Introduction
This guide walks you through creating a simple MQTT client using .NET and the MQTTnet library. The client will connect to an MQTT broker.
Setup & Dependencies
Before you begin, ensure the following are installed and configured:
- .NET SDK (version 6.0 or later recommended)
Check with: - Access to an MQTT broker running locally or remotely
- Add MQTTnet library to your project
Navigate to your project directory and run:
dotnet --version
dotnet add package MQTTnet --version 4.3.6.1152
MQTT Connect
This section covers various ways to connect to an MQTT broker using Python. Before proceeding, ensure your broker supports the desired connection method (TCP, TLS, WebSocket, etc.) and you have the correct connection parameters:
- Broker Address
- Port
- Username/Password (if required)
- CA Certificate (for TLS connections)
Basic TCP Connection
var options = new MqttClientOptionsBuilder()
.WithClientId("testClientDotNet4")
.WithTcpServer("localhost", 1883)
.Build();
// Create MQTT client
var factory = new MqttFactory();
var mqttClient = factory.CreateMqttClient();
mqttClient.UseConnectedHandler(async e =>
{
Console.WriteLine("Connected successfully with MQTT broker.");
});
// Connect to the MQTT broker
await mqttClient.ConnectAsync(options);
Connect with Authentication:
var options = new MqttClientOptionsBuilder()
.WithClientId("testclient")
.WithTcpServer("localhost", 1883)
.WithCredentials("username", "password") // Add username and password
.Build();
Connect over TLS/SSL
var options = new MqttClientOptionsBuilder()
.WithClientId("testcient")
.WithTcpServer(GetHostFromAddress(ADDRESS), GetPortFromAddress(ADDRESS))
.WithTls(new MqttClientOptionsBuilderTlsParameters
{
UseTls = true,
Certificates = new List(), // Optionally add client certificates here
CertificateValidationHandler = context =>
{
// Custom server certificate validation logic
return context.SslPolicyErrors == System.Net.Security.SslPolicyErrors.None;
},
AllowUntrustedCertificates = false, // Do not allow untrusted certificates
IgnoreCertificateChainErrors = false, // Do not ignore certificate chain errors
IgnoreCertificateRevocationErrors = false // Do not ignore certificate revocation errors
})
.Build();
Connect via WebSocket
var options = new MqttClientOptionsBuilder()
.WithClientId("testclient")
.WithWebSocketServer("ws://localhost:10443/mqtt") // Use WebSocket server URI
.Build();
MQTT Publish
var message = new MqttApplicationMessageBuilder()
.WithTopic(topic)
.WithPayload($"Hello, MQTT! Message number {i}")
.WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
.WithRetainFlag()
.Build();
await mqttClient.PublishAsync(message);
await Task.Delay(1000); // Wait for 1 second
MQTT Subscribe
await mqttClient.SubscribeAsync(topic);
MQTT Disconnect
await mqttClient.DisconnectAsync();
Sample Client
using System.Security.Authentication;
using System.Text;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
class Program
{
static async Task Main(string[] args)
{
string broker = "localhost";
int port = 1883;
string clientId = Guid.NewGuid().ToString();
string topic = "sensor/data";
// Create a MQTT client factory
var factory = new MqttFactory();
// Create a MQTT client instance
var mqttClient = factory.CreateMqttClient();
// Create MQTT client options
var options = new MqttClientOptionsBuilder()
.WithTcpServer(broker, port) // MQTT broker address and port
.WithClientId(clientId)
.WithCleanSession()
.WithCredentials("username", "password")
// .WithProtocolVersion(MQTTnet.Formatter.MqttProtocolVersion.V500) //if you use mqtt version 5
.Build();
// Connect to MQTT broker
var connectResult = await mqttClient.ConnectAsync(options);
if (connectResult.ResultCode == MqttClientConnectResultCode.Success)
{
Console.WriteLine("Connected to MQTT broker successfully.");
// Subscribe to a topic
await mqttClient.SubscribeAsync(topic);
// Callback function when a message is received
mqttClient.ApplicationMessageReceivedAsync += e =>
{
Console.WriteLine($"Received message: {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
return Task.CompletedTask;
};
var message = new MqttApplicationMessageBuilder()
.WithTopic(topic)
.WithPayload($"Hello, MQTT!")
.WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
.WithRetainFlag()
.Build();
Console.WriteLine($"Publishing message: {Encoding.UTF8.GetString(message.PayloadSegment)}");
await mqttClient.PublishAsync(message);
await Task.Delay(1000); // Wait for 1 second
// Unsubscribe and disconnect
await mqttClient.UnsubscribeAsync(topic);
await mqttClient.DisconnectAsync();
}
else
{
Console.WriteLine($"Failed to connect to MQTT broker: {connectResult.ResultCode}");
}
}
}
Run the following command to execute the program.
dotnet run
