end pair into finish_io_after_eof so the operation has a name instead of a paragraph at the call site, and cut each remaining comment to the fact a reader cannot get from the code.

robobun · 2026-09-09T20:28:23Z

^{Updated 2:10 PM PT - Sep 9th, 2026}

✅ @robobun, your commit 413c7b18a7a0e1425ebf12eb686f256c12613410 passed in Build #113605! 🎉

🧪 To try this PR locally:

bunx bun-pr 42150

That installs a local version of the PR into your bun-42150 executable, so you can run:

bun-42150 --bun

robobun · 2026-09-09T20:29:28Z

Two bot passes landed on this branch. Here is what changed for them.

The comment-cop pass flagged the comments in Terminal.rs. I took it as fair for the long ones: 4c33aca moves the reader-close and writer-end pair into a named finish_io_after_eof, so the call site reads as one operation, and every remaining comment is cut to the fact a reader cannot get from the code. The pass re-fires on the shortened versions (it flags any multi-line doc comment in a changed region, down to two lines), so the rest stay. Each one carries a fact the code does not show: a pty master answers a write with EAGAIN instead of EPIPE and a read with EIO instead of EOF, PosixStreamingWriter never dispatches on_ready, and the wrapper's cached slots are the only GC root of the three callbacks. Every thread is answered and resolved.

The CodeRabbit pass reported no actionable findings on 39855a5 and 28ee46c.

Also in this push: the release test is Linux-only now (28ee46c). macOS fails the same master write with EIO, the writer reports that as an error, and the error closes the terminal, so the queue never gets stuck there and a write after EOF throws instead of being dropped. The CI failure on the darwin lanes was that difference, not the fix.

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Actionable comments posted: 1

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Inline comments:
In `@src/runtime/api/bun/Terminal.rs`:
- Line 1841: Update the exit-dispatch lifecycle around on_writer_close,
maybe_downgrade_after_eof, and call_exit_callback so the writer wrapper remains
strongly rooted until the exit callback returns. Add or reuse completion state
that maybe_downgrade_after_eof checks, and set that state only after
call_exit_callback completes; preserve the existing downgrade behavior
afterward.

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src/runtime/api/bun/Terminal.rs

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maybe_downgrade_after_eof keyed off READER_DONE, so the writer teardown that now runs inside on_reader_finished (and, on main, any terminal whose writer was idle at EOF) downgraded this_value before the exit callback was dispatched through it. Gate the downgrade on a new EXIT_DISPATCHED flag that on_reader_finished sets once the callback has run, so the wrapper and the callbacks it roots stay strong through the last dispatch.

robobun · 2026-09-09T20:48:03Z

Round-up for 413c7b1, the current head.

The one substantive review finding (the wrapper could be downgraded by on_writer_close before exit was dispatched through it) is fixed structurally: maybe_downgrade_after_eof now waits for a new EXIT_DISPATCHED flag that on_reader_finished sets after call_exit_callback returns, instead of READER_DONE. The reviewer confirmed it and the thread is resolved. That window also existed on main for any terminal whose writer was idle at EOF, and it had no GC safepoint in it, so this is hardening rather than a second bug.

The remaining bot threads are the comment-length check re-firing on two-line doc comments. Each is answered and resolved, nothing further changes for them.

All review threads are resolved. The PR body is updated for the EXIT_DISPATCHED change. Buildkite #113605 is running on this head.

robobun · 2026-09-09T20:50:06Z

The latest automated pass covers the current head (413c7b1) and reports no actionable findings, with the earlier exit-ordering finding marked verified. No review threads are open. Buildkite #113605 is 5 minutes in (6 jobs passed, the rest queued or running); I will act on its result when it lands.

claude

Code review found no issues

No high-confidence issues detected in this change.

robobun · 2026-09-09T21:25:53Z

The second automated review also found no issues on 413c7b1, and Buildkite #113605 finished green on that head (182 of 182 jobs passed, no failures). All review threads are resolved. This is ready for a maintainer to look at.

