c# - .NET Core 中 TCP 服务器的 IHostedService

Question

我正在尝试使用 asp.net core 构建一个小型 tcp 服务器/守护进程作为与服务器交互的 Web 前端。我发现 IHostedService/BackgroundService 似乎提供了一种将服​​务器和前端捆绑在一起的省力替代方案。

目前代码基本上如下所示(用于测试目的的回显服务器):

public class Netcat : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        TcpListener listener = new TcpListener(IPAddress.Any, 8899);
        listener.Start();
        while(!stoppingToken.IsCancellationRequested)
        {
            TcpClient client = await listener.AcceptTcpClientAsync();
            NetworkStream stream = client.GetStream();

            while (!stoppingToken.IsCancellationRequested)
            {
                byte[] data = new byte[1024];
                int read = await stream.ReadAsync(data, 0, 1024, stoppingToken);

                await stream.WriteAsync(data, 0, read, stoppingToken);
            }
        }
    }
}

并在 Startup.cs 中初始化，如下所示:

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddHostedService<Netcat>();
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
    }

现代 Asp.Net 核心应用程序和守护进程应该如何协作是否存在通用模式？

我如何从 Controller 与正在运行的服务本身进行交互？

IHostedService 是否可用于此目的，或者它是否是完全解耦 Asp.Net 前端和服务/服务器的更好方法，例如通过使用某种 IPC 机制将守护进程和 asp.net 作为单独的进程运行？

Answer 1

Is there a common pattern for how modern Asp.Net core applications and daemons should cooperate?

实际上，托管服务目前还没有那么强大。所以人们通常使用第三种产品。 但是，可以与托管服务和 Controller 进行通信。我将使用您的代码作为示例来实现这些目标:

1. TcpServer 能够接收两个命令，以便我们可以从 TcpClient 切换托管服务的状态。
2. WebServer 的 Controller 可以间接调用 TcpServer 的方法(通过中介)，并将其渲染为 html

将 Controller 与托管服务结合起来并不是一个好主意。为了从托管服务调用方法，我们可以引入一个Mediator。中介器只不过是一个充当单例的服务(因为它将被托管服务引用):

public interface IMediator{
    event ExecHandler ExecHandler ; 
    string Exec1(string status);
    string Exec2(int status);
    // ...
}

public class Mediator: IMediator{

    public event ExecHandler ExecHandler ;
    public string Exec1(string status)
    {
        if(this.ExecHandler==null) 
            return null;
        return this.ExecHandler(status);
    }

    public string Exec2(int status)
    {
        throw new System.NotImplementedException();
    }
}

托管服务需要认识到 IMediator 的存在，并以某种方式将其方法公开给 IMediator :

public class Netcat : BackgroundService
{
    private IMediator Mediator ;
    public Netcat(IMediator mediator){
        this.Mediator=mediator;
    }

    // method that you want to be invoke from somewhere else
    public string Hello(string status){
        return $"{status}:returned from service";
    }

    // method required by `BackgroundService`
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        TcpListener listener = new TcpListener(IPAddress.Any, 8899);
        listener.Start();
        while(!stoppingToken.IsCancellationRequested)
        {
            // ...
        }
    }
}

为了允许从 NetCat TcpServer 控制状态，我使其能够从客户端接收两个命令来切换后台服务的状态:

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        TcpListener listener = new TcpListener(IPAddress.Any, 8899);
        listener.Start();
        while(!stoppingToken.IsCancellationRequested)
        {
            TcpClient client = await listener.AcceptTcpClientAsync();
            Console.WriteLine("a new client connected");
            NetworkStream stream = client.GetStream();

            while (!stoppingToken.IsCancellationRequested)
            {
                byte[] data = new byte[1024];
                int read = await stream.ReadAsync(data, 0, 1024, stoppingToken);
                var cmd= Encoding.UTF8.GetString(data,0,read);
                Console.WriteLine($"[+] received : {cmd}");

                if(cmd=="attach") { 
                    this.Mediator.ExecHandler+=this.Hello;
                    Console.WriteLine($"[-] exec : attached");
                    continue;
                }
                if(cmd=="detach") {
                    Console.WriteLine($"[-] exec : detached");
                    this.Mediator.ExecHandler-=this.Hello;
                    continue;
                }

                await stream.WriteAsync(data, 0, read, stoppingToken);
                stream.Flush();
            }
        }
    }

如果你想在 Controller 中调用后台服务的方法，只需注入(inject) IMediator:

public class HomeController : Controller
{
    private IMediator Mediator{ get; }

    public HomeController(IMediator mediator){
        this.Mediator= mediator;
    }

    public IActionResult About()
    {
        ViewData["Message"] = this.Mediator.Exec1("hello world from controller")??"nothing from hosted service";

        return View();
    }
}