Allow hooking into responses

[pi0]

Related: unjs/nitro#1396

Currently, it is not possible to hook into responses (that are handled by h3 not directly with res.end). In order to do this, we might refactor app.ts and allow hooking into directly returned responses and allow to hook into using custom callback onBeforeResponse(event, { body }).

This can be later used by higher order frameworks to support custom response rewrite handling and logging.

At this point, i also like to gether some common usecase ideas before moving forward (mainly because it also adds some overhead even if callback is not used)

[Hebilicious]

I think the most common use cases for this type of feature would be custom logging/metrics. I could also see for applications that are not super performant sensitive having some kind of db read/http request to extend the response after it is handled by the framework.
However there might be some overlap with scoped middlewares.

[emdede]

Just had this today and my use-case would be custom error messages per "middleware" which afaik is currently not possible. Please correct me if I'm wrong.

router.post('/', (event) => somethingThatPotentiallyErrors())

router.onBeforeResponse((event, { body }) => {
  if (body instanceof Error) return { status: 'error', message: body.message }
  return { status: 'ok', ...body }
}

Catching the error in this scenario is not clear to me at the moment. I assume H3 would have already transformed the error at this point.

[tobychidi]

It is needed for stuff like treblle-utils by treblle.com . Then I feel like we are missing out? Cuz there is a solution for this in Express and Fastify.

[Hebilicious]

It is needed for stuff like treblle-utils by treblle.com . Then I feel like we are missing out? Cuz there is a solution for this in Express and Fastify.

I agree that this feature is needed, however looking at Trebble docs (for the first time); based on the Koa integration looks, I think its possible to integrate it with h3 without hooking into the response.

[pi0]

Thanks for the feedbacks @Hebilicious, @emdede and @tobychidi ❤️ 3 hooks will be supported in next release (see #482)