Fix two WebSocket API bugs #3371
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…s already in progress" If writing to the underlying KJ WebSocket throws an exception or is canceled, then the WebSocket is left in an inconsistent state and no further messages can be sent. All further attempts to send messages will throw the above exception. In the WebSocket workerd API code, upon catching an exception from a write, we normally set `outgoingAborted = true`, which causes us to drop all future writes on the floor. The problem is, we weren't actually setting `outgoingAborted = true` until `reportError()` was invoked, which is a few microtasks after the point where `pump()` ended. In the meantime, a new `send()` could be invoked, starting a fresh `pump()`, which would then fail with the `expected !currentlySending` error. To fix the problem, we must set `outgoingAborted = true` promptly on exit from `pump()`. I was unable to reproduce the problem in a test, though, because the WebSocket API code also listens on the underlying WebSocket's `whenAborted()` and, when it resolves, immediately sets `outgoingAborted = true`. There must be some case where `send()` throws but `whenAborted()` doesn't actually fire, but I can't think of what that would be. Nevertheless, it is quite clear that we need to set `outgoingAborted = true` promptly when a send fails, before anyone else could possibly begin another pump. So, this commit does that.
jasnell
approved these changes
Jan 20, 2025
Per the comment: At the end of pump(), while writing out pending auto-response messages, it's possible new regular messages could be queued concurrently. If we don't check for that, they could be discarded without actually being sent. This is probably extremely unlikely and I have no evidence that it has ever happened. I noticed the problem while reading the code.
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One is a spurious (and prolific) error appearing in our sentry.
The other is a serious issue that could cause messages to be dropped when using auto-responses, but is probably exceedingly rare.