C#实现MQTT over WebSocket

如何在网页端实现MQTT消息的发布和订阅？

• 实现MQTT功能，可以发布和订阅主题
• 通过WebSocket协议将MQTT消息转发给对应的网页端

带着这个实现思路，采用C#控制台程序实现MQTT服务端功能，web端可以直接使用websocket插件与服务端双向通讯。

1. 新建C#控制台程序，.net framework框架版本4.5.2
2. 引用Fleck框架，版本1.2.0
3. 引用MQTTnet框架，版本4.3.1.873

1、WebSocket功能实现

socketDic 字典key值记录每个客户端，value记录每个客户端对应的SN，代表设备的序列号；

每当有网页端客户端连接的时候，自动将客户端套接字加入字典中；

每当网页关闭，服务端自动断开客户端套接字连接，并从缓存字典中移除此客户端套接字；

当网页端客户端套接字发送包含SN:开头的字符，表示网页端发送了设备的SN，服务端接收此消息，并解析设备SN，并与对应的客户端套接字绑定对应关系，在缓存字典中维护对应关系。

class Server
{
    static Dictionary socketDic = new Dictionary();
        static void Main()
        {
            FleckLog.Level = LogLevel.Debug;
            var server = new WebSocketServer("ws://0.0.0.0:8181");
            //var socketDic = new Dictionary();
            server.Start(socket =>
                {
                    socket.OnOpen = () =>
                        {
                            Console.WriteLine("Open!");
                            socketDic.Add(socket, null);
                        };
                    socket.OnClose = () =>
                        {
                            Console.WriteLine("Close!");
                            socketDic.Remove(socket);
                        };
                    socket.OnMessage = message =>
                        {
                            if (message.Contains("SN:") && socketDic.ContainsKey(socket))
                            {
                                socketDic[socket] = message.Replace("SN:", "");
                            }
                        };
                });
            Client();
            var input = Console.ReadLine();
            while (input != "exit")
            {
                foreach (var socket in socketDic.ToList())
                {
                    socket.Key.Send(input);
                }
                input = Console.ReadLine();
            }

        }
}

2、MQTT功能实现

MQTT服务器采用EMQX公共服务器测试，服务器域名：broker.emqx.io，端口：1883，用户名：emqx_test，密码：emqx_test

订阅主题名：123、12345

MQTT接收消息事件ApplicationMessageReceivedAsync，判断消息主题与缓存字典中的套接字是否对应，如消息主题与缓存字典SN存在包含关系，则认为此消息与网页端套接字存在关联关系，则将消息推送给此套接字。

具体实现代码：

static IMqttClient client;
        public static async void Client()
        {
            try
            {
                client = new MqttFactory().CreateMqttClient() as MqttClient;
                var build = new MqttClientOptionsBuilder()
                    .WithClientId(Guid.NewGuid().ToString().Replace("-", "").ToUpper())
                    .WithCredentials("emqx_test", "emqx_test")
                    .WithTcpServer("broker.emqx.io", 1883)
                    .WithCleanSession(true)
                    .WithKeepAlivePeriod(TimeSpan.FromSeconds(100.5));
                client.ConnectedAsync += _mqttClient_ConnectedAsync;
                await client.ConnectAsync(build.Build());
                
                client.DisconnectedAsync += _mqttClient_DisconnectedAsync;
                client.ApplicationMessageReceivedAsync += _mqttClient_ApplicationMessageReceivedAsync;
 
                await client.SubscribeAsync(
                    new MqttClientSubscribeOptions
                    {
                        TopicFilters = new List {new MqttTopicFilter() //订阅消息对象
                        {
                            Topic = "123",  //订阅消息主题
                            QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce  //消息类型
                        },new MqttTopicFilter() //订阅消息对象
                        {
                            Topic = "12345",  //订阅消息主题
                            QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce  //消息类型
                        }
                    }
                    });
            }
            catch (Exception e)
            {
                Console.WriteLine($"连接失败");
            }
        }

        private static Task _mqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
        {
            var msg = arg.ApplicationMessage.ConvertPayloadToString();
            foreach (var item in socketDic)
            {
                if (item.Value!=null && arg.ApplicationMessage.Topic.Contains(item.Value))
                {
                    item.Key.Send($"hello {item.Value},{msg}");
                }
            }
            Console.WriteLine(arg.ApplicationMessage.ConvertPayloadToString());
            return Task.FromResult("");
        }

        private static Task _mqttClient_DisconnectedAsync(MqttClientDisconnectedEventArgs arg)
        {
            Console.WriteLine($"客户端“{client.Options.ClientId}”已断开MQTT服务器！");
            return Task.FromResult("");
        }

        private static Task _mqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
        {
            Console.WriteLine($"客户端“{client.Options.ClientId}”已连接MQTT服务器！");
            return Task.FromResult("");
        }

3、网页端实现

4、测试

启动WebSocket服务器控制台应用程序；

运行MQTT.fx工具，新建连接

给12345主题发布消息，

观察网页端是否收到消息，