xamarin Mqtt

1 什么是MQTT?

　　mqtt （Message Queuing Telemetry Transport，消息队列遥测传输）是 IBM 开发的一个即时通讯协议，有可能成为物联网的重要组成部分。MQTT 是基于二进制消息的发布/订阅编程模式的消息协议，如今已经成为 OASIS 规范，由于规范很简单，非常适合需要低功耗和网络带宽有限的 IoT 场景。

2 MQTTnet

　　MQTTnet 是一个基于MQTT协议高度专业的.net库，它同时提供MQTT client和MQTT server（broke），支持v3.1.0,v3.1.1和v5.0.0的标准MQTT协议.

3 MQTTnet支持范围

　　.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) 10.0.1024+(x86,x64,ARM,AnyCPU,Windwos 10 IoT Core)

　　Xamarin.Android 7.5+

　　Xamarin.iOS 10.14+

4 创建服务器

　　MQTT服务器以称为"消息代理"（Broker），可以是一个应用程序或一台设备。它是位于消息发布者和订阅者之间，它可以：

　　（1）接受来自客户的网络连接；

　　（2）接受客户发布的应用信息；

　　（3）处理来自客户端的订阅和退订请求；

　　（4）向订阅的客户转发应用程序消息。

　　服务器创建一个控制台应用，可选>>控制台应用(.NET Core)创建新项目MqttNetServer，代码如下：

　　

  1 sing MQTTnet;
  2 using MQTTnet.Protocol;
  3 using MQTTnet.Server;
  4 using Newtonsoft.Json;
  5 using System;
  6 using System.Collections.Generic;
  7 using System.IO;
  8 using System.Reflection;
  9 using System.Security.Cryptography.X509Certificates;
 10 using System.Text;
 11 using System.Threading.Tasks;
 12 
 13 namespace MqttServerTest
 14 {
 15     class Program
 16     {
 17         public static IMqttServer mqttServer;
 18         static void Main(string[] args)
 19         {
 20             mqttServer = new MQTTnet.MqttFactory().CreateMqttServer();
 21             mqttServer.UseClientConnectedHandler(e =>
 22             {
 23                 Console.WriteLine("***new connect:" + e.ClientId);
 24                 
 25             });
 26             mqttServer.UseClientDisconnectedHandler(e =>
 27             {
 28                 Console.WriteLine("*** disconnect:" + e.ClientId);
 29             });
 30 
 31             //var options = new MqttServerOptions();
 32             //await mqttServer.StartAsync(options);
 33 
 34             //var currentPath = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
 35             //var certificate = new X509Certificate2(Path.Combine(currentPath, "certificate.pfx"), "yourPassword", X509KeyStorageFlags.Exportable);
 36 
 37 
 38             var optionsBuilder = new MqttServerOptionsBuilder()
 39                 .WithConnectionBacklog(100)
 40                 .WithDefaultEndpointPort(1884)
 41                 .WithConnectionValidator(c=> {
 42                     //c.SessionItems.
 43                     //if (c.ClientId.Length < 10)
 44                     //{
 45                     //    c.ReturnCode = MqttConnectReturnCode.ConnectionRefusedIdentifierRejected;
 46                     //    //c.ReasonCode = MqttConnectReasonCode.ClientIdentifierNotValid;
 47                     //    return;
 48                     //}
 49                     //if (c.Username != "mySecretUser")
 50                     //{
 51                     //    c.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
 52                     //    return;
 53                     //}
 54 
 55                     //if (c.Password != "mySecretPassword")
 56                     //{
 57                     //    c.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
 58                     //    return;
 59                     //}
 60 
 61                     c.ReturnCode = MqttConnectReturnCode.ConnectionAccepted;
 62                     Console.WriteLine("***connect validator:"+c.ClientId);
 63                 })
 64                 //.WithEncryptionCertificate(certificate.Export(X509ContentType.Pfx))
 65                 //.WithEncryptionSslProtocol(SslProtocols.Tls12)
 66                 .WithApplicationMessageInterceptor(context=> {
