turns out that using the code suggested won’t work here as error already handled in the RxCocoa Extension on URLSession, or do I missed something?!
return session.rx.response(request: request).map() { response, data in
if 200 ..< 300 ~= response.statusCode {
return JSON(data: data)
} else if 400 ..< 500 ~= response.statusCode {
throw ApiError.cityNotFound
} else {
throw ApiError.serverFailure
}
}
Obviously missed something. 
In case you got no response or no data or (2nd case the response is an HTTPURLResponse) … then you bypass your own error code handling which makes sense because our own error handling is based on data or an response with statusCode. Sry.