.NET Core 中间件 - 在控制器中访问 IApplicationBuilder？

Question

我需要访问控制器内的 IApplicationBuilder。

我尝试过的：-

我已经编写了中间件（app.UseMyMiddleware）如下

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

        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseCookiePolicy();
        app.UseMyMiddleware();

        app.UseAuthentication();
        app.UseSession();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
public class MyMiddleware
{
    private readonly RequestDelegate _next;

    public MyMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        ///TODO - Pass IApplicationBuilder to HttpContext 
        await _next(context);
    }
}
public static class MiddlewareExtensions
{
    public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<MyMiddleware>();
    }
}

但我不知道如何在 Invoke 方法中将 IApplicationBuilder 传递给 HttpContext。所以，我可以在控制器中使用它。 我还提到了以下stackoverflow问答

1. how to access IApplicationBuilder in a controller?
2. .Net Core Middleware - Getting Form Data from Request

问题：-

1. Invoke 方法中如何将 IApplicationBuilder 传递给 HttpContext 以在控制器中使用它？

2. 除了中间件，还有什么更好的方法可以访问控制器内部的 IApplicationBuilder 吗？

Answer 1

IApplicationBuilder 并非按照您希望的方式工作。相反，如果您在构建时创建了一些希望可用于中间件的数据，请向服务添加单例并将单例注入到中间件中。

Answer 2

在完成应用程序构建阶段（运行Configure 方法之后）之后，您将无法访问IApplicationBuilder。它根本不能用于注射。 但是为了在运行时根据请求数据（来自HttpContext）插入或配置中间件，您可以使用.UseWhen。终端中间件的另一个是.MapWhen，但我认为这不适合你的情况。以下是.UseWhen 的示例：

public static class MiddlewareExtensions
{
    public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
    {
        var allOptions = new [] {"option 1","option 2"};
        foreach(var option in allOptions){
            var currentOption = option;
            builder.UseWhen(context => {
              //suppose you can get the user's selected option from query string
              var selectedOption = context.Request.Query["option_key"];
              return selectedOption == currentOption;
            }, app => {
               //your MyMiddleware is supposed to accept one argument
               app.UseMiddleware<MyMiddleware>(currentOption);
            });
        }
        return builder;
    }
}

为了简化，我想您的选项只是字符串，您必须事先知道用户可以通过 UI 选择的所有可能选项。每一个都与插入中间件的条件完全匹配，并且必须都是独占的（所以只要其中一个就可以启用一个对应的中间件），否则会出现重复的中间件，这可能会导致一些问题。

通过将上面的foreach表达得更清楚，它可能表示如下：

//kind of pseudo code
if(selectedOption1){
    app.UseMiddleware<MyMiddleware>("option 1");
} else if(selectedOption2){
    app.UseMiddleware<MyMiddleware>("option 2");
}
...

您必须决定如何从用户那里获得选定的选项（在上面的示例中，我从query string 获得）。您也可以从Cookie 获取它（以记住用户的选择）或从其他来源（例如路由数据、标头、表单、请求正文）获取。我认为这是另一个问题，所以如果您对此有任何疑问，请在另一个问题中提问。

Answer 3

首先感谢@Kingking 和@GlennSills 提供的解决方案和宝贵的cmets。

我已经解决了这个问题

创建了一个继承自Hangfire.JobStorage的类，如下

public class HangfireSqlServerStorageExtension : Hangfire.JobStorage
{
    private readonly HangfireSqlServerStorage _hangfireSqlServerStorage = new HangfireSqlServerStorage();

    public HangfireSqlServerStorageExtension(string nameOrConnectionString)
    {
        _hangfireSqlServerStorage.SqlServerStorageOptions = new SqlServerStorageOptions();
        _hangfireSqlServerStorage.SqlServerStorage = new SqlServerStorage(nameOrConnectionString, _hangfireSqlServerStorage.SqlServerStorageOptions);
    }
    public HangfireSqlServerStorageExtension(string nameOrConnectionString, SqlServerStorageOptions options)
    {
        _hangfireSqlServerStorage.SqlServerStorageOptions = options;
        _hangfireSqlServerStorage.SqlServerStorage = new SqlServerStorage(nameOrConnectionString, _hangfireSqlServerStorage.SqlServerStorageOptions);
    }

    public void UpdateConnectionString(string nameOrConnectionString)
    {
        _hangfireSqlServerStorage.SqlServerStorage = new SqlServerStorage(nameOrConnectionString, _hangfireSqlServerStorage.SqlServerStorageOptions);
    }

    public override IStorageConnection GetConnection()
    {
        return _hangfireSqlServerStorage.SqlServerStorage.GetConnection();
    }

    public override IMonitoringApi GetMonitoringApi()
    {
        return _hangfireSqlServerStorage.SqlServerStorage.GetMonitoringApi();
    }
}

HangfireSqlServerStorage.cs

在上面的HangfireSqlServerStorageExtension类中使用

public class HangfireSqlServerStorage
{
    public SqlServerStorage SqlServerStorage { get; set; }
    public SqlServerStorageOptions SqlServerStorageOptions { get; set; }
}

Startup.cs

在启动文件中为 HangfireSqlServerStorageExtension 实例添加单例服务，并如下配置hangfire仪表板

public class Startup
{
    ///Other necessary code here
    
    public static HangfireSqlServerStorageExtension HangfireSqlServerStorageExtension { get; private set; }

    public void ConfigureServices(IServiceCollection services)
    {
       ///Other necessary code here
       
        HangfireSqlServerStorageExtension = new HangfireSqlServerStorageExtension("DBConnecttionString"));
        services.AddSingleton<HangfireSqlServerStorageExtension>(HangfireSqlServerStorageExtension);
        services.AddHangfire(configuration => configuration.SetDataCompatibilityLevel(CompatibilityLevel.Version_170));
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, IHttpContextAccessor httpContextAccessor)
    {
       //Other necessary code here

        app.UseHangfireDashboard("/Dashboard", new DashboardOptions(), HangfireSqlServerStorageExtension);

        //Other necessary code here
    }
}

在控制器内部我使用它如下

HangfireController.cs

public class HangfireController : Controller
{
   protected readonly HangfireSqlServerStorageExtension 
   hangfireSqlServerStorageExtension;

public HangfireController(HangfireSqlServerStorageExtension hangfireSqlServerStorageExtension)
{
    this.hangfireSqlServerStorageExtension = hangfireSqlServerStorageExtension;
}

public IActionResult DisplayHangfireDashboard()
{
    // Update connString as follows
    hangfireSqlServerStorageExtension.UpdateConnectionString(connString);
    var hangfireDashboardUrl = $"{this.Request.Scheme}://{this.Request.Host}{this.Request.PathBase}" + "/Dashboard";
    return Json(new { url = hangfireDashboardUrl });
}
}