 67                     //if (context.ApplicationMessage.Topic == "my/custom/topic")
 68                     //{
 69                     //    context.ApplicationMessage.Payload = Encoding.UTF8.GetBytes("The server injected payload.");
 70                     //}
 71                     //// It is possible to disallow the sending of messages for a certain client id like this:
 72                     //if (context.ClientId != "Someone")
 73                     //{
 74                     //    context.AcceptPublish = false;
 75                     //    return;
 76                     //}
 77                     // It is also possible to read the payload and extend it. For example by adding a timestamp in a JSON document.
 78                     // This is useful when the IoT device has no own clock and the creation time of the message might be important.
 79 
 80                     context.AcceptPublish = true;
 81                     Console.WriteLine("***Message:" + context.ApplicationMessage.Payload);
 82                 })
 83                 .WithSubscriptionInterceptor(context=>
 84                 {
 85                     //if (context.TopicFilter.Topic.StartsWith("admin/foo/bar") && context.ClientId != "theAdmin")
 86                     //{
 87                     //    context.AcceptSubscription = false;
 88                     //}
 89 
 90                     //if (context.TopicFilter.Topic.StartsWith("the/secret/stuff") && context.ClientId != "Imperator")
 91                     //{
 92                     //    context.AcceptSubscription = false;
 93                     //    context.CloseConnection = true;
 94                     //}
 95 
 96                     context.AcceptSubscription = true;
 97                     Console.WriteLine("***Subscript:" + context.TopicFilter);
 98                 })
 99                 //.WithStorage(new RetainedMessageHandler())
100                 ;
101             var options = optionsBuilder.Build();
102 
103             //// Setting the options
104             //options.Storage=new RetainedMessageHandler();
105 
106             StartServer(options);
107 
108             
109 
110             Console.WriteLine("Press any key to exit.");
111             Console.ReadLine();
112 
113             //await mqttServer.StopAsync();
114         }
115 
116         public static async void StartServer(IMqttServerOptions options)
117         {
118             await mqttServer.StartAsync(options);
119         }
120 
121     }
122 
123     // The implementation of the storage:
124     // This code uses the JSON library "Newtonsoft.Json".
125     public class RetainedMessageHandler : IMqttServerStorage
126     {
127         private const string Filename = "C:\\MQTT\\RetainedMessages.json";
128 
129         public Task SaveRetainedMessagesAsync(IList messages)
130         {
131             File.WriteAllText(Filename, JsonConvert.SerializeObject(messages));
132             return Task.FromResult(0);
133         }
134 
135         public Task> LoadRetainedMessagesAsync()
136         {
137             IList retainedMessages;
138             if (File.Exists(Filename))
139             {
140                 var json = File.ReadAllText(Filename);
141                 retainedMessages = JsonConvert.DeserializeObject>(json);
142             }
143             else
144             {
145                 retainedMessages = new List();
146             }
147 
148             return Task.FromResult(retainedMessages);
149         }
150     }
151 
152 }

