Go SDK: Improve error handling and expose status

[jessicasomaiya]

Hello, I’ve been working with your Go SDK and I’ve enjoyed digging around to see how the generator works.

I’ve seen various discussions about decoding error responses as per the Swagger API spec, specifically #795 (comment) and I’d like to suggest one way of achieving this using the autogenerated models.

As the error models are defined in the v4 package, the rtl package cannot import the models as this would lead to a cyclic dependancy. This means the Do method https://github.com/looker-open-source/sdk-codegen/blob/main/go/rtl/auth.go#L89 must expose the error status and the body so the body can be decoded in the v4 package.

I have a PR of this implementation which I’d be interested to get your thoughts on. resolutionlife#5

As well as this, I need to access the specific status of the error response. This could be done through wrapping the error message in a well defined error type. For example see the below.

if err != nil {
        if errors.Is(err, v4.ErrNotFound) {
            …
        }
       return err
    }

where v4.ErrNotFound is defined like so

 var ErrNotFound = errors.New("not found")

This feature is also covered in my PR against a forked repo.

What are your thoughts on this approach to decoding the error responses?