asp.net的HTTP请求处理过程

1、asp.net的HTTP请求处理过程

说明： 
（1）、客户端浏览器向服务器发出一个http请求，此请求会被inetinfo.exe进程截获，然后转交给aspnet_isapi.dll进程，接着它又通过Http Pipeline的管道，传送给aspnet_wp.exe这个进程，接下来就到了.net framework的HttpRunTime处理中心，处理完毕后就发送给用户浏览器。 
（2）、当一个http请求被送入到HttpRuntime之后，这个Http请求会继续被送入到一个被称之为HttpApplication Factory的一个容器当中，而这个容器会给出一个HttpApplication实例来处理传递进来的http请求，而后这个Http请求会依次进入到如下几个容器中：HttpModule --> HttpHandler Factory --> HttpHandler。当系统内部的HttpHandler的ProcessRequest方法处理完毕之后，整个Http Request就被处理完成了，客户端也就得到相应的东东了。 
（3）完整的http请求在asp.net framework中的处理流程： 
HttpRequest-->inetinfo.exe->ASPNET_ISAPI.DLL-->Http Pipeline-->ASPNET_WP.EXE-->HttpRuntime-->HttpApplication Factory-->HttpApplication-->HttpModule-->HttpHandler Factory-->HttpHandler-->HttpHandler.ProcessRequest() 

也就是说一个HTTP请求在HttpModule容器的传递过程中，会在某一时刻（ResolveRequestCache事件）将这个HTTP请求传递给HttpHandler容器。在这个事件之后，HttpModule容器会建立一个HttpHandler的入口实例，但是此时并没有将HTTP请求控制权交出，而是继续触发AcquireRequestState事件以及PreRequestHandlerExcute事件。在PreRequestHandlerExcute事件之后，HttpModule窗口就会将控制权暂时交给HttpHandler容器，以便进行真正的HTTP请求处理工作。
而在HttpHandler容器内部会执行ProcessRequest方法来处理HTTP请求。在容器HttpHandler处理完毕整个HTTP请求之后，会将控制权交还给HttpModule，HttpModule则会继续对处理完毕的HTTP请求信息流进行层层的转交动作，直到返回到客户端为止。 

（4）如果想在中途截获一个httpRequest并做些自己的处理，就应该在HttpRuntime运行时内部来做到这一点，确切的说是在HttpModule这个容器中来实现。

2、HttpModule工作原理

     负责监听HttpRequest，同时对HttpRequest增添或者过滤掉一部分内容。也就是说，当一个HTTP请求到达HttpModule时，整个ASP.NET Framework系统还并没有对这个HTTP请求做任何处理，也就是说此时对于HTTP请求来讲，HttpModule是一个HTTP请求的“必经之路”，所以可以在这个HTTP请求传递到真正的请求处理中心（HttpHandler）之前附加一些需要的信息在这个HTTP请求信息之上，或者针对截获的这个HTTP请求信息作一些额外的工作，或者在某些情况下干脆终止满足一些条件的HTTP请求，从而可以起到一个Filter过滤器的作用。
HttpModule实现了接口IHttpModule，我们可以自定义实现该接口的类，从而取代HttpModule。 
asp.net默认的HttpModule如下:

 ???????1.System.Web.SessionState.SessionStateModule;

 ???????2.System.Web.Security.WindowsAuthenticationModule;

 ???????3.System.Web.Security.FormsAuthenticationModule;

 ???????4.System.Web.Security.PassportAuthenticationModule;

 ???????5.System.Web.Security.UrlAuthorizationModule;

 ???????6.System.Web.Security.FileAuthorizationModule;

3、编写自己的HttpModule

要实现HttpModule，必须实现接口IHttpModule。下面是IHttpModule接口分析：

using System;

namespace System.Web

{

 ??public interface IHttpModule

 ???{

 ???????// ??销毁不再被HttpModule使用的资源

 ???????void Dispose();

 ???????// 初始化一个Module,为捕获HttpRequest做准备

 ???????void Init(HttpApplication context);

 ???}

}
下面是自己的HttpModule：

using System;

using System.Web;

namespace ClassLibrary1

{

 ???public class MyHttpModule : IHttpModule

 ???{

 ???????public void Dispose() { }

 ???????public void Init(HttpApplication context)

 ???????{

 ???????????context.BeginRequest += new EventHandler(Application_BeginRequest);

 ???????????context.EndRequest += new EventHandler(Application_EndRequest);

 ???????}

 ???????public void Application_BeginRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = sender as HttpApplication;

 ???????????HttpContext context = application.Context;

 ???????????HttpResponse response = context.Response;

 ???????????response.Write("这是来自自定义HttpModule中有BeginRequest");

 ???????}

 ???????public void Application_EndRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = sender as HttpApplication;

 ???????????HttpContext context = application.Context;

 ???????????HttpResponse response = context.Response;

 ???????????response.Write("这是来自自定义HttpModule中有EndRequest");

 ???????}

 ???}

}

web.config:

myHttpModule" type="ClassLibrary1.MyHttpModule,ClassLibrary1"/>

default.aspx.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 

{

 ???protected void Page_Load(object sender, EventArgs e)

 ???{

 ???????Response.Write("来自Default.aspx页面");

 ???}

}

4、HttpModule内部事件机制和生命周期

HttpModule对HttpApplication实例进行处理，而HttpApplication有很多事件（对应不同的生命期），这样就衍生出HttpModule内部事件机制和生命周期。 
（1）、HttpModule的事件

