Support for custom string formats

[dallasanta]

Describe the feature

According to the OpenAPI specification, string "format" is an open value (https://swagger.io/docs/specification/data-models/data-types/#string)

However, format is an open value, so you can use any formats, even not those defined by the OpenAPI Specification, such as:

That's also backed by the JSON Schema Specification Draft 2020-12](https://tools.ietf.org/html/draft-bhutton-json-schema-00#section-7.2.3)

Implementations MAY support custom format attributes.

The feature request is to support custom "format" fields, not only those defined in the above JSON Schema Specification and implemented on https://github.com/eclipse-vertx/vertx-json-schema/blob/4.4.6/src/main/java/io/vertx/json/schema/impl/Format.java

A regular expression pattern should not ideally be used for that as:

• Users can find it hard to understand
• Can't be reused - there's no way to use a $ref for a regular expression pattern in OpenAPI

Use cases

As an organization API provider
I want to be able to create custom string formats
So I can communicate to the API users the expected format
And I can run the correct validation

Contribution

Are you volunteering for implementing this feature? 👍

[pk-work]

Is this maybe fixed with #128?

[dallasanta]

Yes, that fix and eclipse-vertx/vertx-openapi#51 allow you to specify a custom validator. Thanks for that.

I was think that ideally we could override the default string format from here, for scenarios where we want to further restrict some of the validations, but that should be fine as long as we use custom formats anyway.

Happy for this one to be closed.