def handler(request):
    """Scheme handler for qute:// URLs.

    Args:
        request: QNetworkRequest to answer to.

    Return:
        A QNetworkReply.
    """
    try:
        mimetype, data = qutescheme.data_for_url(request.url())
    except qutescheme.NoHandlerFound:
        errorstr = "No handler found for {}!".format(
            request.url().toDisplayString())
        return networkreply.ErrorNetworkReply(
            request, errorstr, QNetworkReply.ContentNotFoundError)
    except qutescheme.QuteSchemeOSError as e:
        return networkreply.ErrorNetworkReply(
            request, str(e), QNetworkReply.ContentNotFoundError)
    except qutescheme.QuteSchemeError as e:
        return networkreply.ErrorNetworkReply(request, e.errorstring, e.error)
    except qutescheme.Redirect as e:
        qtutils.ensure_valid(e.url)
        return networkreply.RedirectNetworkReply(e.url)

    return networkreply.FixedDataNetworkReply(request, data, mimetype)
The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.