说明： 
a、BenginRequest和EndRequest分别是HttpModule容器最开始的和最后的事件； 
b、EndRequest之后还会触发PreSendRequestHeaders事件和PreSendRequestContent事件，这不是在HttpModule外的两个事件，表示HttpModule结束，即将开始向Client发送数据

2）、验证HttpModule生命周期 
与HttpHandler的交互：
说明： 
a、HttpModule容器会将HttpRequest传递到HttpHandler容器，这个时间点是ResolveRequestCache事件 
b、HttpModule容器会建立HttpHandler实例作为入口——Session从此生效 
c、触发AcquireRequestState事件以及PreRequestHandlerExecute事件 
d、HttpModule容器便将对HttpRequest的控制权转让给HttpHandler容器 
e、HttpHandler容器处理HttpRequest——使用自身的ProcessRequest方法，将对其控制权又还给HttpModule容器——之后Session失效。

验证生命周期代码：

using System;

using System.Collections.Generic;

using System.Text;

using System.Web;

namespace MyHttpModule

{

 ???public class ValidaterHttpModuleEvents : IHttpModule

 ???{

 ???????public void Dispose()

 ???????{ }

 ???????/// 

 ???????/// 验证HttpModule事件机制

 ???????/// 

 ???????/// 

 ???????public void Init(HttpApplication application)

 ???????{

 ???????????application.BeginRequest += new EventHandler(application_BeginRequest);

 ???????????application.EndRequest += new EventHandler(application_EndRequest);

 ???????????application.AcquireRequestState += new EventHandler(application_AcquireRequestState);

 ???????????application.AuthenticateRequest += new EventHandler(application_AuthenticateRequest);

 ???????????application.AuthorizeRequest += new EventHandler(application_AuthorizeRequest);

 ???????????application.PreRequestHandlerExecute += new EventHandler(application_PreRequestHandlerExecute);

 ???????????application.PostRequestHandlerExecute += new EventHandler(application_PostRequestHandlerExecute);

 ???????????application.ReleaseRequestState += new EventHandler(application_ReleaseRequestState);

 ???????????application.ResolveRequestCache += new EventHandler(application_ResolveRequestCache);

 ???????????application.PreSendRequestHeaders += new EventHandler(application_PreSendRequestHeaders);

 ???????????application.PreSendRequestContent += new EventHandler(application_PreSendRequestContent);

 ???????}

 ???????private void application_BeginRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_BeginRequest
");

 ???????}

 ???????private void application_EndRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_EndRequest
");

 ???????}

 ???????private void application_PreRequestHandlerExecute(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_PreRequestHandlerExecute
");

 ???????}

 ???????private void application_PostRequestHandlerExecute(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_PostRequestHandlerExecute
");

 ???????}

 ???????private void application_ReleaseRequestState(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_ReleaseRequestState
");

 ???????}

 ???????private void application_AcquireRequestState(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_AcquireRequestState
");

 ???????}

 ???????private void application_PreSendRequestContent(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_PreSendRequestContent
");

 ???????}

 ???????private void application_PreSendRequestHeaders(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_PreSendRequestHeaders
");

 ???????}

 ???????private void application_ResolveRequestCache(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_ResolveRequestCache
");

 ???????}

 ???????private void application_AuthorizeRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_AuthorizeRequest
");

 ???????}

 ???????private void application_AuthenticateRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = (HttpApplication)sender;

 ???????????application.Context.Response.Write("application_AuthenticateRequest");

 ???????}

 ???}

}

HttpModule1" type="MyHttpModule.HttpModule1,MyHttpModule"/>

HttpModule2" type="MyHttpModule.HttpModule2,MyHttpModule"/>

HttpModule1和HttpModule2模仿ValidaterHttpModuleEvents编写（除了类名改变外，事件和方法不变），不贴代码了。

从运行结果可以看到，在web.config文件中引入自定义HttpModule的顺序就决定了多个自定义HttpModule在处理一个HTTP请求的接管顺序。

(3)、利用HttpModule实现终止此次HttpRequest请求

在BeginRequest事件中，使用HttpApplication.CompleteRequest()方法可以实现当满足一定条件时终止此次HttpRequest请求 

using System;

using System.Web;

namespace ClassLibrary1

{

 ???public class MyHttpModule : IHttpModule

 ???{

 ???????public void Dispose() { }

 ???????public void Init(HttpApplication context)

 ???????{

 ???????????context.BeginRequest += new EventHandler(Application_BeginRequest);

 ???????}

 ???????public void Application_BeginRequest(object sender, EventArgs e)

 ???????{

 ???????????HttpApplication application = sender as HttpApplication;

 ???????????application.CompleteRequest();

 ???????????application.Context.Response.Write("请求被终止");

 ???????}

 ???}

}

说明： 
a、对于一个HttpModule，在BeginRquest中终止，但是仍然会调用EndRequest事件，以及PreSendRequestHeaders事件和PreSendRequestContent事件。也可以说是直接跳转到EndRequest事件，而不会调用这期间的事件 
b、如果有两个HttpModule，在第一个HttpModule的BeginRequest中终止，仅仅不会调用第二个HttpModule的BeginRequest，但仍然会调用两个EndRequest事件，以及PreSendRequestHeaders事件和PreSendRequestContent事件。