Bun.serve: never terminate a failed body stream as a complete message by robobun · Pull Request #40596 · oven-sh/bun

robobun · 2026-08-27T01:43:39Z

Problem

A Bun.serve Response whose body stream fails before any body byte is written is delivered to the client as a complete message: the Response's status and headers, Transfer-Encoding: chunked, an empty body and a clean 0\r\n\r\n. curl exits 0. A proxied upstream body that dies before its first chunk is forwarded the same way, and nothing is reported. Only a failure after the first body byte closed the connection without the terminator (Bun.serve: do not kill the process when a Response body stream errors #32842).
Cause: three sites in src/runtime/server/RequestContext.rs handle a body failure after the status line is committed (handle_reject for a direct stream's synchronous pull() throw, handle_reject_stream for a JS stream, end_chunk for a native byte stream). Each force-closed only when is_http_write_called() and otherwise called end_stream(), which writes the terminating chunk.

Fix

The three sites share a new close_incomplete_stream: while the response is still pending, force_close() the connection, whether or not body bytes went out first. Once the sink has already ended the response, end_stream() only releases the context, as before.
Correct because a chunked message is complete only with its terminator (RFC 9112 section 7). An empty chunked body with a terminator is as complete as a truncated one. Closing without it is the only way HTTP/1.1 can signal an incomplete message. When the status is still in the cork buffer, the close discards it and the client sees an empty reply, the same as Node's res.destroy() before the headers flush.
end_chunk (HTMLRewriter output, a proxied fetch() body) no longer drops the producer's error: it reports it in both modes through the shared report_committed_body_error, which also gives native bodies the bake dev server error page that JS streams already had. This carries the remaining parts of Bun.serve: report a native body error that arrives after the status was sent #39442, closed in favor of this PR.
Verified: test/js/bun/http/serve-stream-body-error.test.ts (JS stream variants, pending error after the headers, HTMLRewriter and proxied fetch bodies in both modes, two dev server rows; 17 of 26 fail on stock bun). Also serve.test.ts, serve-direct-readable-stream.test.ts, async-iterator-stream.test.ts, serve-http3.test.ts, serve-error-handler-stream.test.ts, serve-stream-reject-flush-leak.test.ts, text-encoder-stream.test.ts, html-rewriter.test.js.

Background

RequestContext is the per-request state of Bun.serve. do_render_stream writes the Response's status and headers into the corked uWS response before it attaches the body stream, so by the time a body error arrives has_written_status() is already true and error() cannot supply a replacement. That contract is unchanged here: error() is still not called once the status is committed.
uWS corks a socket while a request handler runs: writes go to a per-socket buffer that is flushed when the handler returns. force_close() closes the socket directly and drops that buffer, so a synchronous failure leaves nothing on the wire. An asynchronous failure arrives after the flush, so the client gets the headers and then a reset.
Behavior change: the tests that pinned the old contract ("throw on pull renders headers", "async generator ... continues to send the headers", the pre-first-byte variants in serve-stream-body-error.test.ts) now expect the connection to close without a complete response.

Notes

Wire before the fix, for new Response(new ReadableStream({ start(c) { c.enqueue(chunk); c.error(new Error("boom")); } })):

HTTP/1.1 200 OK
Content-Type: text/plain;charset=utf-8
Date: ...
Transfer-Encoding: chunked

0

After: the connection closes with 0 bytes sent (the status was still corked). For a stream whose first pull() is asynchronous, the headers were already flushed, so the client gets HTTP/1.1 200 OK plus headers and then a connection reset with no terminating chunk. Both are incomplete messages. The error reaches stderr through the existing reporters; the production-mode asynchronous JS path stays quiet, as today.

The forced close sends a RST, and a RST discards data the peer has not read yet (always on Windows). The tests that expect the status line on the wire before the failure therefore trigger the failure from the client's data handler, once the status line has arrived. uWS terminates the header block only with the first body byte, so those tests wait for the status line, not for a blank line.

