[robobun]

Problem

• Inside AsyncLocalStorage.run(), a fetch() upload body or Bun.serve response built from an async generator or a type: "direct" stream sees no store. fetch() regressed in 1.4.0.
• A stream captures the async context at construction, and source callbacks restore it. Three calls into a direct stream's source did not: pull() under a native sink (BunStreamSource.cpp:759), pull() under bytes() (BunStreamConsumers.cpp:1084), the close() hook (JSDirectStreamController.cpp:118).

Fix

• JSDirectStreamSource makes every call of a direct source's functions, each in the stream's async context. The function accessors are private.
• Correct because one stream gets one answer. On main pull() reads the stream's store under text(), the caller's under bytes(), none under fetch().
• Verified: streams.test.js, serve-direct-readable-stream.test.ts, module-graph-callbacks.test.ts, a Node-parity fixture. 62 tests fail on main.
• Self-reviewed: 13 concerns raised, 12 addressed. Rejected: a test pinning HTMLRewriter handler stores (HTMLRewriter: call each content handler in the async context of its transform() #46967 decides those).

Background

• AsyncLocalStorage is one slot per global. Native code that calls script later must restore it.
• A direct stream has no queue: its consumer calls pull(controller). An async-iterable body is one.
• Considered one scope at the native sink start: bytes() and close() stay bare. Considered wrapped functions: 3 cells per body.

Downsides

• Behaviour change: a direct stream built in one store and consumed in another now runs pull() in the first under Bun.write, Bun.spawn stdin, HTMLRewriter and bytes(), and close() too. A maintainer must confirm (Notes).
• A Bun.serve body now reads the handler's store after the handler returned, for example a committed transaction.
• No store: +57 instructions per readableStreamToBytes stream, .text +1536 bytes, 0 cells.

Notes

An audit of AsyncLocalStorage propagation found this. No issue reports it.

Repro

import { AsyncLocalStorage } from "node:async_hooks";
const als = new AsyncLocalStorage();
using server = Bun.serve({ port: 0, fetch: async req => new Response(await req.text()) });
await als.run("u1", async () => {
  async function* body() {
    console.log(als.getStore()); // 1.4.0 to main: undefined. This PR and bun 1.3.14: "u1"
    yield "x";
  }
  await (await fetch(server.url, { method: "POST", body: body(), duplex: "half" })).text();
});

• fetch() upload: a generator body and a direct body read the store in 1.3.14 and read none from 1.4.0 to main. The commit that regressed it is not bisected.
• Bun.serve with als.run() per request, or a server started inside run(): a generator body and a direct body read no store in 1.3.14, 1.4.0, 1.4.4 and main, while every handler reads it.
• Bun.serve with als.enterWith() in a sync handler: the body reads the store in 1.3.14 and 1.4.0 and reads none from 1.4.1 to main.
• hono 4.7.2 with contextStorage(): on main getContext() throws "Context is not available" inside a generator body and a direct body. With this PR it returns the request's context. hono's own stream() helpers and { pull } bodies are not affected.
• Bun.ModuleGraph: a generator body that a graph builds and the host serves runs as the host on main (Bun.ModuleGraph.current is the host, a timer error reaches the host's uncaughtException, an interval survives dispose()). With this PR it runs as the graph.

Which store a direct source sees

The stream is built in C and consumed one macrotask later in F. - is no store. "Direct source" is a type: "direct" stream or an async-iterable body (new Response(gen)). Release binaries of 1.3.14, 1.4.0, 1.4.4, main and this PR.

consumer	1.3.14	1.4.0 to main	this PR
fetch() body	C	-	C
Bun.serve response	-	-	C
reader, for await, text(), blob(), node:stream/consumers text()	C	C	C
arrayBuffer(), bytes(), Bun.readableStreamToArrayBuffer, Bun.readableStreamToBytes	F	F	C
node:stream/consumers arrayBuffer(), bytes(), buffer()	F	F	C
Bun.spawn stdin	F	F	C
HTMLRewriter().transform(new Response(s))	error	F	C
Bun.write(file, new Response(s))	never settles	F (never settles in 1.4.0)	C
close() hook, Bun runs it after close() inside pull(), under a reader	F	F	C
close() hook, Bun runs it after a sync throw in pull(), under a reader	C	F	C
close() hook under a reader, user code closes from a timer in store X, or in no store	X, -	X, -	C
close() hook under arrayBuffer(): Bun runs it, or user code closes from X or from no store	F, X, -	F, X, -	C
cancel() when the client aborts a Bun.serve response	C	C	C

