fun Throwable.toNetworkError(): Error = when (this) {
    is HttpException -> {
        val errorBody = response()?.errorBody()
        if (errorBody != null) {
            when (code()) {
                HTTP_FORBIDDEN -> Forbidden(this)
                HTTP_UNAUTHORIZED -> Unauthorized(this)
                else -> Http(code(), response()?.message(), this)
            }
        } else Http(code(), response()?.message(), this)
    }
    is IOException -> Connection(this)
    else -> GenericError(cause = this)
}

...

sealed class NetworkError(override val cause: Throwable) : Error(cause) {
    data class Http(val code: Int, override val message: String?, override val cause: Throwable) :
        NetworkError(cause)

    data class Forbidden(override val cause: Throwable) : NetworkError(cause)
    data class Unauthorized(override val cause: Throwable) : NetworkError(cause)
    data class Connection(override val cause: Throwable) : NetworkError(cause)
}