Fix preParsing is undefined will error

[fuergaosi233]

if request[kRouteContext].preParsing is error, the framework will error.

Checklist

I don't think this change needs testing 🤔

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Uzlopak]

Well we thought we fixed that issue already. So please provide a test.

[fuergaosi233]

I can only find this problem in other projects, but I don't know what causes this to be undefined, so should I provide you with my local project?

[leandroandrade]

If you provide a simple execution example will help to investigate this issue.

[metcoder95]

Would be extremely helpful to have a reproduction from your side. I tried with a very basic case and the behavior was expected, see the following snippet:

const fastify = require('./fastify')({ logger: true })

fastify.get(
  '/undefined',
  {
    preParsing: undefined // same as none hook registered
  },
  async (request, reply) => {
    reply.send('hello world')
  }
)

fastify.get(
  '/null',
  {
    preParsing: null // throws FST_ERR_HOOK_INVALID_HANDLER
  },
  async (request, reply) => {
    reply.send('hello world')
  }
)

fastify
  .inject({
    method: 'GET',
    url: '/undefined'
  })
  .then(res => {
    console.log(res.raw.req.url)
    console.log(res.body) // hello world
  })

Though, I was able to spot an error when trying to register lifecycle/application hooks by using Fastify#addHook method, as we're not checking non-existent values, and goes directly against the Object#constructor method, see the following snippet:

const fastify = require('./fastify')({ logger: true })

fastify.addHook('onReady', null)
fastify.addHook('onResponse', undefined)

Any of those throws the following error:

/Users/metcoder/Documents/Workspace/MetCoder/Fastify/fastify.js:577
      if (fn.constructor.name === 'AsyncFunction' && fn.length === 3) {
             ^

TypeError: Cannot read properties of null (reading 'constructor')
    at Object.addHook (/Users/metcoder/Documents/Workspace/MetCoder/Fastify/fastify.js:577:14)
    at Object.<anonymous> (/Users/metcoder/Documents/Workspace/MetCoder/Fastify/playground.js:4:9)
    at Module._compile (node:internal/modules/cjs/loader:1105:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47

I'll write a proper error reproduction + tests to open a PR for the latest error

[github-actions]

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