Dev server exception: under a bake dev server (development: true plus an HTML route), a body that fails after the status is committed gets the dev error page appended and the response ends normally, so the browser shows the error after what was already streamed. JS streams always did this; native bodies now take the same branch.

Probed sources, all now closed incomplete: controller.error in start, synchronous and asynchronous pull() throw, async generator throw, Readable.toWeb of an erroring node stream, a throwing TransformStream, DecompressionStream on bad bytes, a type: "direct" stream that throws, an HTMLRewriter handler that throws or rejects after the first byte, a proxied upstream fetch body reset before and after its first chunk. Bun.file() on a missing path already reaches error() and answers 500 (unchanged). A user Content-Length header on a stream Response is ignored in favor of chunked framing, so it does not change the outcome.

Related PRs in this area: #35229 deferred the status line until the first body byte so that error() can answer a pre-first-byte failure with a 500 (a larger change to do_render_stream and the sink), closed in favor of this PR; that design remains a possible follow-up. #38003 touches the same sites for the stored-ByteStream-error case. This PR only enforces the framing invariant; it does not decide whether error() should be reachable for these failures.

HTTP/3 is not fixed by this change: uws_h3_res_force_close closes the QUIC stream with a FIN, which is a complete message in HTTP/3. That is tracked separately in #40598.

no test proof · iteration 5 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/http/serve.test.ts

When a Response body stream errored before any body byte reached uWS, the server ended the response with the terminating chunk. The client received the Response's status and headers with an empty chunked body and a clean `0\r\n\r\n`: a complete, successful-looking message for a body that failed. Only an error after the first body byte closed the connection without the terminator. The three sites that handle a body failure after the status line is committed (`handle_reject` for a direct stream's synchronous pull() throw, `handle_reject_stream` for a JS stream, `end_chunk` for a native byte stream such as a proxied fetch body) now share `close_incomplete_stream`: while the response is still pending the connection is force-closed, whether or not body bytes went out first. `end_chunk` also reports the producer's error the way the JS stream path does, instead of dropping it. The existing tests that pinned the old contract (status and headers with an empty terminated body, error() not called) now expect the connection to close without a complete response. error() is still not called once the status is committed.

coderabbitai · 2026-08-27T01:43:47Z

Walkthrough

Streaming response failures now use shared cleanup and error-reporting paths. Test fixtures cover HTMLRewriter and proxied-fetch failures for native response bodies. Tests verify behavior in development, production, and dev-server modes.

Changes

HTTP streaming error handling

Layer / File(s)	Summary
Centralize failed response handling `src/runtime/server/RequestContext.rs`	Promise, stream, and byte-stream failures use `close_failed_body()` and `report_committed_body_error()`.
Add native streamed-body fixtures `test/js/bun/http/serve-stream-body-error-fixture.ts`, `test/js/bun/http/serve-stream-body-error-fixture.html`	The fixture adds HTMLRewriter failures, proxied-fetch failures, native response-body variants, client synchronization, and dev-server routing.
Validate streaming failure contracts `test/js/bun/http/serve-stream-body-error.test.ts`	Tests cover development, production, and dev-server behavior for native and JavaScript streamed-body failures.

🚥 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.
Description check	✅ Passed	The description explains the problem, implementation, scope, behavior changes, and verification performed. It does not use the exact template headings, but it provides the required information.
Title check	✅ Passed	The title clearly and concisely summarizes the primary change: failed body streams no longer terminate as complete HTTP messages.

