'Search an open port with a particular service.'

@classmethod
def searchservice(cls, srv, port=None, protocol=None):

    req = cls._searchstring_re(Port.service_name, srv)
    if (port is not None):
        req = and_(req, (Port.port == port))
    if (protocol is not None):
        req = and_(req, (Port.protocol == protocol))
    return NmapFilter(port=[(True, req)])
