Json schema validation using meta schema

Question

I need to validate that a property is a valid JSON schema. In the following example, I need to validate the payload property:

message:
  name: userSignedUp
  version: 1.0.0
  payload:
    name:
      type: string
    timestamp:
      type: string
    warningLevel:
      type: string
      enum:
        - HIGH
        - MEDIUM
        - LOW

This is my json-schema:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "title": "Message",
  "properties": {
    "name": {
      "type": "string"
    },
    "version": {
      "type": "string"
    },
    "payload": {
      "$ref": "#/definitions/schema"
    },
  },
  "definitions":{
    "schema": {
     # --> How should the schema be defined?
  },
  "required":[
    "name",
    "version",
    "payload"
  ]
}

To my understanding, I need to use Core/Validation Dialect meta-schema. I didn't really understand how to do so, because simply copying the json-meta schema is not clear - what should I replace meta/* with? Is that how the definition should look like?

How should my schema definition should be defined?

Thanks

Answer 1

So I ended up using the everit-json-schema library, I created a local copy of the draft-07 Core schema meta-schema, loaded it using the library and then validated my schemas against it.

private static Schema META_SCHEMA_VALIDATOR;

static {
    JSONObject metaSchema;

    try {
      metaSchema = new JSONObject((Files.readAllBytes(Paths.get("src/main/resources/meta-schema.json"))));
    } catch (Exception ex) {
      throw new RuntimeException("Failed reading metaschema file");
    }

    var schemaLoader = SchemaLoader
      .builder()
      .schemaJson(metaSchema)
      .draftV7Support()
      .build();

    META_SCHEMA_VALIDATOR = schemaLoader.load().build();
}
...
...
private void validateSchema(Payload schema) {
    var schemaString = new Gson().toJson(schema.getAdditionalProperties(), Map.class);
    var schemaJson = new JSONObject(schemaString);
    try {
      META_SCHEMA_VALIDATOR.validate(schemaJson);
    } catch (Exception ex) {
      throw new InvalidSpecException(String.format("Schema validation failed for schema: `%s`, ex: `%s`", schemaString, ex.getMessage()));
    }
  }