…write() (#42662) ### Problem - On Windows, since v1.4.0, `terminal.write()` after the child of `Bun.spawn({ terminal })` exited leaks the `Terminal`. The write throws `EPIPE`, the terminal closes, but the wrapper, its callbacks and the native object stay rooted. 1.3.14 collects 4 of 4 terminals, 1.4.0 and main collect 0. - The writer fails inside `write()` and calls `Terminal::on_writer_error`, which closes the terminal and sets `WRITER_DONE`. The writer keeps the unsent bytes. - In `Terminal::write` (`src/runtime/api/bun/Terminal.rs:1478`), `has_pending_data()` is still true, so `write()` upgrades `this_value` again (#36962). The writer is done, so nothing downgrades it. ### Fix - `write()` checks `WRITER_DONE` after the writer returns. If set, the kept bytes do not count as pending: no root, no `drain` dispatch. - A done writer sends no more callbacks, so nothing can release a root taken for a pending drain. #42150 added the same check before the write. - With no `drain` dispatch, `exit` stays the last callback when an earlier write had bytes queued. - Verified: `test/js/bun/terminal/terminal.test.ts` (new test: fails on the Windows canary, passes with the fix). Two fault-injected Linux cases in `test/js/bun/spawn/spawn-pipe-start-error.test.ts` fail on main. Also `test/js/bun/terminal/` on both. ### Background - `Terminal` holds its JS wrapper in a `JsRef` (`this_value`), strong while a callback can fire: the wrapper's cached slots are the callbacks' only GC root. `maybe_downgrade_after_eof` makes it weak once `exit` has run and no `drain` is owed. - The streaming writer queues bytes it cannot send at once. `has_pending_data()` reports them, also after the writer closed. - `writer_has_buffered` records that a `drain` is owed. `on_writer_close`, the writer's last callback, sets `WRITER_DONE`. <details><summary>Notes</summary> **Windows reproduction, no fault injection.** Four inline terminals, each child is `cmd.exe /c exit 0`. After `proc.exited` and the `exit` callback, call `terminal.write("x")`, drop every reference, then run `Bun.gc(true)` until a `FinalizationRegistry` has seen all four. | build | collected | runs | | --- | --- | --- | | 1.3.14 | 4 of 4 | 3 of 3 | | 1.4.0 | 0 of 4 | 3 of 3 | | 1.4.3-canary.1+3f7f046cd (main) | 0 of 4 | 5 of 5 | | this branch, debug build | 4 of 4 | 3 of 3 | Every post-exit write threw `EPIPE` (20 of 20). Without the write, every build collects 4 of 4. #36962 (first released in v1.4.0) added the upgrade in `write()`. **Windows chain.** The child's exit does not end the writer on Windows (`finish_io_after_eof` is POSIX only), so `write()` reaches `WindowsStreamingWriter::process_send` (`src/io/PipeWriter.rs:2351`). `uv_write` fails at once, because conhost closed the input pipe. `process_send` already swapped the bytes into `current_payload` and does not clear it on this arm, so `has_pending_data()` stays true. `close()` reports `on_close` synchronously (`PipeWriter.rs:1152`), so `on_writer_close` sets `WRITER_DONE` inside the call. `EXIT_DISPATCHED` is already set at that point, so `maybe_downgrade_after_eof` never runs again. **POSIX chain.