Possible serialization bug with response schema

[Jnig]

Prerequisites

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

Fastify version

3.27.2, 4.0.0-alpha.1

Node.js version

14.19

Operating system

Linux

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

Arch Linux

Description

Hi,

I'm using fastify with a response schema. In the schema I've a property called user, which can be null or a object with id and email.

When the user object has the properties id and email everything works as expected. If the object contains an additional property, the whole user object is converted to null in the response. This was somehow unexpected, but I'm not sure if this is really a bug.

Steps to Reproduce

const fastify = require("fastify")({
  logger: true,
});

const opts = {
  schema: {
    response: {
      "2xx": {
        type: "object",
        properties: {
          id: {
            type: "number",
          },
          name: {
            type: "string",
          },
          user: {
            anyOf: [
              {
                type: "null",
              },
              {
                type: "object",
                properties: {
                  id: {
                    type: "number",
                  },
                  email: {
                    type: "string",
                  },
                },
                additionalProperties: false,
              },
            ],
          },
        },
      },
    },
  },
};

// returns {"id":1,"name":"foo","user":{"id":1,"email":"foobar@local"}}
fastify.get("/", opts, function (request, reply) {
  reply.send({ id: 1, name: "foo", user: { id: 1, email: "foobar@local" } });
});

// returns {"id":1,"name":"foo","user":null}
fastify.get("/with-additional", opts, function (request, reply) {
  reply.send({
    id: 1,
    name: "foo",
    additionalProp: "foo",
    user: { id: 1, email: "foobar@local", firstName: "foobar" },
  });
});

fastify.listen(3000, function (err, address) {
  if (err) {
    fastify.log.error(err);
    process.exit(1);
  }
});

Expected Behavior

Additional properties in the user object should be removed instead of setting the object to null. This would mirror the behavior for other additional properties. additionalProp is removed from the output.

The following code

reply.send({
    id: 1,
    name: "foo",
    additionalProp: "foo",
    user: { id: 1, email: "foobar@local", firstName: "foobar" },
  });

should return

{"id":1,"name":"foo","user":{"id":1,"email":"foobar@local"}

following is returned

{"id":1,"name":"foo","user":null}

[Eomm]

fast-json-stringify does not support the type: null atm

you need to use this schema:

const schema = {
  type: 'object',
  properties: {
    id: {
      type: 'number',
    },
    name: {
      type: 'string',
    },
    user: {
      nullable: true,
      type: 'object',
      properties: {
        id: {
          type: 'number',
        },
        email: {
          type: 'string',
        },
      },
      additionalProperties: false,
    },
  },
}

Closing as duplicates fastify/fast-json-stringify#388

[Jnig]

@Eomm thanks for pointing to the fast-json-stringify issue