Community Server专题三：HttpModule

2020-01-18 01:45:09

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从专题三开始分析Community Server的一些具体的技术实现，根据IIS对请求的处理流程，从HttpModule& HttpHandler切入话题，同时你也可以通过一系列的专题了解CS的运行过程，不只如此，所有的.Net 1.1 构架的Web App都是以同样的顺序执行的。

先了解一下IIS系统。它是一个程序，负责对网站的内容进行管理并且处理对客户的请求做出反应。当用户对一个页面提出请求时，IIS做如下反应（不考虑权限问题）：

1.把对方请求的虚拟路径转换成物理路径

2.根据物理路径搜索请求的文件

3.找到文件后，获取文件的内容

4.生成Http头信息。

5.向客户端发送所有的文件内容：首先是头信息，然后是Html内容，最后是其它文件的内容。

6.客户端IE浏览器获得信息后，解析文件内容，找出其中的引用文件，如.js .css .gif等，向IIS请求这些文件。

7.IIS获取请求后，发送文件内容。

8.当浏览器获取所有内容后，生成内容界面，客户就看到图像/文本/其它内容了。

但是IIS本身是不支持动态页面的，也就是说它仅仅支持静态html页面的内容，对于如.asp，.aspx，.cgi，.php等，IIS并不会处理这些标记，它就会把它当作文本，丝毫不做处理发送到客户端。为了解决这个问题。IIS有一种机制，叫做ISAPI的筛选器，这个东西是一个标准组件(COM组件)，当在在访问IIS所不能处理的文件时，如asp.net 1.1 中的IIS附加ISAPI筛选器如图：

Asp.net 服务在注册到IIS的时候，会把每个扩展可以处理的文件扩展名注册到IIS里面(如：*.ascx、*.aspx等)。扩展启动后，就根据定义好的方式来处理IIS所不能处理的文件，然后把控制权跳转到专门处理代码的进程中。让这个进程开始处理代码，生成标准的HTML代码，生成后把这些代码加入到原有的 Html中，最后把完整的Html返回给IIS，IIS再把内容发送到客户端。

    有上面对ISAPI的简单描述，我们把HttpModule& HttpHandler分开讨论，并且结合CS进行具体的实现分析。

HttpModule：

HttpModule实现了ISAPI Filter的功能，是通过对IhttpModule接口的继承来处理。下面打开CS中的CommunityServerComponents项目下的CSHttpModule.cs文件（放在HttpModule目录）

//------------------------------------------------------------------------------
// <copyright company="Telligent Systems">
//     Copyright (c) Telligent Systems Corporation.  All rights reserved.
// </copyright>
//------------------------------------------------------------------------------

using System;
using System.IO;
using System.Web;
using CommunityServer.Components;
using CommunityServer.Configuration;

namespace CommunityServer
{

    // *********************************************************************
    //  CSHttpModule
    //
    /**//// <summary>
    /// This HttpModule encapsulates all the forums related events that occur
    /// during ASP.NET application start-up, errors, and end request.
    /// </summary>
    // ***********************************************************************/
    public class CSHttpModule : IHttpModule
    {
        Member variables and inherited properties / methods#region Member variables and inherited properties / methods

        public String ModuleName
        {
            get { return "CSHttpModule"; }
        }

        // *********************************************************************
        //  ForumsHttpModule
        //
        /**//// <summary>
        /// Initializes the HttpModule and performs the wireup of all application
        /// events.
        /// </summary>
        /// <param name="application">Application the module is being run for</param>
        public void Init(HttpApplication application)
        {
            // Wire-up application events
            //
            application.BeginRequest += new EventHandler(this.Application_BeginRequest);
            application.AuthenticateRequest += new EventHandler(Application_AuthenticateRequest);
            application.Error += new EventHandler(this.Application_OnError);
            application.AuthorizeRequest += new EventHandler(this.Application_AuthorizeRequest);

            //settingsID = SiteSettingsManager.GetSiteSettings(application.Context).SettingsID;
            Jobs.Instance().Start();
            //CSException ex = new CSException(CSExceptionType.ApplicationStart, "Appication Started " +  AppDomain.CurrentDomain.FriendlyName);
            //ex.Log();
        }

