How to use the crossbar.bridge.mqtt._utils.ParseFailure function in crossbar

def deserialise(cls, flags, data):
        """
        Take an on-wire message and turn it into an instance of this class.
        """
        if flags != (False, False, False, False):
            raise ParseFailure(cls, "Bad flags")

        reserved = data.read(7).uint

        if reserved:
            raise ParseFailure(cls, "Reserved flag used.")

        built = cls(session_present=data.read(1).bool,
                    return_code=data.read(8).uint)

        # XXX: Do some more verification, re conn flags

        if not data.bitpos == len(data):
            # There's some wacky stuff going on here -- data they included, but
            # didn't put flags for, maybe?
            warnings.warn(("Quirky server CONNACK -- packet length was "
                           "%d bytes but only had %d bytes of useful data") % (
                               data.bitpos, len(data)))

        return built

def parse_pair():

            topic_filter = read_string(data)
            reserved = data.read("uint:6")
            max_qos = data.read("uint:2")

            if reserved:
                raise ParseFailure(cls, "Data in QoS Reserved area")

            if max_qos not in [0, 1, 2]:
                raise ParseFailure(cls, "Invalid QoS")

            pairs.append(SubscriptionTopicRequest(topic_filter=topic_filter,
                                                  max_qos=max_qos))

built = cls(
            username=data.read(1).bool,
            password=data.read(1).bool,
            will_retain=data.read(1).bool,
            will_qos=data.read(2).uint,
            will=data.read(1).bool,
            clean_session=data.read(1).bool,
            reserved=data.read(1).bool
        )

        # XXX: Do some more conformance checking here
        # Need to worry about invalid flag combinations

        if built.reserved:
            # MQTT-3.1.2-3, reserved flag must not be used
            raise ParseFailure(cls, "Reserved flag in CONNECT used")

        return built

"""
        Disassemble from an on-wire message.
        """
        if flags != (False, False, False, False):
            raise ParseFailure(cls, "Bad flags")

        protocol = read_string(data)

        if protocol != "MQTT":
            print(protocol)
            raise ParseFailure(cls, "Bad protocol name")

        protocol_level = data.read('uint:8')

        if protocol_level != 4:
            raise ParseFailure(cls, "Bad protocol level")

        flags = ConnectFlags.deserialise(data.read(8))

        # Keep alive, in seconds
        keep_alive = data.read('uint:16')

        # The client ID
        client_id = read_string(data)

        if flags.will:
            # MQTT-3.1.3-10, topic must be UTF-8
            will_topic = read_string(data)
            will_message = read_prefixed_data(data)
        else:
            will_topic = None
            will_message = None

def read_string(data):
    """
    Reads the next MQTT pascal-style string from `data`.
    """
    byte_data = read_prefixed_data(data)
    _validator.reset()

    if _validator.validate(byte_data)[0]:
        decoded = byte_data.decode('utf8', 'strict')
        if "\u0000" in decoded:
            raise ParseFailure("Invalid UTF-8 string (contains nulls)")
        return decoded
    else:
        raise ParseFailure("Invalid UTF-8 string (contains surrogates)")

def parse_pair():

            topic_filter = read_string(data)
            reserved = data.read("uint:6")
            max_qos = data.read("uint:2")

            if reserved:
                raise ParseFailure(cls, "Data in QoS Reserved area")

            if max_qos not in [0, 1, 2]:
                raise ParseFailure(cls, "Invalid QoS")

            pairs.append(SubscriptionTopicRequest(topic_filter=topic_filter,
                                                  max_qos=max_qos))

def deserialise(cls, flags, data):
        if flags != (False, False, True, False):
            raise ParseFailure(cls, "Bad flags")

        topics = []
        packet_identifier = data.read('uint:16')

        while not data.bitpos == len(data):
            topics.append(read_string(data))

        if len(topics) == 0:
            raise ParseFailure(cls, "Must contain a payload.")

        return cls(packet_identifier=packet_identifier, topics=topics)

def deserialise(cls, flags, data):
        """
        Disassemble from an on-wire message.
        """
        if flags != (False, False, False, False):
            raise ParseFailure(cls, "Bad flags")

        protocol = read_string(data)

        if protocol != "MQTT":
            print(protocol)
            raise ParseFailure(cls, "Bad protocol name")

        protocol_level = data.read('uint:8')

        if protocol_level != 4:
            raise ParseFailure(cls, "Bad protocol level")

        flags = ConnectFlags.deserialise(data.read(8))

        # Keep alive, in seconds
        keep_alive = data.read('uint:16')

        # The client ID
        client_id = read_string(data)

        if flags.will:
            # MQTT-3.1.3-10, topic must be UTF-8

def deserialise(cls, flags, data):
        if flags != (False, False, True, False):
            raise ParseFailure(cls, "Bad flags")

        topics = []
        packet_identifier = data.read('uint:16')

        while not data.bitpos == len(data):
            topics.append(read_string(data))

        if len(topics) == 0:
            raise ParseFailure(cls, "Must contain a payload.")

        return cls(packet_identifier=packet_identifier, topics=topics)