代码直接运行起来，就是一个简单的Mqtt server。

5 创建xamarin APP

　　一个使用MQTT协议的应用程序或者设备，它总是建立到服务器的网络连接。客户端可以：

　　（1）发布其他客户端可能会订阅的信息；

　　（2）订阅其它客户端发布的消息；

　　（3）退订或删除应用程序的消息；

　　（4）断开与服务器连接。

　　在VS中新建一个xamarin.Forms的移动应用，创建好后在Nuget上搜索mqttnet，添加对MQTTnet包的引用。更改代码如下：

　　

 1 "1.0" encoding="utf-8" ?>
 2 "http://xamarin.com/schemas/2014/forms"
 3              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 4              xmlns:local="clr-namespace:CatShell"
 5              x:Class="CatShell.MainPage">
 6 
 7     
 8         
 9         "SubscribeTopic"/>
10         "txtSubTopic" Placeholder="Subscribe Topic" />
11         "BtnSubscribe" Clicked="SubButton_Clicked"/>
12         "txtReceiveMessage"/>
13         "PublishTopic"/>
14         "txtPubTopic"/>
15         "txtSendMessage" />
16         "Publish" Clicked="PubButton_Clicked"/>
17         
18             
19         
20 
21     
22 
23 

  1 using MQTTnet;
  2 using MQTTnet.Client;
  3 using MQTTnet.Client.Options;
  4 using System;
  5 using System.Collections.Generic;
  6 using System.Linq;
  7 using System.Text;
  8 using System.Threading;
  9 using System.Threading.Tasks;
 10 using Xamarin.Forms;
 11 
 12 namespace CatShell
 13 {
 14     public partial class MainPage : ContentPage
 15     {
 16         public IMqttClient mqttClient;
 17         public IMqttClientOptions options;
 18         public MainPage()
 19         {
 20             InitializeComponent();
 21             InitMqttClient();
 22             ConnectMqttServer();
 23         }
 24 
 25         public void InitMqttClient()
 26         {
 27             // Create a new MQTT client.
 28             var factory = new MqttFactory();
 29             mqttClient = factory.CreateMqttClient();
 30 
 31             mqttClient.UseConnectedHandler(e => {
 32 
 33                 Device.BeginInvokeOnMainThread(() =>
 34                 {
 35                     txtReceiveMessage.Text = txtReceiveMessage.Text + $">> connect success." + Environment.NewLine;
 36                 });
 37             });
 38             mqttClient.UseDisconnectedHandler(e =>
 39             {
 40                 Device.BeginInvokeOnMainThread(() =>
 41                 {
 42                     txtReceiveMessage.Text = txtReceiveMessage.Text + $">> Disconnect." + Environment.NewLine;
 43                 });
 44             });
 45             mqttClient.UseApplicationMessageReceivedHandler(e =>
 46             {
 47                 Device.BeginInvokeOnMainThread(() =>
 48                 {
 49                     txtReceiveMessage.Text = $">> {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}" + Environment.NewLine;
 50                 });
 51             });
 52 
 53             // Create TCP based options using the builder.
 54             options = new MqttClientOptionsBuilder()
 55                 .WithClientId("Client4")
 56                 .WithTcpServer("10.100.1.247", 1884) // Use TCP connection, Port is opptinal
 57                                                      //.WithWebSocketServer("broker.hivemq.com:8000/mqtt") // Use WebSocket connection.
 58                                                      //.WithCredentials("bud", "%spencer%")
 59                                                      //.WithTls()
 60                                                      //.WithTls(new MqttClientOptionsBuilderTlsParameters
 61                                                      //{
 62                                                      //    UseTls = true,
 63                                                      //    CertificateValidationCallback = (X509Certificate x, X509Chain y, SslPolicyErrors z, IMqttClientOptions o) =>
 64                                                      //    {
 65                                                      //        // TODO: Check conditions of certificate by using above parameters.
 66                                                      //        return true;
 67                                                      //    }
 68                                                      //})
 69                 .WithCleanSession()
 70                 .Build();
 71 
 72         }
 73 
 74         public async void ConnectMqttServer()
 75         {
 76             await mqttClient.ConnectAsync(options, CancellationToken.None); // Since 3.0.5 with CancellationToken
 77 
 78         }
 79 
 80         private async void SubButton_Clicked(object sender, EventArgs e)
 81         {
 82             
 83             string topic = txtSubTopic.Text.Trim();
 84 
 85             if (string.IsNullOrEmpty(topic))
 86             {
 87                 //MessageBox.Show("订阅主题不能为空！");
 88                 return;
 89             }
 90 
 91             if (!mqttClient.IsConnected)
 92             {
 93                 //MessageBox.Show("MQTT客户端尚未连接！");
 94                 return;
 95             }
 96 
 97             // Subscribe to a topic
 98             await mqttClient.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).Build());
 99 
100             txtReceiveMessage.Text = txtReceiveMessage.Text + $"已订阅[{topic}]主题" + Environment.NewLine;
101             txtSubTopic.IsReadOnly = false;
102             //BtnSubscribe.Enabled = false;
103         }
104 
105         private async void PubButton_Clicked(object sender, EventArgs e)
106         {
107             string topic = txtPubTopic.Text.Trim();
108 
109             if (string.IsNullOrEmpty(topic))
110             {
111                 //MessageBox.Show("发布主题不能为空！");
112                 return;
113             }
114 
115             string inputString = txtSendMessage.Text.Trim();
116 
117             PublishMessages(topic, inputString);
118         }
119 
120         public async void PublishMessages(string topicMsg, string payloadMsg)
121         {
122             var message = new MqttApplicationMessageBuilder()
123                 .WithTopic(topicMsg)
124                 .WithPayload(payloadMsg)
125                 .WithExactlyOnceQoS()
126                 .WithRetainFlag()
127                 .Build();
128 
129             await mqttClient.PublishAsync(message);
130         }
131 
132     }
133 }