        //int settingsID;
        public void Dispose()
        {
            //CSException ex = new CSException(CSExceptionType.ApplicationStop, "Application Stopping " +  AppDomain.CurrentDomain.FriendlyName);
            //ex.Log(settingsID);
            Jobs.Instance().Stop();
        }

        Installer#region Installer

        #endregion

        #endregion

        Application OnError#region Application OnError
        private void Application_OnError (Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            CSException csException = context.Server.GetLastError() as CSException;

            if(csException == null)
                csException = context.Server.GetLastError().GetBaseException() as CSException;

            try
            {
                if (csException != null)
                {
                    switch (csException.ExceptionType)
                    {
                        case CSExceptionType.UserInvalidCredentials:
                        case CSExceptionType.AccessDenied:
                        case CSExceptionType.AdministrationAccessDenied:
                        case CSExceptionType.ModerateAccessDenied:
                        case CSExceptionType.PostDeleteAccessDenied:
                        case CSExceptionType.PostProblem:
                        case CSExceptionType.UserAccountBanned:
                        case CSExceptionType.ResourceNotFound:
                        case CSExceptionType.UserUnknownLoginError:
                        case CSExceptionType.SectionNotFound:
                            csException.Log();
                            break;
                    }
                }
                else
                {
                    Exception ex = context.Server.GetLastError();
                    if(ex.InnerException != null)
                        ex = ex.InnerException;

                    csException = new CSException(CSExceptionType.UnknownError, ex.Message, context.Server.GetLastError());

                    System.Data.SqlClient.SqlException sqlEx = ex as System.Data.SqlClient.SqlException;
                    if(sqlEx == null || sqlEx.Number != -2) //don't log time outs
                        csException.Log();
                }
            }
            catch{} //not much to do here, but we want to prevent infinite looping with our error handles

            CSEvents.CSException(csException);
        }

        #endregion

        Application AuthenticateRequest#region Application AuthenticateRequest

        private void Application_AuthenticateRequest(Object source, EventArgs e)
        {
            HttpContext context = HttpContext.Current;
            Provider p = null;
            ExtensionModule module = null;

            // If the installer is making the request terminate early
            if (CSConfiguration.GetConfig().AppLocation.CurrentApplicationType == ApplicationType.Installer) {
                return;
            }

            // Only continue if we have a valid context
            //
            if ((context == null) || (context.User == null))
                return;

            try
            {
                // Logic to handle various authentication types
                //
                switch(context.User.Identity.GetType().Name.ToLower())
                {

                        // Microsoft passport
                    case "passportidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["PassportAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Windows
                    case "windowsidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["WindowsAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Forms
                    case "formsidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["FormsAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Custom
                    case "customidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["CustomAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                    default:
                        CSContext.Current.UserName = context.User.Identity.Name;
                        break;

                }

            }
            catch( Exception ex )
            {
                CSException forumEx = new CSException( CSExceptionType.UnknownError, "Error in AuthenticateRequest", ex );
                forumEx.Log();

                throw forumEx;
            }

            //            // Get the roles the user belongs to
            //            //
            //            Roles roles = new Roles();
            //            roles.GetUserRoles();
        }
        #endregion

        Application AuthorizeRequest#region Application AuthorizeRequest
        private void Application_AuthorizeRequest (Object source, EventArgs e) {

            if (CSConfiguration.GetConfig().AppLocation.CurrentApplicationType == ApplicationType.Installer)
            {
                //CSContext.Create(context);
                return;
            }

            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            CSContext csContext = CSContext.Current;
            //bool enableBannedUsersToLogin = CSContext.Current.SiteSettings.EnableBannedUsersToLogin;

//            // If the installer is making the request terminate early
//            if (csContext.ApplicationType == ApplicationType.Installer) {
//                return;
//            }

            //csContext.User = CSContext.Current.User;

            CSEvents.UserKnown(csContext.User);

            ValidateApplicationStatus(csContext);

            // Track anonymous users
            //
            Users.TrackAnonymousUsers(context);

            // Do we need to force the user to login?
            //

            if (context.Request.IsAuthenticated)
            {
                string username = context.User.Identity.Name;
                if (username != null)
                {
                    string[] roles = CommunityServer.Components.Roles.GetUserRoleNames(username);
                    if (roles != null && roles.Length > 0)
                    {
                        csContext.RolesCacheKey = string.Join(",",roles);
                    }
                }
            }
        }

