Out schema for non 2xx response about fastify

[mcollina]

@delvedor I'm +1 on the idea.

[delvedor]

Since we must support also swagger, I think the best (and more elegant) solution will be something like:

out: {
  '200': {},
  '500': {}
}

And so on.
Maybe we can rename out in response.
Since we are building the schema at compilation time we can check if the user is passing directly the schema or the different status codes, and create the function(s) accordingly.
An even better solution could be:

out: {
  '2xx': {},
  '4xx': {},
  '404': {}
  '5xx': {}
}

[delvedor]

My bad, I thought that use numbers as key in objects was incorrect, but I was wrong :D

[delvedor]

Hi, thank you for the interest!
The out schema is not applied to all the routes, but only in the routes where you pass it as parameter.
Example:

fastify.get('/no-schema', (req, reply) => {
  reply.send({ hello: 'world' })
})

fastify.get('/schema', {
  out: {
    type: 'object',
    properties: {
      hello: { type: 'string' }
    }
  }
}, (req, reply) => {
  reply.send({ hello: 'world' })
})

The out schema is applied in every case, not matter of the status code and there is no way to set it for all the routes. However, you could store it in a variable and pass it to all the routes.

const schema = {
  out: {
    type: 'object',
    properties: {
      hello: { type: 'string' }
    }
  }
}

fastify.get('/route', schema, (req, reply) => {
  reply.send({ hello: 'world' })
})

fastify.get('/other-route', schema, (req, reply) => {
  reply.send({ hello: 'world' })
})

If you want to use an out schema for the "correct" response and support also a completely different object, you must use the .serializer method of reply, that forces reply to use a custom serializer.
Example:

const schema = {
  out: {
    type: 'object',
    properties: {
      hello: { type: 'string' }
    }
  }
}

fastify.get('/route', schema, (req, reply) => {
  if (someError) {
    reply
      .serializer(JSON.stringify)
      .send({ error: 'message' })
    return
  }
  reply.send({ hello: 'world' })
})

---

@mcollina could be a nice idea support different output schema based on the status code, it will be useful for the swagger generator as well :)

[allevo]

Maybe a replacement for default serializer is enough.

I'd like to be sure to have all my 5xx and 4xx response bodies with the same structure.

[allevo]

Can we declare a specification for this issue ?

Maybe the out key could be used only for 200 and, if specified, the out500 or out5xx could be used for 5xx responses.

In that way, the back compatibility is kept.

Let me know if this approach is fine for you

[mcollina]

@allevo the approach is fine for me.. @delvedor what do you think?

[mcollina]

I'm 👍 with the change, the only things I do not like is that we need ', do you see any way around that?

[mcollina]

@allevo, would you like to fire up a PR?

[allevo]

@mcollina I'll start as soon as possible

[delvedor]

Closed in #96.