Default request additional properties vs default response additional properties

[Zeds112]

💬 Question here

By default, fastify allows the request body to have additional properties but by default the response has any additional properties removed. I could not find some documentation on this.

Is there a simple way to allow additional properties on all responses similar to the default for request bodies? Thanks.

const Fastify = require('fastify');

const fOpts = {};

const fastify = Fastify(fOpts);

const schema = {
  description: 'test',
  body: {
    type: 'object',
    properties: {
      test1: { type: 'string' },
    },
  },
  response: {
    200: {
      type: 'object',
      properties: {
        test3: { type: 'string' },
      },
    },
  },
};

fastify.post('/test', { schema }, async (req: any, res: any) => {
  console.log({
    body: req.body,
  })

  // curl -X POST http://localhost:3003/test \
  //   -H "Content-Type: application/json" \
  //   -d '{
  //     "test1": "test1",
  //     "test2": "test2"
  //   }'

  // { body: { test1: 'test1', test2: 'test2' } }

  return res.status(200).send({
    test3: 'test3',
    test4: 'test4',
  });

  // client receives: {"test3":"test3"}

});


const run = async () => {
  await fastify.listen({
    host: 'localhost',
    port: 3003,
  });

};

run();


export { };

Your Environment

• node version: 18
• fastify version: 4.28.1
• os: Windows
• any other relevant information

[mcollina]

You can just add the additionalProperties: true to the object.

[Zeds112]

Hi thanks I understand that but I'm specifically wondering if there's a default option so that you don't have to add additionalProperties: true to everything manually.

[mcollina]

Unfortunately no.