introspection: give a clear error message when introspection is maybe just disabled

[abernix]

By default, and since it can be a best-practice for many servers, Apollo Server disables introspection in production (determined by process.env.NODE_ENV === "production"). This, coupled with the current error messaging behavior of the apollo CLI results in a sub-par user-experience for those who are trying to introspect their production server.

While I'm not sure what all the error messaging considerations are right now, we can help the user by offering "introspection might be disabled" as part of the error output if we just literally do not get any introspection response from an endpoint.

[abernix]

For Apollo Server specifically, which offers its own instructions on how to enable introspection, there is an HTTP status code of 400, coupled with a GraphQL ValidationError that we could match for and customize the error message for.

[lrlna]

@abernix do you have a particular endpoint I can test on that would return a 400 when introspection is disabled? I can currently get endpoints to return a 405 and am not able to replicate this exact behaviour you're describing.

[abernix]

@lrlna Sure! Here's a CodeSandbox with Apollo Server running with introspection: false. You may have to visit that link for it to spin up prior to invoking this curl command (which is a vastly simplified "introspection-like query):

curl -vvv 'https://orekg.sse.codesandbox.io/' -H 'Content-Type: application/json' --data-binary '{"query":"{ __schema { type } }"}'