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MQTTnetDemo是用聊天室來展示如何用MQTTnet來進行MQTT基本的subscribe和publish的功能
PS: 本範例MQTTnet版本為3.1.1，而.NET版本為.NET Core 3.1
目前Server有二個版本
- MQTTBrokerConsole
- MQTTBrokerAspDotNetWebSocket
擇一開啟即可，接下來會以MQTTBrokerAspDotNetWebSocket為例子
點擊MQTTBrokerAspDotNetWebSocket.exe啟動MQTT web server
點擊MQTTChatClient.exe啟動客戶端UI
下拉選單選擇TCP，輸入server ip、port(1883)以及UserName和密碼連線即可
(若UserName不存在，server會自動註冊該帳號密碼，若存在則會檢查密碼)
下拉選單選擇WebSocket，輸入server ip、port(5000)、path(mqtt)以及UserName和密碼連線即可
(若UserName不存在，server會自動註冊該帳號密碼，若存在則會檢查密碼)
連線後點選加入聊天室，輸入要加入的聊天室名稱(MQTT的Topic)，加入後即可開始使用
此為用MQTTnet實作的聊天室server，這邊開始講解如何使用MqttServer
要建立MQTT伺服器前，必須先建立MQTT的IMqttServerOptions，建立方法如下
var serverOptions = new MqttServerOptionsBuilder()
.WithConnectionBacklog(100)
.WithDefaultEndpointPort(1883)
// 設定連線者的驗證
.WithConnectionValidator(ValidateConnector)
// 設定訂閱的攔截事件
.WithSubscriptionInterceptor(InterCeptSubscription)
// 設定訊息的攔截事件
.WithApplicationMessageInterceptor(InterceptMessage)
.Build();其中WithConnectionValidator、WithSubscriptionInterceptor、WithApplicationMessageInterceptor為非必要，
如果要對客戶端進行驗證，就用WithConnectionValidator
ServerOptions建立好後，再來就要開始準備MqttServer，建立方法如下
var mqttServer = new MqttFactory().CreateMqttServer();基本上mqttServer就已經可以直接啟動了，不過MQTTnet還提供了很多Handler來處理客戶端的連線，接下來會開始講解IMqttServer提供的Handler要如何使用
首先IMqttServer提供的Handler總共有以下幾個
var mqttServer = new MqttFactory().CreateMqttServer();
// 設定server接收到客戶端發送的訊息的事件
mqttServer.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(OnApplicationMessageReceived);
// 設定客戶端成功連線server的事件
mqttServer.ClientConnectedHandler = new MqttServerClientConnectedHandlerDelegate(OnClientConnected);
// 設定客戶端斷線的事件
mqttServer.ClientDisconnectedHandler = new MqttServerClientDisconnectedHandlerDelegate(OnClientDisconnected);
// 設定客戶端向server訂閱特定Topic的事件
mqttServer.ClientSubscribedTopicHandler = new MqttServerClientSubscribedTopicHandlerDelegate(OnTopicSubscribe);
// 客戶端向server取消訂閱特定Topic的事件
mqttServer.ClientUnsubscribedTopicHandler = new MqttServerClientUnsubscribedTopicHandlerDelegate(OnTopicUnsubscribe);ApplicationMessageReceivedHandler是一個MqttApplicationMessageReceivedHandlerDelegate，是用來處理客戶端發送的訊息， 其delegate的method如下
/// <summary>
/// 處理server接收到客戶端發送的訊息
/// </summary>
/// <param name="e"></param>
private void OnApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
{
// 客戶針對的Topic
string topic = e.ApplicationMessage.Topic;
// Payload是客戶端發送過來的訊息，為byte[]，請依照自己的需求轉換
string message = Encoding.UTF8.GetString(e.ApplicationMessage.Payload ?? new byte[0]);
// TODO 看你想要對訊息做甚麼
}使用者傳送的訊息都在e.ApplicationMessage內，Topic跟Payload都在裡面
ClientConnectedHandler是一個MqttServerClientConnectedHandlerDelegate，用來處理客戶端成功連線server的事件， 其delegate的method如下
/// <summary>
/// 客戶端成功連線server的事件
/// </summary>
/// <param name="e"></param>
private void OnClientConnected(MqttServerClientConnectedEventArgs e)
{
Console.WriteLine($"客戶端: { e.ClientId } 已連接!");
// TODO 看你想要做甚麼
}ClientDisconnectedHandler是一個MqttServerClientDisconnectedHandlerDelegate，用來處理客戶端斷線的事件， 其delegate的method如下
/// <summary>
/// 客戶端斷線的事件
/// </summary>
/// <param name="e"></param>
private void OnClientDisconnected(MqttServerClientDisconnectedEventArgs e)
{
Console.WriteLine($"客戶端: { e.ClientId } 已離線!");
// TODO 看你想要做甚麼
}ClientSubscribedTopicHandler是一個MqttServerClientSubscribedTopicHandlerDelegate，用來處理客戶端向server訂閱特定Topic的事件， 其delegate的method如下
/// <summary>
/// 客戶端向server訂閱特定Topic
/// </summary>
/// <param name="e"></param>
private void OnTopicSubscribe(MqttServerClientSubscribedTopicEventArgs e)
{
Console.WriteLine($"客戶端: { e.ClientId } 已訂閱「{ e.TopicFilter.Topic }」!");
// TODO 看你想要做甚麼
}ClientUnsubscribedTopicHandler是一個MqttServerClientUnsubscribedTopicHandlerDelegate，用來處理客戶端向server取消訂閱特定Topic的事件， 其delegate的method如下
/// <summary>
/// 客戶端向server取消訂閱特定Topic
/// </summary>
/// <param name="e"></param>
private void OnTopicUnsubscribe(MqttServerClientUnsubscribedTopicEventArgs e)
{
Console.WriteLine($"客戶端: { e.ClientId } 已取消訂閱「{ e.TopicFilter }」!");
// TODO 看你想要做甚麼
}在serverOptions以及handler都設定好後，就可以啟動server了
await mqttServer.StartAsync(serverOptions);到這裡server就大功告成了!