** `PosixStreamingWriter::write` queues the bytes and calls `register_poll` (`PipeWriter.rs:787`). Its error arm calls `on_error`, then `close()`. Unlike `_on_error` (`PipeWriter.rs:741`) it does not set `is_done` or reset `outgoing`, so `has_pending_data()` stays true. On Linux only fault injection reaches this arm. The re-arm is an `EPOLL_CTL_MOD`, and the kernel's `ep_modify` does not fail when watches or memory run out. What the kernel can return there is `EBADF` or `ENOENT`, after other code closed the writer's private fd by number. I found the POSIX path by a read of the code after #42150. It costs one `Terminal` object graph. It holds no fds and does not spin. **Why the check is in `Terminal::write`.** A change in the writer (reset `outgoing` in the `register_poll` error arm) does not remove the need for it. With `has_pending_data()` false, `write()` takes the `had_buffered && !has_pending` branch and dispatches `drain` after `exit`. The second Linux case covers that: an earlier write is still queued when the re-arm fails. The Windows path goes through a different writer. `this_value.upgrade()` has one call site, and `WRITER_DONE` is the condition that `maybe_downgrade_after_eof` already uses. **Not in this PR.** - `FileSink` is the other parent of the streaming writer, and `FileSink::to_result` has a similar shape. It takes a keep-alive ref for a `Pending` result only. On Windows a `uv_write` that fails at once makes the writer return `Err`, so the trigger above takes no ref there. On POSIX a write that gets `EAGAIN` and then fails to re-arm its poll returns `Pending` after `on_close` already ran, and nothing releases that ref. Only the failed registration reaches that case, so on Linux it needs fault injection (see the POSIX chain). I excluded it on purpose: I did not change or measure it here. - A caller that still holds a leaked terminal can release it. `Symbol.asyncDispose` downgrades `this_value` unconditionally. - #42654 (merged) fixed the reader's failed registration in `init_terminal` and added the `FAIL_EPOLL_CTL` shim modes. This branch is rebased on it. The test file change here only adds to it: the `pty-writer-mod` mode, a skip count, two fixture kinds and one `describe`. **Tests.** - The Linux cases assert `closed`, `drains`, `leakedFds` and `leakedWrappers` only. They do not pin the return value of the failing `write()` or the `exit` code. - Linux, debug ASAN build, after the rebase on #42654: `spawn-pipe-start-error.test.ts` 9 pass. With `src/` at main the two new cases fail with `leakedWrappers: 1` and every other field equal. 1.4.3-canary.1 fails them the same way. `test/js/bun/terminal/` 134 pass, 2 skip. - Windows Server 2019, debug build: `test/js/bun/terminal/` 114 pass, 10 skip, 12 todo, 0 fail. I measured this on the first shape of the patch (the same check, wrapped around the block). The current shape folds the check into `has_pending` and is the same logic. - The new `terminal.test.ts` test passes on Linux with and without the fix. On POSIX the check that #42150 added drops the write. Self-reviewed: 6 concerns raised, 6 addressed (Linux trigger stated as fault injection only, Windows trigger confirmed and tested, writer-level cause and `FileSink` sibling named, shim aligned with #42654, fewer pinned fields in the assertions, wording on collection). One part not done: no follow-up issue for `FileSink`, because I did not measure that leak myself. </details>  --- **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/terminal/terminal.test.ts, test/js/bun/spawn/spawn-pipe-start-error.test.ts

