.Net Core下使用MQTT协议直连IoT平台

【摘要】 .Net平台通过原生MQTT接口，作为南向设备对接OceanConnect平台

因为种种历史原因吧，目前华为平台上对.net的支持案例SDK确实比较少，当看到各种语言的SDK和Demo，唯独缺.net平台的，广大.net开发者也会怀疑.net是不是真的不适合IoT，甚至是互联网。

我的分析是

1、微软从.Net Framework开始所谓的跨平台，仅仅局限在Windows个版本的平台，对其他系统并不支持

2、微软多年以来给人的感觉是闭源，和Linux是死对头，在华为2019HC大会上和一位鲲鹏的工程师聊天也佐证了这一点，他们2019年了还依然对微软是这种认识

一提到开源，一提到互联网、分布式，.net就被轻视，这种态度很常见。

但是，我说的是但是，广大的.neter为什么选择.net平台的，为何mono这么多年都对.net跨平台不懈努力？为什么visual studio被称为宇宙第一的IDE？

那就是生产力。

以前的种种都成为历史了，自从.net core被提出，微软已经是一个亲Linux的代表了，跨平台、高性能已经是核心基础 。且不提Windows IoT, .net core在Linux,Arm上已经非常成熟了，树莓派们的小设备都能轻松玩转。

作为平台也好，工具也好就是为了提高生产力的。再来看看.net对接华为IoT平台，我现在从之前羡慕C/C++,Java,PHP等，在华为的帮助文档中都提供了南向设备的SDK，北向接口的SDK。我也一度怀疑华为为何不提供.net的SDK？没有SDK的帮助，对接将是比其他语言更要复杂，困难要一点点的肯。我也尝试在.net里用[DllImport]特性用c的sdk。

到现在，其实我可以负责任的告诉大家，.net根本不需要华为提供SDK，SDK本身对接口封装后就有不少限制，.net就利用公开的原始接口开发，非常简单和便捷，而且应用起来也灵活。这就是.net的强大生产力，而且.net framework(也可对接桌面程序)和.net core都可以实现。

1、北向接口对接

因为工作关系，对北向接口比较熟悉，华为提供的是restful的接口，和语言无关，实现起来轻车熟路。当时遇到一个困难就是用错了证书密码，现在回头看帮助文档中也说明了用哪个证书和密码，我也专门写过一个帖子来说明北向接口对接。

2、南向设备对接

南向设备比较复杂，对我来说确实是陌生的领域，小熊派这种MCU的板子恐怕只能有C来搞了，借助LiteOS+IoT Studio 也可以胜任。在我的计划中类似小熊派这样的设备甚至是定制更轻巧的，是物联网的常用终端类型。但还有些场景需要配合更丰富的应用，C恐怕做不到(起码需要带个界面啥的我做不到)，或者说做到成本太高，在类似树莓派的独立设备，甚至是在Windows电脑上外接其他设备的场景，.net正是用武之地。

.Net core + Mqttnet 作为南向设备对接华为IoT平台

开发工具：Visual Studio 2019，.Net core 2.2和.net framework 4.7.2

Nuget包：MQTTnet 版本v3.0.8

核心内容三个事件

连接Mqtt服务器：

mqttClient.ConnectAsync(options);

订阅服务器Topic

var result = await mqttClient.SubscribeAsync(new TopicFilter()
{
    Topic = topicSubscribe,
    QualityOfServiceLevel = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce

});

服务器发送命令的响应

mqttClient.UseApplicationMessageReceivedHandler(async handle =>
{
    var payload = Encoding.Default.GetString(handle.ApplicationMessage.Payload);
    var data = JsonConvert.DeserializeObject<ReceivedMessage>(payload);
    Console.WriteLine($"收到MSG：{payload}");
    var result = await mqttClient.PublishAsync(topicPublish, $"{{"msgType":"deviceRsp","mid":{data.Mid},"errcode":0,"body":{{"response":"ok"}}}}");
    Console.WriteLine($"设备响应命令:{result.ReasonCode}");
});

上报设备多信息到服务器：

var msg = new SendMessage
{
	Data = new List<Service>
	{
		 new Service
		 {
			 ServiceData = new Dictionary<string, dynamic> { { "storage", st }, { "usedPercent", 10 }  },
			 ServiceId = "Storage",
			 EventTime = DateTime.UtcNow.ToString("yyyyMMddTHHmmssZ")
		 }
	}
};
var payload = JsonConvert.SerializeObject(msg, new JsonSerializerSettings { ContractResolver = new CamelCasePropertyNamesContractResolver() });
var result = await mqttClient.PublishAsync(topicPublish, payload);