• A raw generator passed to fetch() becomes a stream inside fetch(). It reads the fetch() caller's store in 1.3.14, in Node and with this PR, and none from 1.4.0 to main.
• A stream built with nothing current in the async context is not changed in any row. An empty snapshot restores nothing, so such a source runs in the store of the code that calls it.
• Probe totals: 16 of 28 rows move (7 from no store, 9 from the caller's store), 12 do not change. A 27-cell upload probe (3 body shapes, 9 steps each) prints the store in 25 cells, against 7 on main. The other 2 are the first next() of ReadableStream.from.

Question for a maintainer

The rule "source callbacks run in the construction context" is #33193's (JSReadableStream::finishCreation). This PR applies it to the direct-source calls that did not follow it. These cells leave a store that user code was in. Each needs a yes or a no:

1. pull() under Bun.write, Bun.spawn stdin and HTMLRewriter: the stream's store, not the caller's?
2. pull() under arrayBuffer(), bytes() and the three node:stream/consumers functions: the stream's store, as under text() and blob() today?
3. The close() hook: the stream's store, also when user code calls controller.close() from another store?
4. A stream built inside another storage's run() (a tracer, a server started in run()) restores that whole context. The consumer's store is then not visible in pull(). With two storages the consumer's store is absent in 27 of 27 direct rows, against 9 of 27 on main. Accepted?

What other runtimes do for an async-iterable body, built in C and consumed one macrotask later in F:

runtime	text(), blob(), reader	arrayBuffer(), bytes()	new Response(gen).body as a fetch() body
bun 1.3.14	C	F	C
bun 1.4.0 to main	C	F	-
this PR	C	C	C
Node 26.3.0	F	F	F
Node 26.12.1	C, then F	C, then F	C, then F
Node 27 nightly 2026-10-26	C	C	C

Node changed between the 2026-10-24 and 2026-10-26 nightlies (nodejs/node#66907 merged between them).

The same question is open for generic sources, and this PR does not touch them:

new ReadableStream({ pull }) built in made	Node 26.3.0, 26.12.1, nightly	bun 1.3.14	1.4.0 to main
read by a reader in used, one macrotask later	used	used	made
read outside any store, one macrotask later	no store	no store	made
read in the same tick	made	made	made
pipeTo(sink) called in used: pull, write, close	used	used	made
cancel() in used	used	made	made
fetch() body built in u0, fetch() called in u1	u1	no store	u0

• A: the snapshot applies only where the runtime is the consumer. A reader's store wins for generic sources, as in Node and 1.3.14.
• B: the construction store everywhere, as the comment in JSReadableStream::finishCreation says.

ReadableStream.from waits for that answer. Under A it gets a scope at the native pump start. Under B it gets a scope in its two algorithms, and next() / return() under a reader move from the reader's store to the stream's.

What moves besides the store of pull()

• HTMLRewriter calls its handlers bare, so a handler reads the store of whatever feeds the rewriter. For a direct body that feed is now pull() in the stream's store. One transform() of 200 elements read in F: main element: F x200, this PR C x17, F x183 for a sync pull(). A { pull } body already reads F x1, C x199 on main. HTMLRewriter: call each content handler in the async context of its transform() #46967 gives handlers the context of transform(), which ends the split. The two PRs are not built together yet.
• Bun.serve: a body that reads als.getStore() ?? fallback got the fallback on main. It now gets the handler's store after the handler returned. Middleware that commits a transaction when the handler returns now sees the body use the committed transaction, as a { pull } body already does. Building the body inside als.exit() keeps the old result.
• Bun.ModuleGraph: after graph.dispose(), a host consumer (readableStreamToBytes, Bun.write, Bun.serve) of a direct or generator body that the graph built runs the source as the graph, not as the host. Bun.write of such a body then never settles. The docs already say that an operation on a disposed graph's stream may never complete, and a { pull } stream already ran as the graph.
• als.enterWith() inside a sync pull() under readableStreamToBytes no longer leaks into the caller. The close() hook reads the stream's store even when pull() called enterWith() before close().
• A failed pull() under a buffer consumer errors the stream, and the stream releases its snapshot there. The one-shot sink keeps that snapshot while it holds the source, so close() on a kept controller still runs the hook in the stream's store. A review found this case.
• No callback moves in time, and no call is added or removed. callDirectPull keeps its one function-level scope and passes it to pull(), so a reader-driven pull enters the snapshot once, as on main.

