Globally configure custom exception type for IApiResponse?

[Robin-CSPlus]

Hi,

Our backend returns a response body when an exception occurs, this is similar to the problemdetail, but still quite different. Now I was wondering if I can somehow configure IApiResponse to return that as response.Error type in a global context, instead of having to use .GetContentAsync everwhere an error could occur?

[glennawatson]

There is no setting that swaps IApiResponse.Error to a custom type globally. Error is an ApiExceptionBase (ApiException for response errors), so the strongly typed body is not surfaced there directly. But you have two clean global options:

1. Deserialize the error body on demand from the exception.
   ApiException exposes GetContentAsAsync(), so you do not need GetContentAsync everywhere:

if (response.Error is ApiException apiEx && apiEx.HasContent)
{
    var myError = await apiEx.GetContentAsAsync<MyErrorBody>();
}

2. Plug in a custom ExceptionFactory on RefitSettings to produce your own exception type carrying the parsed body. This is exactly how Refit's built-in ValidationApiException works (it parses ProblemDetails in its factory). Pattern:

public sealed class MyApiException : ApiException
{
    private MyApiException(ApiException inner)
        : base(inner.RequestMessage, inner.HttpMethod, inner.Content, inner.StatusCode,
               inner.ReasonPhrase, inner.Headers, inner.RefitSettings!) { }

    public MyError? Error { get; private set; }

    public static async Task<MyApiException> CreateAsync(ApiException inner)
    {
        var ex = new MyApiException(inner);
        if (inner.HasContent)
            ex.Error = await inner.GetContentAsAsync<MyError>();
        return ex;
    }
}

var settings = new RefitSettings
{
    ExceptionFactory = async response =>
    {
        if (response.IsSuccessStatusCode) return null;
        var apiEx = await ApiException.Create(
            response.RequestMessage!, response.RequestMessage!.Method, response, settings);
        return await MyApiException.CreateAsync(apiEx);
    }
};

Register that settings instance once (AddRefitClient(settings) / RestService.For(client, settings)) and the typed error flows into response.Error for every call. Cast response.Error to MyApiException to read .Error.

Recommendation: option 2 if you want it globally typed; option 1 if you just want to avoid repeating GetContentAsync at call sites.