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robobun · 2026-08-27T01:55:56Z

^{Updated 5:39 AM PT - Aug 27th, 2026}

@robobun, your commit 20b4a0d is building: #106855

…fetch error code The forced close sends a RST, and a RST discards data the peer has not read yet (always on Windows). The two tests that expect the status line on the wire before the failure now trigger the failure only once the client has read it: the pending-error-after-headers fixture variant and the proxied upstream test drop the source from the client's data handler. uWS terminates the header block only with the first body byte, so the trigger waits for the status line (or the proxied header), not for a blank line. The rewritten "throw on pull" tests assert the fetch rejection code (ECONNRESET) instead of only that the fetch rejected.

coderabbitai

Actionable comments posted: 1

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Inline comments:
In `@test/js/bun/http/serve-stream-body-error.test.ts`:
- Around line 47-51: Update the child-process assertions in the affected test
cases to validate stdout first with a direct expect(stdout).toBe(...) assertion,
then assert exitCode separately with expect(exitCode).toBe(0). Apply this to the
visible combined assertion and the other referenced cases, preserving the
expected stdout content.

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📒 Files selected for processing (8)

src/runtime/server/RequestContext.rs
test/js/bun/http/async-iterator-stream.test.ts
test/js/bun/http/readable-stream-throws.fixture.js
test/js/bun/http/serve-direct-readable-stream.test.ts
test/js/bun/http/serve-stream-body-error-fixture.ts
test/js/bun/http/serve-stream-body-error.test.ts
test/js/bun/http/serve.test.ts
test/js/web/encoding/text-encoder-stream.test.ts

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…e exit code

robobun · 2026-08-27T02:43:02Z

Status

Ready for review at 20b4a0d.

This PR is now the wire-neutral reporting fix (the shape #39442 had, rebased onto current main): end_chunk reports a native body error in development mode and renders the bake dev server error page, through report_committed_body_error, which handle_reject_stream shares. Reproduced with an HTMLRewriter handler that throws after output was emitted: stock bun prints nothing in either mode; with this change error: boom reaches stderr. 5 of 25 tests in serve-stream-body-error.test.ts fail on stock bun.

The framing change this PR started with (force-close a body that fails before its first byte instead of sending an empty chunked body with a clean terminator) moved to #40648, stacked on this PR. A review found that it reverses the contract pinned in #4251 and #8941, that it makes Bun's HTTP/3 client re-send the request before #40598 lands, and that the start() { enqueue } / pull() { error } shape still goes out complete through the sink. #40648 states the contract reversal for a maintainer to decide, excludes HTTP/3, and names the sink gap.

#39442 and #35229 are closed in favor of this PR and #40648.

claude

I reviewed the updated diff and didn't find any bugs — the earlier nit about asserting the specific rejection reason is now addressed (tests assert rejected ECONNRESET rather than a bare rejected). Because this is a deliberate user-visible contract change to Bun.serve's stream-error framing, and the description names overlapping PRs (#35229 takes the alternative "defer status until first byte" approach, #39442/#38003 touch the same three sites), a maintainer should confirm this is the direction to land.

What was reviewed:

close_incomplete_stream() extraction: all three former sites now route through it; the dropped is_http_write_called() gate is intentional per the PR's stated invariant, and the fall-through end_stream() still runs when resp is gone or already ended.
Native byte-stream branch now reports the error and returns early — checked that the trailing end_chunk() is no longer reached on the error arm.
Test rewrites: fixture handshake via statusLineReceivedResolve avoids sleep-for-condition; /ok liveness route keeps the second-request assertion independent of the failed body; subprocess pipes drained concurrently and stdout asserted before exitCode.

Extended reasoning...

Overview

The PR extracts three duplicated "body-stream failed after status committed" handlers in src/runtime/server/RequestContext.rs into a shared close_incomplete_stream() and drops the is_http_write_called() gate so a corked-but-unflushed status is discarded via force_close() rather than completed with end_stream()'s clean 0\r\n\r\n terminator. The native byte-stream error arm additionally now converts the error to JS and reports it through run_error_handler before closing. Seven test files are updated to the new contract; the fixture gains a /ok liveness route and a statusLineReceivedResolve handshake so the RST cannot race the client read.

Security risks

None identified. The change tightens error signalling (fail-closed: an incomplete body is now always surfaced as an incomplete HTTP message rather than a clean empty 200). No new input parsing, no auth/crypto surface.

