asp.net Forums 之HttpHandler和HttpModule

我们先说说IHttpHandler和IHttpModule这两个接口。
微软的解释为：
IHttpHandler: 定义 ASP.NET 为使用自定义 HTTP 处理程序同步处理 HTTP Web 请求而实现的协定。 
IHttpModule: 向继承类提供模块初始化和处置事件。 
有点看不懂，微软的解释一向如此。

那我们来看看代码：
public　interface　IHttpHandler
{
 bool　IsReusable　{　get;　}
 void　ProcessRequest(HttpContext　context);
}
IsReusable获取一个值，该值指示其他请求是否可以使用 System.Web.IHttpHandler 实例。
ProcessRequest()方法是处理请求的，System.Web.HttpContext 对象，它提供对用于为 HTTP 请求提供服务的内部服务器对象（如 Request、Response、Session 和 Server）的引用。

public　interface　IHttpModule
{
 void　Dispose();
 void　Init(HttpApplication　context);
}

Dispose()方法用于释放资源。
Init()方法初始化这个HttpApplication,你可以在这时注册各类事件，如：Application_BeginRequest，Application_AuthenticateRequest，Application_OnError等。

那IHttpHandler与IHttpModule有什么区别呢：
1.先后次序.先IHttpModule,后IHttpHandler. 注:Module要看你响应了哪个事件，一些事件是在Handler之前运行的，一些是在Handler之后运行的
2.对请求的处理上:
IHttpModule是属于大小通吃类型,无论客户端请求的是什么文件,都会调用到它;例如aspx,rar,html的请求.
IHttpHandler则属于挑食类型,只有ASP.net注册过的文件类型(例如aspx,asmx等等)才会轮到调用它.
3.IHttpHandler按照你的请求生成响应的内容，IHttpModule对请求进行预处理，如验证、修改、过滤等等，同时也可以对响应进行处理    HttpHandler是HTTP请求的处理中心，真正地对客户端请求的服务器页面做出编译和执行，并将处理过后的信息附加在HTTP请求信息流中再次返回到HttpModule中。
    HttpHandler与HttpModule不同，一旦定义了自己的HttpHandler类，那么它对系统的HttpHandler的关系将是“覆盖”关系。

接下来，我们再来看看ANF中的IHttpModule和IHttpHandler。
ForumsHttpModule类是ANF中自定义的HttpModule，它位于AspNetForums命名空间下。
在这个HttpModule中，自定义了

/// <summary>
        /// 应用程序初始化
        /// </summary>
        /// <param name="application"></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);

#if DEBUG
            application.ReleaseRequestState += new EventHandler(this.Application_ReleaseRequestState);
#endif

            ForumConfiguration forumConfig = ForumConfiguration.GetConfig();
            if (forumConfig != null
                && forumConfig.IsBackgroundThreadingDisabled == false)
            {
                if (emailTimer == null)
                    emailTimer = new Timer(new TimerCallback(ScheduledWorkCallbackEmailInterval), application.Context, EmailInterval, EmailInterval);

                if (forumConfig.IsIndexingDisabled == false
                    && statsTimer == null)
                {
                    statsTimer = new Timer(new TimerCallback(ScheduledWorkCallbackStatsInterval), application.Context, StatsInterval, StatsInterval);
                }
            }
        }

应用程序错误处理 Application_OnError

private void Application_OnError(Object source, EventArgs e)
        {
            ForumConfiguration forumConfig = ForumConfiguration.GetConfig();
            string defaultLanguage = forumConfig.DefaultLanguage;
            HttpApplication application = (HttpApplication) source;
            HttpContext context = application.Context;
            ForumException forumException;
            string html;
            StreamReader reader;
            // 增加异常信息不同级别显示--开始
            // 如果为管理员,显示异常详细信息 by venjiang 2004-11-3
            // 发布时注释此代码
//            if(Users.GetUser().IsAdministrator)
//            {
//                context.Response.Write(context.Server.GetLastError().Message);
//                return;
//            }

            // 增加异常信息不同级别显示--结束

            if (context.Server.GetLastError().GetBaseException() is ForumException)
            {
                forumException = (ForumException) context.Server.GetLastError().GetBaseException();

                switch (forumException.ExceptionType)
                {
                    case ForumExceptionType.DataProvider:

                        // We can't connect to the data store
                        //
                        reader = new StreamReader(context.Server.MapPath("~/Languages/" + defaultLanguage + "/errors/DataStoreUnavailable.htm"));
                        html = reader.ReadToEnd();
                        reader.Close();

                        html = html.Replace("[DATASTOREEXCEPTION]", forumException.Message);
                        context.Response.Write(html);
                        context.Response.End();
                        break;

                    case ForumExceptionType.UserInvalidCredentials:
                        forumException.Log();
                        break;

                    case ForumExceptionType.AccessDenied:
                        forumException.Log();
                        break;

                    case ForumExceptionType.AdministrationAccessDenied:
                        forumException.Log();
                        break;

                    case ForumExceptionType.ModerateAccessDenied:
                        forumException.Log();
                        break;

                    case ForumExceptionType.PostDeleteAccessDenied:
                        forumException.Log();
                        break;

                    case ForumExceptionType.PostProblem:
                        forumException.Log();
                        break;

                    case ForumExceptionType.UserAccountBanned:
                        forumException.Log();
                        break;

