Detect aborted requests


We are trying to detect requests where the client closes the connection.
We haven’t found any information of events being triggered when the connection is closed and it does in most cases not seem to throw any errors (guess the data is written to the TransformStream which is waiting for it to drain before accepting more bytes?).
We tried hooking a timer to event.waitUntil and can see that no bytes are being sent, but we can’t find anyway to be certain that the connection to the client is closed or if it’s just keeping the connection open.
Can you think of anyway to get this information?