René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"stream/iter: toWritable() duplicates writes when writeSync() returns false after accepting chunk","articleBody":"### Version\n\n26.1.0\n\n### Platform\n\n```text\nmacOS 26.5.0\n```\n\n### Subsystem\n\nstream\n\n### What steps will reproduce the bug?\n\n```js\nimport { push, text, toWritable } from 'node:stream/iter';\n\nconst { writer, readable } = push({ highWaterMark: 1, backpressure: 'block' });\nconst writable = toWritable(writer);\n\nawait new Promise((resolve, reject) =\u003e {\n  writable.write('a', (err) =\u003e err ? reject(err) : resolve());\n});\n\nwritable.write('b');\nwritable.end();\n\nconsole.log(await text(readable)); // abb, expected ab\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways\n\n### What is the expected behavior? Why is that the expected behavior?\n\n```console\nab\n```\n\nThe adapter should not write the same chunk twice; the repro should output `ab`.\n\n### What do you see instead?\n\n```console\nabb\n```\n\n`toWritable()` retries via `writer.write()` when `PushWriter.writeSync()` returns false, even though `PushWriter` already accepted the chunk under `backpressure: 'block'`, producing `abb`.\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-05-16T02:18:40.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/63359/node/issues/63359"}