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stream/iter: falsy cancellation reasons become clean EOF in broadcast and share #64704
Description
Version
main
Platform
macOS 26.5.2
Subsystem
stream
What steps will reproduce the bug?
import { broadcast, share, shareSync } from 'node:stream/iter';
const reasons = [0, '', false, null];
async function run(name, make) {
for (const reason of reasons) {
const { stream, iterator } = make();
stream.cancel(reason);
try {
console.log(name, JSON.stringify(reason), await iterator.next());
} catch (error) {
console.log(name, JSON.stringify(reason), 'rejected:', error);
}
}
}
await run('broadcast', () => {
const { broadcast: stream } = broadcast();
return {
stream,
iterator: stream.push()[Symbol.asyncIterator](),
};
});
await run('share', () => {
const stream = share([]);
return {
stream,
iterator: stream.pull()[Symbol.asyncIterator](),
};
});
await run('shareSync', () => {
const stream = shareSync([]);
return {
stream,
iterator: stream.pull()[Symbol.iterator](),
};
});How often does it reproduce? Is there a required condition?
Always
What is the expected behavior? Why is that the expected behavior?
async next() should reject—and sync next() should throw—with the exact supplied reason, consistent with §13.1.4 Broadcast.cancel() and the corresponding §13.2.4 Share.cancel().
If reason is provided, each consumer sees it as an error; otherwise they see clean completion.
What do you see instead?
broadcast 0 { done: true, value: undefined }
broadcast "" { done: true, value: undefined }
broadcast false { done: true, value: undefined }
broadcast null { done: true, value: undefined }
share 0 { done: true, value: undefined }
share "" { done: true, value: undefined }
share false { done: true, value: undefined }
share null { done: true, value: undefined }
shareSync 0 { done: true, value: undefined }
shareSync "" { done: true, value: undefined }
shareSync false { done: true, value: undefined }
shareSync null { done: true, value: undefined }every falsy reason is converted into clean completion for consumers that had not called next() before cancellation.
Additional information
No response
Activity
theSnackOverflow commentedon Jul 31, 2026
I'd like to work on this. Here's what I found while tracing it:
cancel()stores falsy reasons correctly — it guards onreason !== undefined:node/lib/internal/streams/iter/broadcast.js
Lines 240 to 242 in 598693b
But every read site tests the stored value for truthiness, so a falsy reason is invisible and the consumer falls through to the clean-completion path instead:
broadcast.js: L179, L196, L341share.js(Share): L132, L144, L170, L179, L263share.js(SyncShare): L473, L538The obvious fix (
#error !== null) doesn't work, because those fields initialize tonull— socancel(null)would still be indistinguishable from "never cancelled".push.jsalready solves exactly this problem with a symbol sentinel:Would applying that same sentinel pattern to
Broadcast,Share, andSyncSharebe the direction you'd want here? Happy to open a PR if so.trivikr commentedon Jul 31, 2026
A fix has been up at #64705 for a week
stream: preserve falsy cancellation reasons
stream: preserve falsy cancellation reasons
stream: preserve falsy cancellation reasons
stream: preserve falsy cancellation reasons