def get_service_state_list() -> List[ServiceState]:
    """Return a list of ServiceState objects known to SDP."""
    keys = DB.get_keys('states*')
    LOG.debug('Loading list of known services.')
    services = []
    for key in keys:
        values = key.split(':')
        if len(values) == 4:
            services.append(ServiceState(*values[1:4]))
    return services
Return a list of ServiceState objects known to SDP.