…write() (oven-sh#42662) ### Problem - On Windows, since v1.4.0, `terminal.write()` after the child of `Bun.spawn({ terminal })` exited leaks the `Terminal`. The write throws `EPIPE`, the terminal closes, but the wrapper, its callbacks and the native object stay rooted. 1.3.14 collects 4 of 4 terminals, 1.4.0 and main collect 0. - The writer fails inside `write()` and calls `Terminal::on_writer_error`, which closes the terminal and sets `WRITER_DONE`. The writer keeps the unsent bytes. - In `Terminal::write` (`src/runtime/api/bun/Terminal.rs:1478`), `has_pending_data()` is still true, so `write()` upgrades `this_value` again (oven-sh#36962). The writer is done, so nothing downgrades it. ### Fix - `write()` checks `WRITER_DONE` after the writer returns. If set, the kept bytes do not count as pending: no root, no `drain` dispatch. - A done writer sends no more callbacks, so nothing can release a root taken for a pending drain. oven-sh#42150 added the same check before the write. - With no `drain` dispatch, `exit` stays the last callback when an earlier write had bytes queued. - Verified: `test/js/bun/terminal/terminal.test.ts` (new test: fails on the Windows canary, passes with the fix). Two fault-injected Linux cases in `test/js/bun/spawn/spawn-pipe-start-error.test.ts` fail on main. Also `test/js/bun/terminal/` on both. ### Background - `Terminal` holds its JS wrapper in a `JsRef` (`this_value`), strong while a callback can fire: the wrapper's cached slots are the callbacks' only GC root. `maybe_downgrade_after_eof` makes it weak once `exit` has run and no `drain` is owed. - The streaming writer queues bytes it cannot send at once. `has_pending_data()` reports them, also after the writer closed. - `writer_has_buffered` records that a `drain` is owed. `on_writer_close`, the writer's last callback, sets `WRITER_DONE`. <details><summary>Notes</summary> **Windows reproduction, no fault injection.** Four inline terminals, each child is `cmd.exe /c exit 0`. After `proc.exited` and the `exit` callback, call `terminal.write("x")`, drop every reference, then run `Bun.gc(true)` until a `FinalizationRegistry` has seen all four. | build | collected | runs | | --- | --- | --- | | 1.3.14 | 4 of 4 | 3 of 3 | | 1.4.0 | 0 of 4 | 3 of 3 | | 1.4.3-canary.1+3f7f046cd (main) | 0 of 4 | 5 of 5 | | this branch, debug build | 4 of 4 | 3 of 3 | Every post-exit write threw `EPIPE` (20 of 20). Without the write, every build collects 4 of 4. oven-sh#36962 (first released in v1.4.0) added the upgrade in `write()`. **Windows chain.** The child's exit does not end the writer on Windows (`finish_io_after_eof` is POSIX only), so `write()` reaches `WindowsStreamingWriter::process_send` (`src/io/PipeWriter.rs:2351`). `uv_write` fails at once, because conhost closed the input pipe. `process_send` already swapped the bytes into `current_payload` and does not clear it on this arm, so `has_pending_data()` stays true. `close()` reports `on_close` synchronously (`PipeWriter.rs:1152`), so `on_writer_close` sets `WRITER_DONE` inside the call. `EXIT_DISPATCHED` is already set at that point, so `maybe_downgrade_after_eof` never runs again. **POSIX chain.