StackOverflowError when calling hashCode on mutually recursive schemas

[cpchen]

Example schema to reproduce:

{
  "$schema": "http://json-schema.org/draft-06/schema#",
  "id": "foo",
  "type": "object",
  "title": "Foo Schema",
  "allOf": [
    {
      "$ref": "#/definitions/Foo"
    }
  ],
  "definitions": {
    "Bar": {
      "type": "object",
      "properties": {
        "foo": {
          "$ref": "#/definitions/Foo"
        }
      }
    },
    "Foo": {
      "type": "object",
      "properties": {
        "bar": {
          "$ref": "#/definitions/Bar"
        }
      }
    }
  }
}

Calling hashCode on the corresponding schema object yields the following (truncated) SO:

java.lang.StackOverflowError
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.Schema.hashCode(Schema.java:224)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ReferenceSchema.hashCode(ReferenceSchema.java:102)
	at java.base/java.util.Objects.hashCode(Objects.java:116)
	at java.base/java.util.HashMap$Node.hashCode(HashMap.java:297)
	at java.base/java.util.AbstractMap.hashCode(AbstractMap.java:527)
	at java.base/java.util.Collections$UnmodifiableMap.hashCode(Collections.java:1488)
	at java.base/java.util.Arrays.hashCode(Arrays.java:4684)
	at java.base/java.util.Objects.hash(Objects.java:146)
	at org.everit.json.schema.ObjectSchema.hashCode(ObjectSchema.java:358)

[tmarsteel]

Would it suffice to have ReferenceSchema not include the referred schema into the hashCode? Actually, that would make a lot of sense to me. The referred schema depends on the schema loader pretty much and the correctness of ReferenceSchemas equals+hashCode shouldn't depend on the schema loader.

[erosb]

Hello @tmarsteel , you can give it a go, but in that case I'm afraid the equals()will still run into an infinite recursion, so not sure if that helps a lot. Feel free to raise a PR with the fix and a passing test, if you want. Thanks for your idea anyway.

[rayokota]

We use this library in Confluent Schema Registry, and are seeing this error as well when equals or hashCode is called on a recursive schema. confluentinc/schema-registry#1549

[shionefaye]

@rayokota Conflunece Schema Registry issue on recursive schema has been fixed and merged recently. What is needed to be done in this package?

[rayokota]

@shionefaye , the issue still exists in this library. For Schema Registry the code has been changed to compare instances of JsonNode from Jackson rather than instances of Schema from this library.

[shionefaye]

@shionefaye , the issue still exists in this library. For Schema Registry the code has been changed to compare instances of JsonNode from Jackson rather than instances of Schema from this library.

Got you. I misread your early message and thought this package depends on Conflunece Schema Registry.