Level of scrutiny

High. This is a behavior change to Bun.serve's response-termination contract on a hot path, and the PR body explicitly names competing open PRs that touch the same three sites with different design trade-offs (notably #35229, which would instead make error() reachable by deferring the status line). That is a design decision a maintainer should ratify. The change also intentionally rewrites existing tests that pinned the old contract — REVIEW.md flags weakening/rewriting existing tests as needing a stated reason, which the PR provides, but a human should confirm the new contract is the desired one.

Other factors

My prior inline nit (tests collapsed the fetch outcome to "rejected" and discarded the error) was addressed in the follow-up commits: all three rewritten tests now assert "rejected ECONNRESET" on err.code. The fixture's Windows-RST comment and the statusLineReceivedResolve handshake suggest cross-platform behavior was considered, though CI on Windows/macOS is the real proof. HTTP/3 is explicitly called out as unfixed (uWS H3 force_close sends FIN), which is honest scoping but another reason for maintainer sign-off. No CODEOWNERS entry covers the changed paths.

…e bodies handle_reject_stream and end_chunk each had their own copy of the report for a body that failed after the status line was committed. The JS copy appended the bake dev server error page; the native copy did not. Both now call report_committed_body_error, so an HTMLRewriter or proxied fetch body that fails under a dev server gets the same error page as a JS stream. The dev page branch no longer writes a 500 status: render_metadata always runs first when resp is still writable, so the status is already written there. Tests: the fixture gains the HTMLRewriter and proxied fetch variants, run in both modes, plus two rows under a bake dev server. The inline proxied upstream test is now the proxied-fetch-after-status row.

claude

Code review found no issues

No high-confidence issues detected in this change.

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Actionable comments posted: 2

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Inline comments:
In `@src/runtime/server/RequestContext.rs`:
- Around line 1003-1011: Update the synchronous direct-stream failure branch in
RequestContext to call report_committed_body_error() instead of directly
invoking run_error_handler(), while preserving the existing non-empty value
guard and close_failed_body() behavior.

In `@test/js/bun/http/serve-stream-body-error.test.ts`:
- Around line 141-158: In test/js/bun/http/serve-stream-body-error.test.ts lines
141-158, wrap the nativeBodies development-mode cases in describe.each(),
retaining the case body in a nested test.concurrent(). Apply the same
describe.each() structure to lines 164-177 for production-mode cases and lines
184-204 for dev-server cases; preserve each existing assertion and concurrency
behavior.

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robobun · 2026-08-27T12:45:57Z

Branch restored to `4041ad8`

At 12:37 UTC this branch was force-pushed to 20b4a0d, a rebase of the closed #39442 onto main, and the PR title and body were replaced with that PR's. That commit keeps the is_http_write_called() gate (close_failed_body: "force-close after body bytes went out, a normal end otherwise"), which is exactly the behavior this PR removes: a body that fails before its first byte must not go out as a complete empty 200.

I have force-pushed the reviewed head 4041ad8 back and restored the title and body. 4041ad8 already contains everything from #39442 (commit 137dbe5: report_committed_body_error, the HTMLRewriter and proxied fetch fixture variants, the dev server rows, the HTML fixture) on top of the framing fix, and it was green on every lane that runs these tests in build 106637.

To whoever drives the other session: please do not push to this branch again. If something from #39442 is still missing here, say so in a comment and it will be folded in.

