【源码】进入ASP.NET MVC流程的大门 - UrlRoutingModule

 1 protected virtual void Init(HttpApplication application)
 2 {
 3     // 检查 UrlRoutingModule 是否已经被加入到请求管道中
 4     if (application.Context.Items[_contextKey] != null)
 5     {
 6         // 已经添加到请求管道则直接返回
 7         return;
 8     }
 9     application.Context.Items[_contextKey] = _contextKey;
10 
11     // 理想情况下， 我们应该注册 MapRequestHandler 事件。但是，MapRequestHandler事件在
12     // II6 或 IIS7 ISAPI 模式下是不可用的，所以我们注册在 MapRequestHandler 之前执行的事件，
13     // 该事件适用于所有的IIS版本。
14     application.PostResolveRequestCache += OnApplicationPostResolveRequestCache;
15 }

1 private void OnApplicationPostResolveRequestCache(object sender, EventArgs e)
2 {
3     //HttpContextWrapper继承自HttpContextBase，用于替换HttpContext以实现可测试的接口
4     HttpApplication app = (HttpApplication)sender;
5     HttpContextBase context = new HttpContextWrapper(app.Context);
6     PostResolveRequestCache(context);
7 }

 1 public virtual void PostResolveRequestCache(HttpContextBase context)
 2 {
 3     // 匹配传入的URL，检查路由表中是否存在与之匹配的URL
 4     RouteData routeData = RouteCollection.GetRouteData(context);
 5 
 6     // 如果没有找到匹配的路由信息，直接返回
 7     if (routeData == null)
 8     {
 9         return;
10     }
11 
12     // 如果找到的匹配的路由，则从路由信息的RouteHandler中获取IHttpHandler
13     IRouteHandler routeHandler = routeData.RouteHandler;
14     if (routeHandler == null)
15     {
16         throw new InvalidOperationException(String.Format(CultureInfo.CurrentCulture, SR.GetString(SR.UrlRoutingModule_NoRouteHandler)));
17     }
18 
19     // 如果该IRouteHandler是StopRoutingHandler，路由模块会停止继续处理该请求
20     // routes and to let the fallback handler handle the request.
21     if (routeHandler is StopRoutingHandler)
22     {
23         return;
24     }
25 
26     RequestContext requestContext = new RequestContext(context, routeData);
27 
28     // 将路由信息添加到请求上下文
29     context.Request.RequestContext = requestContext;
30 
31     IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);
32     if (httpHandler == null)
33     {
34         throw new InvalidOperationException(String.Format(CultureInfo.CurrentUICulture, SR.GetString(SR.UrlRoutingModule_NoHttpHandler), routeHandler.GetType()));
35     }
36 
37     // 如果该IHttpHandler是认证失败的IHttpHandler，返回401权限不足错误
38     if (httpHandler is UrlAuthFailureHandler)
39     {
40         if (FormsAuthenticationModule.FormsAuthRequired)
41         {
42             UrlAuthorizationModule.ReportUrlAuthorizationFailure(HttpContext.Current, this);
43             return;
44         }
45         else
46         {
47             throw new HttpException(401, SR.GetString(SR.Assess_Denied_Description3));
48         }
49     }
50 
51     // Remap IIS7 to our handler
52     context.RemapHandler(httpHandler);
53 }

 1 internal static void ReportUrlAuthorizationFailure(HttpContext context, object webEventSource) 
 2 {
 3     // 拒绝访问
 4     context.Response.StatusCode = 401;
 5     WriteErrorMessage(context);
 6 
 7     if (context.User != null && context.User.Identity.IsAuthenticated) {
 8         // 这里AuditUrlAuthorizationFailure指示在Web请求过程中URL授权失败的事件代码
 9         WebBaseEvent.RaiseSystemEvent(webEventSource, WebEventCodes.AuditUrlAuthorizationFailure);
10     }
11     context.ApplicationInstance.CompleteRequest();
12 }

 1 public RouteData GetRouteData(HttpContextBase httpContext) 
 2 {
 3     if (httpContext == null) 
 4     {
 5         throw new ArgumentNullException("httpContext");
 6     }
 7     if (httpContext.Request == null) 
 8     {
 9         throw new ArgumentException(SR.GetString(SR.RouteTable_ContextMissingRequest), "httpContext");
10     }
11 
12     // Optimize performance when the route collection is empty.当路由集合是空的的时候优化性能.  The main improvement is that we avoid taking
13     // a read lock when the collection is empty.主要的改进是当集合为空的时候避免添加只读锁。  Without this check, the UrlRoutingModule causes a 25%-50%
14     // 没有这个检查的话，UrlRoutingModule 性能会因为锁的缘故而下降25%-50%
15     // regression in HelloWorld RPS due to lock contention.  The UrlRoutingModule is now in the root web.config,
16     // UrlRoutingModule目前被配置在根目录的web.config
17     // so we need to ensure the module is performant, especially when you are not using routing.
18     // 所以我们应该确认下这个module是否是高效的，尤其是当没有使用路由的时候。
19     // This check does introduce a slight bug, in that if a writer clears the collection as part of a write
20     // transaction, a reader may see the collection when it‘s empty, which the read lock is supposed to prevent.
21     // We will investigate a better fix in Dev10 Beta2.  The Beta1 bug is Dev10 652986.
22     if (Count == 0) {
23         return null;
24     }
25 
26     bool isRouteToExistingFile = false;
27     // 这里只检查一次
28     bool doneRouteCheck = false; 
29     if (!RouteExistingFiles) 
30     {
31         isRouteToExistingFile = IsRouteToExistingFile(httpContext);
32         doneRouteCheck = true;
33         if (isRouteToExistingFile) 
34         {
35             // If we‘re not routing existing files and the file exists, we stop processing routes
36             // 如果文件存在，但是路由并没有匹配上，则停止继续处理当前请求。
37             return null;
38         }
39     }
40 
41     // Go through all the configured routes and find the first one that returns a match
42     // 遍历所有已配置的路由并且返回第一个与之匹配的
43     using (GetReadLock())
44     {
45         foreach (RouteBase route in this)
46         {
47             RouteData routeData = route.GetRouteData(httpContext);
48             if (routeData != null)
49             {
50                 // If we‘re not routing existing files on this route and the file exists, we also stop processing routes
51                 if (!route.RouteExistingFiles)
52                 {
53                     if (!doneRouteCheck)
54                     {
55                         isRouteToExistingFile = IsRouteToExistingFile(httpContext);
56                         doneRouteCheck = true;
57                     }
58                     if (isRouteToExistingFile)
59                     {
60                         return null;
61                     }
62                 }
63                 return routeData;
64             }
65         }
66     }
67     return null;
68 }

1 // 如果当前请求的是一个存在的文件，则返回true
2 private bool IsRouteToExistingFile(HttpContextBase httpContext)
3 {
4     string requestPath = httpContext.Request.AppRelativeCurrentExecutionFilePath;
5     return ((requestPath != "~/") &&
6         (VPP != null) &&
7         (VPP.FileExists(requestPath) ||
8         VPP.DirectoryExists(requestPath)));
9 }