Fix ReadableStream controller double-close crash #940
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Guard against calling controller.close() when the stream has already been closed by an external cancellation. This can happen when the SDK cancels the stream before the underlying Node stream emits its 'end' event. - Add `closed` flag to track controller state - Guard all controller operations with closed check - Add `cancel()` callback to handle external cancellation - Properly destroy the Node stream on cancellation
🎭 Playwright E2E Test Results✅ 24 passed Details24 tests across 3 suites 📊 View Detailed HTML Report (download artifacts) |
cliffhall
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Nov 28, 2025
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Seems like robust stream handling.
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Summary
Motivation and Context
When the server disconnects (as allowed by SEP-1699 for SSE polling), the fetch response body stream gets cancelled. This closes the ReadableStream controller, but the underlying Node PassThrough stream still emits its "end" event, which then tries to close the already-closed controller.
The fix:
closedflagcancel()callback to properly clean up the Node streamWith this fix + JSON fix in modelcontextprotocol/typescript-sdk#1184 the inspector works again:
How Has This Been Tested?
Tested locally with the everything-server via Streamable HTTP transport.
Breaking Changes
None
Types of changes
Checklist