retrieving chain data in Mono/Flux error handlers

I would like to be able to use chain data in an error handler. Condensed my issue looks like this:

request.bodyToMono(MyRequest.class)
.map(dosomestuff)
.onErrorResume(dosomeerrorhandling)

request is a ServerRequest. In the request message is a requestId field. I don't know the requestId until the message has been extracted. The message is then processed (dosomestuff) during which an exception may occur. That will be "caught" by onErrorResume and at that point I'd like to know the requestId.

I don't think I can put the requestId into the Mono context as it's not available until after the Mono has started. I could write a custom exception and place the requestId and that, but I'm concerned the extra exception handling will get messy.

Any other suggestions appreciated. Perhaps I'm just not thinking about the problem in the right way? - it's been a long day.

A possible approach:

    request.bodyToMono(MyRequest.class).flatMap(request -> Mono.just(request)
            .map()
            // whatever
            .onErrorResume(/* any lambda, the request is available there */)
    );