def build_acs_action(action, xml=True):
    """
    Returns a string similar to
    x-akamai-acs-action:version=1&action=du&format=xml'
    """
    acs_action = 'x-akamai-acs-action:version=1&action={0}'.format(action)
    acs_action = acs_action + '&format=xml' if xml else acs_action
    return acs_action