c# uses MQTT communication

For the functions of mqtt, please refer to Baidu Encyclopedia, MQTT_ Baidu Encyclopedia .

Simply put here, the function of mqtt is a publish/subscribe function

For example, next, let's make an example. Now there is server A as the publisher and client B as the subscriber. If A publishes a message, it will send a message to B, and vice versa, so that the function of communication takes place.

1. A server code

1. Create a .net5 web api project

2. nuget quote mqttnet

3. MqttService code

using MQTTnet;
using MQTTnet.Protocol;
using MQTTnet.Server;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace mqtt
{
    public class MqttService
    {
        public static MqttServer _mqttServer { get; set; }

        public static void PublishData(string data)
        {
            var message = new MqttApplicationMessage
            {
                Topic = "topic1",
                Payload = Encoding.Default.GetBytes(data),
                QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                Retain = true  // 服务端是否保留消息。true为保留，如果有新的订阅者连接，就会立马收到该消息。
            };

            _mqttServer.InjectApplicationMessage(new InjectedMqttApplicationMessage(message) // 发送消息给有订阅 topic_01的客户端
            {
                SenderClientId = "Server_01"
            }).GetAwaiter().GetResult();
        }

    }
}

4. MqttHostService code

using Microsoft.Extensions.Hosting;
using MQTTnet;
using MQTTnet.Protocol;
using MQTTnet.Server;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace mqtt
{
    public class MqttHostService : IHostedService, IDisposable
    {
        public void Dispose()
        {

        }
        const string ServerClientId = "SERVER";
        public Task StartAsync(CancellationToken cancellationToken)
        {
            MqttServerOptionsBuilder optionsBuilder = new MqttServerOptionsBuilder();
            optionsBuilder.WithDefaultEndpoint();
            //optionsBuilder.WithDefaultEndpointBoundIPAddress(IPAddress.Parse("127.0.0.1"));
            optionsBuilder.WithDefaultEndpointPort(10086); // 设置 服务端 端口号
            optionsBuilder.WithConnectionBacklog(1000); // 最大连接数
            MqttServerOptions options = optionsBuilder.Build();

            MqttService._mqttServer = new MqttFactory().CreateMqttServer(options);

            MqttService._mqttServer.ClientConnectedAsync += _mqttServer_ClientConnectedAsync; //客户端连接事件
            MqttService._mqttServer.ClientDisconnectedAsync += _mqttServer_ClientDisconnectedAsync; // 客户端关闭事件
            MqttService._mqttServer.ApplicationMessageNotConsumedAsync += _mqttServer_ApplicationMessageNotConsumedAsync; // 消息接收事件

            MqttService._mqttServer.ClientSubscribedTopicAsync += _mqttServer_ClientSubscribedTopicAsync; // 客户端订阅主题事件
            MqttService._mqttServer.ClientUnsubscribedTopicAsync += _mqttServer_ClientUnsubscribedTopicAsync; // 客户端取消订阅事件
            MqttService._mqttServer.StartedAsync += _mqttServer_StartedAsync; // 启动后事件
            MqttService._mqttServer.StoppedAsync += _mqttServer_StoppedAsync; // 关闭后事件
            MqttService._mqttServer.InterceptingPublishAsync += _mqttServer_InterceptingPublishAsync; // 消息接收事件
            MqttService._mqttServer.ValidatingConnectionAsync += _mqttServer_ValidatingConnectionAsync; // 用户名和密码验证有关

            MqttService._mqttServer.StartAsync();
            return Task.CompletedTask;
        }

        /// <summary>
        /// 客户端订阅主题事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_ClientSubscribedTopicAsync(ClientSubscribedTopicEventArgs arg)
        {
            Console.WriteLine($"ClientSubscribedTopicAsync：客户端ID=【{arg.ClientId}】订阅的主题=【{arg.TopicFilter}】 ");
            return Task.CompletedTask;
        }

        /// <summary>
        /// 关闭后事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_StoppedAsync(EventArgs arg)
        {
            Console.WriteLine($"StoppedAsync：MQTT服务已关闭……");
            return Task.CompletedTask;
        }