完整代码如下：

using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Client.Connecting;
using MQTTnet.Client.Options;
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Threading.Tasks;
using System.Linq;
using MQTTnet.Client.Receiving;
using System.Text;
using System.Security.Cryptography.X509Certificates;
using MQTTnet.Client.Subscribing;
using MQTTnet.Extensions.ManagedClient;
using System.Security.Cryptography;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;

namespace CampusApp
{
    class Program
    {
        private static IMqttClient mqttClient;
                    
        private static string topicPublish = "/huawei/v1/devices/00b1db5e-5331-4ade-8b62-6c670e6c8d98/data/json";
        private static string topicSubscribe = "/huawei/v1/devices/00b1db5e-5331-4ade-8b62-6c670e6c8d98/command/json";
        private static async Task ConnectMqttServerAsync()
        {
            if (mqttClient == null)
            {
                mqttClient = new MqttFactory().CreateMqttClient();

                mqttClient.UseConnectedHandler(async handle =>
                {
                   
                        var result = await mqttClient.SubscribeAsync(new TopicFilter()
                        {
                            Topic = topicSubscribe,
                            QualityOfServiceLevel = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce

                        });
                        Console.WriteLine("连接成功");
                  
                });
                mqttClient.UseApplicationMessageReceivedHandler(async handle =>
                {
                    
                        var payload = Encoding.Default.GetString(handle.ApplicationMessage.Payload);
                        var data = JsonConvert.DeserializeObject<ReceivedMessage>(payload);
                        Console.WriteLine($"收到MSG：{payload}");
                        var result = await mqttClient.PublishAsync(topicPublish, $"{{"msgType":"deviceRsp","mid":{data.Mid},"errcode":0,"body":{{"response":"ok"}}}}");
                        Console.WriteLine($"设备响应命令:{result.ReasonCode}");
                  

                });
                mqttClient.UseDisconnectedHandler(handle =>
                {
                    Console.WriteLine($"MQTT 断开连接");
                });
            }
           
			var utctime =  DateTime.UtcNow.ToString("yyyyMMddhh");
			var pwd = Encrypt("9e4fbd64f6be2337732a", utctime);
			var options = new MqttClientOptionsBuilder()
				.WithProtocolVersion(MQTTnet.Formatter.MqttProtocolVersion.V311)
				.WithClientId($"00b1db5e-5331-4ade-8b62-6c670e6c8d98_0_0_{utctime}")
				.WithTcpServer("49.4.93.24", 8883)
				.WithCredentials("00b1db5e-5331-4ade-8b62-6c670e6c8d98", pwd)
				//.WithKeepAlivePeriod(TimeSpan.FromSeconds(10))
				.WithKeepAliveSendInterval(TimeSpan.FromSeconds(3))
				.WithTls(new MqttClientOptionsBuilderTlsParameters()
				{
					AllowUntrustedCertificates = false,
					UseTls = true,
					Certificates = new List<byte[]> { new X509Certificate2("rootcert.pem").Export(X509ContentType.Cert) },
					CertificateValidationCallback = delegate { return true; },
					IgnoreCertificateChainErrors = false,
					IgnoreCertificateRevocatireplaceStrings = false
				})
				.WithCleanSession()
				.Build();
			try
            {
                var result = await mqttClient.ConnectAsync(options);
                Console.WriteLine(result.ResultCode);
            }
            catch (Exception ex)
            {

                Console.WriteLine(ex.Message);
            }
        }
        static string Encrypt(string message, string secret)
        {
            secret = secret ?? "";
            //var encoding = new System.Text.ASCIIEncoding();
            var encoding = new System.Text.UTF8Encoding();
            byte[] keyByte = encoding.GetBytes(secret);
            byte[] messageBytes = encoding.GetBytes(message);
            using (var hmacsha256 = new HMACSHA256(keyByte))
            {
                byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);
                //return Convert.ToBase64String(hashmessage);
                StringBuilder rst = new StringBuilder();
                for (int i = 0; i < hashmessage.Length; i++)
                {
                    rst.Append(hashmessage[i].ToString("x2"));
                }
                return rst.ToString();
            }
        }
        static async Task Main(string[] args)
        {
            try
            {
                _ = Task.Run(async () =>
                {
                    await ConnectMqttServerAsync();
                });

                while (mqttClient?.IsConnected != true)
                {
                    await Task.Delay(1000);
                }

                while (true)
                {
                    Console.WriteLine("输入数字 storage：");
                    var input = Console.ReadLine();
                    if (!int.TryParse(input, out int st))
                        continue;

                    var msg = new SendMessage
                    {
                        Data = new List<Service>
                        {
                             new Service
                             {
                                 ServiceData = new Dictionary<string, dynamic> { { "storage", st }, { "usedPercent", 10 }  },
                                 ServiceId = "Storage",
                                 EventTime = DateTime.UtcNow.ToString("yyyyMMddTHHmmssZ")
                             }
                        }
                    };
                    var payload = JsonConvert.SerializeObject(msg, new JsonSerializerSettings { ContractResolver = new CamelCasePropertyNamesContractResolver() });
                    var result = await mqttClient.PublishAsync(topicPublish, payload);
                    Console.WriteLine($"Publish Result: {result.ReasonCode}");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message + ex.StackTrace);
            }
        }
    }
}

看这段代码多买的简单，就搞定了整个过程。

我在开发中重新整理了一下，作为一个SDK提供给.net framework和.net core两边使用，封装之后更加简单。完成之后作为nuget包再分享。 

作者：神龙居市