** `PosixStreamingWriter::write` queues the bytes and calls `register_poll` (`PipeWriter.rs:787`). Its error arm calls `on_error`, then `close()`. Unlike `_on_error` (`PipeWriter.rs:741`) it does not set `is_done` or reset `outgoing`, so `has_pending_data()` stays true. On Linux only fault injection reaches this arm. The re-arm is an `EPOLL_CTL_MOD`, and the kernel's `ep_modify` does not fail when watches or memory run out. What the kernel can return there is `EBADF` or `ENOENT`, after other code closed the writer's private fd by number. I found the POSIX path by a read of the code after oven-sh#42150. It costs one `Terminal` object graph. It holds no fds and does not spin. **Why the check is in `Terminal::write`.** A change in the writer (reset `outgoing` in the `register_poll` error arm) does not remove the need for it. With `has_pending_data()` false, `write()` takes the `had_buffered && !has_pending` branch and dispatches `drain` after `exit`. The second Linux case covers that: an earlier write is still queued when the re-arm fails. The Windows path goes through a different writer. `this_value.upgrade()` has one call site, and `WRITER_DONE` is the condition that `maybe_downgrade_after_eof` already uses. **Not in this PR.** - `FileSink` is the other parent of the streaming writer, and `FileSink::to_result` has a similar shape. It takes a keep-alive ref for a `Pending` result only. On Windows a `uv_write` that fails at once makes the writer return `Err`, so the trigger above takes no ref there. On POSIX a write that gets `EAGAIN` and then fails to re-arm its poll returns `Pending` after `on_close` already ran, and nothing releases that ref. Only the failed registration reaches that case, so on Linux it needs fault injection (see the POSIX chain). I excluded it on purpose: I did not change or measure it here. - A caller that still holds a leaked terminal can release it. `Symbol.asyncDispose` downgrades `this_value` unconditionally. - oven-sh#42654 (merged) fixed the reader's failed registration in `init_terminal` and added the `FAIL_EPOLL_CTL` shim modes. This branch is rebased on it. The test file change here only adds to it: the `pty-writer-mod` mode, a skip count, two fixture kinds and one `describe`. **Tests.** - The Linux cases assert `closed`, `drains`, `leakedFds` and `leakedWrappers` only. They do not pin the return value of the failing `write()` or the `exit` code. - Linux, debug ASAN build, after the rebase on oven-sh#42654: `spawn-pipe-start-error.test.ts` 9 pass. With `src/` at main the two new cases fail with `leakedWrappers: 1` and every other field equal. 1.4.3-canary.1 fails them the same way. `test/js/bun/terminal/` 134 pass, 2 skip. - Windows Server 2019, debug build: `test/js/bun/terminal/` 114 pass, 10 skip, 12 todo, 0 fail. I measured this on the first shape of the patch (the same check, wrapped around the block). The current shape folds the check into `has_pending` and is the same logic. - The new `terminal.test.ts` test passes on Linux with and without the fix. On POSIX the check that oven-sh#42150 added drops the write. Self-reviewed: 6 concerns raised, 6 addressed (Linux trigger stated as fault injection only, Windows trigger confirmed and tested, writer-level cause and `FileSink` sibling named, shim aligned with oven-sh#42654, fewer pinned fields in the assertions, wording on collection). One part not done: no follow-up issue for `FileSink`, because I did not measure that leak myself. </details>  --- **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/terminal/terminal.test.ts, test/js/bun/spawn/spawn-pipe-start-error.test.ts

