MQTT连接秒断，MQTT连接测试程序可以连接代码无法连接，Best MQTT发送数据提示版本不一致

MQTT测试程序连接秒断

问题描述

使用MQTT测试程序MQTTX连接服务器，点击连接后直接断开，或者无限重新连接。

解决方式

方式1： 切换协议，试试MQTT 3.0，MQTT 3.1.1，MQTT 5.0，看看那个可行就用那个，或者问问服务器方使用的MQTT服务器的版本，客户端的版本需要和服务器端的版本保持一致。
方式2：检查测试程序的Clean Session，设置为true试试再试试false

MQTT连接测试程序可以连接代码无法连接

以下的代码是基于BestMQTT和BestMQTT实现的。

问题描述

使用MQTTX或者MQTTFX可以连接到MQTT服务器并发送数据，使用自己写的代码不能发送到服务器。

解决方式

方式1： 设置MQTT连级对象的Session，再MQTT测试工具中的位置

方式二：强制指定MQTT客户端的版本

 var c = new ConnectionOptionsBuilder()
      .WithTCP(hostName, port)
      .WithProtocolVersion(SupportedProtocolVersions.MQTT_3_1_1);


   public enum SupportedProtocolVersions
   {
       MQTT_3_1_1,
       MQTT_5_0
   }

Best MQTT发送数据提示版本不一致

问题描述

使用BestMQTT发送数据的时候，提示

{
	"tid": 1,
	"div": "MQTTClient",
	"msg": "OnConnected",
	"ex": [{
		"msg": "WithContentType is available with MQTT v5.0 or newer."
	}]
}			

版本过高，服务器的是MQTT3.1.1 但是使用的发送数据是的5.0的方式

		//5.0的发送方式
       //发送数据
        client.CreateApplicationMessageBuilder(SendTopic)
                .WithPayload(Message)
                .WithQoS(QoSLevels.ExactlyOnceDelivery)
                .WithContentType("text/plain; charset=UTF-8")
                .BeginPublish();

//3.1.1的发送方式
        client.CreateApplicationMessageBuilder(SendTopic)
          .WithPayload(Message)
            .BeginPublish();

BestMQTT 连接的全部代码

代码中包括：

1. 使用MQTT 3.1.1发送数据，使用MQTT 5.0发送数据，
2. 使用MQTT 3.1.1断开连接，使用MQTT 5.0断开连接，
3. 订阅
4. 设置Session
5. 设置连接的用户名密码Clientid
6. 连接中的事件以及连接中的连接状态的改变

Best MQTT文档

https://bestdocshub.pages.dev/MQTT/
https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901100

连接代码需要有BEST MQTT ,BEST HTTP

using BestMQTT;
using BestMQTT.Packets;
using BestMQTT.Packets.Builders;
using System;
using System.Text;
using UnityEngine;

public class myMqttOetTest : MonoBehaviour
{
    private string hostName = "com";
    private int port = 1883;
    private string userName = "L24";//用户名
    private string psd = "ver3D";//密码
    private string clientId = "lind1";//客户端ID
    private string Telling = "Telling";//标识符

    private string Message = "Form C#";

    private string SendTopic = "";//发送消息的Topic
    private string GetTopic = "";//订阅的Topic

    private MQTTClient client;

    // Start is called before the first frame update
    void Start()
    {
        var c = new ConnectionOptionsBuilder()
             .WithTCP(hostName, port)
             .WithProtocolVersion(SupportedProtocolVersions.MQTT_3_1_1);

        client = new MQTTClientBuilder()
                            .WithOptions(c)
                           .WithEventHandler(OnConnected)
                           .WithEventHandler(OnDisconnected)
                           .WithEventHandler(OnStateChanged)
                           .WithEventHandler(OnError)
                         .CreateClient();

        client.BeginConnect(ConnectPacketBuilderCallback);
    }

    private void OnConnected(MQTTClient client)
    {
        
        //订阅主题1
        client.CreateSubscriptionBuilder(GetTopic)
            .WithMessageCallback(OnMessage)
            .WithAcknowledgementCallback(OnSubscriptionAcknowledged)
            .WithMaximumQoS(QoSLevels.ExactlyOnceDelivery)
            .BeginSubscribe();

		//订阅主题2
        //client.CreateSubscriptionBuilder("")
        //    .WithMessageCallback(OnMessage)
        //    .WithAcknowledgementCallback(OnSubscriptionAcknowledged)
        //    .WithMaximumQoS(QoSLevels.ExactlyOnceDelivery)
        //    .BeginSubscribe();


