def validate_href(image_href):
        """Validate HTTP image reference.

        :param image_href: Image reference.
        :raises: exception.ImageRefValidationFailed if HEAD request failed or
            returned response code not equal to 200.
        :returns: Response to HEAD request.
        """
        try:
            response = requests.head(image_href)
            if response.status_code != http_client.OK:
                raise exception.ImageRefValidationFailed(
                    image_href=image_href,
                    reason=("Got HTTP code %s instead of 200 in response to "
                            "HEAD request." % response.status_code))
        except requests.RequestException as e:
            raise exception.ImageRefValidationFailed(image_href=image_href,
                                                     reason=e)
        return response
Validate HTTP image reference.

        :param image_href: Image reference.
        :raises: exception.ImageRefValidationFailed if HEAD request failed or
            returned response code not equal to 200.
        :returns: Response to HEAD request.