                        // LN 6/9/04: New exception added 
                    case ForumExceptionType.ResourceNotFound:
                        //context.Response.Write(context.Server.GetLastError().Message);
                        forumException.Log();
                        break;

                    case ForumExceptionType.UserUnknownLoginError:
                        forumException.Log();
                        break;
                }
            }
            else
            {
                forumException = new ForumException(ForumExceptionType.UnknownError, context.Server.GetLastError().Message, context.Server.GetLastError());
                forumException.Log();
            }

            if (forumException.ExceptionType == ForumExceptionType.UnknownError)
            {
                if ((context.IsCustomErrorEnabled) && (!context.Request.Url.IsLoopback))
                    ForumContext.RedirectToMessage(context, forumException);
            }
            else
            {
                //context.Response.Write(context.Server.GetLastError().Message);
                ForumContext.RedirectToMessage(context, forumException);
            }
        }

当安全模块已建立用户标识时发生 Application_AuthenticateRequest

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

            // 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.AuthenticationType.ToLower())
                {
                        // Microsoft passport
                    case "passport":
                        p = (Provider) ForumConfiguration.GetConfig().Extensions["PassportAuthentication"];
                        module = ExtensionModule.Instance(p);

                        module.ProcessRequest();
                        break;

                        // Windows
                    case "negotiate":
                        p = (Provider) ForumConfiguration.GetConfig().Extensions["WindowsAuthentication"];
                        module = ExtensionModule.Instance(p);

                        module.ProcessRequest();
                        break;

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

                }

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

                throw forumEx;
            }

            // 获取用户角色
            Roles roles = new Roles();
            roles.GetUserRoles();
        }

验证用户授权 Application_AuthorizeRequest

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

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

            // Do we need to force the user to login?
            //
            if (Users.GetUser().ForceLogin)
            {
                Moderate.ToggleUserSettings(ModerateUserSetting.ToggleForceLogin, Users.GetUser(), 0);
                context.Response.Redirect(Globals.GetSiteUrls().Logout, true);
            }


        }

响应应用程序请求开始事件 Application_BeginRequest

private void Application_BeginRequest(Object source, EventArgs e)
        {
            if (HttpContext.Current.Request.Path.IndexOf('\\') >= 0 ||
                Path.GetFullPath(HttpContext.Current.Request.PhysicalPath) != HttpContext.Current.Request.PhysicalPath)
            {
                throw new HttpException(404, "not found");
            }

            //2005-6-25
            //阻止IP访问

//            

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

                if (application == null
                    || context == null)
                    return;

                // Url Rewriting

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

                if (isReWritten && newPath != null)
                    context.RewritePath(newPath);

                ForumContext frmContext = CreateForumContext(context);
                frmContext.CurrentUrl = context.Request.RawUrl.ToString();


                // 2005/04/07
                //safe to set url rewrite data;
                if (isReWritten && newPath != null)
                {
                    frmContext.IsUrlReWritten = true;
                }

                // Capture any pingback information
                //
                CaptureForumPingback();

                // Are the forums disabled?
                //
                if ((Globals.GetSiteSettings().ForumsDisabled) && (HttpContext.Current.Request.Url.Host != "localhost"))
                {
                    ForumConfiguration forumConfig = ForumConfiguration.GetConfig();
                    string defaultLanguage = forumConfig.DefaultLanguage;

                    // Forums is disabled
                    //
                    StreamReader reader = new StreamReader(context.Server.MapPath("~/Languages/" + defaultLanguage + "/errors/ForumsDisabled.htm"));
                    string html = reader.ReadToEnd();
                    reader.Close();

                    context.Response.Write(html);
                    context.Response.End();

                }
            }
            catch (Exception ex)
            {
                ForumException forumEx = new ForumException(ForumExceptionType.UnknownError, "Unknown error in BeginRequest", ex);
                forumEx.Log();
            }

            if (HttpContext.Current.Request.Path.ToLower().IndexOf("msgs/default") < 0)
            {
                if (BlockedIpAddresses.AddressIsBlocked(Globals.IPAddress))
                    throw new ForumException(ForumExceptionType.BlockedIpAddress);
            }


        }

等事件。
在Web.Config文件中配置

<!-- 指定应用程序HttpModule -->
  <httpModules>
   <add name="AspNetForums" type="AspNetForums.ForumsHttpModule, AspNetForums.Components" />
  </httpModules>

AvatarHttpHandler类是ANF中的自定义HttpHandler,它位于AspNetForums.Components.HttpHandler命名空间下。
这个HttpHandler主要用于处理用户头像的处理。

public void ProcessRequest(HttpContext context)
        {
            try
            {
                Avatar userAvatar = Resources.GetAvatar(int.Parse(context.Request.QueryString["UserID"]));

                context.Response.ContentType = userAvatar.ContentType;
                context.Response.OutputStream.Write(userAvatar.Content, 0, userAvatar.Length);

                context.Response.Cache.SetCacheability(HttpCacheability.Public);
                // Terry Denham 7/16/2004
                // changing default cache for avatars from 1 day to 30 minutes
                context.Response.Cache.SetExpires(DateTime.Now.AddMinutes(10));
                context.Response.Cache.SetAllowResponseInBrowserHistory(true);
                context.Response.Cache.SetValidUntilExpires(true);
                context.Response.Cache.VaryByParams["UserID"] = true;
            }
            catch
            {
            }

        }

在Web.Config文件中的配置。

<!-- 指定应用程序HttpHandlers -->
        <httpHandlers>
            <add verb="GET" path="avatar.aspx" type="AspNetForums.Components.HttpHandler.AvatarHttpHandler, AspNetForums.Components" />
            <add verb="GET" path="vcard.aspx" type="AspNetForums.Components.HttpHandler.VCardHttpHandler, AspNetForums.Components" />

 注： 本文引用了网络上的一些资料。