Python Demo

Prerequisites

Knowledge of basic Python syntax and how to configure development environments.

Development Environment

In this example, Python 3.8.8 is used.

Dependency

In this example, paho-mqtt (version 2.0.0) is used. You can run the following command to download the dependency:

pip install paho-mqtt==2.0.0

Sample Code

ClientConf code:

from typing import Optional
class ClientConf:
    def __init__(self):
        # MQTT subscription address
        self.__host: Optional[str] = None
        # MQTT subscription port number
        self.__port: Optional[int] = None
        # MQTT access credential access_key
        self.__access_key: Optional[str] = None
        # MQTT access credential access_code
        self.__access_code: Optional[str] = None
        # MQTT subscription topic
        self.__topic: Optional[str] = None
        # Instance ID. This parameter is mandatory when multiple instances of the standard edition are purchased in the same region.
        self.__instance_id: Optional[str] = None
        # mqtt qos
        self.__qos = 1

    @property
    def host(self):
        return self.__host
    @host.setter
    def host(self, host):
        self.__host = host
    @property
    def port(self):
        return self.__port
    @port.setter
    def port(self, port):
        self.__port = port
    @property
    def access_key(self):
        return self.__access_key
    @access_key.setter
    def access_key(self, access_key):
        self.__access_key = access_key
    @property
    def access_code(self):
        return self.__access_code
    @access_code.setter
    def access_code(self, access_code):
        self.__access_code = access_code
    @property
    def topic(self):
        return self.__topic
    @topic.setter
    def topic(self, topic):
        self.__topic = topic
    @property
    def instance_id(self):
        return self.__instance_id
    @instance_id.setter
    def instance_id(self, instance_id):
        self.__instance_id = instance_id
    @property
    def qos(self):
        return self.__qos
    @qos.setter
    def qos(self, qos):
        self.__qos = qos

MqttClient code:

import os
import ssl
import threading
import time
import traceback
import secrets
from client_conf import ClientConf
import paho.mqtt.client as mqtt
class MqttClient:
    def __init__(self, client_conf: ClientConf):
        self.__host = client_conf.host
        self.__port = client_conf.port
        self.__access_key = client_conf.access_key
        self.__access_code = client_conf.access_code
        self.__topic = client_conf.topic
        self.__instance_id = client_conf.instance_id
        self.__qos = client_conf.qos
        self.__paho_client: Optional[mqtt.Client] = None
        self.__connect_result_code = -1
        self.__default_backoff = 1000
        self.__retry_times = 0
        self.__min_backoff = 1 * 1000  # 1s
        self.__max_backoff = 30 * 1000  # 30s

    def connect(self):
        self.__valid_params()
        rc = self.__connect()
        while rc != 0:
            # Backoff reconnection
            low_bound = int(self.__default_backoff * 0.8)
            high_bound = int(self.__default_backoff * 1.0)
            random_backoff = secrets.randbelow(high_bound - low_bound)
            backoff_with_jitter = int(pow(2, self.__retry_times)) * (random_backoff + low_bound)
            wait_time_ms = self.__max_backoff if (self.__min_backoff + backoff_with_jitter) > self.__max_backoff else (
                    self.__min_backoff + backoff_with_jitter)
            wait_time_s = round(wait_time_ms / 1000, 2)
            print("client will try to reconnect after " + str(wait_time_s) + " s")
            time.sleep(wait_time_s)
            self.__retry_times += 1
            self.close() # Release the previous connection.
            rc = self.__connect()
            # If the value of rc is 0, the connection is set up successfully. Otherwise, the connection fails.
            if rc != 0:
                print("connect with result code: " + str(rc))
                if rc == 134:
                    print("connect failed with bad username or password, "
                          "reconnection will not be performed")
                    pass
        return rc
    def __connect(self):
        try:
            timestamp = self.current_time_millis()
            user_name = "accessKey=" + self.__access_key + "|timestamp=" + timestamp
            if self.__instance_id:
                user_name = user_name + "|instanceId=" + self.__instance_id
            pass_word = self.__access_code
            self.__paho_client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2, "mqttClient")
            # Disable automatic retry and update the timestamp by manual retry.
            self.__paho_client._reconnect_on_failure = False
            # Set the callback function.
            self._set_callback()
            # Topics are stored in userdata. The callback function directly subscribes to topics.
            self.__paho_client.user_data_set(self.__topic)
            self.__paho_client.username_pw_set(user_name, pass_word)
            # Currently, the MQTT broker supports only TLS 1.2.
            context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
            # Not verifying the server certificate.
            context.verify_mode = ssl.CERT_NONE
            context.check_hostname = False
            self.__paho_client.tls_set_context(context)
            rc = self.__paho_client.connect(self.__host, self.__port)
            self.__connect_result_code = rc
            if rc == 0:
                threading.Thread(target=self.__paho_client.loop_forever, args=(1, False), name="MqttThread").start()
            # Wait for connection establishment.
            time.sleep(1)
        except Exception as e:
            self.__connect_result_code = -1
            print("Mqtt connection error. traceback: " + traceback.format_exc())
        if self.__paho_client.is_connected():
            return 0
        else:
            return self.__connect_result_code
    def __valid_params(self):
        assert self.__access_key is not None
        assert self.__access_code is not None
        assert self.__topic is not None

