MQTT学习（七）--使用MQTTNet+ASP.NET Core创建MQTT服务器(broker)

经过漫长的等待，MQTT专题终于等到了第七篇，本次将在ASP.NET Core框架下利用MQTTnet创建自有服务器。

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由于最近刚开始接触ASP.NET Core，很多具体的用法还没有研究透彻，所以本篇重点在核心的几段代码，示例参考了MQTTnet官方源码。

本示例将融合ASP.NET Core WebAPI，以便在API接口调用中实现消息推送。

1.创建项目并引用MQTTnet

在VS2017中新建ASP.NET Core Web应用程序，打开NuGet管理器，搜索并安装MQTTnet.AspNetCore。

2.实现MQTT服务器功能

2.1.启动配置项-Startup.cs

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

            #region MQTT配置
            string hostIp = Configuration["MqttOption:HostIp"];//IP地址
            int hostPort = int.Parse(Configuration["MqttOption:HostPort"]);//端口号
            int timeout = int.Parse(Configuration["MqttOption:Timeout"]);//超时时间
            string username = Configuration["MqttOption:UserName"];//用户名
            string password = Configuration["MqttOption:Password"];//密码

            //构建配置项
            var optionBuilder = new MqttServerOptionsBuilder()
                .WithDefaultEndpointBoundIPAddress(System.Net.IPAddress.Parse(hostIp))
                .WithDefaultEndpointPort(hostPort)
                .WithDefaultCommunicationTimeout(TimeSpan.FromMilliseconds(timeout))
                .WithConnectionValidator(t =>
                {
                    if (t.Username != username || t.Password != password)
                    {
                        t.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                    }
                    t.ReturnCode = MqttConnectReturnCode.ConnectionAccepted;
                });
            var option = optionBuilder.Build();

            //服务注入
            services
                .AddHostedMqttServer(option)
                .AddMqttConnectionHandler()
                .AddConnections();
            #endregion

        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseMvc();


            app.UseConnections(c => c.MapConnectionHandler<MqttConnectionHandler>("/data", options =>
            {
                options.WebSockets.SubProtocolSelector = MQTTnet.AspNetCore.ApplicationBuilderExtensions.SelectSubProtocol;
            }));

            app.UseMqttEndpoint("/data");
            //MQTT声明周期事件
            app.UseMqttServer(server =>
            {
                //服务启动事件
                server.Started += async (sender, args) =>
                {
                    var msg = new MqttApplicationMessageBuilder().WithPayload("welcome to mqtt").WithTopic("start");
                    while (true)
                    {
                        try
                        {
                            await server.PublishAsync(msg.Build());
                            msg.WithPayload("you are welcome to mqtt");
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine(e);
                        }
                        finally
                        {
                            await Task.Delay(TimeSpan.FromSeconds(5));
                        }
                    }
                };
                //服务停止事件
                server.Stopped += (sender, args) =>
                {

                };

                //客户端连接事件
                server.ClientConnected += (sender, args) =>
                {
                    var clientId = args.ClientId;
                };
                //客户端断开事件
                server.ClientDisconnected += (sender, args) =>
                {
                    var clientId = args.ClientId;
                };

            });
        }

    }

2.2.配置文件-appsetting.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*",
  "MqttOption": {
    "HostIp": "127.0.0.1",
    "HostPort": 61613,
    "Timeout": 5000,
    "UserName": "admin",
    "Password": "passwod"
  }
}

2.3.程序入口-Program.cs

    public class Program
    {
        public static void Main(string[] args)
        {
            CreateWebHostBuilder(args).Build().Run();
            //上述方法与下方注释代码效果一致
            //WebHost
            //    .CreateDefaultBuilder(args)
            //    .UseKestrel()
            //    .UseStartup()
            //    .Build()
            //    .Run();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseKestrel(o =>
                {
                    o.ListenAnyIP(61613, m => m.UseMqtt());//绑定MQTT服务端口
                    //o.ListenAnyIP(5000);
                })
                .UseStartup<Startup>();
    }

3.在API接口中使用MQTT服务

由于ASP.NET Core使用依赖注入（Dependency Injection）来实现控制反转（IoC），MQTTServer正是通过依赖注入添加到应用程序的服务集合中去，同样通过ASP.NET Core中的机制可以在API控制器类中获取当前实例中的MQTT服务。具体实现要借助接口IServiceProvider。创建一个辅助类如下：

    public static class ServiceLocator
    {
        public static IServiceProvider Instance { get; set; }
    }

在Startup类的Configure方法中添加如下代码：

//获取当前应用的服务集合
ServiceLocator.Instance = app.ApplicationServices;

在API控制器中就可以通过ServiceLocator获取服务并使用了。

    [Route("v1/api/values")]
    [ApiController]
    public class ValuesController : RootController
    {

        public string Test()
        {
            string result = "";
            //从服务集合中获取MQTT服务
            var service = ServiceLocator.Instance.GetService(typeof(MQTTnet.Server.MqttServer));
            var messager = (MQTTnet.Server.MqttServer)service;
            
            //这里你可以构建消息并发布

            return result;
        }
    }

示例代码

经过上述过程中的探索研究，虽然暂未实现图形化界面，但基本了解了如何使用ASP.NET Core构建MQTT代理服务器，同时掌握了在API接口中使用MQTT服务的方法，后续将做更深一步的研究。