Is it possible to create a recursive schema definition?

[timfrans]

Is it possible to create a recursive schema definition?

I stumbled on this issue when implementing a hierarchical scheme using recursion schemas.
To define our JSON schemas we use sinclair/typebox like so:

export const ArticleCategorySchemaTest = Type.Array(
  Type.Rec(
    (Self) =>
      Type.Object({
        sequenceNumber: Type.Number({ minimum: 1 }),
        subCategories: Type.Optional(Type.Array(Self)),
      }),

    { $id: 'ArticleCategoryTest' },
  ),
);

This generates following schema:

{
  kind: Symbol(ArrayKind),
  type: 'array',
  items: {
    '$id': 'ArticleCategoryTest',
    '$ref': 'ArticleCategoryTest#/$defs/self',
    '$defs': {
      self: {
        kind: Symbol(ObjectKind),
        type: 'object',
        properties: {
          sequenceNumber: { minimum: 1, kind: Symbol(NumberKind), type: 'number' },
          subCategories: {
            kind: Symbol(ArrayKind),
            type: 'array',
            items: { '$ref': 'ArticleCategoryTest#/$defs/self' },
            modifier: Symbol(OptionalModifier)
          }
        },
        required: [ 'sequenceNumber' ]
      }
    }
  }
}

When starting up the fastify server i get following error:

Failed building the serialization schema for ..., due to error Maximum call stack size exceeded

I've seen following issues:

• Is it possible model a recursive reference with JSON Schema without using arrays?
• Recursion
  These issues should be solved according to the comments and pull requests.

I'm just not sure what casues this error.

Your Environment

• node version: 16.13.0
• fastify version: 3.23.0
• os: Mac
• fast-json-stringify: 2.7.13
• sinclair/typebox: 0.21.2

[mcollina]

Maybe something regressed. Could you include a runnable example to reproduce? I'd also be if you'd like to send a PR to fix this.

[ThaDaVos]

I am running into the same issue as my schema is based on an OpenAPI schema (using https://github.com/seriousme/fastify-openapi-glue to include it) - but our models have relations back and forth (as is in my eyes usual) and this seems to be causing the Maximum call stack size exceeded error as Fastify tries the resolve the references going back and forth....

[seriousme]

FYI: just tested the following

import { test } from "tap";
import Fastify from "fastify";

const opts = {
    schema: {
        body: {
            type: 'object',
            additionalProperties: false,
            properties: {
                str1: {
                    type: "string"
                },
                obj1: {
                    $ref: "#"
                }
            },
            required: [
                "str1"
            ]
        }
    },
}

test("fastify validation works", (t) => {
    t.plan(5);
    const fastify = Fastify();

    async function routes(fastify) {
        fastify.post("/", opts, async (request) => {
            return request.body;
        });
    }
    fastify.register(routes);
    fastify.inject(
        {
            method: "POST",
            url: "/",
            payload: {
                str1: "test data",
                obj1: {
                    str1: "test data"
                }
              },

        },
        (err, res) => {
            t.error(err);
            t.equal(res.body, '{"str1":"test data","obj1":{"str1":"test data"}}', "expected value");
            t.equal(res.statusCode, 200, "expected HTTP code");
        }
    );
    fastify.inject(
        {
            method: "GET",
            url: "/blah",
        },
        (err, res) => {
            t.error(err);
            t.equal(res.statusCode, 404, "expected HTTP code");
        }
    );
});

And that works ok using Fastify 4.2.0:

TAP version 13
# Subtest: fastify validation works
    1..5
    ok 1 - should not error
    ok 2 - expected HTTP code
    ok 3 - should not error
    ok 4 - expected value
    ok 5 - expected HTTP code
ok 1 - fastify validation works # time=385.477ms

1..1
# time=395.021ms

[seriousme]

Bad news :-(

Upgrading to fastify 4.5.3 and running the test again results in an error:

TAP version 13
# Subtest: fastify validation works
    1..5
    not ok 1 - Failed building the validation schema for POST: /, due to error can't resolve reference \# from id \#
      ---

I tried to reproduce the result at fastify 4.x (4.2.0 and 4.0.0) but failed :-(
The test does succeed however when going back to fastify 3.x (3.29.1 to be exact).
Could this be due to a newer version of AJV ?

Kind regards,
Hans

[kibertoad]

@seriousme Have you tried locking ajv version? if that helps, likely you need to raise issue with ajv

[seriousme]

I think I found a solution:

const opts = {
    schema: {
        body: {
            $id: "https://example.com/tree",
            type: 'object',
            additionalProperties: false,
            properties: {
                str1: {
                    type: "string"
                },
                obj1: {
                    $ref: "#"
                }
            },
            required: [
                "str1"
            ]
        }
    },
}

Basically following what AJV indicated, but could have been communicated more clearly, namely adding an $id attribute.

This is using:

└─┬ fastify@4.5.3
  ├─┬ @fastify/ajv-compiler@3.2.0
  │ └── ajv@8.11.0 deduped
  └─┬ @fastify/fast-json-stringify-compiler@4.1.0
    └─┬ fast-json-stringify@5.1.0
      └── ajv@8.11.0 deduped

This again results in:

TAP version 13
# Subtest: fastify validation works
    1..5
    ok 1 - should not error
    ok 2 - expected HTTP code
    ok 3 - should not error
    ok 4 - expected value
    ok 5 - expected HTTP code
ok 1 - fastify validation works # time=451.045ms

1..1

Apologies for any confusion caused :-(

Kind regards,
Hans