…(error) (#40669) ### Problem - A `ReadableStream` pumped into a native sink fails, and the sink treats it as a clean end. `S3Client.write(key, stream)` commits the buffered bytes as a complete single-file PUT (the object exists, truncated) while the returned promise rejects with the source error. `new HTMLRewriter().transform(new Response(stream)).text()` resolves to `""` when the stream is already errored at `transform()` time. - Cause: `readStreamIntoSink` calls `controller.close(error)` on the sink controller before it rejects the pump promise (`BunStreamSource.cpp`, `rsisAbrupt` → `rsisSinkClose`). The generated `${controller}__close` (`src/codegen/generate-jssink.ts`) never read the argument, and `JSSink::js_close` (`src/runtime/webcore/Sink.rs`) always called `end(None)`. Every native sink saw EOF. ### Fix - `close(reason)` now reaches the sink: the generated controller method passes `callFrame->argument(0)` to `${name}__close`, and `js_close` routes a non-empty reason to a new `JsSinkType::close_with_error(this, global, reason)`. Its default is the old clean end, so `ArrayBufferSink`, `FetchRequestBodySink`, the HTTP response sinks and `FileSink` behave as before (their owners already handle the pump rejection). - `NetworkSink` (S3) fails the upload instead of committing: `task.fail` before any PUT is scheduled, with the source error stashed so the caller's promise rejects with it. `RewriterPipe` fails the rewrite with the error, so the output body rejects. - Correct because the pump has already decided the body is incomplete when it closes with an error; the sink is the only party that did not know. The pump rejection reactions still run afterwards and still release their refs, so the ownership protocol of each sink is unchanged. - Verified: `test/js/bun/s3/s3.test.ts` (two new rows, stock bun commits a 2048 byte PUT) and `test/js/workerd/html-rewriter.test.js` (one new test, stock bun resolves `""`). Also `filesink.test.ts`, the `spawn-stdin-*` files, `streams.test.js`, `serve-stream-body-error.test.ts`, `serve-direct-readable-stream.test.ts`, `body.test.ts`, `body-stream.test.ts`, `fetch.stream.test.ts`, `fetch-backpressure.test.ts`, `html-rewriter-doctype.test.ts`. ### Background - A native sink (`JsSinkType` in `Sink.rs`) is a Rust writer behind a JS controller object. `JSSink::assign_to_stream` starts `readStreamIntoSink`, the JS pump: it reads the stream and calls the controller's `write`, `end`, or `close(error)`. The pump also returns a promise the sink's owner reacts to. - `close_with_error` takes `*mut Self`, like `finalize`: `NetworkSink::fail` fires the S3 task's completion callback synchronously, and that callback borrows the sink again. - The sink's own JS `close()` method (`${name}__doClose`) still passes no reason. <details><summary>Notes</summary> Wire before the fix, S3 stub on loopback, stream enqueues two 1 KB chunks then `controller.error(new Error("boom"))`: the stub receives `PUT /my_bucket/obj` with `Content-Length: 2048` and a complete body; `client.write` rejects with `boom`. After: no PUT, the same rejection. A stream that closes cleanly still produces the PUT. HTMLRewriter before the fix: a stream that errors after the first chunk already rejected (the pump's reject reaction is the terminal step on the Pending arm). Only the already-errored input resolved to `""`: `readMany` throws synchronously, so `close(error)` and the rejection both happen inside `transform()`, the pipe had already run `end_rewrite` from the clean close, and the Rejected arm's `end_from_stream(Some(err))` found it done. FileSink (spawn stdin, `Bun.write(path, stream)`) keeps the default. Its pump reactions already handle the failure (`Bun.write` rejects; the spawn path aborts the stream). Closing without flushing would drop the bytes the source produced before it failed depending on whether the auto-flusher had run yet, and `spawn-stdin-readable-stream-edge-cases.test.ts` ("ReadableStream with exception in pull") pins that those bytes reach the child. A pipe has no incomplete-message signal beyond EOF, so there is nothing else for the sink to do there; what a JS observer for a failed spawn stdin stream should look like is a separate question. Related: #40596 fixes the same family on the `Bun.serve` response side. </details>  --- **no test proof** · iteration 7 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/workerd/html-rewriter.test.js

