URLResponse as HTTPURLResponse and check if call has status code 2xx

URLResponse+HTTP.swift

extension URLResponse {
    /// Returns casted `HTTPURLResponse`
    var http: HTTPURLResponse? {
        return self as? HTTPURLResponse
    }
}

extension HTTPURLResponse {
    /// Returns `true` if `statusCode` is in range 200...299.
    /// Otherwise `false`.
    var isSuccessful: Bool {
        return 200 ... 299 ~= statusCode
    }
}