    @staticmethod
    def current_time_millis():
        return str(int(round(time.time() * 1000)))
    def _set_callback(self):
        # Execute self._on_connect() when the platform responds to the connection request.
        self.__paho_client.on_connect = self._on_connect
        # Execute self._on_disconnect() when disconnecting from the platform.
        self.__paho_client.on_disconnect = self._on_disconnect
        # Execute self._on_subscribe when subscribing to a topic.
        self.__paho_client.on_subscribe = self._on_subscribe
        # Execute self._on_message() when an original message is received.
        self.__paho_client.on_message = self._on_message
    def _on_connect(self, client, userdata, flags, rc: mqtt.ReasonCode, properties):
        if rc == 0:
            print("Connected to Mqtt Broker! topic " + self.__topic)
            client.subscribe(userdata, 1)
        else:
            # Automatic reconnection is not performed only when the username or password is incorrect.
            # If the disconnect() method is not used here, loop_forever keeps reconnecting.
            if rc == 134:
                self.__paho_client.disconnect()
            print("Failed to connect. return code :" + str(rc.value) + ", reason" + rc.getName())
    def _on_subscribe(self, client, userdata, mid, granted_qos, properties):
        print("Subscribed: " + str(mid) + " " + str(granted_qos) + " topic: " + self.__topic)
    def _on_message(self, client, userdata, message: mqtt.MQTTMessage):
        print("topic " + self.__topic + " Received message: " + message.payload.decode())
    def _on_disconnect(self, client, userdata, flags, rc, properties):
        print("Disconnect to Mqtt Broker. topic: " + self.__topic)
        # Shut down the client after the disconnection and manually reconnect the client to refresh the timestamp.
        try:
            self.__paho_client.disconnect()
        except Exception as e:
            print("Mqtt connection error. traceback: " + traceback.format_exc())
        self.connect()
    def close(self):
        if self.__paho_client is not None and self.__paho_client.is_connected():
            try:
                self.__paho_client.disconnect()
                print("Mqtt connection close")
            except Exception as e:
                print("paho client disconnect failed. exception: " + str(e))
        else:
            pass

MqttDemo code:

from client_conf import ClientConf
from mqtt_client import MqttClient
import os
from typing import Optional
def main():
    client_conf = ClientConf()
    client_conf.host = "your ip host"
    client_conf.port = 8883
    client_conf.topic = "your mqtt topic"
    # MQTT access credential access_key can be injected using environment variables.
    client_conf.access_key = os.environ.get("MQTT_ACCESS_KEY")
    # MQTT access credential access_code can be injected using environment variables.
    client_conf.access_code = os.environ.get("MQTT_ACCESS_CODE")
    client_conf.instance_id = "your instance id"
    mqtt_client = MqttClient(client_conf)
    if mqtt_client.connect() != 0:
        print("init failed")
        return
if __name__ == "__main__":
    main()

Success Example

After the access is successful, the following information is displayed on the client.

Figure 1 Example of successful MQTT subscription using Python