Measurements

Release builds of main 99ee03e and of this PR (d75a08a) on it. Instructions are instructions:u of the whole process, with concurrent JIT off. Per operation = (I(big N) - I(small N)) / (big N - small N), 5 interleaved runs, median. Spread is max - min per binary (main / PR).

workload	no store	in a store
{ pull } stream under getReader(), per pull	-1.3 (2151.9 to 2150.7, spread 0.5 / 1.6)	-0.9 (2233.2 to 2232.2, spread 2.5 / 2.6)
direct stream under getReader(), per pull	-19.7 (2080.8 to 2061.1, spread 2.8 / 2.8)	-20.1 (2143.3 to 2123.1, spread 1.1 / 0.7)
ReadableStream.from under getReader(), per next()	-1.2 (4928.0 to 4926.9, spread 1.5 / 1.7)	not measured, code not touched
direct stream under readableStreamToBytes, per stream, collector off	+57.1 (11570.7 to 11627.8, spread 18.9 / 7.5)	+79.7 (13480.0 to 13559.7, spread 37.8 / 26.1)
direct stream under readableStreamToBytes, per stream	+66.7 (11751.0 to 11817.7, spread 15.1 / 13.9)	+89.4 (12951.9 to 13041.3, spread 20.6 / 38.7)
direct stream under Bun.write, per stream	+15.8 (9275.8 to 9291.6, spread 90.1 / 75.7)	+105.3 (10721.1 to 10826.5, spread 85.5 / 67.3)

• The rows with the collector on ran with concurrent GC off. The no-store Bun.write delta is inside the spread.
• The kept context for a failed pull() costs nothing that the runs can see. The PR before that change reads 11630.1 per readableStreamToBytes stream (collector off, spread 9.7), against 11627.8 with it.
• source callbacks: 16 of 28 probe rows move (no store to construction store: 7, caller's to construction store: 9), the upload probe prints the store in 25 of 27 cells (main: 7), rows built with no store changed: 0.
• Scope sites (objdump of both release binaries): 3 new ones, in assignToStream (the inlined readDirectStream), consumeDirectStreamToArrayBuffer and JSDirectStreamSource::close. Each makes 2 out-of-line calls, the AsyncContextScope constructor and destructor, as every existing site does. callDirectPull has 1 scope on both binaries.
• Release binary .text: +1536 bytes (size -A).
• Cells per stream (heapStats().objectTypeCounts, GC off, 300 streams of 100 chunks), no AsyncLocalStorage in the process: Promise, InternalFieldTuple, AsyncContextFrame, DirectStreamSource and ReadableStream counts are equal on both binaries in 15 of 15 consumer x source cells. The Promise count of a fetch() upload of a direct stream varies from run to run on both binaries (18 to 23.5).
• Cells inside als.run(): an async-iterable body of 100 chunks allocates 101 InternalFieldTuple under Bun.write, readableStreamToBytes and Bun.serve, and 201 under a fetch() upload. On main those are 0, and the same body under getReader() allocates 102 on both binaries. They are the promise reactions of the body that now carry the store.
• sizeof(JSDirectStreamSource) 48 and sizeof(JSReadableStream) 96 on both. JSOneShotDirectSink gets a fifth internal field for the kept context: sizeof 56 to 64, and both fit the same 64-byte cell. Host functions +0. Rust files touched: 0.
• perf and valgrind are not installed in the build container. The counts come from a perf_event_open wrapper that reads the same event.

