How to return a custom NextResponse when error handling via instrumentation onRequestError?

[thomasoreilly]

Looking for guidance on how to return a custom NextResponse when handling errors with the onRequestError callback.
If I catch the error in the route handler to return a custom NextResponse then the onRequestError function is never called.

[Lochy2000]

The problem is one of execution flow in Next.js:

If your route handler uses a try...catch block to return an error, Next.js sees this as a handled execution.

The onRequestError callback only fires on a truly uncaught exception that bubbles up to the network layer.

trigger onRequestError while controlling the response:

Stop using return NextResponse.json({ error: '...' }, { status: 400 }) inside your catch block. This prevents onRequestError from ever running.

Instead, create and throw a custom error inside your route handler's catch block. This ensures an uncaught exception fires the onRequestError function.

In your onRequestError function, check the type of the thrown error and return the custom NextResponse there.

[Lochy2000]

yes this is more a workaround. But you could try to seperate concerns here. Use onRequestError only for true, uncaught server crashes, and handle expected errors manually.

[thomasoreilly]

Yeah that return type is void, this solution didn't work for me. I'm on v15.5.4

[thomasoreilly]

I'll go with the approach that onRequestError is is a failsafe for uncaught errors 👍

[icyJoseph]

You could still report against another service, etc, you know like, inside onRequestError, you likely have some handling, which, if correctly parametrized could be dropped in to the Route Handler, to process errors you explicitly catch.

[thomasoreilly]

Yes, I'm going to abstract a handler to handle both, it's being used to report errors to otel collector.