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fix(core): properly propagate stream cancellation on disconnect (#1349) #1354

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fix(core): properly propagate stream cancellation on disconnect (#1349) #1354

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2ac57d3
fix(core): propagate stream cancellation to avoid leaking listeners
Sigmabrogz Mar 12, 2026
8b9ba82
Merge branch 'main' into fix-1349-stream-cancel
Sigmabrogz Mar 12, 2026
52c3fd0
test(core): add flushablePipe abort test
Mar 14, 2026
3b0cf54
test(core): fix unit test assertions for flushablePipe
Mar 17, 2026
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13 changes: 12 additions & 1 deletion packages/core/src/flushable-stream.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -219,7 +219,12 @@ export async function flushablePipe(

// Read from source - don't count as pending op since we're just waiting for data
// The important ops are writes to the sink (server)
const readResult = await reader.read();
const readResult = await Promise.race([
reader.read(),
writer.closed.then(() => {
throw new Error('Writable stream closed prematurely');
}),
]);

// Check if stream has ended (e.g., due to error in another path) before processing
if (state.streamEnded) {
Expand Down Expand Up @@ -257,8 +262,14 @@ export async function flushablePipe(
// while other callers may depend on this rejection. Some known callers
// explicitly ignore this rejection (`.catch(() => {})`) and rely solely
// on `state.reject(err)` for error handling.

// Attempt to cancel the upstream reader so the source knows it should stop generating data.
reader.cancel(err).catch(() => {});
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@VaguelySerious VaguelySerious Mar 13, 2026

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Should all of these .catch(() => {}); statements instead log a warning? Presumably closing should work in most cases, and we'd like to know if it's not possible to close cleanly

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@VaguelySerious VaguelySerious Mar 16, 2026

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Let's log a warning for any cancel failures

throw err;
} finally {
// If we're exiting normally but the stream was externally ended before completion,
// we should cancel the reader to notify the source.
reader.cancel().catch(() => {});
reader.releaseLock();
writer.releaseLock();
}
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6 changes: 6 additions & 0 deletions packages/core/src/serialization.ts
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Expand Up @@ -445,6 +445,12 @@ export class WorkflowServerReadableStream extends ReadableStream<Uint8Array> {
controller.enqueue(result.value);
}
},
cancel: async (reason) => {
if (this.#reader) {
await this.#reader.cancel(reason).catch(() => {});
this.#reader = undefined;
}
},
});
}
}
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