目录：
1、Core 处理HTTP请求流程
2、中间件（Middleware）&&处理流程
3、创建自定义中间件&&模拟Core的请求管道
Core 处理HTTP请求流程
Http请求来到之后，会先由WebServer（ 例如IIS，Nginx） 拿到然后丢给Kestrel WebServer，再有Kestrel 将Http请求封装为HttpContext后传入给.net core 请求管道(RequestDelegate)。HttpContext经过一系列middleware后返回response给WebServer。
中间件（Middleware）&&处理流程
微软官方文档给出的解释是这样的：中间件是加载在应用程序管道中以处理和相应请求的组件。其中每个组件都可以 选择是否可以将请求传递给管道中下一个组件；可以在调用管道的下一个组件之前或之后执行。下面是官方文档给出的一张图。
也就是说一个http请求的处理过程为，经过中间件1的处理逻辑（这个时候可以在中间件1中对httpcontext做一些处理，例如写入一段内容）,调用next()方法，进入到中间件2中，重复以上步骤。最终，所有中间件的处理逻辑的输出结果都会叠加到HttpResponse中去。
.net core 中有三种方式调用中间件。在StartUp的Configure方法中，分别可以调用app.Use()，app.Run()，app.Map() 来调用中间件。接下来让我们来看下：
app.Use方法有两个重载形式：
第一个方法接收一个中间件，第二个方法接收一个上下文和一个中间件。让我们来分别调用下：
1 ????????????app.Use(next => 2 ????????????{ 3 ????????????????return context => 4 ????????????????{ ?5 ????????????????????context.Response.WriteAsync("this is middleware1 start... ?"); 6 ????????????????????return next(context); 7 ????????????????}; 8 ????????????}); 9 ????????????app.Use(async (context, next) =>10 ????????????{11 ????????????????await context.Response.WriteAsync("this is middleware2 start... ??");12 ????????????????await next();13 ????????????});app.Run方法会终止管道，返回HttpResponse。在我们Configure方法中，默认最后一个方法就是app.Run 输出一句HelloWorld ，如下图
Use和Run都比较简单，不再详细介绍了。来看一眼程序运行结果：
app.Map 方法用来构建分支管线，它会启用一个新的ApplicationBuilder。Map根据请求的路径来匹配分支管线。Map方法也可以根据不同的PathString来匹配多个分支管线或嵌套匹配。
???????????app.Map("/task", build => ???????????{ ???????????????build.Run(async (context) => ???????????????{ ???????????????????await context.Response.WriteAsync("this is middleware3 For Map start... ?"); ???????????????}); ???????????});1 ????????????app.Map("/map", build =>2 ????????????{3 ????????????????build.Map("/mapTest2", MapHandleTest2);4 ????????????????build.Run(async (context) =>5 ????????????????{6 ????????????????????await context.Response.WriteAsync("this is middleware3 For Map start... ?");7 ????????????????});8 ????????????});9 ????????????app.Map("/mapTest1", MapHandleTest1); 1 ????????private void MapHandleTest1(IApplicationBuilder applicationBuilder) 2 ????????{ 3 ????????????applicationBuilder.Run(async context => 4 ????????????{ 5 ????????????????await context.Response.WriteAsync("this is middleware3HandleTest1 For Map start... ?"); 6 ????????????}); 7 ????????} 8 ????????private void MapHandleTest2(IApplicationBuilder applicationBuilder) 9 ????????{10 ????????????applicationBuilder.Run(async context =>11 ????????????{12 ????????????????await context.Response.WriteAsync("this is middleware3HandleTest2 For Map start... ?");13 ????????????});14 ????????}Map还有个特殊的方法，MapWhen， 它接收一个Func<HttpContext, bool>的参数，可以根据Http请求上下文做一些逻辑判断。然后继续执行管道
1 ????????????app.MapWhen(context => context.Request.Query.ContainsKey("branch"),2 ????????????????build =>3 ????????????????????build.Run(async context =>4 ????????????????????{5 ????????????????????????var branchVer = context.Request.Query["branch"];6 ????????????????????????await context.Response.WriteAsync($"Branch used = {branchVer}");7 ????????????????????})8 ????????????????);，这里再贴张.net core 自带的中间件
