preHandler called twice when rejecting CORS

[10xLaCroixDrinker]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.25.2

Plugin version

8.5.0

Node.js version

20.10.0

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

13.6.1

Description

When the delegator returns a false origin, the preHandler hook is called twice for the request

Steps to Reproduce

I've created a sample application that reproduces the issue:

https://github.com/10xLaCroixDrinker/fastify-cors-issue-290

There are instructions in the README.

Expected Behavior

preHandler hooks should only be called once for a single request.

[mcollina]

That is expected because that preHandler is applied to your not found handler as well.

This should solve it:

'use strict'

const Fastify = require('fastify')
const fastifyCors = require('@fastify/cors');
const hookLoggingPlugin = require('./hookLogging');

(async function startServer () {
  const fastify = Fastify({
    logger: {
      transport: {
        target: 'pino-pretty',
      },
    },
  });
  fastify.register(hookLoggingPlugin);

  fastify.register(async function (fastify) {

  fastify.register(fastifyCors, {
    // hook: 'preHandler',
    delegator: (req, callback) => {
      const corsOptions = { origin: false };
      if (/^success$/m.test(req.headers.origin)) {
        corsOptions.origin = true;
      }
      callback(null, corsOptions);
    },
  });

  fastify.get('/', async function (request, reply) {
    return reply.code(200).type('text/plain').send('Hello world');
  })

  fastify.post('/', async function (request, reply) {
    return reply.code(200).type('text/plain').send('Hello world');
  })

  fastify.setNotFoundHandler(async (_request, reply) => {
    reply.code(404).type('text/plain').send('Not found');
  });

  })
  
  return fastify.listen({ port: 3000 });
})();

[10xLaCroixDrinker]

That did not resolve it

[10xLaCroixDrinker]

Interestingly, this does not happen when using fastify-cli

[mcollina]

Oh, I've

This should solve it:

```js
'use strict'

const Fastify = require('fastify')
const fastifyCors = require('@fastify/cors');
const hookLoggingPlugin = require('./hookLogging');

(async function startServer () {
  const fastify = Fastify({
    logger: {
      transport: {
        target: 'pino-pretty',
      },
    },
  });

  fastify.register(async function (fastify) {
  // the logging should be inside ;)
  fastify.register(hookLoggingPlugin);

  fastify.register(fastifyCors, {
    // hook: 'preHandler',
    delegator: (req, callback) => {
      const corsOptions = { origin: false };
      if (/^success$/m.test(req.headers.origin)) {
        corsOptions.origin = true;
      }
      callback(null, corsOptions);
    },
  });

  fastify.get('/', async function (request, reply) {
    return reply.code(200).type('text/plain').send('Hello world');
  })

  fastify.post('/', async function (request, reply) {
    return reply.code(200).type('text/plain').send('Hello world');
  })

  fastify.setNotFoundHandler(async (_request, reply) => {
    reply.code(404).type('text/plain').send('Not found');
  });

  })
  
  return fastify.listen({ port: 3000 });
})();

[10xLaCroixDrinker]

Thank you Matteo!!