addContentTypeParser doesn't work well after await register

[scott1028]

Prerequisites

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

Fastify version

v4.26.2

Plugin version

No response

Node.js version

20

Operating system

Linux

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

20.04

Description

addContentTypeParser doesn't work as expected when previous statement is register with await.

Steps to Reproduce

ex:

'use strict'

const main = async () => {
  const server = require('fastify')({
    logger: true,
  });

  const schema = {
    schema: {
      response: {
        200: {
          type: 'object',
          properties: {
            hello: {
              type: 'string',
            },
          },
        },
      },
    },
  };

  await server.register((fastify, options, done) => {
    fastify.get('/api/upload', async (req, res) => {
      return { hello: 'world0' };
    })
    fastify.post('/api/upload', async (req, res) => {
      return { hello: 'world1' };
    })
    done();
  });

  server.get('/', schema, function (req, res) {
    res.send({ hello: 'world2' });
  });

  // This parser will not work after "server.register" in "await"
  server.addContentTypeParser(
    'text/csv',
    { parseAs: 'string' },
    (req, body, done) => {
      // Custom parsing logic for text/csv content type for api plugin
      const csvData = body.split('\n').map((row) => row.split(','));
      done(null, csvData);
    },
  );

  server.listen({ port: 3000 }, (err, address) => {
    if (err) {
      throw err;
    }
  });
};

main();

curl -H "Content-Type: text/csv" -X POST --data "a,b,c" http://localhost:3000/api/upload
// you will get below
{"statusCode":415,"code":"FST_ERR_CTP_INVALID_MEDIA_TYPE","error":"Unsupported Media Type","message":"Unsupported Media Type: text/csv"}

Expected Behavior

the CSV parser should work as expected.

curl -H "Content-Type: text/csv" -X POST --data "a,b,c" http://localhost:3000/api/upload
{"hello":"world1"}

[Uzlopak]

So you claim there is a race condition?

[scott1028]

So you claim there is a race condition?

I don't think it a race condition issue because it can work by removing await from await server.register.
Also, I'm not sure if this was caused by avvio used by fastify or not.

[climba03003]

Not sure if is it mentioned in document.
But await fastify.register is the same as fastify.after which means all the later code will be after context finalize from that plugin.

My suggestion is that only add await when necessary.

[climba03003]

I believe similar fix can be used like setErrorHandler.
See #4204 (comment) #4205

[mcollina]

Albeit surprisingly, this is expected behavior. This should be clarified in our docs.