def subscribe(self, topic, requestedQoS=0, messageId=None):
        header = bytearray()
        varHeader = bytearray()
        payload = bytearray()

        # Type = subscribe, QoS = 1
        header.append(0x08 << 4 | 0x01 << 1)

        if messageId is None:
            varHeader.extend(self._encodeValue(random.randint(1, 0xFFFF)))
        else:
            varHeader.extend(self._encodeValue(messageId))

        payload.extend(self._encodeString(topic))
        payload.append(requestedQoS)

        header.extend(self._encodeLength(len(varHeader) + len(payload)))

        self.transport.write(str(header))
        self.transport.write(str(varHeader))
        self.transport.write(str(payload))
Returns the str username of the user that has logged in the most.
dataset/ETHPy150Open adamvr/MQTT-For-Twisted-Python/MQTT.py/MQTTProtocol.subscribe--crossover with--dataset/ETHPy150Open google/simian/src/simian/mac/client/flight_common.py/_GetPrimaryUser