Throw Exception if 'data' and 'errors' coexist in the request body

[Art4]

Hello and thank you for this great library.

I have noticed a behavior that is against the JSON:API spec.

The top level document could contain a data or errors attribute, but both MUST NOT coexist in the same document. See https://jsonapi.org/format/1.0/#document-top-level
While this is never the case in the response, it can also occur in the request.

What I do:

As an example let one send the following request:

POST https://api.example.com/posts

{
  "data": {
    "type": "posts",
    "attributes": {
      "content": "Lorem ipsum dolor sit amet, sed libris elaboraret eu."
    }
  },
  "errors": [
    {
      "detail": "The members data and errors MUST NOT coexist in the same document."
      "links": {
        "about": "https://jsonapi.org/format/1.0/#document-top-level"
      }
    }
  ]
}

What happend:

The server accepted the request.

What I expect:

The Server refuses the request because the body does not contain valid JSON:API.

[kocsismate]

@Art4 Thank you very much for reporting the issue! I can confirm, this validation is currently missing from the library. I'll implement it in the following week(s), but you can also do so if you are up to prepare a PR. :)

[Art4]

I'm glad if I could help with a PR but I need a little help for the right place to implement. I also assume we would need a new exception class?

[kocsismate]

I also assume we would need a new exception class?

Right! Additionally, a new RequestValidator::validateBody() method should throw it by using the ExceptionFactoryInterface. :)