### Problem - `test/js/bun/spawn/spawn-stdio-syscall-error.test.ts` is red on alpine: `"lost": -82000`, not `0` (build 120303). #43739 added the case, not the bug. - `read_loop` (`src/io/PipeReader.rs:766`) delivers the bytes read before a failed read, then the error. The consumer asks for more inside that delivery, and the reader reads the fd past the error. The error comes late, or never. ### Fix - `read_once` sets `PosixFlags::READ_FAILED` on a fatal error, and `begin_read` does not read while it is set. The request parks, then `on_reader_error` rejects it. Nothing clears the flag. - Correct: libuv `uv__read` clears `UV_HANDLE_READABLE` before it reports a read error. - Verified: `test/js/bun/spawn/spawn-stdio-syscall-error.test.ts`, 17 pass. The four new cases fail without the fix. Suites: Notes. - Self-reviewed: 15 concerns raised, 14 addressed. Not taken: a flag reset in `start()`, which nothing on main needs. ### Background - `PosixBufferedReader` reads the fd behind subprocess stdio, file streams and the shell. Its parent gets `on_read_chunk`, then `on_reader_done` or `on_reader_error`. - `FileReader` is the parent behind a `ReadableStream`. `on_read_chunk` resolves the parked `pull()`, and the reaction runs before it returns. - Considered: a repeating shim failure hides the lost error. An error stored in `FileReader` first needs a callback in every parent. - #43920 is a newer PR with the same change. Its test trigger is here. ### Downsides - After a read error, a stream that ended with `'end'` now ends with `'error'`, as in Node. With no listener the process stops. - After a read error, `bun run --filter` no longer drains that pipe at exit. - Reads that do not fail pay nothing: `begin_read` tests one more bit. <details><summary>Notes</summary> **Trace without the fix** (bun 1.4.3-canary.1+367d939d9, shim logs each `recv()`, writer `dd bs=1025`). The debug build of main at 8d36bff does the same: 3 of 8 runs, two with no `'error'` and `lost` -7714150: ``` recv #5 len=262144 -> 95325 recv #6 len=166819 -> EIO (injected) same fill_scratch call as #5 JS data 95325 recv #7 len=65536 -> 65536 pull from inside the delivery, read_into recv #8 .. #116 to EOF {"received":452025,"got":8000125,"lost":-7548100,"events":["stdout.close","close"]} ``` No `'error'` event: the reads reached EOF before `on_reader_error` ran, and a stored error is only returned by a later pull. When the reads park first, `on_reader_error` rejects that pull and `'error'` comes late. That is the CI signature: the events match and `lost` is a negative multiple of 1025. **Why alpine.** In CI the failure is injected: the shim fails only the Nth `recv()`, so a later `recv()` succeeds and the extra bytes show. The failing `recv()` must follow bytes in the same wakeup. BusyBox `head` writes 1025 bytes at a time, so a wakeup often holds a short `recv()` and then the failing one. coreutils `head` fills the buffer in one `recv()`. The same run fails on debian when the writer is slow. With a writer that copies BusyBox `head` (stdio, 1024-byte buffer), the `RECV_AT=6` case fails 7 of 40 runs on bun 1.4.3-canary (release), and 36 of 40 when the writer also spins between chunks. This branch (debug): 0 of 120, and 0 of 60 with `dd bs=1025`. **With no shim.** A child with one AF_UNIX socket as fd 0 and fd 1 writes a line to stdout and reads stdin. The peer leaves that line unread, sends 8192 bytes and closes. The kernel gives the child 8192 bytes, then `ECONNRESET`, then EOF. | Runtime | stdin events | |---|---| | Node v26.3.0 | `'error'` `ECONNRESET` after 8192 bytes | | bun 1.4.3-canary.1+367d939d9 | `'end'` after 8192 bytes, no error | | this branch | `'error'` `ECONNRESET` after 8192 bytes | **The new cases.** Each one reaches the reader from inside the delivery in a different way. Whole-file runs of the describe block: | Case | Entry | Release, no fix | Debug, no fix | Debug, guard in `read_into` only | Debug, this branch | |---|---|---|---|---|---| | `child_process`, `'data'` listener | pull, `read_into` | fails 6 of 6 | fails 5 of 5 | passes | passes | | `child_process`, `'readable'` and `read()` | `set_flowing(true)`, `read` | fails 6 of 6 | fails 5 of 5 | fails 3 of 3 | passes | | `Bun.spawn`, `lazy` | pull, `read_into` | fails 6 of 6 | fails 5 of 5 | passes | passes | | `Bun.spawn`, reader started at spawn | pull, `read_into` | fails 6 of 6 | fails 5 of 5 | passes | passes | - The first three use counts: `SPAWN_FAULT_RECV_CAP=4096` makes every `recv()` short, so `fill_scratch` calls `recv()` again in the same wakeup. `SPAWN_FAULT_RECV_EAGAIN_AT=2` ends the first read loop, so the consumer's read parks and the