添加自定义中间件在使用 IMiddleware 时不起作用

Question

我正在尝试向管道添加自定义中间件（为了更容易，我将选择 .NET Core 文档示例）。假设我们希望在触发对 API 的调用时设置西班牙文化。这是运行完美的代码：

public class RequestCultureMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task InvokeAsync(HttpContext context)
    {
        CultureInfo.CurrentCulture = new CultureInfo("es-ES");
        CultureInfo.CurrentUICulture = new CultureInfo("es-ES");

        // Call the next delegate/middleware in the pipeline
        await _next(context);
    }
}

public static class RequestCultureMiddlewareExtensions
{
    public static IApplicationBuilder UseRequestCulture(
        this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<RequestCultureMiddleware>();
    }
}

和启动 class：

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.AddControllers();
    }

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

        //here is our custom middleware!
        app.UseRequestCulture();

        app.UseHttpsRedirection();

        app.UseRouting();

        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

很好，但是如您所见，RequestCultureMiddleware 没有实现接口或基础 class/abstract class。您只需要记住在定义中间件时创建接收下一个中间件的构造函数，还需要创建一个专门调用 "InvokeAsync" 并使用 "HttpContext" 作为参数的方法。

我试图找到一个合同...一个基础 class 或一个接口，你猜怎么着，我们有 "IMiddleware"，它是 "Microsoft.AspNetCore.Http" 程序集的一部分。哇，太完美了。让我们来实施吧。

界面是这样的：

namespace Microsoft.AspNetCore.Http
{
    //
    // Summary:
    //     Defines middleware that can be added to the application's request pipeline.
    public interface IMiddleware
    {
        //
        // Summary:
        //     Request handling method.
        //
        // Parameters:
        //   context:
        //     The Microsoft.AspNetCore.Http.HttpContext for the current request.
        //
        //   next:
        //     The delegate representing the remaining middleware in the request pipeline.
        //
        // Returns:
        //     A System.Threading.Tasks.Task that represents the execution of this middleware.
        Task InvokeAsync(HttpContext context, RequestDelegate next);
    }
}

这里是实现：

    public class RequestCultureMiddleware : IMiddleware
    {

        public Task InvokeAsync(HttpContext context, RequestDelegate next)
        {
            CultureInfo.CurrentCulture = new CultureInfo("es-ES");
            CultureInfo.CurrentUICulture = new CultureInfo("es-ES");

            // Call the next delegate/middleware in the pipeline
            return next(context);
        }
    }


    public static class RequestCultureMiddlewareExtensions
    {
        public static IApplicationBuilder UseRequestCulture(
            this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<RequestCultureMiddleware>();
        }
    }
}

但是，当运行连接 API 时，我在运行时收到以下错误：

System.InvalidOperationException: No service for type 'WebApplication1.RequestCultureMiddleware' has been registered.
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.AspNetCore.Http.MiddlewareFactory.Create(Type middlewareType)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.<>c__DisplayClass5_1.<<UseMiddlewareInterface>b__1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

如果不使用扩展 "UseMiddleware"，我应该如何注册这个中间件？谢谢。

Answer 1

您正在使用 factory-based middleware。如这些文档中所述，您错过了重要的一步：

... the IMiddlewareFactory instance registered in the container is used to resolve the IMiddleware implementation instead of using the convention-based middleware activation logic. The middleware is registered as a scoped or transient service in the app's service container.

在您的情况下，该注册看起来像这样：

public void ConfigureServices(IServiceCollection services)
{
    // ...

    services.AddTransient<RequestCultureMiddleware>();
}

Answer 2

我确定这个问题在 5 个月后很久以前就已经解决了，但我写这个建议是为了以防万一。

问题是您的自定义中间件程序的“InvokeAsync”方法没有被执行，即使您在 Startup 的“Configure”方法中内置了它。

前几天我遇到了同样的问题并解决了它，但是我在 app.UseEndpoints 方法之前放置了内置代码。

你的情况

app.UseAuthorization();
app.UseRequestCulture();  // <- this way.
app.UseEndpoints(endpoints =>
{
    endpoints.MapControllers();
});

顺便说一下，如果你把它放在app.UseEndpoints方法之后，构造函数会被调用，但是InvokeAsync方法不会被执行。

添加自定义中间件在使用 IMiddleware 时不起作用

Adding custom middleware not working when using IMiddleware

.net

c#

.net-core

asp.net-core

asp.net-core-middleware