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TDMQ for MQTT

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DocumentationTDMQ for MQTTSDK Reference.NET

.NET

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Last updated: 2026-04-01 16:37:52

Feature Overview

MQTTnet is a high-performance .NET MQTT client library that supports MQTT protocol versions 3.1.1 and 5.0. Written entirely in C#, it provides feature-rich MQTT client and server implementations.

Key Features

Supports .NET Framework 4.5.2+ and .NET Core/.NET 5+.
Supports both synchronous and asynchronous operations.
Fully supports the MQTT v3.1.1 and v5.0 protocols.
Supports TCP, WebSocket, and TLS/SSL encrypted connections.
Supports advanced features such as shared subscriptions, retained messages, and will messages.

Cloud Resource Preparation

Please refer to the relevant documentation to complete cloud resource preparation and obtain the following information:
MQTT Broker address
Port number (typically 1883 or 8883)
Username and password (if authentication is required)
TLS/SSL certificate (if using encrypted connections)

Environment Preparation

System Requirements

.NET 6.0 or later (recommended)
.NET Framework 4.5.2+ or .NET Core 2.0+

Installing the MQTTnet SDK

Method 1: using the NuGet package manager
dotnet add package MQTTnet
Method 2: using Visual Studio
1.1 Right-click Project > Manage NuGet Packages.
1.2 Search for "MQTTnet".
1.3 Install the latest stable version.
Method 3: editing the .csproj file

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="MQTTnet" Version="4.3.7.1207" />
  </ItemGroup>
</Project>

Sample Code

MQTT5
MQTT5 TLS
MQTT3.1.1
MQTT3.1.1 TLS
using System;
using System.Text;
using System.Threading.Tasks;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
using MQTTnet.Formatter;

class MQTT5_TCP_Sample
{
    static async Task Main(string[] args)
    {
        // ============ Connection Configuration ============
        String serverUri = "tcp://mqtt-xxx.mqtt.tencenttdmq.com:1883";
        String clientId = "QuickStart";
        String username = "YOUR_USERNAME";
        String password = "YOUR_PASSWORD";
        String pubTopic = "home/test";
        String[] topicFilters = new String[] { pubTopic, "home/#", "home/+" };
        int[] qos = new int[] { 1, 1, 1 };

        // Parse the URI.
        var uri = new Uri(serverUri);
        
        // Create a client.
        var factory = new MqttFactory();
        var client = factory.CreateMqttClient();

        // Configure connection options.
        var options = new MqttClientOptionsBuilder()
            .WithTcpServer(uri.Host, uri.Port)
            .WithCredentials(username, password)
            .WithClientId(clientId)
            .WithProtocolVersion(MqttProtocolVersion.V500)
            .WithCleanStart(true)
            .Build();

        // Message receiving and processing
        client.ApplicationMessageReceivedAsync += e =>
        {
            Console.WriteLine($"Received message: {e.ApplicationMessage.Topic} -> {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
            return Task.CompletedTask;
        };

        try
        {
            // 1. Connect
            await client.ConnectAsync(options);
            Console.WriteLine("Connected");

            // 2. Subscribe
            for (int i = 0; i < topicFilters.Length; i++)
            {
                await client.SubscribeAsync(new MqttClientSubscribeOptionsBuilder()
                    .WithTopicFilter(f => f.WithTopic(topicFilters[i]).WithQualityOfServiceLevel((MqttQualityOfServiceLevel)qos[i]))
                    .Build());
            }
            Console.WriteLine("Subscribed");

            // 3. Publish
            for (int i = 1; i <= 16; i++)
            {
                await client.PublishAsync(new MqttApplicationMessageBuilder()
                    .WithTopic(pubTopic)
                    .WithPayload($"Message #{i}")
                    .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                    .Build());
                
                await Task.Delay(500);
            }
            Console.WriteLine("Published");

            // 4. Wait to receive
            await Task.Delay(2000);

            // 5. Disconnect
            await client.DisconnectAsync();
            Console.WriteLine("Disconnected");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}

using System;
using System.Text;
using System.Threading.Tasks;
using System.Security.Authentication;
using System.Security.Cryptography.X509Certificates;
using System.Net.Security;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
using MQTTnet.Formatter;

class MQTT5_TLS_Sample
{
    static async Task Main(string[] args)
    {

        // ============ Connection Configuration ============
        String serverUri = "ssl://mqtt-xxx.mqtt.tencenttdmq.com:8883";
        String clientId = "QuickStart";
        String username = "YOUR_USERNAME";
        String password = "YOUR_PASSWORD";
        String pubTopic = "home/test";
        String[] topicFilters = new String[] { pubTopic, "home/#", "home/+" };
        int[] qos = new int[] { 1, 1, 1 };