Tests

• direct-stream-contract.ts has the store shapes (direct sync pull, direct async pull, new Response(asyncGenerator).body). Each cell builds the stream in one store and consumes it one macrotask later in another. The macrotask is what separates Bun's rule from Node 26.3.0's.
• streams.test.js: +72 tests, 42 fail on main. Every shape under 18 consumers, the close() hook under a reader and a buffer consumer, close() after a failed pull(), a stream built with no context, a stream built in a second storage.
• serve-direct-readable-stream.test.ts: +22 tests, 18 fail on main. Bun.serve over http and https, a fetch() request body, a body built in a sync and an async handler, a server started inside run(), a client abort.
• module-graph-callbacks.test.ts: two new entries in its one test. A graph's own Bun.serve and fetch() upload of direct and generator bodies, and a graph-built body that the host serves. Every step checks Bun.ModuleGraph.current. The test fails on main with "ran in host".
• async-context-fetch-request-body.js, which AsyncLocalStorage-tracking.test.ts runs under bun and Node: five upload shapes at the same time, each in its own store. It fails on 1.4.0, 1.4.4 and main. It passes on 1.3.14 and on Node 24.22.1, 26.3.0, 26.12.1 and the 27 nightly. It builds and consumes in one store, so it cannot tell Bun's rule from Node's.
• Of the 62 tests that fail on main, 20 are cells where main has no store or the wrong graph. 42 are cells where main reads the caller's or the closer's store. The 42 are questions 1 to 4 above.
• Release build of main: streams.test.js 42 fail, serve-direct-readable-stream.test.ts 18 fail, module-graph-callbacks.test.ts and the fixture fail. Debug build of this PR: 799 pass and 2 skip, 197 pass, 1 pass.
• Each scope removed alone, debug build at 2b380fe: the scope in pull(stream) fails 47 tests, the scope in callDirectPull 28, the scope in close() 10, the scope in cancelFromSink() 1. The two close() after a failed pull() tests came later. They fail on a build that does not keep the released context.
• The direct-stream tests of streams.test.js (429, the new ones included) and all of serve-direct-readable-stream.test.ts pass with BUN_JSC_validateExceptionChecks=1.
• On release builds of main and of this PR, 46 related suites give equal results: the other test/js/web/streams files except streams-leak.test.ts, the other 7 module-graph suites, 11 test/js/web/fetch body and stream suites, 2 html-rewriter suites, 5 spawn-stdin suites, 6 Bun.serve stream suites, AsyncLocalStorage.test.ts, async-local-storage-thenable, bun-write, filesink, websocket-client, ws-client-compat-events. fetch.stream.test.ts has the same failure on both ("Fetch: Empty request on read stream #4500").

Not changed here

• ReadableStream.from: next() and return() enter no scope. As a fetch() body it loses the first next(). As a Bun.serve body it reads no store until the socket first pushes back.
• The generic pump does not enter the stream's context at its start (rsisBegin in BunStreamSource.cpp). That is what the two cells above need under A. A scope there also moves ReadableStream.from under Bun.write, Bun.spawn stdin and HTMLRewriter from the caller's store to the stream's, so it is a separate change.
• Sink and transformer callbacks (write, close, abort, transform, flush, cancel) enter no scope. streams: carry the async context in queued jobs and shut pipeTo() down from its own reactions #47015 covers the pipe.
• A native sink does not call the close() hook. 1.3.14 called it for a fetch() upload body.
• A body built with no store and handed to fetch() or returned from a handler inside a store sees no store.

Related

• streams: follow a promise returned by direct pull() or async-iterable next() through its own then() #46295 gives JSDirectStreamSource the same method set (hasPull, pull, cancelFromSink, private accessors) for another bug and changes no async context. The two touch the same statements, so one rebases on the other. Its new test expects ['the stream', 'the caller', 'the caller'] for a reader, readableStreamToBytes and Bun.write. With this PR that is 'the stream' three times.
• http: consolidate the open fetch, Bun.serve, node:http, node:http2 and HTTP/3 pull requests #46528 edits 6 of these C++ files for other reasons.
• streams: settle bytes()/arrayBuffer() on a direct stream when the close() hook throws and pull() completes #41472 also touches the one-shot close() hook.
• This PR replaces its first version from September, which bracketed call sites that Direct streams read from JS: own the buffer, signal backpressure, run cancel() #41757 and Bun.serve direct streams: flush on controller.close(), end the response once, call cancel() only on a client abort #41894 have since rewritten.

