René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"stream/iter: pipeToSync() ignores writeSync() backpressure and overcounts bytes","articleBody":"### Version\n\n26.2.0\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 { setTimeout as delay } from 'node:timers/promises';\nimport { pipeToSync, push } from 'node:stream/iter';\n\nconst decoder = new TextDecoder();\nconst { writer, readable } = push({ highWaterMark: 1 });\n\nconst total = pipeToSync(['a', 'b'], writer, { preventClose: true });\n\nconst iter = readable[Symbol.asyncIterator]();\nconst first = await iter.next();\n\nconst second = await Promise.race([\n  iter.next().then((r) =\u003e r.done ? '\u003cdone\u003e' : decoder.decode(r.value[0])),\n  delay(20, '\u003cno second chunk\u003e'),\n]);\n\nawait iter.return?.();\n\nconsole.log(`pipeToSync returned: ${total}`);\nconsole.log(`first buffered chunk: ${decoder.decode(first.value[0])}`);\nconsole.log(`second buffered chunk: ${second}`);\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\npipeToSync returned: 1\nfirst buffered chunk: a\nsecond buffered chunk: \u003cno second chunk\u003e\n```\n\n`pipeToSync()` should throw or otherwise signal that the second sync write was not accepted. It should not count bytes for a chunk when `writeSync()` or `writevSync()` returns false without accepting the data.\n\n### What do you see instead?\n\n```console\npipeToSync returned: 2\nfirst buffered chunk: a\nsecond buffered chunk: \u003cno second chunk\u003e\n```\n\n`pipeToSync()` reports that 2 bytes were written even though the strict `push({ highWaterMark: 1 })` writer only accepted `a`. The failed `writeSync('b')` return value is ignored, so data is silently dropped and byte accounting is incorrect.\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-05-25T16:27:33.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/63562/node/issues/63562"}