        // CA certificate path (optional, used to verify the server certificate)
        String caCertPath = null; // e.g. "/path/to/ca.crt"

        // Parse the URI.
        var uri = new Uri(serverUri);
        
        // Create a client.
        var factory = new MqttFactory();
        var client = factory.CreateMqttClient();

        // Configure connection options (including TLS).
        var options = new MqttClientOptionsBuilder()
            .WithTcpServer(uri.Host, uri.Port)
            .WithCredentials(username, password)
            .WithClientId(clientId)
            .WithProtocolVersion(MqttProtocolVersion.V500)
            .WithCleanStart(true)
            .WithTlsOptions(tls =>
            {
                tls.UseTls();
                tls.WithSslProtocols(SslProtocols.Tls12 | SslProtocols.Tls13);
                
                // If a CA certificate is provided, load it.
                if (!string.IsNullOrEmpty(caCertPath))
                {
                    var caCert = new X509Certificate2(caCertPath);
                    tls.WithClientCertificates(new[] { caCert });
                }
                
                // Certificate verification callback
                tls.WithCertificateValidationHandler(context =>
                {
                    var certificate = context.Certificate as X509Certificate2;
                    
                    // Test environment: accept all certificates
                    // return true;
                    
                    // Production environment: strict certificate verification
                    return ValidateServerCertificate(certificate, context.Chain, context.SslPolicyErrors);
                });
            })
            .Build();

        // Message receiving and processing
        client.ApplicationMessageReceivedAsync += e =>
        {
            Console.WriteLine($"Received message: {e.ApplicationMessage.Topic} -> {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
            return Task.CompletedTask;
        };

        try
        {
            // 1. Connect
            await client.ConnectAsync(options);
            Console.WriteLine("Connected (TLS encrypted)");

            // 2. Subscribe
            for (int i = 0; i < topicFilters.Length; i++)
            {
                await client.SubscribeAsync(new MqttClientSubscribeOptionsBuilder()
                    .WithTopicFilter(f => f.WithTopic(topicFilters[i]).WithQualityOfServiceLevel((MqttQualityOfServiceLevel)qos[i]))
                    .Build());
            }
            Console.WriteLine("Subscribed");

            // 3. Publish
            for (int i = 1; i <= 16; i++)
            {
                await client.PublishAsync(new MqttApplicationMessageBuilder()
                    .WithTopic(pubTopic)
                    .WithPayload($"Message #{i}")
                    .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                    .Build());
                
                await Task.Delay(500);
            }
            Console.WriteLine("Published");

            // 4. Wait to receive
            await Task.Delay(2000);

            // 5. Disconnect
            await client.DisconnectAsync();
            Console.WriteLine("Disconnected");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }

    /// <summary>
    /// Verify the server certificate.
    /// </summary>
    static bool ValidateServerCertificate(X509Certificate2 certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
    {
        // If there is no error, proceed directly.
        if (sslPolicyErrors == SslPolicyErrors.None)
        {
            return true;
        }

        // If the certificate is null, reject.
        if (certificate == null)
        {
            Console.WriteLine("Certificate verification failed: The certificate is null");
            return false;
        }

        // 1. Check the certificate validity period.
        DateTime now = DateTime.Now;
        if (now < certificate.NotBefore || now > certificate.NotAfter)
        {
            Console.WriteLine($"Certificate verification failed: The certificate has expired or is not yet valid (validity period: {certificate.NotBefore} - {certificate.NotAfter})");
            return false;
        }

        // 2. Check the certificate chain.
        if (chain != null && chain.ChainStatus.Length > 0)
        {
            foreach (var status in chain.ChainStatus)
            {
                // Ignore offline revocation check errors (optional).
                if (status.Status == X509ChainStatusFlags.RevocationStatusUnknown ||
                    status.Status == X509ChainStatusFlags.OfflineRevocation)
                {
                    continue;
                }
                
                if (status.Status != X509ChainStatusFlags.NoError)
                {
                    Console.WriteLine($"Certificate verification failed: {status.StatusInformation}");
                    return false;
                }
            }
        }