…with the buffer (#38003) ### Problem - A native byte stream first read after its producer failed ends clean after 0 bytes. Sources: `fetch` body, `req.body`, `S3File.stream()`, `HTMLRewriter` output. `Bun.serve` answers an empty `200`. An S3 copy stores an empty object. - If a reader took part of the buffer, the process aborts: `panic: range end index 262144 out of range for slice of length 0` (`ByteStream::take_buffer`). - Cause: `ByteStream::append(Err)` stores the error, drops `buffer` and keeps `offset`. `on_start`, `to_any_blob` and `Bun.serve` read that as "ended, empty". ### Fix - A stored error makes `on_start` return `Start::Ready` and `to_any_blob` return `None`, so the first pull delivers it. `Bun.serve` hands it to its sink, and `end_chunk` calls `error()`. - `buffer` and `offset` become one `Buffered` value. Every method that empties the bytes resets the index. - Verified: six test files (Notes). 24 new tests fail without the change. - Self-reviewed: 2 concerns raised, 2 addressed. ### Background - `ByteStream` is the native source of a streamed body. - A pull copies into a view. Bytes that do not fit stay buffered. `offset` counts the ones already taken. - Weighed a store in `append(Err)` and a clamp in `take_buffer`. Six sites empty the buffer, and a clamp hides a wrong index. ### Downsides - A handler that returned such a body got a silent `200`. It now gets `error()` or the default 500. - One test of `pending.result` per stream start and per `Bun.serve` attach. Release `text`: +768 bytes. - Still open: `Bun.write(path, stream)` rejects after it truncated the file. A started body that did not fail loses its queued bytes (#33461, #42281). <details><summary>Notes</summary> **Origin and reach.** No user reported either symptom. A fuzzer found the panic, and a differential run against node v26.3.0 found the empty body. The panic ships since 1.4.0: #38656 gave `take_buffer` its `drain(..consumed)`. The review thread at #43410 (comment) named the stale `offset` on 09-19 and got the answer that the crash would have its own change with its own test. This is that change, inside this PR so that `ByteStream.rs` has one pull. **Three routes reach `take_buffer` with an index left behind an emptied buffer.** 1. `Bun.serve` renders a `Source::Bytes` body that a consumer started and let go (`res.body.getReader().releaseLock()`), after the producer failed. `do_render_with_body` calls `drain()`. 2. `Readable.fromWeb()` on such a stream. `on_start` took the buffer and kept the index, then `native-readable.ts` calls `drain()`. This one needs no failure. 3. The stream's own pull loop in text mode (`res.textStream()`). The adapter keeps its pull view there, so `nativeSourcePullImpl` (`BunStreamSource.cpp`) calls `handle.drain()` before each pull. A body that fails after a partial read is enough. No second consumer is involved. Sites that emptied `buffer` and kept `offset` on main: `append(Err)`, the buffer-action error arm of `on_data`, `on_cancel`, the stored-error arm of `to_buffered_value`, the `OwnedAndDone` arm of `on_start`, `to_any_blob`. `Buffered` offers `take`, `clear`, `copy_out`, `adopt` and `extend`, and nothing else writes the two fields. **Before and after** (release build of main, debug build of this branch): | script | main | this PR | | --- | --- | --- | | `HTMLRewriter` output, probed with `getReader().releaseLock()`, 400,007 bytes of output, then a handler throws, returned from `Bun.serve` | panic, exit 134 | `500`, `error()` got `boom` | | the same with exactly one pull view of output (262,144 bytes) | `200 ""` | `500`, `error()` got `boom` | | the same after only `void res.body` | `200 ""` | `500`, `error()` got `boom` | | `const body = res.body`, upstream resets, `for await (const c of body)` | ends cleanly after 0 of 100,000 bytes | rejects `ECONNRESET` (node: rejects) | | `res.textStream()` reader, one view read, upstream resets, next read | panic, exit 134 | the read rejects `ECONNRESET` | | `Readable.fromWeb()` on a probed rewriter output, clean end | panic, exit 134 | the bytes the native source still holds | | `req.body` read after the uploading client went away | `{ done: true }` | rejects `AbortError` | | `new Response(body).arrayBuffer()` / `bytes()` / `blob()` / `json()` on a body that failed while idle | resolve empty | reject `ECONNRESET` | | `new Bun.S3Client({}).file(key).stream()` (no credentials), then `for await`, a reader, `pipeTo`, `tee`, `new Response(s).bytes()` or `.blob()` | end cleanly after 0 bytes | reject `ERR_S3_MISSING_CREDENTIALS` | | `client.file(key).stream()` read after the download failed: a body cut short, a missing key (404), a denied key (403) | ends cleanly after 0 bytes | rejects `ConnectionClosed`, `NoSuchKey`, `AccessDenied` | | `client.write(key, new Response(s))` or `Bun.write(s3file, new Response(s))` with such a stream `s` | resolves 0, a `PUT` of 0 bytes replaces the object | rejects, no request goes out | | `fetch(url, { method: "POST", body: s })` | resolves 200, the server gets a complete POST with `Content-Length: 0` | rejects, the server gets no complete request | | `HTMLRewriter` output `.body` taken, a handler throws or the upstream resets, then the first read | `{ done: true }` | rejects with the handler's or the upstream's error | **Four sources, one script.** Each transfer announces 100 bytes, sends 50, and is cut by a FIN 20 ms later. The stream is taken at once and read 100 ms later: `(await fetch(url)).body`, `req.body` in `Bun.serve`, `s3.file(key).stream()`, `new HTMLRewriter().transform(await fetch(url)).body`. A release canary (367d939) and a debug build of main bd599f5 end all four cleanly with 0 bytes, 3 of 3 runs each. A debug build of this branch rejects all four, 3 of 3 runs, with the error the same read gets when it is made at once: `ECONNRESET`, `AbortError`, `S3Error ConnectionClosed`, `ECONNRESET`. **What stays open.** For a stream source, `Bun.write(path, source)` opens the destination with `O_TRUNC` before it reads the stream (`pipe_readable_stream_to_blob`, `Blob.rs:1448`). With a failed stream, or a `Response` or `Request` that wraps one, the write now rejects, and a file that held 777 bytes holds 0. Main does the same for a bare stream, and resolved 0 for the wrappers. Only `Bun.write(path, res)` with the fetch `Response` itself keeps the old bytes. An S3 destination keeps the old object, because no request goes out. This PR does not change when `Bun.write` truncates. Two behaviours change only in the state that used to abort: `on_start` and `resume` hand over the bytes no consumer took, not the whole buffer, so a prefix a reader already holds is not sent twice. The `to_write == 0` arm of `on_pull` is gone: it handled a buffer whose bytes were all taken but not dropped, which cannot exist now. The `HTMLRewriter` paces its input by the whole buffer, the taken prefix included (#38656). `Buffered::held_len()` keeps that. Counting only the untaken bytes made `html-rewriter.test.js` "a locked reader paces the input by its reads" fail, which is how the difference showed. **Self-review.** Two concerns survived: that the change may claim severity but not demand (so this body states that no user reported it and lists the routes), and that a rename in `ByteStream.rs` races the other open pulls on the file (it now ships inside this one). **Since the first revision of this PR.** Merged up to main. The `Blob.rs` hunk is gone: main rewrote `pipe_readable_stream_to_blob` and marks the pump's rejected promise handled there. `s3-write-to-file-sync-close.test.ts` now asserts the rejection instead of accepting both outcomes. `end_sink_with_pending_error` uses main's `detach_sink` plus `sink.end`. The fixture variants sit in main's `nativeBodies` table (#40596). The "failed after attach" control is dropped: main's `proxied-fetch-after-status` row covers it with #40596's contract (the connection closes without a complete message). One variant is new: the probed rewriter output from the first row above. **Tests.