Improve error messages from error handlers

[p1c2u]

Discussed in https://github.com/python-openapi/openapi-core/discussions/757

^{Originally posted by jtherrmann January 11, 2024} All of the API endpoints for the test deployment of our Flask app, which is deployed via Amazon API Gateway, are currently returning a response like the one below:

{
  "detail": "Server not found for https://vd2gh6uqw3.execute-api.us-west-2.amazonaws.com/api/user",
  "status": 400,
  "title": "Bad Request",
  "type": "about:blank"
}

We depend on the latest pre-release of openapi-core, https://github.com/python-openapi/openapi-core/releases/tag/0.19.0a1.

The error message leads me to believe that openapi-core is raising a ServerNotFound exception from BasePathFinder.find (here), which is called from BaseAPICallValidator._find_path (here).

I have a couple of questions:

• Is BaseAPICallValidator for validating requests, responses, or both?
• Why does the validator need to validate the server URL? What exactly does APICallPathFinder._get_servers_iter do? What is the fundamental meaning of a ServerNotFound exception?