        // 3. Check the certificate subject name (optional, based on actual requirements).
        // string expectedSubject = "CN=*.mqtt.tencenttdmq.com";
        // if (!certificate.Subject.Contains(expectedSubject))
        // {
        //     Console.WriteLine($"Certificate verification failed: Subject mismatch (expected: {expectedSubject}, actual: {certificate.Subject})");
        //     return false;
        // }

        Console.WriteLine("Certificate verification passed");
        return true;
    }
}



using System;
using System.Text;
using System.Threading.Tasks;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
using MQTTnet.Formatter;

class MQTT311_TCP_Sample
{
    static async Task Main(string[] args)
    {
        // ============ Connection Configuration ============
        String serverUri = "tcp://mqtt-xxx.mqtt.tencenttdmq.com:1883";
        String clientId = "QuickStart";
        String username = "YOUR_USERNAME";
        String password = "YOUR_PASSWORD";
        String pubTopic = "home/test";
        String[] topicFilters = new String[] { pubTopic, "home/#", "home/+" };
        int[] qos = new int[] { 1, 1, 1 };

        // Parse the URI.
        var uri = new Uri(serverUri);
        
        // Create a client.
        var factory = new MqttFactory();
        var client = factory.CreateMqttClient();

        // Configure connection options.
        var options = new MqttClientOptionsBuilder()
            .WithTcpServer(uri.Host, uri.Port)
            .WithCredentials(username, password)
            .WithClientId(clientId)
            .WithProtocolVersion(MqttProtocolVersion.V311)
            .WithCleanSession(true)
            .Build();

        // Message receiving and processing
        client.ApplicationMessageReceivedAsync += e =>
        {
            Console.WriteLine($"Received message: {e.ApplicationMessage.Topic} -> {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
            return Task.CompletedTask;
        };

        try
        {
            // 1. Connect
            await client.ConnectAsync(options);
            Console.WriteLine("Connected");

            // 2. Subscribe
            for (int i = 0; i < topicFilters.Length; i++)
            {
                await client.SubscribeAsync(new MqttClientSubscribeOptionsBuilder()
                    .WithTopicFilter(f => f.WithTopic(topicFilters[i]).WithQualityOfServiceLevel((MqttQualityOfServiceLevel)qos[i]))
                    .Build());
            }
            Console.WriteLine("Subscribed");

            // 3. Publish
            for (int i = 1; i <= 16; i++)
            {
                await client.PublishAsync(new MqttApplicationMessageBuilder()
                    .WithTopic(pubTopic)
                    .WithPayload($"Message #{i}")
                    .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                    .Build());
                
                await Task.Delay(500);
            }
            Console.WriteLine("Published");

            // 4. Wait to receive
            await Task.Delay(2000);

            // 5. Disconnect
            await client.DisconnectAsync();
            Console.WriteLine("Disconnected");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}


using System;
using System.Text;
using System.Threading.Tasks;
using System.Security.Authentication;
using System.Security.Cryptography.X509Certificates;
using System.Net.Security;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
using MQTTnet.Formatter;

class MQTT311_TLS_Sample
{
    static async Task Main(string[] args)
    {

        // ============ Connection Configuration ============
        String serverUri = "ssl://mqtt-xxx.mqtt.tencenttdmq.com:8883";
        String clientId = "QuickStart";
        String username = "YOUR_USERNAME";
        String password = "YOUR_PASSWORD";
        String pubTopic = "home/test";
        String[] topicFilters = new String[] { pubTopic, "home/#", "home/+" };
        int[] qos = new int[] { 1, 1, 1 };

        // CA certificate path (optional, used to verify the server certificate)
        String caCertPath = null; // e.g. "/path/to/ca.crt"

        // Parse the URI.
        var uri = new Uri(serverUri);
        
        // Create a client.
        var factory = new MqttFactory();
        var client = factory.CreateMqttClient();

        // Configure connection options (including TLS).
        var options = new MqttClientOptionsBuilder()
            .WithTcpServer(uri.Host, uri.Port)
            .WithCredentials(username, password)
            .WithClientId(clientId)
            .WithProtocolVersion(MqttProtocolVersion.V311)
            .WithCleanSession(true)
            .WithTlsOptions(tls =>
            {
                tls.UseTls();
                tls.WithSslProtocols(SslProtocols.Tls12 | SslProtocols.Tls13);
                