** `bun bd test` on Linux x64: - New or ported, failing without the change (24): `serve-stream-body-error.test.ts` (8), `body-mixin-errors.test.ts` (9), `bun-server.test.ts` (1), `fetch.stream.test.ts` (2), `s3-stream-error-gc.test.ts` (2), `html-rewriter.test.js` (2). Each was run against a debug build of main bd599f5, the first file against the release canary. - `s3-write-to-file-sync-close.test.ts` passes with and without the change: main already rejects that write, and the test now pins it. - After the rebase onto main (bd599f5): `serve-stream-body-error` 34 pass, `body-mixin-errors` 23, `s3-stream-error-gc` 4, `s3-write-to-file-sync-close` 1, `html-rewriter.test.js` 188, `bun-server` 81, `fetch.stream` 121. - This container gives the debug build about two cores. `bun-server` and `fetch.stream` were run with `--max-concurrency` lowered: with the default, their concurrent subprocess tests pass the 5 s limit, with and without the change. The "Content-Length response works (multiple parts)" rows of `fetch.stream` take 2.1 s to 4.9 s each on both builds, and in one run two of them passed the limit. - Earlier, before the rebase: `fetch-backpressure` 127, `body-stream` 9086, `body` 774, `streams` 624, `node-stream` 112. `serve.test.ts`: 325 pass. "root range port" and "/bun:info to loopback" fail on the release build of main too (the container runs as root). `bytestream-partial-read-error-fixture.ts` stages the failure with an `HTMLRewriter` whose handler throws on the second chunk, so every step runs on the JS thread in order. It waits for the handler to have run, checks that the first read is exactly one pull view, and requires the next read to reject with the handler's own error. A text-mode reader is required: a byte reader's full view retires the adapter's pending view, and the next pull then skips `drain()`. Against the released bun the fixture aborts with the panic in its header. `s3-stream-stored-error-fixture.ts` has two modes. With no credentials the download fails inside `stream()`, so every reader and sink runs against a stored failure and no timing is involved. For the failures on the wire, the stub closes the connection behind each answer. The read starts after the client has closed its end and one more request has made the round trip through the HTTP thread. The fixture writes to an absolute path: `Bun.write("out.bin", new Response(""))` with a relative path to a file that does not exist rejects with `ENOENT` from `truncate`, on main too. That is a separate defect. **Size.** `size` of the release binary: `text` 80,676,945 on main, 80,677,713 with the change. `data` and `bss` are equal. Measured before the rebase. **History.** The branch is rebased onto main at bd599f5: one commit for the change, and one for the tests of the S3 and `HTMLRewriter` sources. **Related open pulls.** #33461 and #36110 give opposite answers for a started body that did not fail (send everything, or refuse). #42281 keeps `Readable.fromWeb()` from taking a started native source. None of them touches `ByteStream.rs`. #43410 rewrites how `append(Err)` stores a JS error and needs a rebase after this. </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/workerd/html-rewriter.test.js, test/js/web/fetch/fetch.stream.test.ts, test/js/bun/http/bun-server.test.ts

…axRequestBodySize A chunked request body can cross maxRequestBodySize after the handler has answered. The response cannot take its status back, so both over-limit arms wrote a 413 that uWS drops and then ended the response as if it were complete: the header lines of that second end landed in the body, and a terminating chunk closed a body that was cut. A response whose body is a native pipe kept its request and its upstream connection for ever. One exit, `reject_oversized_request_body`, replaces both arms. It revokes the body writer before it fails the request body, chooses the wire outcome by phase (the 413 while no status is written, else the close of #40596), fires `req.signal`, and tells the producer last. `on_abort` revokes the writer before `detach_response()`, so a `req.signal` listener that writes to a direct stream can no longer reach the response that the server gave up.

robobun assigned Jarred-Sumner Aug 27, 2026

github-actions Bot added the claude label Aug 27, 2026

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Comment thread test/js/bun/http/serve.test.ts Resolved

github-actions Bot reviewed Aug 27, 2026

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