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Connect via C# SDK ​

C# is an object-oriented programming language provided by Microsoft that runs on .NET Framework.

This article mainly introduces how to use the paho.mqtt.m2mqtt client library in a C# project to connect, subscribe, publish and receive messages from the client to the MQTT server.

Prerequisites ​

Before connecting your application to the EMQX Cloud using the C# client, ensure you have completed the following prerequisites:

  • Deploy MQTT Broker
  • Check .NET version
  • Choose the MQTT Client
  • Install M2Mqtt

Deploy MQTT Broker ​

To connect your application to the EMQX Cloud, you need to create and configure a deployment.

Serverless Deployment ​

  1. Create a Serverless deployment in the EMQX Cloud Console.

  2. Once the deployment is created and running, go to the deployment Overview page to find the MQTT connection information, including:

    • Broker address

    • Port number (only TLS ports are supported in Serverless)

  3. Serverless deployments require TLS connections. Make sure to download the CA certificate from the Overview page and use port 8883 for TLS.

  4. Configure the default authentication (username/password) under Access Control -> Client Authentication in the deployment.

For more details, refer to the Serverless Port Guide.

Dedicated Flex or BYOC Deployment ​

  1. You can create a Dedicated Flex or BYOC deployment in the EMQX Cloud Console.
  2. After creation, go to the deployment Overview page to retrieve MQTT connection information, including:
    • Broker address
    • TCP and TLS port numbers for MQTT and WebSocket (Both TCP and TLS connections are supported).
  3. Configure the default authentication (username/password) under Access Control -> Client Authentication in the deployment.

For detailed port configurations, see the Dedicated & BYOC Port Guide.

Check .NET Version ​

This project uses .NET 5.0 to develop and test. You can use the following command to confirm the .NET version.

bash
~ dotnet --version            
5.0.301

Choose the MQTT client ​

paho.mqtt.m2mqtt is a MQTT client available for all .NET platforms with support for both MQTT v3.1 and v3.1.1.

Install M2Mqtt Using .NET CLI ​

Use the following command in the root of the project to install M2Mqtt.

bash
dotnet add package M2Mqtt --version 4.3.0

Connection ​

Please find the relevant address and port information in the Deployment Overview of the Console. Please note that if it is the basic edition, the port is not 1883 or 8883, please confirm the port.

Connect to the MQTT broker ​

This article will use the free public MQTT broker provided by EMQX. This service is created based on MQTT IoT cloud platform to create. The accessing information of the broker is as follows:

  • Broker: broker.emqx.io
  • TCP Port: 1883
  • WebSocket Port: 8083

Import the M2Mqtt ​

csharp
using uPLibrary.Networking.M2Mqtt;

Set the parameter of MQTT Broker connection ​

Set the address, port and topic of MQTT Broker connection. At the same time, we call the C# Guid.NewGuid() to randomly generate uid as the MQTT client id.

csharp
string broker = "broker.emqx.io";
int port = 1883;
string topic = "Csharp/mqtt";
string clientId = Guid.NewGuid().ToString();
// If the broker requires authentication, set the username and password
string username = "emqx";
string password = "public";

Write the MQTT connect method ​

Write static class method ConnectMQTT to create an MQTT client and connect it to the specified broker. We can determine whether the client is connected successfully according to the client's property of IsConnected. In the end, the client is returned.

csharp
static MqttClient ConnectMQTT(string broker, int port, string clientId, string username, string password)
{
    MqttClient client = new MqttClient(broker, port, false, MqttSslProtocols.None, null, null);
    client.Connect(clientId, username, password);
    if (client.IsConnected)
    {
        Console.WriteLine("Connected to MQTT Broker");
    }
    else
    {
        Console.WriteLine("Failed to connect");
    }
    return client;
}

Publish messages ​

We define a while loop. In this loop we will set the MQTT client Publish method to publish messages to the specified topic every second.

csharp
static void Publish(MqttClient client, string topic)
{
    int msg_count = 0;
    while (true)
    {
        System.Threading.Thread.Sleep(1*1000);
        string msg = "messages: " + msg_count.ToString();
        client.Publish(topic, System.Text.Encoding.UTF8.GetBytes(msg));
        Console.WriteLine("Send `{0}` to topic `{1}`", msg, topic);
        msg_count++;
    }
}

Subscribe to a topic ​

Write the static method client_MqttMsgPublishReceived. This method will be called after the client received messages from the MQTT Broker. In this method, we will print the topic and payload of the messages.

csharp
static void Subscribe(MqttClient client, string topic)
{
    client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
    client.Subscribe(new string[] { topic }, new byte[] { MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE });
}
static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
{
    string payload = System.Text.Encoding.Default.GetString(e.Message);
    Console.WriteLine("Received `{0}` from `{1}` topic", payload, e.Topic.ToString());
}

The complete code ​

csharp
using System;
using uPLibrary.Networking.M2Mqtt;
using uPLibrary.Networking.M2Mqtt.Messages;

namespace csharpMQTT
{
    class Program
    {
        static MqttClient ConnectMQTT(string broker, int port, string clientId, string username, string password)
        {
            MqttClient client = new MqttClient(broker, port, false, MqttSslProtocols.None, null, null);
            client.Connect(clientId, username, password);
            if (client.IsConnected)
            {
                Console.WriteLine("Connected to MQTT Broker");
            }
            else
            {
                Console.WriteLine("Failed to connect");
            }
            return client;
        }

        static void Publish(MqttClient client, string topic)
        {
            int msg_count = 0;
            while (true)
            {
                System.Threading.Thread.Sleep(1*1000);
                string msg = "messages: " + msg_count.ToString();
                client.Publish(topic, System.Text.Encoding.UTF8.GetBytes(msg));
                Console.WriteLine("Send `{0}` to topic `{1}`", msg, topic);
                msg_count++;
            }
        }

        static void Subscribe(MqttClient client, string topic)
        {
            client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
            client.Subscribe(new string[] { topic }, new byte[] { MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE });
        }
        static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
        {
            string payload = System.Text.Encoding.Default.GetString(e.Message);
            Console.WriteLine("Received `{0}` from `{1}` topic", payload, e.Topic.ToString());
        }

        static void Main(string[] args)
        {
            string broker = "broker.emqx.io";
            int port = 1883;
            string topic = "Csharp/mqtt";
            string clientId = Guid.NewGuid().ToString();
            string username = "emqx";
            string password = "public";
            MqttClient client = ConnectMQTT(broker, port, clientId, username, password);
            Subscribe(client, topic);
            Publish(client, topic);
        }
    }
}

Test ​

Run the code, the console output is as follows. c_sharp_connect