代码运行起来，在APP上可以直接发信息。

6 创建winForm client（可选）

　　可以创建一个winForm来相互互动，在VS上新建一个windows窗体应用(.NET Framework)，界面设计如下

　　

　　后台代码如下：

　　

  1 using MQTTnet;
  2 using MQTTnet.Client.Options;
  3 using MQTTnet.Client;
  4 using System;
  5 using System.Collections.Generic;
  6 using System.ComponentModel;
  7 using System.Data;
  8 using System.Drawing;
  9 using System.Linq;
 10 using System.Net.Security;
 11 using System.Security.Cryptography.X509Certificates;
 12 using System.Text;
 13 using System.Threading;
 14 using System.Threading.Tasks;
 15 using System.Windows.Forms;
 16 
 17 namespace MqttClientWin
 18 {
 19     public partial class Form1 : Form
 20     {
 21         public IMqttClient mqttClient;
 22         public IMqttClientOptions options;
 23         public Form1()
 24         {
 25             InitializeComponent();
 26             InitMqttClient();
 27             ConnectMqttServer();
 28         }
 29 
 30         public void InitMqttClient()
 31         {
 32             // Create a new MQTT client.
 33             var factory = new MqttFactory();
 34             mqttClient = factory.CreateMqttClient();
 35 
 36             mqttClient.UseApplicationMessageReceivedHandler(e =>
 37             {
 38                 Console.WriteLine("### RECEIVED APPLICATION MESSAGE ###");
 39                 Console.WriteLine($"+ Topic = {e.ApplicationMessage.Topic}");
 40                 Console.WriteLine($"+ Payload = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
 41                 Console.WriteLine($"+ QoS = {e.ApplicationMessage.QualityOfServiceLevel}");
 42                 Console.WriteLine($"+ Retain = {e.ApplicationMessage.Retain}");
 43                 Console.WriteLine();
 44 
 45                 this.Invoke(new Action(() =>
 46                 {
 47                     txtReceiveMessage.AppendText($">> {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}{Environment.NewLine}");
 48                 }));
 49 
 50                 //Task.Run(() => mqttClient.PublishAsync("hello/world"));
 51             });
 52 
 53             mqttClient.UseConnectedHandler(async e =>
 54             {
 55                 Console.WriteLine("### CONNECTED WITH SERVER ###");
 56 
 57                 //// Subscribe to a topic
 58                 //await mqttClient.SubscribeAsync(new TopicFilterBuilder().WithTopic("my/topic").Build());
 59 
 60                 //Console.WriteLine("### SUBSCRIBED ###");
 61 
 62                 this.Invoke(new Action(() =>
 63                 {
 64                     txtReceiveMessage.AppendText($">> connect success.{Environment.NewLine}");
 65                 }));
 66             });
 67 
 68             mqttClient.UseDisconnectedHandler(e =>
 69             {
 70                 this.Invoke(new Action(() =>
 71                 {
 72                     txtReceiveMessage.AppendText($">> Disconnect .{Environment.NewLine}");
 73                 }));
 74             });
 75 
 76             // Create TCP based options using the builder.
 77             options = new MqttClientOptionsBuilder()
 78                 .WithClientId("Client5")
 79                 .WithTcpServer("10.100.1.247", 1884) // Use TCP connection, Port is opptinal
 80                                                           //.WithWebSocketServer("broker.hivemq.com:8000/mqtt") // Use WebSocket connection.
 81                 //.WithCredentials("bud", "%spencer%")
 82                 //.WithTls()
 83                 //.WithTls(new MqttClientOptionsBuilderTlsParameters
 84                 //{
 85                 //    UseTls = true,
 86                 //    CertificateValidationCallback = (X509Certificate x, X509Chain y, SslPolicyErrors z, IMqttClientOptions o) =>
 87                 //    {
 88                 //        // TODO: Check conditions of certificate by using above parameters.
 89                 //        return true;
 90                 //    }
 91                 //})
 92                 .WithCleanSession()
 93                 .Build();
 94             
 95         }
 96 
 97         public async void ConnectMqttServer()
 98         {
 99             await mqttClient.ConnectAsync(options, CancellationToken.None); // Since 3.0.5 with CancellationToken
100             
101         }
102 
103         public void ReconnectMqttServer()
104         {
105             mqttClient.UseDisconnectedHandler(async e =>
106             {
107                 Console.WriteLine("### DISCONNECTED FROM SERVER ###");
108                 await Task.Delay(TimeSpan.FromSeconds(5));
109 
110                 try
111                 {
112                     await mqttClient.ConnectAsync(options, CancellationToken.None); // Since 3.0.5 with CancellationToken
113                 }
114                 catch
115                 {
116                     Console.WriteLine("### RECONNECTING FAILED ###");
117                 }
118             });
119         }
120 
121         public async void PublishMessages(string topicMsg,string payloadMsg)
122         {
123             var message = new MqttApplicationMessageBuilder()
124                 .WithTopic(topicMsg)
125                 .WithPayload(payloadMsg)
126                 .WithExactlyOnceQoS()
127                 .WithRetainFlag()
128                 .Build();
129 
130             await mqttClient.PublishAsync(message);
131         }
132 
133         private async void BtnSubscribe_Click(object sender, EventArgs e)
134         {
135             string topic = txtSubTopic.Text.Trim();
136 
137             if (string.IsNullOrEmpty(topic))
138             {
139                 MessageBox.Show("订阅主题不能为空！");
140                 return;
141             }
142 
143             if (!mqttClient.IsConnected)
144             {
145                 MessageBox.Show("MQTT客户端尚未连接！");
146                 return;
147             }
148             
149             // Subscribe to a topic
150             await mqttClient.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).Build());
151 
152             txtReceiveMessage.AppendText($"已订阅[{topic}]主题" + Environment.NewLine);
153             txtSubTopic.Enabled = false;
154             BtnSubscribe.Enabled = false;
155         }
156 
157         private void BtnPublish_Click(object sender, EventArgs e)
158         {
159             string topic = txtPubTopic.Text.Trim();
160 
161             if (string.IsNullOrEmpty(topic))
162             {
163                 MessageBox.Show("发布主题不能为空！");
164                 return;
165             }
166 
167             string inputString = txtSendMessage.Text.Trim();
168 
169             PublishMessages(topic, inputString);
170             
171         }
172     }
173 }