        #endregion

        Application BeginRequest#region Application BeginRequest
        private void Application_BeginRequest(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;


            CSConfiguration config = CSConfiguration.GetConfig();

            // If the installer is making the request terminate early
            if (config.AppLocation.CurrentApplicationType == ApplicationType.Installer)
            {
                //CSContext.Create(context);
                return;
            }

            CheckWWWStatus(config,context);



            CSContext.Create(context, ReWriteUrl(context));


        }

        private void CheckWWWStatus(CSConfiguration config, HttpContext context)
        {
            if(config.WWWStatus == WWWStatus.Ignore)
                return;

            const string withWWW = "http://www.";
            const string noWWW = "http://";
            string rawUrl = context.Request.Url.ToString().ToLower();
            bool isWWW = rawUrl.StartsWith(withWWW);


            if(config.WWWStatus == WWWStatus.Remove && isWWW)
            {
                context.Response.Redirect(rawUrl.Replace(withWWW, noWWW));
            }
            else if(config.WWWStatus == WWWStatus.Require && !isWWW)
            {
                context.Response.Redirect(rawUrl.Replace(noWWW, withWWW));
            }


        }

        ReWriteUrl#region ReWriteUrl
        private bool ReWriteUrl(HttpContext context)
        {

            // we're now allowing each individual application to be turned on and off individually. So before we allow
            // a request to go through we need to check if this product is disabled and the path is for the disabled product,
            // if so we display the disabled product page.
            //
            // I'm also allowing the page request to go through if the page request is for an admin page. In the past if you
            // disabled the forums you were locked out, now with this check, even if you're not on the same machine but you're accessing
            // an admin path the request will be allowed to proceed, where the rest of the checks will ensure that the user has the
            // permission to access the specific url.

            // Url Rewriting
            //
            //RewriteUrl(context);

            string newPath = null;
            string path = context.Request.Path;
            bool isReWritten = SiteUrls.RewriteUrl(path,context.Request.Url.Query,out newPath);

            //very wachky. The first call into ReWritePath always fails with a 404.
            //calling ReWritePath twice actually fixes the probelm as well. Instead,
            //we use the second ReWritePath overload and it seems to work 100%
            //of the time.
            if(isReWritten && newPath != null)
            {
                string qs = null;
                int index = newPath.IndexOf('?');
                if (index >= 0)
                {
                    qs = (index < (newPath.Length - 1)) ? newPath.Substring(index + 1) : string.Empty;
                    newPath = newPath.Substring(0, index);
                }
                context.RewritePath(newPath,null,qs);
            }

            return isReWritten;
        }

        #endregion

        private void ValidateApplicationStatus(CSContext cntx)
        {
            if(!cntx.User.IsAdministrator)
            {
                string disablePath = null;
                switch(cntx.Config.AppLocation.CurrentApplicationType)
                {
                    case ApplicationType.Forum:
                        if(cntx.SiteSettings.ForumsDisabled)
                            disablePath = "ForumsDisabled.htm";
                        break;
                    case ApplicationType.Weblog:
                        if(cntx.SiteSettings.BlogsDisabled)
                            disablePath = "BlogsDisabled.htm";
                        break;
                    case ApplicationType.Gallery:
                        if(cntx.SiteSettings.GalleriesDisabled)
                            disablePath = "GalleriesDisabled.htm";
                        break;
                    case ApplicationType.GuestBook:
                        if(cntx.SiteSettings.GuestBookDisabled)
                            disablePath = "GuestBookDisabled.htm";
                        break;
                    case ApplicationType.Document:                   //新增 ugoer
                        if(cntx.SiteSettings.DocumentDisabled)
                            disablePath = "DocumentsDisabled.htm";
                        break;
                }

                if(disablePath != null)
                {

                    string errorpath = cntx.Context.Server.MapPath(string.Format("~/Languages/{0}/errors/{1}",cntx.Config.DefaultLanguage,disablePath));
                    using(StreamReader reader = new StreamReader(errorpath))
                    {
                        string html = reader.ReadToEnd();
                        reader.Close();

                        cntx.Context.Response.Write(html);
                        cntx.Context.Response.End();
                    }
                }
            }
        }