        //5.0的发送数据
        client.CreateApplicationMessageBuilder(SendTopic)
                .WithPayload(Message)
                .WithQoS(QoSLevels.ExactlyOnceDelivery)
                .WithContentType("text/plain; charset=UTF-8")
                .BeginPublish();

        //3.0的发送数据 
        //client.CreateApplicationMessageBuilder(SendTopic)
        //  .WithPayload(Message)
        //    .BeginPublish();

     
    }

    private void OnMessage(MQTTClient client, SubscriptionTopic topic, string topicName, ApplicationMessage message)
    {
        // Convert the raw payload to a string
        var payload = Encoding.UTF8.GetString(message.Payload.Data, message.Payload.Offset, message.Payload.Count);

        Debug.Log($"收到消息：Content-Type: '{message.ContentType}' Payload: '{payload}'");

        //取消订阅
        //client.CreateUnsubscribePacketBuilder("best_mqtt/test_topic")
        //    .WithAcknowledgementCallback((client, topicFilter, reasonCode) => Debug.Log($"Unsubscribe request to topic filter '{topicFilter}' returned with code: {reasonCode}"))
        //    .BeginUnsubscribe();
    }

    /// 

    /// 在 MQTT 客户端订阅一个主题后接收到服务器的确认响应时被调用。
    /// 
    /// MQTT 客户端对象
    ///  代表已订阅的主题的信息对象
    /// 服务器返回的订阅确认码，表示订阅请求的结果
    private void OnSubscriptionAcknowledged(MQTTClient client, SubscriptionTopic topic, SubscribeAckReasonCodes reasonCode)
    {
        if (reasonCode <= SubscribeAckReasonCodes.GrantedQoS2)
        {
            //订阅成功
            Debug.Log($"订阅成功。Successfully subscribed with topic filter '{topic.Filter.OriginalFilter}'. QoS granted by the server: {reasonCode}");
        }
        else
        {
            Debug.Log($"订阅失败：Could not subscribe with topic filter '{topic.Filter.OriginalFilter}'! Error code: {reasonCode}");
        }
    }

    private void OnDestroy()
    {
        if (client != null)
        {
            //5.0的断开连接
            //DisconnectPacketBuilder disconnectPacketBuilder = client.CreateDisconnectPacketBuilder();//创建一个用于构建断开连接请求的构建器对象。
            //disconnectPacketBuilder.WithReasonCode(DisconnectReasonCodes.NormalDisconnection);//设置断开连接的原因代码为 NormalDisconnection，表示这是一个正常的断开连接请求。
            //disconnectPacketBuilder.WithReasonString("Bye");//设置断开连接的原因字符串为 "Bye"，这个字符串可以提供额外的描述信息，说明为什么断开连接。
            //disconnectPacketBuilder.BeginDisconnect();

            //3.0的断开连接 
            DisconnectPacketBuilder disconnectPacketBuilder = client.CreateDisconnectPacketBuilder();//创建一个用于构建断开连接请求的构建器对象。
            disconnectPacketBuilder.BeginDisconnect();
        }
        else
        {
            // 可以选择在这里添加一个日志消息，表示客户端对象已经为 null，无需断开连接。
            Debug.Log("Client is already null, no need to disconnect.");
        }
    }


     /// 

    /// 构建连接对象
    /// 
    /// 
    /// 
    /// 
    private ConnectPacketBuilder ConnectPacketBuilderCallback(MQTTClient client, ConnectPacketBuilder builder)
    {

        //设置账号密码clientId，Session
        return builder.WithUserName(userName).WithPassword(psd).WithClientID(clientId).WithCleanStart();

       // return builder.WithUserName(userName).WithPassword(psd).WithClientID(clientId);
    }

    //记录Mqtt客户端连接状态的改变
    private void OnStateChanged(MQTTClient client, ClientStates oldState, ClientStates newState)
    {
        Debug.Log($"状态改变：{oldState} => {newState}");
    }

    //在断开连接的时候调用
    private void OnDisconnected(MQTTClient client, DisconnectReasonCodes code, string reason)
    {
        Debug.Log($"连接断开: OnDisconnected - code: {code}, reason: '{reason}'");
    }

    //在出错的时候调用
    private void OnError(MQTTClient client, string reason)
    {
        Debug.Log($"发生错误：OnError reason: '{reason}'");
    }
}