September 17, 2023

Managing MQTT Session Persistence in C and Python Applications: Intermediate Techniques

As an intermediate developer building MQTT-based applications in C and Python, you may find that managing session persistence becomes a critical aspect of your implementation. In this blog post, we’ll explore advanced techniques for managing MQTT session persistence, with extensive examples in both C and Python.

Understanding MQTT Session Persistence

In MQTT, a session is established when a client connects to a broker. The session may be either persistent or non-persistent. A persistent session ensures that messages are delivered reliably, even if the client disconnects and reconnects. On the other hand, a non-persistent session does not store any messages while the client is disconnected.

Managing Session Persistence in C

In C, you can leverage the Eclipse Paho MQTT client library to handle session persistence effectively. Here’s an example of using the Paho MQTT library to create a persistent session:

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#include <stdio.h>
#include <string.h>
#include "MQTTClient.h"

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ExampleClientPersist"
#define QOS         1
#define TIMEOUT     10000L

int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 0; // Set to 0 for persistent session

    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    
    // Connect to the broker with persistence options
    if (MQTTClient_connect(client, &conn_opts) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect to broker\n");
        return -1;
    }

    // ... (further publish and subscribe code)

    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return 0;
}

In this example, setting conn_opts.cleansession to 0 indicates that a persistent session should be created.

Managing Session Persistence in Python

When working in Python, the Eclipse Paho MQTT client also provides a mechanism to manage session persistence. Here’s an example using the Paho MQTT library in Python to establish a persistent session:

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import paho.mqtt.client as mqtt

def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("topic")

client = mqtt.Client(client_id="ExampleClientPersist")
client.on_connect = on_connect
client.connect("localhost", 1883, 60)

# Infinite loop to maintain the connection
client.loop_forever()

In this Python code snippet, the client_id parameter is used to specify the client identifier, and the client connects with a default persistence option, which is persistent.

Conclusion

In this blog post, we’ve delved into the intermediate techniques for managing MQTT session persistence in C and Python applications. By understanding the concepts of session persistence and leveraging the appropriate client libraries, you can build robust and reliable MQTT-based applications that seamlessly handle disconnections and reconnections.

Feel free to experiment with the provided code examples and explore further customization options offered by the Eclipse Paho MQTT client library. Happy coding!

➡️ Exploring MQTT Message Filtering in C and Python Development: Intermediate Concepts

⬅️ ESP32 programmer

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