7 MQTT协议中的订阅、主题、会话

　　一、订阅（Subscription）

　　订阅包含主题筛选器（Topic Filter）和最大服务质量（QoS）。订阅会与一个会话（Session）关联。一个会话可以包含多个订阅。每一个会话中的每个订阅都有一个不同的主题筛选器。

　　二、会话（Session）

　　每个客户端与服务器建立连接后就是一个会话，客户端和服务器之间有状态交互。会话存在于一个网络之间，也可能在客户端和服务器之间跨越多个连续的网络连接。

　　三、主题名（Topic Name）

　　连接到一个应用程序消息的标签，该标签与服务器的订阅相匹配。服务器会将消息发送给订阅所匹配标签的每个客户端。

　　四、主题筛选器（Topic Filter）

　　一个对主题名通配符筛选器，在订阅表达式中使用，表示订阅所匹配到的多个主题。

　　五、负载（Payload）

　　消息订阅者所具体接收的内容。

8 MQTT协议中的方法

　　MQTT协议中定义了一些方法（也被称为动作），来于表示对确定资源所进行操作。这个资源可以代表预先存在的数据或动态生成数据，这取决于服务器的实现。通常来说，资源指服务器上的文件或输出。主要方法有：

　　（1）Connect。等待与服务器建立连接。

　　（2）Disconnect。等待MQTT客户端完成所做的工作，并与服务器断开TCP/IP会话。

　　（3）Subscribe。等待完成订阅。

　　（4）UnSubscribe。等待服务器取消客户端的一个或多个topics订阅。

　　（5）Publish。MQTT客户端发送消息请求，发送完成后返回应用程序线程。