AspNetCore中的中间件详解

 public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            //判断是否为开发环境
            if (env.IsDevelopment())
            {
                //使用异常开发页面中间件
                app.UseDeveloperExceptionPage();
            }
            //静态文件中间件
            app.UseStaticFiles();
            //Http请求转https请求
            app.UseHttpsRedirection();
            //身份验证
            app.UseAuthentication();
            //相较于netcore2来说,Routing 中间件是拆分出来的，原来是属于mvc中间件的一部分
            app.UseRouting();
            //端点中间件，请求处理路径,结合Routing中间件一起使用的
            app.UseEndpoints(endpoints =>
            {
                //当请求"/"时，响应输出HelloWorld【可通过lamda表达式进行配置】
                endpoints.MapGet("/", async context =>
                {
                    await context.Response.WriteAsync("Hello World!");
                });
                //请求路径匹配到 /home/index/1 这种路径时，将会到指定的handler处理器上,默认会处理到
                endpoints.MapControllerRoute("default","/{controller=home}/{action=index}/{id?}");
            });
        }

    //一个能处理请求的方法
    public delegate Task RequestDelegate(HttpContext context);
   //中间件原生定义，委托，输入是一个RequestDelegate，输出也是一个RequestDelegate，
    Func<RequestDelegate, RequestDelegate> middleware = new Func<RequestDelegate, RequestDelegate>((RequestDelegate requestdelegate) =>
        {
            return new RequestDelegate(async (context) =>
            {
                await context.Response.WriteAsync("接收1个带RequestDelegate类型的参数，返回RequestDelegate类型的委托");
            });
        });
  // 上述中间件的定义代码可根据lamda表达式规则进行缩写
   Func<RequestDelegate, RequestDelegate> middleware = new Func<RequestDelegate, RequestDelegate>((RequestDelegate requestdelegate) =>
        {
            return new RequestDelegate(async (context) =>
            {
                await context.Response.WriteAsync("接收1个带RequestDelegate类型的参数，返回RequestDelegate类型的委托");
            });
        });
   Func<RequestDelegate, RequestDelegate> middleware = (request=>{
        return new RequestDelegate(async (context) =>
            {
                await context.Response.WriteAsync("接收1个带RequestDelegate类型的参数，返回RequestDelegate类型的委托");
            });
   });

//增加中间件到请求管道中
IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware);

     app.Use(async (context, next) =>
     {
        await context.Response.WriteAsync(" Rquest The first middleware");
        //调用下一个中间件
        await next.Invoke();
        await context.Response.WriteAsync(" Response The first middleware");
    });

    app.Use(next =>
      {
          return new RequestDelegate(async context =>
          {
             await context.Response.WriteAsync(" Rquest The first middleware");
             await next.Invoke(context);
             await context.Response.WriteAsync(" Response The first middleware");
           });
      }
   );

   public static void Run(this IApplicationBuilder app, RequestDelegate handler);

  app.Run( async context=> {
        await context.Response.WriteAsync(" Rquest The final middleware");
  });

//pathMatch 请求路径匹配字符串
//configuration 符合匹配规则时采取的 请求处理逻辑.
//configuration 是一个无返回，请求参数类型为 IApplicationBuilder的回调函数。
public static IApplicationBuilder Map(this IApplicationBuilder app, PathString pathMatch, Action<IApplicationBuilder> configuration);

 app.Map("/secondturl", appBuilder => {
   appBuilder.Run(async context =>
    {
         await context.Response.WriteAsync(" the request'url is  secondturl" + "\n");
         });
    });

   public class RequestIpMiddleware
    {
        private readonly RequestDelegate requestDelegate;
        public RequestIpMiddleware(RequestDelegate requestDelegate) {
            this.requestDelegate = requestDelegate;
        }
        public async Task Invoke(HttpContext context) {
            context.Response.WriteAsync("The Request Ip is " + context.Request.HttpContext.Connection.RemoteIpAddress.ToString()+"\n");
            //调用下一个请求中间件
            await requestDelegate.Invoke(context);
        }
    }

    /// <summary>
    /// 调用中间件的扩展方法
    /// </summary>
    public static class MiddlewareExtensions
    {
        /// <summary>
        ///this 关键字不能省略
        /// </summary>
        /// <param name="app"></param>
        /// <returns></returns>
        public static IApplicationBuilder UseIpMiddleware( this IApplicationBuilder app ) 
        {
           return  app.UseMiddleware<RequestIpMiddleware>();
        }
    }

     app.UseIpMiddleware();

public static IApplicationBuilder UseMiddleware<TMiddleware>(this IApplicationBuilder app, params object[] args);

    /// <summary>
    /// 自定义中间件 
    /// </summary>
    public class IPMiddleware : IMiddleware
    {
        /// <summary>
        /// IMiddleware接口定义了唯一的InvokeAsync方法，用来实现对请求的处理。
        /// </summary>
        /// <param name="context"> 当前请求上下文</param>
        /// <param name="next">下一个请求requestDelegate</param>
        /// <returns></returns>
        public Task InvokeAsync(HttpContext context, RequestDelegate next)
        {
            //获取请求的IP
            var ip = context.Request.HttpContext.Connection.RemoteIpAddress.ToString();
            context.Response.WriteAsync("IP is "+ip+"\n");
            //调用下一个中间件
            return  next.Invoke(context);
        }
    }