        #endregion

    }

}

在Web.Config中的配置：

        <httpModules>
            <add name="CommunityServer" type="CommunityServer.CSHttpModule, CommunityServer.Components" />
            <add name="Profile" type="Microsoft.ScalableHosting.Profile.ProfileModule, MemberRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b7c773fb104e7562"/>
            <add name="RoleManager" type="Microsoft.ScalableHosting.Security.RoleManagerModule, MemberRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b7c773fb104e7562" />
        </httpModules>

CSHttpModule.cs   UML：

要实现HttpModule功能需要如下步骤：

1.编写一个类，实现IhttpModule接口

2.实现Init 方法，并且注册需要的方法

3.实现注册的方法

4.实现Dispose方法，如果需要手工为类做一些清除工作，可以添加Dispose方法的实现，但这不是必需的，通常可以不为Dispose方法添加任何代码。

5.在Web.config文件中，注册您编写的类

到这里我们还需要了解一个Asp.Net的运行过程：

在图中第二步可以看到当请求开始的时候，马上就进入了HttpModule，在CS中由于实现了HttpModule的扩展CSHttpModule.cs 类，因此当一个web请求发出的时候（如：一个用户访问他的blog），CS系统首先调用CSHttpModule.cs类，并且进入

public void Init(HttpApplication application)

该方法进行初始化事件：

application.BeginRequest += new EventHandler(this.Application_BeginRequest);

application.AuthenticateRequest += new EventHandler(Application_AuthenticateRequest);

application.Error += new EventHandler(this.Application_OnError);

application.AuthorizeRequest += new EventHandler(this.Application_AuthorizeRequest);

有事件就要有对应的处理方法：

private void Application_BeginRequest(Object source, EventArgs e)

private void Application_AuthenticateRequest(Object source, EventArgs e)

private void Application_OnError (Object source, EventArgs e)

private void Application_AuthorizeRequest (Object source, EventArgs e)

事件被初始化后就等待系统的触发，请求进入下一步此时系统触发Application_BeginRequest事件，事件处理内容如下：

private void Application_BeginRequest(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;


            CSConfiguration config = CSConfiguration.GetConfig();

            // If the installer is making the request terminate early
            if (config.AppLocation.CurrentApplicationType == ApplicationType.Installer)
            {
                //CSContext.Create(context);
                return;
            }

            CheckWWWStatus(config,context);



            CSContext.Create(context, ReWriteUrl(context));


        }

        private void CheckWWWStatus(CSConfiguration config, HttpContext context)
        {
            if(config.WWWStatus == WWWStatus.Ignore)
                return;

            const string withWWW = "http://www.";
            const string noWWW = "http://";
            string rawUrl = context.Request.Url.ToString().ToLower();
            bool isWWW = rawUrl.StartsWith(withWWW);


            if(config.WWWStatus == WWWStatus.Remove && isWWW)
            {
                context.Response.Redirect(rawUrl.Replace(withWWW, noWWW));
            }
            else if(config.WWWStatus == WWWStatus.Require && !isWWW)
            {
                context.Response.Redirect(rawUrl.Replace(noWWW, withWWW));
            }


        }

        ReWriteUrl#region ReWriteUrl
        private bool ReWriteUrl(HttpContext context)
        {

            // we're now allowing each individual application to be turned on and off individually. So before we allow
            // a request to go through we need to check if this product is disabled and the path is for the disabled product,
            // if so we display the disabled product page.
            //
            // I'm also allowing the page request to go through if the page request is for an admin page. In the past if you
            // disabled the forums you were locked out, now with this check, even if you're not on the same machine but you're accessing
            // an admin path the request will be allowed to proceed, where the rest of the checks will ensure that the user has the
            // permission to access the specific url.

