René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"stream/web: TransformStream race can throw internal \"transformAlgorithm is not a function\"","articleBody":"### Version\n\n- v22.9.0\n- v24.10.0\n\n### Platform\n\n```txt\nDarwin MacBook-Air.local 25.3.0 Darwin Kernel Version 25.3.0: Wed Jan 28 20:49:24 PST 2026; root:xnu-12377.81.4~5/RELEASE_ARM64_T8132 arm64\n```\n\n### Subsystem\n\nstream/web (TransformStream)\n\n### What steps will reproduce the bug?\n\nRun:\n\n```js\nimport { TransformStream } from 'node:stream/web';\nimport { setTimeout } from 'node:timers/promises';\n\nconst stream = new TransformStream({\n  transform(chunk, controller) {\n    controller.enqueue(chunk);\n  },\n});\n\n// Important for reproducing this race consistently in my environment.\nawait setTimeout(500);\n\nconst reader = stream.readable.getReader();\nconst writer = stream.writable.getWriter();\n\n// Release backpressure.\nconst pendingRead = reader.read();\n\n// Simulate client disconnect / shutdown.\nconst pendingCancel = reader.cancel(new Error('client disconnected'));\n\n// Late write racing with cancel.\nconst pendingLateWrite = writer.write('late-write');\n\nconst results = await Promise.allSettled([\n  pendingRead,\n  pendingCancel,\n  pendingLateWrite,\n]);\n\nconsole.log(results);\n```\n\n### How often does it reproduce? Is there a required condition?\n\nIntermittent race. In my environment, adding `await setTimeout(...)` before acquiring reader/writer is required for reliable reproduction.\n\n### What is the expected behavior? Why is that the expected behavior?\n\nNo internal implementation TypeError should leak.\n\nMy understanding is that, when shutdown starts concurrently (cancel/abort/close paths), pending or in-flight `write()` operations are expected to settle coherently with stream shutdown semantics (resolve/reject according to stream state), rather than failing because an internal algorithm slot became non-callable.\n\n### What do you see instead?\n\n`pendingLateWrite` can reject with an internal error:\n\n```txt\nTypeError: controller[kState].transformAlgorithm is not a function\n    at transformStreamDefaultControllerPerformTransform (node:internal/webstreams/transformstream:527:37)\n    at transformStreamDefaultSinkWriteAlgorithm (node:internal/webstreams/transformstream:573:10)\n    ...\n```\n\n### Additional information\n\nThis looks like a race where:\n\n1. [`transformStreamDefaultSinkWriteAlgorithm`](https://github.com/nodejs/node/blob/main/lib/internal/webstreams/transformstream.js#L551) has accepted/scheduled a write,\n2. shutdown starts (`readable.cancel()` / `writable.abort()` / close path),\n3. [`transformStreamDefaultControllerClearAlgorithms`](https://github.com/nodejs/node/blob/main/lib/internal/webstreams/transformstream.js#L489) clears `transformAlgorithm`,\n4. pending write continues and reaches [`transformStreamDefaultControllerPerformTransform`](https://github.com/nodejs/node/blob/main/lib/internal/webstreams/transformstream.js#L525).\n\nRelated discussions:\n- https://github.com/whatwg/streams/issues/1296\n- https://github.com/vercel/next.js/discussions/75995\n- https://github.com/sourcebot-dev/sourcebot/issues/170\n\n","author":{"url":"https://github.com/y-hsgw","@type":"Person","name":"y-hsgw"},"datePublished":"2026-02-28T06:30:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/62036/node/issues/62036"}