$ the-wire · showcase
Undici unrefs keep h2 WebSockets alive, adds private-field brand checks
By RepoJournal · Filed · About Node.js · Composed from the cited sources · methodology
Undici fixed an HTTP/2 WebSocket bug where the session was unref'd while a stream was still open, causing programs to exit with status 0 right after open, and moved brand checks to private fields.
Undici's HTTP/2 path no longer unrefs a session that still has open streams [1]. Once the h2 WebSocket handshake completed, `onUpgradeResponse()` completed the request and resumed the client; because the queue was empty (`client[kSize] === 0`), `resumeH2()` unref'd the session even though the WebSocket was still using that stream (`session[kOpenStreams]` was still 1). A program with nothing else holding the event loop therefore exited with status 0 right after `open`. The fix adds `session[kOpenStreams] === 0` to the unref condition [2].
The same PR body states the precondition plainly: "Once the h2 WebSocket handshake completes, `onUpgradeResponse()` completes the request and resumes the client" [1]. That is the moment the queue drains and the old unref logic fired.
Separately, KhafraDev moved undici's brand checks to private fields [3], inspired by nodejs/node#65846, with the change landing as commit 3c3db8d [4]. Brand checks now rely on private fields rather than the previous mechanism.
On the reliability desk, the Node.js GitHub Bot added the report for 2026-09-11 [5], a routine scheduled entry.
Action items
- → Upgrade undici to pick up the h2 WebSocket unref fix if your services open WebSockets over HTTP/2 nodejs/undici [plan]
- → Monitor the private-field brand check change for any downstream compatibility impact nodejs/undici [monitor]
References
- [1] fix(h2): do not unref a session with open streams ↗ nodejs/undici
- [2] fix(h2): do not unref a session with open streams (#5782) ↗ nodejs/undici
- [3] use private fields for brand checks ↗ nodejs/undici
- [4] use private fields for brand checks (#5792) ↗ nodejs/undici
- [5] Add report for 2026-09-11 ↗ nodejs/reliability