詳細實作方式請參閱MQTTChatService.cs
由於內容比較多，請移至Wiki觀看
此為用MQTTnet實作的客戶端聊天室Winform視窗，這邊講解MQTTChatClient的核心部分MQTTChatClientHandler.cs的實作方法
要建立MQTT客戶端前，必須先建立MQTT的IMqttClientOptions，建立方法如下
var options = new MqttClientOptionsBuilder()
.WithTcpServer(ip, port)
.WithCredentials(userName, password)
// ClientId不給的話，系統會自動生成
// PS: 所有連線的ClientId要一致，才有辦法收到離線的訊息
.WithClientId(userName)
.WithCleanSession(true)
.WithCommunicationTimeout(TimeSpan.FromSeconds(2))
.Build();ClientOptions建立好後，再來就要開始準備MqttClient，建立方法如下
var mqttClient = new MqttFactory().CreateMqttClient();基本上mqttClient就已經可以直接啟動了，不過MQTTnet還提供了很多Handler來處理連線，接下來會開始講解IMqttClient提供的Handler要如何使用
首先IMqttClient提供的Handler總共有以下幾個
mqttClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(OnMessageReceived);
mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(OnClientConnected);
mqttClient.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(OnClientDisconnected);ApplicationMessageReceivedHandler是一個MqttApplicationMessageReceivedHandlerDelegate，是用來處理發送訊息的事件， 其delegate的method如下
/// <summary>
/// 處理收到server傳來的訊息要怎麼處理
/// </summary>
/// <param name="e"></param>
private void OnMessageReceived(MqttApplicationMessageReceivedEventArgs e)
{
var message = Encoding.UTF8.GetString(e.ApplicationMessage.Payload ?? new byte[0]);
// Do whatever you want
}server端傳送的訊息都在e.ApplicationMessage內，Topic跟Payload都在裡面
ConnectedHandler是一個MqttClientConnectedHandlerDelegate，是用來處理連線成功的事件， 其delegate的method如下
/// <summary>
/// 處理客戶端連線成功時要處理的事情
/// </summary>
/// <param name="e"></param>
private void OnClientConnected(MqttClientConnectedEventArgs e)
{
// Do whatever you want
}DisconnectedHandler是一個MqttClientDisconnectedHandlerDelegate，是用來處理連線失敗的事件， 其delegate的method如下
/// <summary>
/// 處理客戶端離線時要處理的事情，記得處理中斷狀態與server的exception
/// </summary>
/// <param name="e"></param>
private void OnClientDisconnected(MqttClientDisconnectedEventArgs e)
{
// ClientWasConnected為true表示斷線是發生在連線成功後，反之表示連一開始的連線都沒有成功
if (e.Exception != null && e.ClientWasConnected)
{
MessageBox.Show($"發生錯誤{Environment.NewLine}{e.Exception.Message}", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
// TODO Do whatever you want
}其中e.Exception != null && e.ClientWasConnected為連線成功後中斷的狀態
向server發送訂閱請求
/// <summary>
/// 向MQTT伺服器訂閱Topic
/// </summary>
/// <param name="topic">Topic名稱</param>
/// <returns></returns>
public async Task SubscribeAsync(string topic, Action<string> OnError)
{
try
{
var topicFilter = new MqttTopicFilterBuilder()
.WithTopic(topic)
// Qos要大於0，客戶端才可收到離線訊息
// AtMostOnce = 0, AtLeastOnce = 1, ExactlyOnce = 2
.WithQualityOfServiceLevel(MqttQualityOfServiceLevel.ExactlyOnce)
.Build();
await mqttClient.SubscribeAsync(topicFilter);
}
catch (Exception e)
{
OnError(e.ToString());
}
}向server發佈訊息
/// <summary>
/// 非同步發布訊息
/// </summary>
/// <param name="topic">向指定Topic發布</param>
/// <param name="chatMessage">發布訊息</param>
/// <returns></returns>
public async Task PublishAsync(string topic, string userInput, Action<string> OnError)
{
try
{
// 將ChatMessage轉換成json字串
ChatRoomMessage chatRoomMessage = new ChatRoomMessage { UserName = userName, ChatMessage = new ChatText(userInput), Topic = topic };
//ChatMessage chatMessage = new ChatMessage() { UserName = userName, Message = userInput };
var message = JsonConvert.SerializeObject(chatRoomMessage);
var applicationMessage = new MqttApplicationMessageBuilder()
.WithTopic(topic)
.WithPayload(Encoding.UTF8.GetBytes(message))
// Qos要大於0，客戶端才可收到離線訊息
// AtMostOnce = 0, AtLeastOnce = 1, ExactlyOnce = 2
.WithQualityOfServiceLevel(MqttQualityOfServiceLevel.ExactlyOnce)
//.WithRetainFlag(true)
.Build();
await mqttClient.PublishAsync(applicationMessage);
}
catch (Exception e)
{
OnError(e.ToString());
}
}在clientOptions以及handler都設定好後，就可以啟動client了
await mqttClient.ConnectAsync(options);到這裡client就大功告成了!
詳細實作方式請參閱MQTTChatClientHandler.cs與MqttService.cs