---

no test proof · iteration 2 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/web/streams/streams.test.js, test/js/bun/http/serve-direct-readable-stream.test.ts

[robobun]

Status: reproduced on release builds of main (99ee03e), 1.4.0 and 1.4.4. Inside AsyncLocalStorage.run(), an async generator or a type: "direct" stream reads no store as a fetch() upload body or as a Bun.serve response. 1.3.14 reads the store for the fetch() upload. The new tests fail on main (streams.test.js 42, serve-direct-readable-stream.test.ts 18, module-graph-callbacks.test.ts 1) and pass with this branch. The branch is rebuilt on current main as one commit (d75a08a).

CI on d75a08a (build 133463, finished): 180 of 181 jobs passed and no test failed on every retry. The one failed job is a darwin aarch64 - test-bun shard that stopped before any test ran, with buildkite-agent artifact download timed out after 120s for step 'darwin-aarch64-build-bun'. A retry of that job is enough.

The PR needs a maintainer's answer to the four questions in the Notes of the PR body. The sibling PR for the bundler plugin hooks is #41562.

[coderabbitai]

No actionable comments were generated in the recent review.

Recent review info

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• Source mode: Auto
• Repository: oven-sh/bun
• Branch: robobun/98827ce5/als-direct-stream-hooks
• File: .coderabbit.yaml
• Commit: d75a08a
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• Run ID: f4be786c-0922-4ae4-bc2f-cad2315adb1b

Commits

Reviewing files that changed from the base of the PR and between 2b380fe and d75a08a.

Files selected for processing: 4

• src/jsc/bindings/webcore/streams/BunStreamConsumers.cpp
• src/jsc/bindings/webcore/streams/JSDirectStreamSource.h
• src/jsc/bindings/webcore/streams/JSOneShotDirectSink.h
• test/js/web/streams/streams.test.js

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 3 remain after this review.

Walkthrough

Direct-stream pull, cancel, and close callbacks now use the applicable stream async context through shared source methods. Source clearing returns the captured context for close handling. Tests cover AsyncLocalStorage behavior across stream consumers, HTTP bodies, cancellation, and module-graph runners.

Changes

Direct stream async context

Layer / File(s)	Summary
Callback context operations src/jsc/bindings/webcore/streams/JSDirectStreamSource.h, src/jsc/bindings/webcore/streams/JSDirectStreamController.cpp, src/jsc/bindings/webcore/streams/WebStreamsInternals.h, src/jsc/STREAMS.md, src/jsc/bindings/webcore/streams/JSReadableStream.cpp	Direct-source pull, cancel, and close methods now establish the applicable async context. Clearing a source returns the stream context, which error and normal-close paths pass to the close callback. The documentation describes context capture and callback exclusions.
Direct pull and consumer integration src/jsc/bindings/webcore/streams/BunStreamSource.cpp, src/jsc/bindings/webcore/streams/JSDirectStreamController.cpp, src/jsc/bindings/webcore/streams/BunStreamConsumers.cpp, src/jsc/bindings/webcore/streams/JSOneShotDirectSink.h	Direct-stream pull and sink-cancellation paths delegate to JSDirectStreamSource. One-shot consumers pass the stream context to close handling and use the promise result from the pull method.
Stream context contract tests test/js/web/streams/direct-stream-contract.ts, test/js/web/streams/streams.test.js	Shared fixtures and tests check async context during direct-stream pulls, closes, and consumption by stream readers, HTMLRewriter, and Node stream consumers.
HTTP and runner context tests test/js/bun/http/serve-direct-readable-stream.test.ts, test/js/bun/module-graph/module-graph-callbacks.test.ts, test/js/node/async_hooks/async-context/async-context-fetch-request-body.js	Tests cover direct-stream and async-generator HTTP bodies, client aborts, module-graph runners, and async-local context during request-body uploads.

Suggested reviewers: dylan-conway, alii

Priority: Normal

Merge Risk: Minimal · up to d75a0

The identified close-hook context-loss paths are addressed; no remaining issue in the supplied evidence prevents merging after normal checks.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title names the main change: direct-source callbacks now run in the stream's AsyncLocalStorage context. The changeset matches this. It adds JSDirectStreamSource methods (pull, cancelFromSink…
Linked Issues check		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 is complete and relevant. It explains the problem, implementation, behavior changes, scope, trade-offs, performance impact, test coverage, verification results, and known limitations. …

Full details: Title check

Explanation

The title names the main change: direct-source callbacks now run in the stream's AsyncLocalStorage context. The changeset matches this. It adds JSDirectStreamSource methods (pull, cancelFromSink, close with async context), updates readDirectStream, directStreamOnClose, and the one-shot sink, and adds tests for the store behavior. The title is 88 characters, which is long but still a single readable sentence.

