networknt / json-schema-validator - Unknown Metaschema: http://json-schema.org/draft-07/schema#

[harpreetk1986]

Hi,

While using networknt / json-schema-validator, I am getting error while validating schema -06 and above. Getting following error:
com.networknt.schema.JsonSchemaException: Unknown Metaschema: http://json-schema.org/draft-07/schema#

Only schema-04 is working fine.

Here is sample schema I am using:
{
"$schema" : "http://json-schema.org/draft-07/schema#",
"$id" : "http://json-schema.org/draft-07/schema#"
}

[stevehu]

@harpreetk1986 Thanks a lot for raising this issue. I am wondering if this is due to the recent update on the json-schema.org to redirect all HTTP requests to HTTPS. I have updated the draft-2019-09 at this location. https://github.com/networknt/json-schema-validator/blob/master/src/main/java/com/networknt/schema/JsonMetaSchema.java#L151

Have you debugged into it to see where the error message is coming from?

[harpreetk1986]

@stevehu. Thanks for the reply. I just did a debug and found the following:

Issue is coming in findMetaSchemaForSchema() function of JsonSchemaFactory Class at below line of code:
final JsonMetaSchema jsonMetaSchema = jsonMetaSchemas.get(uri);

Here uri is "http://json-schema.org/draft-07/schema#"
jsonMetaSchema is coming as null.

[harpreetk1986]

@stevehu : I debug more and found out that, I am calling JsonSchemaFactory.getInstance() and this function is always returning Version flag as V4. Do I need to call getInstance() by passing the version flag. If yes, from where should I fetch that from?

[stevehu]

Yes. You need to specify which draft version to use unless you are using v4 which is the default.

https://github.com/networknt/json-schema-validator/blob/master/src/test/java/com/networknt/schema/V201909JsonSchemaTest.java#L39

[stevehu]

To prevent users to use the old method. I am thinking to deprecate the getInstance(). What do you think?

+    /**
+     * @deprecated
+     * This is a method that is kept to ensure backward compatible. You shouldn't use it anymore.
+     * Please specify the draft version when get an instance.
+     *
+     * @return JsonSchemaFactory
+     */
+    @Deprecated
     public static JsonSchemaFactory getInstance() {
         return getInstance(SpecVersion.VersionFlag.V4);
     }

[harpreetk1986]

@stevehu . It is a good idea, it makes complete sense to me.

I am thinking , how it can be more dynamic to pass the version flag which supports multiple versions. Since schema can contain any draft version. May be we have to fetch the Draft versions from Schema and create mapping to map to the corresponding version to pass as parameters of getInstance has format like V4, V6 etc.

And once if new draft version is released, that needs to be added to the mapping to map to the corresponding version to pass.

[stevehu]

I thought about it when I implement the versioning. We can just decide the version based on the $schema in the schema file; however, we cannot make a decision for the reference schemas if there are any. For example, if you have a schema v7 that refers to another remote schema v4. Which version should the library use? To let the user specify the version at least make them aware of this issue. The other reason is that not all schema files have the $schema.

[stevehu]

I just checked in the @deprecated code. It is not the final solution but just to reduce the risk. Let's keep this conversation going to have a better solution.

[harpreetk1986]

I just checked in the @deprecated code. It is not the final solution but just to reduce the risk. Let's keep this conversation going to have a better solution.

Sure. Thank you.

[harpreetk1986]

I thought about it when I implement the versioning. We can just decide the version based on the $schema in the schema file; however, we cannot make a decision for the reference schemas if there are any. For example, if you have a schema v7 that refers to another remote schema v4. Which version should the library use? To let the user specify the version at least make them aware of this issue. The other reason is that not all schema files have the $schema.

Sure, this way also it will work for me. Thanks.

[andrhamm]

I'm getting this error and I believe I'm specifying the correct version

val config = SchemaValidatorsConfig()
config.isFailFast = true
val mapper = ObjectMapper()
val validatorFactory = JsonSchemaFactory.builder(JsonSchemaFactory.getInstance(SpecVersion.VersionFlag.V7)).objectMapper(mapper).build();
validatorFactory.getSchema(schemaString, config)

[stevehu]

@andrhamm Thanks for raising it. It looks like the scope of the problem is getting bigger. I will take a look at it once I have free cycles. It would be great if someone in the community can take a look at your case.