René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"stream/iter: Share \"drop-newest\" can eagerly drain the upstream source","articleBody":"### Version\n\nmain\n\n### Platform\n\n```text\nN/A\n```\n\n### Subsystem\n\nstream\n\n### What steps will reproduce the bug?\n\n```js\nimport { share } from 'node:stream/iter';\n\nlet batchesYielded = 0;\n\nasync function* source() {\n  for (let i = 0; i \u003c 7; i++) {\n    batchesYielded++;\n    console.log('source yielded', i);\n    yield [new Uint8Array(16_384).fill(i)];\n  }\n}\n\nconst shared = share(source(), {\n  budget: 16_384,\n  backpressure: 'drop-newest',\n});\n\nconst fast = shared.pull()[Symbol.asyncIterator]();\nconst stalled = shared.pull();\n\nlet result = await fast.next();\nconsole.log('after first next', {\n  done: result.done,\n  firstByte: result.value?.[0][0],\n  batchesYielded,\n});\n\nconst second = fast.next();\n\nawait new Promise(setImmediate);\nconsole.log('batches after one event-loop turn:', batchesYielded);\n\nshared.cancel();\nconsole.log('second next:', await second);\n\nvoid stalled;\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\nsource yielded 0\nafter first next { done: false, firstByte: 0, batchesYielded: 1 }\nsource yielded 1\nbatches after one event-loop turn: 2\nsecond next: [Object: null prototype] { done: true, value: undefined }\n```\n\nThe second `fast.next()` should discard only one upstream result and then wait for buffer space. `shared.cancel()` subsequently settles that pending call so the repro exits cleanly.\n\nFrom [§13.2.2: Share buffering and backpressure](https://iter-streams.proposal.wintertc.org/#share-backpressure):\n> “With `\"drop-newest\"`, the upstream pull result is discarded.”\n\n### What do you see instead?\n\n```console\nsource yielded 0\nafter first next { done: false, firstByte: 0, batchesYielded: 1 }\nsource yielded 1\nsource yielded 2\nsource yielded 3\nsource yielded 4\nsource yielded 5\nsource yielded 6\nbatches after one event-loop turn: 7\nsecond next: [Object: null prototype] { done: true, value: undefined }\n```\n\nOne `fast.next()` pulls and discards all six remaining batches while the buffer is full.\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-08-16T21:27:46Z","url":"https://github.com/nodejs/node/issues/65337"}