Full details: Description check

Explanation

The description is complete and relevant. It explains the problem, implementation, behavior changes, scope, trade-offs, performance impact, test coverage, verification results, and known limitations. Although it does not use the exact template headings, it provides the required information under equivalent sections.

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[robobun]

^{Updated 12:38 AM PT - Oct 27th, 2026}

❌ @robobun, your commit d75a08a has 1 failures in Build #133463 (All Failures):

• step failed outside runner - exit 1 on 🍎 any aarch64 - test-bun

---

🧪   To try this PR locally:

bunx bun-pr 41561

That installs a local version of the PR into your bun-41561 executable, so you can run:

bun-41561 --bun

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Additional findings (outside the current diff — GitHub can't attach inline comments there):

• 🟣 src/jsc/bindings/webcore/streams/BunStreamConsumers.cpp — The one-shot ArrayBuffer/bytes consumer's close() hook is still called without the stream's async context: jsWebStreamsHandler_boundOneShotDirectClose invokes sink->m_closeFunction at line 1709 with no StreamAsyncContextScope, so a user who stashes the controller and calls controller.close() from outside pull() (the exact pattern the new streams.test.js reader test exercises) sees als.getStore() === undefined in close() under Bun.readableStreamToArrayBuffer/toBytes while the reader path now sees the store. Fix: enter StreamAsyncContextScope(globalObject, sink->m_stream.get()) around the JSC::call here, matching callUnderlyingSourceClose and oneShotCallPull. Pre-existing, but same bug class this PR states it closes.

  Extended reasoning...

  installOneShotMethods (BunStreamConsumers.cpp:1008-1013) binds the sink's close/end methods to boundOneShotDirectClose. When the user stores the controller inside pull() and later calls controller.close() from a callback outside the pull's async continuation chain — exactly mirroring the new test at streams.test.js:601-626 for the reader path — boundOneShotDirectClose runs with whatever ambient $asyncContext the caller had. It then calls the user's underlying-source close() at line 1709 with no StreamAsyncContextScope, so AsyncLocalStorage.getStore() returns undefined rather than the constructor-time store. The PR fixed this for JSDirectStreamController::onClose/handleError via callUnderlyingSourceClose (JSDirectStreamController.cpp:443) and for oneShotCallPull (line 1031), but not for this sibling. The stream is still available via sink->m_stream and its m_asyncContext has not yet been cleared at this point (nothing on this path calls readableStreamClearSourceBarriers before line 1701), so the same one-line scope works. On base both reader-close…

  Verification: pre-existing — jsWebStreamsHandler_boundOneShotDirectClose (BunStreamConsumers.cpp:1693-1718) invokes the underlying source's close() hook at line 1709 (JSC::call(globalObject, closeFunction, callData, jsUndefined(), noArguments)) with no StreamAsyncContextScope. sink->m_closeFunction is documented as "The underlying source's optional close() method" (JSOneShotDirectSink.h:58-59),…

[robobun]

Applied the finding on the one-shot sink: jsWebStreamsHandler_boundOneShotDirectClose now runs the close() hook under StreamAsyncContextScope (commit 55873b5). Added a test in streams.test.js that stashes the controller in pull() and closes it from outside under readableStreamToArrayBuffer. It fails on 1.4.3 and passes with the branch.

[claude]

I reviewed the updated revision (including the one-shot close() coverage added in 55873b5) and didn't find any bugs. Since this threads GC-visible state through several JSC-binding call sites, a human pass is still worth having.

What was reviewed

• The asyncContext local read before directStreamControllerClearSource in handleError/onClose follows the same stack-rooted lifetime as the pre-existing underlyingSource local at those sites, and directStreamControllerClearSource does not clear m_stream itself.
• The new StreamAsyncContextScope(JSGlobalObject*, JSValue) overload keeps the empty-snapshot fast-path no-op and the destructor's m_asyncContextData guard; the delegating stream ctor now null-guards stream.
• Exception discipline at each new scope site: every wrapped JSC::call still hits RETURN_IF_EXCEPTION/RELEASE_AND_RETURN immediately after, and the one-shot close scope is block-limited so restore runs before end() is invoked.
• Tests: added to existing files, port: 0, await observable conditions (no sleeps), combined-object .toEqual, cover the negative case and the full consumer matrix (server sink, reader, readableStreamToArrayBuffer/toBytes/Response.arrayBuffer, the no-pull cancel exit).

