Add hook to access response in instrumentation-undici

[mydea]

It would be great to have a hook that allows us access to request & response in instrumentation-undici.

Would you be open to add support for this? If so, I could work on a PR adding this. I am thinking about something like this which exists in instrumentation-http:

applyCustomAttributesOnSpan: (
  span,
  request,
  response,
) : void

Alternatively, if we could make certain things protected (e.g. subscribeToChannel) we could also extend the instrumentation class and add such things ourselves. If that's preferable I could also PR this?

[timfish]

It doesn't look like it would be that easy to add a applyCustomAttributesOnSpan hook that's called as late in the http instrumentation.

Using the undici:request:headers diagnostic channel event, we could add:

{
  responseHook?: (span: Span, request: UndiciRequest, response: UndiciResponse): void;
}

[mydea]

yeah, this is basically what I would have thought of :) that would be great!

[cpatti97100]

would this request be related to #2179?

[mydea]

would this request be related to #2179?

Probably, it's basically a generic hook that gives access to both request and response at the same time, which can be used for more specialised needs.