创建自定义中间件&&模拟Core的请求管道
管道的实现机制由ApplicationBuilder 和 RequestDelegate 组成。RequestDelegate是Middleware的核心，Use方法会将RequestDelegate加入到ApplicationBuilder 中去，最后执行Build方法，把所有RequestDelegate reverse之后挨个执行一遍。
接下来编写一个自定义的Middleware。
???public class RequestTestMiddleware ???{ ???????private readonly RequestDelegate _next; ????//中间件核心RequestDelegate，_next 表示执行下一个中间件。 ???????public RequestTestMiddleware(RequestDelegate next) ???????{ ???????????_next = next; ???????} ???????public Task Invoke(HttpContext context) ???????{ ???????????context.Response.WriteAsync("hello this is my RequestTestMiddleware"); ???????????return _next(context); ????????????????//覆盖delegate 的Inboke方法，将http上下文传入下一个中间件 ???????} ???} ???public static class RequestTestMiddlewareExtensions ???{ ???????public static IApplicationBuilder UseRequestTest(this IApplicationBuilder builder) ?????//使用扩展方法使我们的中间件对外开放。 ???????{ ???????????return builder.UseMiddleware<RequestTestMiddleware>(); ?//将我们中间件加入到IApplicationBuilder中去。 ???????} ???} //在StartUp 中使用我们的自定义中间件。 ???app.UseRequestTest();Http请求管道的模拟构建
1 ????/// <summary> 2 ????/// 拿到请求上下文，返回一个委托 3 ????/// </summary> 4 ????/// <param name="contex"></param> 5 ????/// <returns></returns> 6 ????public delegate Task RequestDelegate(Context contex); 7 ????/// <summary> 8 ????/// 模拟http请求上下文 9 ????/// </summary>10 ????public class Context11 ????{12 13 ????} 1 ????????public static IList<Func<RequestDelegate, RequestDelegate>> _list = new 2 ????????????List<Func<RequestDelegate, RequestDelegate>>(); 3 ????????static void Main(string[] args) 4 ????????{ 5 ????????????Use(next => ????????????????????????????????//加入中间件1 6 ????????????{ 7 ????????????????return context => 8 ????????????????{ 9 ????????????????????Console.WriteLine("this is use middleware1");10 ????????????????????return next.Invoke(context);11 ????????????????};12 ????????????});13 ????????????Use(next => ??????????????????????????????//加入中间件214 ????????????{15 ????????????????return context =>16 ????????????????{17 ????????????????????Console.WriteLine("this is use middleware2");18 ????????????????????return next.Invoke(context);19 ????????????????};20 ????????????});21 ????????????RequestDelegate end = context =>22 ????????????{23 ????????????????Console.WriteLine("this is end..."); ???????//管道24 ????????????????return Task.CompletedTask; ?????25 ????????????};26 ????????????_list.Reverse();27 ????????????foreach (var middleware in _list)28 ????????????{29 ????????????????end = middleware.Invoke(end);30 ????????????}31 ????????????end.Invoke(new Context()); ?????????????//实例化一个上下文实例32 ????????????Console.ReadLine();33 ????????}34 ????????/// <summary>35 ????????/// 将middleware 加入到list(applicationbuilder)中36 ????????/// </summary>37 ????????public static void Use(Func<RequestDelegate, RequestDelegate> iMiddleware)38 ????????{39 ????????????_list.Add(iMiddleware);40 ????????}Core篇——初探Core的Http请求管道&&Middleware
原文地址：https://www.cnblogs.com/liumengchen-boke/p/8227608.html