Extended reasoning...

Overview

The PR wraps five native direct-stream user-callback entry points in the existing StreamAsyncContextScope RAII guard so pull(), close() and the no-pull cancel() path see the AsyncLocalStorage context captured at stream construction. It adds a JSValue-taking constructor overload so callers that have already cleared the stream's barriers can still enter the snapshot, and threads that snapshot as a local through handleError/onClose in JSDirectStreamController.cpp. Seven files touched: five C++ bindings files under src/jsc/bindings/webcore/streams/ and two test files.

Security risks

None identified. This is a context-propagation fix inside the streams runtime; no parsing of untrusted input, no auth/crypto/permission surface. The scope guard writes only to the per-global $asyncContext internal-field tuple and restores it in its destructor — the same mechanism already used by the default, byte, and direct-pull controllers.

Level of scrutiny

Moderate-to-high: C++ JSC bindings with GC-visible state carried across calls that re-enter JS. The specific concern I checked was whether the new JSValue asyncContext locals in handleError (line 459) and onClose (line 666) survive the intervening JS calls (rejectPromise, readableStreamError, closeDirectSinkForError, endDirectSink, finishClose) after directStreamControllerClearSource clears stream->m_asyncContext. They rely on the same conservative stack rooting the pre-existing underlyingSource local at those exact sites already relies on — the pattern is not new to this PR. I also confirmed directStreamControllerClearSource does not clear controller->m_stream, so the earlier m_stream ? … : JSValue() guard is defensive rather than covering a real null-after-clear.

Other factors

The pattern is mechanical — five call sites gain the same one-line RAII bracket that the default/byte/direct controllers already use, and the empty-snapshot path early-returns so the no-ALS common case is unchanged. Test coverage is thorough and follows repository conventions (existing files, port: 0, awaited events, combined-object assertions, negative case, full consumer matrix). The PR was updated after earlier review feedback (commit 55873b5 added the one-shot sink close() site and its test), and the last two commits are a net-zero comment edit. Deferring rather than approving because JSC bindings are the review guide's most-blocked category and a human should confirm the stack-rooted-local pattern is acceptable here as it is for the sibling underlyingSource local.

[robobun]

@Jarred-Sumner this PR needs a decision before it can merge.

#33193 made source callbacks run in the async context of the stream's construction. A direct source (a type: "direct" stream or an async-iterable body) did not follow that at three call sites, and this PR closes them. 20 of the tests that fail on main are cells where main has no store at all: a fetch() upload, a Bun.serve response, a Bun.ModuleGraph body. The other 42 replace a store that user code was in. Nobody has decided those:

1. pull() under Bun.write, Bun.spawn stdin and HTMLRewriter: the stream's store, not the caller's?
2. pull() under arrayBuffer(), bytes() and the node:stream/consumers functions arrayBuffer(), bytes(), buffer(): the stream's store, as under text() and blob() on main?
3. The close() hook: the stream's store, also when user code calls controller.close() from another store?
4. A stream built inside another storage's run() restores that whole context, so the consumer's store is not visible in pull(). Is that accepted?

For a no, I take that scope out and keep the cells where main has no store.

The same answer decides two more things. #46295 pins ['the stream', 'the caller', 'the caller'] for a reader, readableStreamToBytes and Bun.write. And a generic { pull } source under a reader reads the reader's store in Node and in 1.3.14, and the construction store since 1.4.0. The Notes of the PR body have the tables for both.

[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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Inline comments:
Review comments at @src/jsc/bindings/webcore/streams/BunStreamConsumers.cpp:
- Line 1687: Update the one-shot sink flow around oneShotDirectFail and
source->close so a pull failure does not make a later close hook receive an
empty async context: retain the captured context until the hook runs, or skip
invoking the hook after failure.

