HttpModule
Community Server专题三：HttpModule
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 { #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(); } #region Installer #endregion #endregion #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 #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 #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 #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)); } } #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)); } } #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。