next read is poll-driven. `SPAWN_FAULT_RECV_AT` then fails after bytes in that wakeup. For the `'readable'` case it is 19: #3 to #18 return 64 KiB, the highWaterMark, so the reader is stopped and `read()` starts it again. - The fourth uses state, and comes from #43920: the writer waits for a line on stdin, so the first read is parked when the bytes arrive. `SPAWN_FAULT_RECV_MID_FILL=1` fails the `recv()` that follows one that returned bytes, and `SPAWN_FAULT_READS_AFTER` counts the `recv()` calls after it. Without the fix it is 1. - With a count-based trigger and the reader started at spawn, the case passed without the fix on a debug build: the buffered reader that runs before JS reads `.stdout` took the bytes and the error. That is why this case uses state. - With the BusyBox-like writer at four speeds, the whole file passes 20 of 20 on this branch. **With the fix**, `CAP=4096 EAGAIN_AT=2 RECV_AT=5`: ``` recv #3 -> 4096, recv #4 -> 4096, recv #5 -> EIO JS data 8192 close(fd) JS error EIO ``` **Node.** libuv `uv__read` (`src/unix/stream.c`): on a read error other than `EAGAIN` it clears `UV_HANDLE_READABLE | UV_HANDLE_WRITABLE`, calls `read_cb` with the error, then stops the watcher. It calls `read_cb` once for each `read()`, so it never holds bytes and an error from one batch. **Placement.** EOF and the `maxBuffer` stop have the same guard at this site: `close_if_final` closes the reader before the final chunk is delivered. An error cannot use it, because a closed reader with no stored error reads as a clean end. For the same reason `READ_FAILED` is not part of `is_done()`. **Parents** (14 `BufferedReaderParent` implementations, what each does in `on_reader_error`): - 3 release the fd: `FileReader`, `SubprocessPipeReader`, `Terminal`. - 2 drop the reader: `FileResponseStream`, shell `subproc.rs`. - 8 only do accounting: `filter_run.rs`, `multi_run.rs`, `lifecycle_script_runner.rs`, `security_scanner.rs`, `git_runner.rs`, both cron jobs, test `Worker.rs`. `lifecycle_script_runner.rs` and `cron.rs` build a new reader with `init()` for each spawn. - 1 is shared and can restart: the shell `IOReader`. Only two read the same reader after an error. `filter_run.rs` `drain_and_close_pipes` reads once more at exit. That read is now a no-op, and `deinit()` follows. Before, it could reach a second terminal callback and decrement `remaining_fds` twice. The shell `IOReader::start()` does not restart a reader after a failed read on main, because the fired one-shot poll still counts as registered. The Windows reader gets one libuv callback for each read, so it has no bytes-then-error batch. **Left open.** - The flag is permanent. #39638 and #37901 change `IOReader::start()` to restart the shell's stdin reader. After this PR they must clear `READ_FAILED` there, or a `cat` that follows a stdin read error gets no data, no EOF and no error. - Not in this PR: a batch that stops because the buffer is full is labelled `ReadState::Eof` when the poll event carries the hangup (`read_state`, `None if received_hup`). `Bun.write(file, proc.stdout)` then writes 262144 of 400000 pending bytes and resolves. It is on main and in 1.4.3-canary, and this PR does not change it. It needs its own change. - Not in this PR: release the fd on a read error once, in `PosixBufferedReader::on_error`. #41456 names it as a follow-up. #41420, #41456 and #42150 did it for one parent each. **Suites run on the debug build:** `test/js/web/streams/streams.test.js` (624 pass), `test/js/node/stream/node-stream.test.js` (112 pass), `test/js/bun/spawn/spawn-streaming-stdout.test.ts` (pass), `test/js/node/child_process/child_process.test.ts` (81 pass, 2 fail in my container for reasons outside this change: "spawn in the default shell" reads an empty `$SHELL`, and "extra stdio pipes are not double-closed on GC" needs 5.0 s in a debug build against the 5 s timeout, its script prints `OK`). With this branch's build, the test file of #43920 passes 17 of 17 in 3 runs. #43790 is open and edits the comment above the failing case. It changes the event order in `native-readable.ts`, not the reader. </details>  --- **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/spawn/spawn-stdio-syscall-error.test.ts

robobun added 3 commits September 9, 2026 09:51

test: take the fd baseline after a warm-up spawn

39855a5

github-actions Bot added the claude label Sep 9, 2026

test(terminal): run the post-EOF release test on Linux only

28ee46c

macOS fails a master write with no slave with EIO. The writer reports that as an error, which closes the terminal, so the queue never gets stuck there and a write after EOF throws instead of being dropped.