        /// <summary>
        /// 用户名和密码验证有关
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_ValidatingConnectionAsync(ValidatingConnectionEventArgs arg)
        {
            arg.ReasonCode = MqttConnectReasonCode.Success;
            if ((arg.Username ?? string.Empty) != "admin" || (arg.Password ?? String.Empty) != "123456")
            {
                arg.ReasonCode = MqttConnectReasonCode.Banned;
                Console.WriteLine($"ValidatingConnectionAsync：客户端ID=【{arg.ClientId}】用户名或密码验证错误 ");

            }
            return Task.CompletedTask;
        }

        /// <summary>
        /// 消息接收事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_InterceptingPublishAsync(InterceptingPublishEventArgs arg)
        {
            if (string.Equals(arg.ClientId, ServerClientId))
            {
                return Task.CompletedTask;
            }

            Console.WriteLine($"InterceptingPublishAsync：客户端ID=【{arg.ClientId}】 Topic主题=【{arg.ApplicationMessage.Topic}】 消息=【{Encoding.UTF8.GetString(arg.ApplicationMessage.Payload)}】 qos等级=【{arg.ApplicationMessage.QualityOfServiceLevel}】");
            return Task.CompletedTask;

        }

        /// <summary>
        /// 启动后事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_StartedAsync(EventArgs arg)
        {
            Console.WriteLine($"StartedAsync：MQTT服务已启动……");
            return Task.CompletedTask;
        }

        /// <summary>
        /// 客户端取消订阅事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_ClientUnsubscribedTopicAsync(ClientUnsubscribedTopicEventArgs arg)
        {
            Console.WriteLine($"ClientUnsubscribedTopicAsync：客户端ID=【{arg.ClientId}】已取消订阅的主题=【{arg.TopicFilter}】  ");
            return Task.CompletedTask;
        }

        private Task _mqttServer_ApplicationMessageNotConsumedAsync(ApplicationMessageNotConsumedEventArgs arg)
        {
            Console.WriteLine($"ApplicationMessageNotConsumedAsync：发送端ID=【{arg.SenderId}】 Topic主题=【{arg.ApplicationMessage.Topic}】 消息=【{Encoding.UTF8.GetString(arg.ApplicationMessage.Payload)}】 qos等级=【{arg.ApplicationMessage.QualityOfServiceLevel}】");
            return Task.CompletedTask;

        }

        /// <summary>
        /// 客户端断开时候触发
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        /// <exception cref="NotImplementedException"></exception>
        private Task _mqttServer_ClientDisconnectedAsync(ClientDisconnectedEventArgs arg)
        {
            Console.WriteLine($"ClientDisconnectedAsync：客户端ID=【{arg.ClientId}】已断开, 地址=【{arg.Endpoint}】  ");
            return Task.CompletedTask;

        }

        /// <summary>
        /// 客户端连接时候触发
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttServer_ClientConnectedAsync(ClientConnectedEventArgs arg)
        {
            Console.WriteLine($"ClientConnectedAsync：客户端ID=【{arg.ClientId}】已连接, 用户名=【{arg.UserName}】地址=【{arg.Endpoint}】  ");
            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            return Task.CompletedTask;
        }
    }
}

5. Inject code in Startup

 services.AddHostedService<MqttHostService>();

6. Add a method for the server to send messages

  public IActionResult Test(string data)
        {
            MqttService.PublishData(data);
            return Ok();
        }

 2. Client B

1. Create a .net5 web api project

2. nuget quote mqttnet

 3.MqttClientService code

using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Protocol;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace mqttClient
{
    public class MqttClientService
    {
        public static IMqttClient _mqttClient;
        public void MqttClientStart()
        {
            var optionsBuilder = new MqttClientOptionsBuilder()
                .WithTcpServer("127.0.0.1", 10086) // 要访问的mqtt服务端的 ip 和 端口号
                .WithCredentials("admin", "123456") // 要访问的mqtt服务端的用户名和密码
                .WithClientId("testclient02") // 设置客户端id
                .WithCleanSession()
                .WithTls(new MqttClientOptionsBuilderTlsParameters
                {
                    UseTls = false  // 是否使用 tls加密
                });

            var clientOptions = optionsBuilder.Build();
            _mqttClient = new MqttFactory().CreateMqttClient();