                // If a CA certificate is provided, load it.
                if (!string.IsNullOrEmpty(caCertPath))
                {
                    var caCert = new X509Certificate2(caCertPath);
                    tls.WithClientCertificates(new[] { caCert });
                }
                
                // Certificate verification callback
                tls.WithCertificateValidationHandler(context =>
                {
                    var certificate = context.Certificate as X509Certificate2;
                    
                    // Test environment: accept all certificates
                    // return true;
                    
                    // Production environment: strict certificate verification
                    return ValidateServerCertificate(certificate, context.Chain, context.SslPolicyErrors);
                });
            })
            .Build();

        // Message receiving and processing
        client.ApplicationMessageReceivedAsync += e =>
        {
            Console.WriteLine($"Received message: {e.ApplicationMessage.Topic} -> {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
            return Task.CompletedTask;
        };

        try
        {
            // 1. Connect
            await client.ConnectAsync(options);
            Console.WriteLine("Connected (TLS encrypted)");

            // 2. Subscribe
            for (int i = 0; i < topicFilters.Length; i++)
            {
                await client.SubscribeAsync(new MqttClientSubscribeOptionsBuilder()
                    .WithTopicFilter(f => f.WithTopic(topicFilters[i]).WithQualityOfServiceLevel((MqttQualityOfServiceLevel)qos[i]))
                    .Build());
            }
            Console.WriteLine("Subscribed");

            // 3. Publish
            for (int i = 1; i <= 16; i++)
            {
                await client.PublishAsync(new MqttApplicationMessageBuilder()
                    .WithTopic(pubTopic)
                    .WithPayload($"Message #{i}")
                    .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                    .Build());
                
                await Task.Delay(500);
            }
            Console.WriteLine("Published");

            // 4. Wait to receive
            await Task.Delay(2000);

            // 5. Disconnect
            await client.DisconnectAsync();
            Console.WriteLine("Disconnected");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }

    /// <summary>
    /// Verify the server certificate.
    /// </summary>
    static bool ValidateServerCertificate(X509Certificate2 certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
    {
        // If there is no error, proceed directly.
        if (sslPolicyErrors == SslPolicyErrors.None)
        {
            return true;
        }

        // If the certificate is null, reject.
        if (certificate == null)
        {
            Console.WriteLine("Certificate verification failed: The certificate is null");
            return false;
        }

        // 1. Check the certificate validity period.
        DateTime now = DateTime.Now;
        if (now < certificate.NotBefore || now > certificate.NotAfter)
        {
            Console.WriteLine($"Certificate verification failed: The certificate has expired or is not yet valid (validity period: {certificate.NotBefore} - {certificate.NotAfter})");
            return false;
        }

        // 2. Check the certificate chain.
        if (chain != null && chain.ChainStatus.Length > 0)
        {
            foreach (var status in chain.ChainStatus)
            {
                // Ignore offline revocation check errors (optional).
                if (status.Status == X509ChainStatusFlags.RevocationStatusUnknown ||
                    status.Status == X509ChainStatusFlags.OfflineRevocation)
                {
                    continue;
                }
                
                if (status.Status != X509ChainStatusFlags.NoError)
                {
                    Console.WriteLine($"Certificate verification failed: {status.StatusInformation}");
                    return false;
                }
            }
        }

        // 3. Check the certificate subject name (optional, based on actual requirements).
        // string expectedSubject = "CN=*.mqtt.tencenttdmq.com";
        // if (!certificate.Subject.Contains(expectedSubject))
        // {
        //     Console.WriteLine($"Certificate verification failed: Subject mismatch (expected: {expectedSubject}, actual: {certificate.Subject})");
        //     return false;
        // }

        Console.WriteLine("Certificate verification passed");
        return true;
    }
}




Parameter Description

Parameter
Description
ADDRESS
Broker connection address, copied from the Basic Information > Access Information section of the target cluster in the console, as shown below. Format: mqtt-xxx-gz.mqtt.qcloud.tencenttdmq.com:1883.
CLIENTID
Client ID, obtained from the Client Management page on the cluster details page in the console.
USERNAME
Username, obtained on the Authentication Management page in the console.
PASSWORD
Password, obtained on the Authentication Management page in the console.
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