preHandler vs onRequest

[gajus]

It is not entirely clear when one would use one or another.

[Eomm]

The main difference is that the onRequest has not the body payload parsed, the preHandler has it
https://www.fastify.io/docs/latest/Reference/Lifecycle/#lifecycle

So, do you need to manipulate the body? Use preHandler
Do you need to know that a request has come into the server? Use onRequest

[steven-gpa]

I was analyzing the https://github.com/fastify/fastify-auth package, but the code example (see below) of the implementation was passing the fastify.auth in the preHandler property, so based on the above scenario, it will be better to implement the fastify.auth in the onRequest property.

fastify.route({
  method: 'GET',
  url: '/run-all',
  preHandler: fastify.auth([ // ---> onRequest rather than preHandler
    (request, reply, done) => { console.log('executed 1'); done() },
    (request, reply, done) => { console.log('executed 2'); done() },
    (request, reply, done) => { console.log('executed 3'); done(new Error('you are not authenticated')) },
    (request, reply, done) => { console.log('executed 4'); done() },
    (request, reply, done) => { console.log('executed 5'); done(new Error('you shall not pass')) }
  ], { run: 'all' }),
  handler: (req, reply) => { reply.send({ hello: 'world' }) }
})

[Uzlopak]

The problem is, that not all authentication methods are only based on http headers. E.g. OAuth2 needs the body. So for that the body has to be parsed.

[steven-gpa]

Gotcha, thanks again for the prompt response 🙇

[Uzlopak]

Created fastify/fastify-auth#180 ;)

[steven-gpa]

Awesome!! 🕺 , thanks @Uzlopak !! 🥇