使用 IMiddleware 时添加自定义中间件不起作用

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）。假设我们希望在调用 API 时设置西班牙文化。这是完美运行的代码：

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>();
    }
}

和启动类：

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();
        });
    }
}

这很好，但是正如您所看到的，RequestCultureMiddleware 没有实现接口或基类/抽象类。您只需要记住在定义中间件以创建接收下一个中间件的构造函数时，您还需要创建一个专门名为“InvokeAsync”的方法，并将“HttpContext”作为参数。

我试图找到一个合同......一个基类或一个接口，猜猜是什么，我们有“IMiddleware”，它是“Microsoft.AspNetCore.Http”程序集的一部分。哇，这太完美了。让我们实施它。

界面如下所示：

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，在运行 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)

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

Answer 1

我确信这个问题在 5 个月后早就解决了，但我写这个建议是为了以防万一。

问题是即使您在启动的“配置”方法中内置了自定义中间件程序的“InvokeAsync”方法，也不会执行它。

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

在你的情况下

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

顺便说一句，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。

Answer 2

您正在使用基于工厂的中间件。如这些文档中所述，您错过了一个重要步骤：

...容器中注册的IMiddlewareFactory实例用于解析IMiddleware实现，而不是使用基于约定的中间件激活逻辑。中间件在应用程序的服务容器中注册为作用域或临时服务。

在您的情况下，该注册将如下所示：

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

    services.AddTransient<RequestCultureMiddleware>();
}