準備

• 本客戶端使用VS2015進行開發，所以需要實現安裝VS2015。
• 開發之前需要下載M2MQTT庫。m2mqtt庫的獲取，可以使用vs的nuget來獲取。
• 重啟VS2015後，開啟自己的C#工程，然後開啟“工具”-“Nuget包管理器”-“程式包管理器控制檯”
  在控制檯中輸入“Install-Package M2Mqtt -Version 4.3.0”即可自動完成配置。

程式碼

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using
 
 System.Net;
using System.Security.Cryptography.X509Certificates;
using uPLibrary.Networking.M2Mqtt;
using uPLibrary.Networking.M2Mqtt.Messages;
using System.Net.Security;

namespace m2mqtt_test
{
    class Program
    {
        static void messageReceive(object sender, MqttMsgPublishEventArgs e)
        {
            string
 
 msg = "Topic:" + e.Topic + "   Message:" + System.Text.Encoding.Default.GetString(e.Message);
            Console.WriteLine(msg);
        }
        static bool cafileValidCallback(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            string
 
 msg = "X509 鏈狀態:";
            foreach (X509ChainStatus status in chain.ChainStatus)
            {
                msg += status.StatusInformation + "\n";
            }
            msg += "SSL策略問題：" + (int)sslPolicyErrors;

            Console.WriteLine(msg);

            if (sslPolicyErrors != SslPolicyErrors.None)
                return false;
            return true;
        }

        static void Main(string[] args)
        {
            string brokerHostName = "192.168.1.38";
            int brokerPort = 8883;
            string clientId = "m2mqtt";
            string username = "develop";
            string password = "666666";
            string[] topic = {"topic"};
            byte[] qosLevels = { MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE};
            string caPath = "C:/MqttSSL/ca.crt";
            X509Certificate caCert = new X509Certificate(caPath);
            Console.WriteLine(caCert.ToString(true)+"\n"+caCert.ToString());
            Console.ReadKey();
            Console.WriteLine("------------------------分割線-------------------------------");
            //無SSL連線
            //MqttClient client = new MqttClient(brokerHostName,brokerPort,false,null,null,MqttSslProtocols.None);
            try {
                //單向SSL通訊
                MqttClient client = new MqttClient(brokerHostName, brokerPort, true, caCert, null, MqttSslProtocols.TLSv1_2, new RemoteCertificateValidationCallback(cafileValidCallback));
                //訊息接受
                client.MqttMsgPublishReceived += new MqttClient.MqttMsgPublishEventHandler(messageReceive);
                //連線Broker
                client.Connect(clientId, username, password);

                client.Subscribe(topic, qosLevels);
            }
            catch (System.Exception)
            {
                Console.WriteLine("連線失敗!");
                Console.ReadKey();
            }

        }
    }
}

• 可能C#遇到的問題：一個是因為客戶端和服務端以及簽發機構的證書資訊相同，導致客戶端和服務端不能識別證書，導致連線失敗。另外一個原因是因為自己生成的證書沒有新增到系統的根證書中，不被根證書所信任導致連線失敗。