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• Source mode: Auto
• Repository: oven-sh/bun
• Branch: robobun/98827ce5/als-direct-stream-hooks
• File: .coderabbit.yaml
• Commit: 2b380fe
• Layers: Repository YAML
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Commits

Reviewing files that changed from the base of the PR and between b12533f and 2b380fe.

Files selected for processing: 12

• src/jsc/STREAMS.md
• src/jsc/bindings/webcore/streams/BunStreamConsumers.cpp
• src/jsc/bindings/webcore/streams/BunStreamSource.cpp
• src/jsc/bindings/webcore/streams/JSDirectStreamController.cpp
• src/jsc/bindings/webcore/streams/JSDirectStreamSource.h
• src/jsc/bindings/webcore/streams/JSReadableStream.cpp
• src/jsc/bindings/webcore/streams/WebStreamsInternals.h
• test/js/bun/http/serve-direct-readable-stream.test.ts
• test/js/bun/module-graph/module-graph-callbacks.test.ts
• test/js/node/async_hooks/async-context/async-context-fetch-request-body.js
• test/js/web/streams/direct-stream-contract.ts
• test/js/web/streams/streams.test.js

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 0 remain after this review.

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline findings, I also checked the refactor's ordering and lifetime edges in this push: handleError and onClose read m_asyncContext via directStreamControllerClearSource before readableStreamError/readableStreamClearSourceBarriers drop it, so the close() hook gets the construction snapshot on both paths; the stream-gone branch in oneShotDirectClose passes an empty JSValue, which AsyncContextScope treats as a no-op; both callers of the stream-taking pull() overload pass a non-null stream (the scope dereferences it); and no caller outside JSDirectStreamSource still uses the now-private accessors, and the new WebStreamsInternals.h include in the header does not cycle. The behavior-change questions the description poses for a maintainer are design calls this review does not settle.

Extended reasoning...

The change centralizes direct-source callback invocation in JSDirectStreamSource so pull/cancel/close run under the stream's captured async context, touching four streams .cpp/.h files plus tests and STREAMS.md; it touches no auth, crypto, or injection surface. It is a behavior change in which AsyncLocalStorage store user callbacks observe, and the PR itself lists open questions for a maintainer, so a human decision is required regardless of the inline findings.

[claude]

The new commit addresses the one-shot close() hook context I raised earlier, and this pass found no bugs in the C++ changes; a maintainer still needs to answer the behaviour questions in the description (which store pull()/close() see under Bun.write, Bun.spawn stdin, HTMLRewriter, arrayBuffer()/bytes()), since that is a user-visible change rather than a code defect.

What was reviewed:

• JSOneShotDirectSink's new ReleasedAsyncContext field: covered by visitInternalFieldsHidden and analyzeHeap; errorStream stashes m_asyncContext before readableStreamError clears it and only while the source is still held, and takeCloseHookAsyncContext clears it on use.
• Exception handling in the new pull()/cancelFromSink()/close() paths: every JSC::call is followed by RETURN_IF_EXCEPTION or RELEASE_AND_RETURN; AsyncContextScope tolerates an empty snapshot and restores on throw via its destructor.
• Refactor equivalence: callDirectPull still throws the same TypeError when the source or its pull is missing; directStreamOnClose keeps the sinkClosed gate and no-cancel-function early return; the three duplicated unlock-and-error sites now share errorStream with the same m_lockedWithoutReader/state ordering.
• No stale callers of the now-private pullFunction/cancelFunction/closeFunction/thisValue or of the old 2-argument close()/void directStreamControllerClearSource remain.

Extended reasoning...

The change reworks the direct-source call sites in src/jsc/bindings/webcore/streams (JSDirectStreamSource.h, JSDirectStreamController.cpp, BunStreamSource.cpp, BunStreamConsumers.cpp, JSOneShotDirectSink.h) so every pull/cancel/close callback of a type:"direct" source runs in the stream's captured AsyncContext, plus tests across streams.test.js, serve-direct-readable-stream.test.ts, module-graph-callbacks.test.ts and a new node-parity fixture. It touches no auth, crypto or input-parsing surface; the sensitive surface is GC rooting of a new internal field and exception checks around user-JS calls, both of which check out. Deferral rather than approval is because this is a deliberate, user-visible behaviour change in which AsyncLocalStorage store direct-source callbacks observe under several consumers, and the author explicitly asks a maintainer to confirm those semantics; the hunt itself ran dry with no defects.