.Net Core：Middleware中间件管道

.NetCore中的Middleware是装配到管道处理请求和响应的组件；每个组件都可以决定是否继续进入下一个管道、并且可以在进入下一个管道前后执行逻辑；

最后一个管道或者中断管道的中间件叫终端中间件；

1、创建中间件管道IApplicationBuilder

app.Run()拦截请求后中断请求，多个Run()只执行第一个；

            app.Run(async httpcontenxt =>
            {
                httpcontenxt.Response.ContentType = "text/plain; charset=utf-8";
                await httpcontenxt.Response.WriteAsync("截获请求！并在此后中断管道");
            });
            app.Run(async httpcontenxt =>
            {
                httpcontenxt.Response.ContentType = "text/plain; charset=utf-8";
                await httpcontenxt.Response.WriteAsync("排序第二个的RUN");
            });

2、连接下一个管道 Use()

使用next.invoke调用下一个管道，在向客户端发送响应后，不允许调用 next.Invoke，会引发异常

            app.Use(async (context, next) =>
            {
                // 执行逻辑，但不能写Response
                //调用管道中的下一个委托
                await next.Invoke();
                // 执行逻辑，如日志等，但不能写Response
            });

            app.Run(async httpcontenxt =>
            {
                httpcontenxt.Response.ContentType = "text/plain; charset=utf-8";
                await httpcontenxt.Response.WriteAsync("截获请求！并在此后中断管道");
            });
            app.Run(async httpcontenxt =>
            {
                httpcontenxt.Response.ContentType = "text/plain; charset=utf-8";
                await httpcontenxt.Response.WriteAsync("排序第二个的RUN");
            });

3、通过路径或条件处理管道 Map()

public class Startup
{
    private static void HandleBranch(IApplicationBuilder app)
    {
        app.Run(async context =>
        {
            var branchVer = context.Request.Query["branch"];
            await context.Response.WriteAsync($"Branch used = {branchVer}");
        });
    }

    private static void HandleMapTest2(IApplicationBuilder app)
    {
        app.Run(async context =>
        {
            await context.Response.WriteAsync("Map Test 2");
        });
    }

    public void Configure(IApplicationBuilder app)
    {
        app.MapWhen(context => context.Request.Query.ContainsKey("branch"),
                               HandleBranch);//localhost:1234/?branch=master

        app.Map("/map2", HandleMapTest2);//localhost:1234/map2

        app.Run(async context =>
        {
            await context.Response.WriteAsync("Hello from non-Map delegate. <p>");
        });
    }
}

4、中间件的顺序很重要

异常/错误处理
HTTP 严格传输安全协议
HTTPS 重定向
静态文件服务器
Cookie 策略实施
身份验证
会话
MVC

app.UseExceptionHandler("/Home/Error"); // Call first to catch exceptions

app.UseStaticFiles();                   // Return static files and end pipeline.

app.UseAuthentication();               // Authenticate before you access

app.UseMvcWithDefaultRoute();  

资源

https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/middleware/index?view=aspnetcore-2.2