            // Url Rewriting
            //
            //RewriteUrl(context);

            string newPath = null;
            string path = context.Request.Path;
            bool isReWritten = SiteUrls.RewriteUrl(path,context.Request.Url.Query,out newPath);

            //very wachky. The first call into ReWritePath always fails with a 404.
            //calling ReWritePath twice actually fixes the probelm as well. Instead,
            //we use the second ReWritePath overload and it seems to work 100%
            //of the time.
            if(isReWritten && newPath != null)
            {
                string qs = null;
                int index = newPath.IndexOf('?');
                if (index >= 0)
                {
                    qs = (index < (newPath.Length - 1)) ? newPath.Substring(index + 1) : string.Empty;
                    newPath = newPath.Substring(0, index);
                }
                context.RewritePath(newPath,null,qs);
            }

            return isReWritten;
        }

        #endregion

这个事件主要做两个事情

a：为发出请求的用户初始化一个Context，初始化Context用到了线程中本地数据槽(LocalDataStoreSlot)，把当前用户请求的上下文(contextb)保存在为此请求开辟的内存中。

b：判断是否需要重写 URL（检查是否需要重写的过程是对SiteUrls.config文件中正则表达式和对应Url处理的过程），如果需要重写URL，就执行asp.net级别上的RewritePath方法获得新的路径，新的路径才是真正的请求信息所在的路径。这个专题不是讲URL Rewrite，所以只要明白URL在这里就进行Rewrite就可以了，具体的后面专题会叙述。

处理完 Application_BeginRequest 后进程继向下执行，随后触发了Application_AuthenticateRequest（如果有朋友不明白这个执行过程，可以通过调试中设置多个断点捕获事件执行的顺序。如果你还不会调试，可以留言偷偷的告诉我，嘿嘿。）， Application_AuthenticateRequest事件初始化一个context的Identity,其实CS提供了很多的 Identity支持，包括Microsoft passport，但是目前的版本中使用的是默认值 System.Web.Security.FormsIdentity。具体代码如下：

private void Application_AuthenticateRequest(Object source, EventArgs e)
        {
            HttpContext context = HttpContext.Current;
            Provider p = null;
            ExtensionModule module = null;

            // If the installer is making the request terminate early
            if (CSConfiguration.GetConfig().AppLocation.CurrentApplicationType == ApplicationType.Installer) {
                return;
            }

            // Only continue if we have a valid context
            //
            if ((context == null) || (context.User == null))
                return;

            try
            {
                // Logic to handle various authentication types
                //
                switch(context.User.Identity.GetType().Name.ToLower())
                {

                        // Microsoft passport
                    case "passportidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["PassportAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Windows
                    case "windowsidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["WindowsAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Forms
                    case "formsidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["FormsAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                        // Custom
                    case "customidentity":
                        p = (Provider) CSConfiguration.GetConfig().Extensions["CustomAuthentication"];
                        module = ExtensionModule.Instance(p);
                        if(module != null)
                            module.ProcessRequest();
                        else
                            goto default;
                        break;

                    default:
                        CSContext.Current.UserName = context.User.Identity.Name;
                        break;

                }

            }
            catch( Exception ex )
            {
                CSException forumEx = new CSException( CSExceptionType.UnknownError, "Error in AuthenticateRequest", ex );
                forumEx.Log();

                throw forumEx;
            }

            //            // Get the roles the user belongs to
            //            //
            //            Roles roles = new Roles();
            //            roles.GetUserRoles();
        }

再下来是Application_AuthorizeRequest事件被触发，事件代码如下：

private void Application_AuthorizeRequest (Object source, EventArgs e) {

            if (CSConfiguration.GetConfig().AppLocation.CurrentApplicationType == ApplicationType.Installer)
            {
                //CSContext.Create(context);
                return;
            }

            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            CSContext csContext = CSContext.Current;
            //bool enableBannedUsersToLogin = CSContext.Current.SiteSettings.EnableBannedUsersToLogin;

//            // If the installer is making the request terminate early
//            if (csContext.ApplicationType == ApplicationType.Installer) {
//                return;
//            }

            //csContext.User = CSContext.Current.User;

            CSEvents.UserKnown(csContext.User);

            ValidateApplicationStatus(csContext);

            // Track anonymous users
            //
            Users.TrackAnonymousUsers(context);

            // Do we need to force the user to login?
            //

            if (context.Request.IsAuthenticated)
            {
                string username = context.User.Identity.Name;
                if (username != null)
                {
                    string[] roles = CommunityServer.Components.Roles.GetUserRoleNames(username);
                    if (roles != null && roles.Length > 0)
                    {
                        csContext.RolesCacheKey = string.Join(",",roles);
                    }
                }
            }
        }