            _mqttClient.ConnectedAsync += _mqttClient_ConnectedAsync; // 客户端连接成功事件
            _mqttClient.DisconnectedAsync += _mqttClient_DisconnectedAsync; // 客户端连接关闭事件
            _mqttClient.ApplicationMessageReceivedAsync += _mqttClient_ApplicationMessageReceivedAsync; // 收到消息事件

            _mqttClient.ConnectAsync(clientOptions);


        }

        /// <summary>
        /// 客户端连接关闭事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttClient_DisconnectedAsync(MqttClientDisconnectedEventArgs arg)
        {
            Console.WriteLine($"客户端已断开与服务端的连接……");
            return Task.CompletedTask;
        }

        /// <summary>
        /// 客户端连接成功事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
        {
            Console.WriteLine($"客户端已连接服务端……");

            // 订阅消息主题
            // MqttQualityOfServiceLevel: （QoS）:  0 最多一次，接收者不确认收到消息，并且消息不被发送者存储和重新发送提供与底层 TCP 协议相同的保证。
            // 1: 保证一条消息至少有一次会传递给接收方。发送方存储消息，直到它从接收方收到确认收到消息的数据包。一条消息可以多次发送或传递。
            // 2: 保证每条消息仅由预期的收件人接收一次。级别2是最安全和最慢的服务质量级别，保证由发送方和接收方之间的至少两个请求/响应（四次握手）。
            _mqttClient.SubscribeAsync("topic1", MqttQualityOfServiceLevel.AtLeastOnce); //topic_02

            return Task.CompletedTask;
        }

        /// <summary>
        /// 收到消息事件
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        private Task _mqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
        {
            Console.WriteLine($"ApplicationMessageReceivedAsync：客户端ID=【{arg.ClientId}】接收到消息。 Topic主题=【{arg.ApplicationMessage.Topic}】 消息=【{Encoding.UTF8.GetString(arg.ApplicationMessage.Payload)}】 qos等级=【{arg.ApplicationMessage.QualityOfServiceLevel}】");
            return Task.CompletedTask;
        }

        public void Publish(string data)
        {
            var message = new MqttApplicationMessage
            {
                Topic = "topic2",
                Payload = Encoding.Default.GetBytes(data),
                QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                Retain = true  // 服务端是否保留消息。true为保留，如果有新的订阅者连接，就会立马收到该消息。
            };
            _mqttClient.PublishAsync(message);
        }
    }
}

4. When starting, instantiate the call and send message 456

  3. Effect

1. Start 2 projects at the same time

 2. Enter the sent message in the API of the server.

3. You can see that client B has received the message

4. I clicked Enter in the B client, and the 456 just mentioned was sent to the A server.

 Note: One publish, one subscribe, the published topic and the subscribed topic must be the same, just like making a phone call, both parties must be on the same line.

If it doesn't work, get a different computer, it could be a system component problem, I had this problem.

expand

In fact, the server code does not need to be written, we only need to write the client code. The client only needs to control the published and subscribed topics, and the server is just a conversion function.

1. Server installation

1. At present, the mainstream platforms of MQTT agent are as follows

• Mosquitto：https://mosquitto.org/
• VerneMQ：https://vernemq.com/
• EMQTT：http://emqtt.io/

 2. We choose the first one to download and install directly

3. After the installation is complete, enter the folder, press and Shifthold it, right-click the blank space, and then open it Powershell. Open a terminal software normally

• Enter ./mosquitto.exe -h to view the corresponding help;
• Enter ./mosquitto.exe -p 10086, the MQTT service is started, the listening address is 127.0.0.1and the port is 10086;

 

2. The client still uses the above code

1. Because we want to communicate directly between two clients, we need to modify the Topic corresponding to publishing and subscribing 

Client 1

Modify 3 places to produce an EXE 

Client 2 

 Modify 3 places to produce an EXE.

2. Two folders of EXE were produced

3. Run them separately. As a result, you can see that the two clients have sent 456 messages to each other.

3. Code link

mqtt, mqtt, mqtt, mqtt-C# Documentation Resources-CSDN Download