How to detect requests that did send a response

[jeroen]

I would like to detect a bug in my express 5 app where a request has been handled by express, but it somehow did not send a response to the client. This results in leaving the client hanging and is difficult to debug.

A typical scenario in which this occurs is when a router code does something async in a promise, but you forgot to return this promise in the router. In this case, when the promise gets rejected, express will not catch it and send a error message to the client.

What I need is a hook or type of middleware (postware?) that always runs after express is done with the request, including waiting for a promise returned by the router to get settled and running the error handler on rejection. Once all this has completed I want to run a final check if anything has actually been sent to the client.

I understand this does not work for express applications in general, because it requires routers always return the promise that will sending a response, which express does not require. But I think it is good practice and it will make it possible to use such a postware handler.