在Application_AuthorizeRequest中分析关键几行代码：

1：CSContext csContext = CSContext.Current;  //该代码取出在前一个事件中保存在LocalDataStoreSlot中的Context，说明白点就是从内存中取出之前保存的一些数据。

2： CSEvents.UserKnown(csContext.User);  //这里触发了一个UserKnown事件，涉及到CS中大量使用委托与事件的一个类CSApplication（CSApplication.cs文件），后续对这个类做专题分析，这里只要先了解该事件起到判断登陆用户是否 ForceLogin以及登录的帐户是否是禁用就可以了（把对user的判断移入Application_AuthorizeRequest事件处理程序中是很好的一种处理方法）

3：ValidateApplicationStatus(csContext); //判断论坛、blog、相册是否被禁用，如果登录用户的角色不为IsAdministrator，就跳转到相应的禁用警告页面，如Blog被禁用即跳转到 BlogsDisabled.htm页面显示。

4：Users.TrackAnonymousUsers(context); //如果是匿名用户，在这个方法中跟踪记录。

处理完上面三个事件后，CS将开始处理请求页面中的具体业务逻辑，如果用户请求的是登录页面，接下来就处理登录页面需要的业务逻辑和呈现，当然这里还会触发一系列其他事件，因为这些事件没有在这里定义我们暂时不做考虑。要说明一点，HttpModule在整个web请求到响应完成过程中都没有退出进程，而是处于监控状态。Application_OnError正是处于其监控范围下的一个事件，一旦有Exception或者继承Exception的类被异常抛出，HttpModule就捕获它，之后就可以根据Exception中ExceptionType值统一处理这些不同的错误信息。CS中就是这样实现错误处理的，具体的我们看一下代码：

private void Application_OnError (Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            CSException csException = context.Server.GetLastError() as CSException;

            if(csException == null)
                csException = context.Server.GetLastError().GetBaseException() as CSException;

            try
            {
                if (csException != null)
                {
                    switch (csException.ExceptionType)
                    {
                        case CSExceptionType.UserInvalidCredentials:
                        case CSExceptionType.AccessDenied:
                        case CSExceptionType.AdministrationAccessDenied:
                        case CSExceptionType.ModerateAccessDenied:
                        case CSExceptionType.PostDeleteAccessDenied:
                        case CSExceptionType.PostProblem:
                        case CSExceptionType.UserAccountBanned:
                        case CSExceptionType.ResourceNotFound:
                        case CSExceptionType.UserUnknownLoginError:
                        case CSExceptionType.SectionNotFound:
                            csException.Log();
                            break;
                    }
                }
                else
                {
                    Exception ex = context.Server.GetLastError();
                    if(ex.InnerException != null)
                        ex = ex.InnerException;

                    csException = new CSException(CSExceptionType.UnknownError, ex.Message, context.Server.GetLastError());

                    System.Data.SqlClient.SqlException sqlEx = ex as System.Data.SqlClient.SqlException;
                    if(sqlEx == null || sqlEx.Number != -2) //don't log time outs
                        csException.Log();
                }
            }
            catch{} //not much to do here, but we want to prevent infinite looping with our error handles

            CSEvents.CSException(csException);
        }

当抛出Exception后，CS开始处理Application_OnError，根据抛出的Exception的ExceptionType类型不同做不同的处理（ForumExceptionType.cs中定义所有的CS ExceptionType）。随后调用Log()保存错误信息到数据库中，以便管理员跟踪这些错误的原因。这里还有重要的一句：CSEvents.CSException(csException)它触发了2个事件类 CSCatastrophicExceptionModule与CSExceptionModule中的处理程序，与 Application_AuthorizeRequest中UserKnown处理机制是一样的，会在以后的专题讨论。只要知道这里会执行 RedirectToMessage方法，把页面重新定向到一个友好的错误显示页即可，如下图所示：

至此，CSHttpModule类已经全部分析完毕。在CS里还有另外两个HttpModule,属于Membership范畴，由于CS引用的是 Membership的程序集无非进行内部的运行细节分析，但是工作原理与CSHttpModule是一致的，当你真正理解CSHttpModule的时候要去分析其他HttpModule也就不在话下了。希望我的这些分析能对你有帮助。

原文地址:http://www.cnblogs.com/ugoer/archive/2005/09/06/230917.html

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