Error Handling

GenHTTP.Modules.ErrorHandling

If an exception occurs while a request is handled, the server will render the exception into a structured response (JSON, XML, … depending on what the client accepts) via ErrorHandler.Default(), which is an alias for ErrorHandler.Structured(). To customize the serialization used, pass a SerializationBuilder to Structured(...).

HTML Error Pages

To get a HTML error response instead of JSON, you can add the HTML error renderer to your app as a concern:

var app = Layout.Create()
                .AddService<...>()
                .Add(ErrorHandler.Html());

Custom Error Responses

If you would like to control the response generated for exceptions, you can implement a custom IErrorMapper and add it to your app as needed. The following example will render any exception to a text response:

using GenHTTP.Api.Content;
using GenHTTP.Api.Protocol;

using GenHTTP.Modules.ErrorHandling;
using GenHTTP.Modules.Layouting;
using GenHTTP.Modules.IO;

var errorHandling = ErrorHandler.From(new TextErrorMapper());

var api = Layout.Create()
                .AddService<...>()
                .Add(errorHandling);

public record ErrorModel(String Message);

public class TextErrorMapper : IErrorMapper<Exception>
{

    public ValueTask<IResponse?> GetNotFound(IRequest request, IHandler handler, ByteString? acceptedFormat)
    {
        // hint: return null here to render the default error page of the server
        return new(GetResponse(request, ResponseStatus.NotFound, "The requested content was not found"));
    }

    public ValueTask<IResponse?> Map(IRequest request, IHandler handler, Exception error, ByteString? acceptedFormat)
    {
        var errorModel = new ErrorModel(error.Message);

        if (error is ProviderException providerException)
        {
            return new(GetResponse(request, providerException.Status, error.ToString()));
        }

        return new(GetResponse(request, ResponseStatus.InternalServerError, error.ToString()));
    }

    private static IResponse GetResponse(IRequest request, ResponseStatus status, string message)
    {
        return request.Respond()
                      .Status(status)
                      .Content(message, ContentType.TextPlain)
                      .Build();
    }

}

acceptedFormat is the format negotiated from the client’s Accept header (as also used by serialization) - use it if your mapper wants to honor content negotiation like ErrorHandler.Structured() does; the example above ignores it and always renders plain text.