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官方介绍：

MQTTnet

MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker). The implementation is based on the documentation from http://mqtt.org/.

Features

General

• Async support
• TLS 1.2 support for client and server (but not UWP servers)
• Extensible communication channels (i.e. In-Memory, TCP, TCP+TLS, WS)
• Lightweight (only the low level implementation of MQTT, no overhead)
• Performance optimized (processing ~70.000 messages / second)*
• Interfaces included for mocking and testing
• Access to internal trace messages
• Unit tested (~90 tests)

* Tested on local machine (Intel i7 8700K) with MQTTnet client and server running in the same process using the TCP channel. The app for verification is part of this repository and stored in /Tests/MQTTnet.TestApp.NetCore.

Client

• Communication via TCP (+TLS) or WS (WebSocket) supported
• Included core MqttClient with low level functionality
• Also included ManagedMqttClient which maintains the connection and subscriptions automatically. Also application messages are queued and re-scheduled for higher QoS levels automatically.
• Rx support (via another project)
• Compatible with Microsoft Azure IoT Hub

Server (broker)

• List of connected clients available
• Supports connected clients with different protocol versions at the same time
• Able to publish its own messages (no loopback client required)
• Able to receive every message (no loopback client required)
• Extensible client credential validation
• Retained messages are supported including persisting via interface methods (own implementation required)
• WebSockets supported (via ASP.NET Core 2.0, separate nuget)
• A custom message interceptor can be added which allows transforming or extending every received application message
• Validate subscriptions and deny subscribing of certain topics depending on requesting clients

Supported frameworks

• .NET Standard 1.3+
• .NET Core 1.1+
• .NET Core App 1.1+
• .NET Framework 4.5.2+ (x86, x64, AnyCPU)
• Mono 5.2+
• Universal Windows Platform (UWP) 10.0.10240+ (x86, x64, ARM, AnyCPU, Windows 10 IoT Core)
• Xamarin.Android 7.5+
• Xamarin.iOS 10.14+

Supported MQTT versions

• 5.0.0 (planned)
• 3.1.1
• 3.1.0

Nuget

This library is available as a nuget package: https://www.nuget.org/packages/MQTTnet/

创建项目 

使用vs创建mqtt项目，选择winform项目，方便创建界面，查看相关数据信息。项目包括两个，server和client。

 服务器端界面结构如下：

Server在程序中添加本机IP：

var ips = Dns.GetHostAddressesAsync(Dns.GetHostName());

foreach (var ip in ips.Result)
{
    switch (ip.AddressFamily)
    {
        case AddressFamily.InterNetwork:
           TxbServer.Text = ip.ToString();
           break;
        case AddressFamily.InterNetworkV6:
           break;
     }
}

 添加一个Action ，用来想listbox中添加数据：

private Action<string> _updateListBoxAction;


//在load方法中定义
//超过1000条数据时，自动删除第一个
//出现滚动条时，滚动条自动向下移动
_updateListBoxAction = new Action<string>((s) =>
{
    listBox1.Items.Add(s);
    if (listBox1.Items.Count > 1000)
    {
        listBox1.Items.RemoveAt(0);
    }
    var visibleItems = listBox1.ClientRectangle.Height/listBox1.ItemHeight;

    listBox1.TopIndex = listBox1.Items.Count - visibleItems + 1;
});


//添加按键事件，按c时清空listbox
listBox1.KeyPress += (o, args) =>
{
    if (args.KeyChar == 'c' || args.KeyChar=='C')
    {
         listBox1.Items.Clear();
    }
};

 mqttserver

        private async void MqttServer()
        {
            if (null != _mqttServer)
            {
                return;
            }

            var optionBuilder =
                new MqttServerOptionsBuilder().WithConnectionBacklog(1000).WithDefaultEndpointPort(Convert.ToInt32(TxbPort.Text));

            if (!TxbServer.Text.IsNullOrEmpty())
            {
                optionBuilder.WithDefaultEndpointBoundIPAddress(IPAddress.Parse(TxbServer.Text));
            }
            
            var options = optionBuilder.Build();
            
            
            (options as MqttServerOptions).ConnectionValidator += context =>
            {
                if (context.ClientId.Length < 10)
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedIdentifierRejected;
                    return;
                }
                if (!context.Username.Equals("admin"))
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                    return;
                }
                if (!context.Password.Equals("public"))
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                    return;
                }
                context.ReturnCode = MqttConnectReturnCode.ConnectionAccepted;
                
            };
            

            _mqttServer = new MqttFactory().CreateMqttServer();
            _mqttServer.ClientConnected += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $">Client Connected:ClientId:{args.ClientId},ProtocalVersion:");

                var s = _mqttServer.GetClientSessionsStatusAsync();
                label3.BeginInvoke(new Action(() => { label3.Text = $"连接总数：{s.Result.Count}"; }));
            };

            _mqttServer.ClientDisconnected += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"<Client DisConnected:ClientId:{args.ClientId}");
                var s = _mqttServer.GetClientSessionsStatusAsync();
                label3.BeginInvoke(new Action(() => { label3.Text = $"连接总数：{s.Result.Count}"; }));
            };

            _mqttServer.ApplicationMessageReceived += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction,
                    $"ClientId:{args.ClientId} Topic:{args.ApplicationMessage.Topic} Payload:{Encoding.UTF8.GetString(args.ApplicationMessage.Payload)} QualityOfServiceLevel:{args.ApplicationMessage.QualityOfServiceLevel}");

            };

            _mqttServer.ClientSubscribedTopic += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"@ClientSubscribedTopic ClientId:{args.ClientId} Topic:{args.TopicFilter.Topic} QualityOfServiceLevel:{args.TopicFilter.QualityOfServiceLevel}");
            };
            _mqttServer.ClientUnsubscribedTopic += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"%ClientUnsubscribedTopic ClientId:{args.ClientId} Topic:{args.TopicFilter.Length}");
            };

            _mqttServer.Started += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, "Mqtt Server Start...");
            };

            _mqttServer.Stopped += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, "Mqtt Server Stop...");
                
            };

            await _mqttServer.StartAsync(options);
        }

把mqttserver中定义的事件都进行了绑定

(options as MqttServerOptions).ConnectionValidator 为进行mqttclient连接时进行的验证工作

想要查看完整代码，请移步到gitee

https://gitee.com/sesametech-group/MqttNetSln

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