深入ASP.NET MVC 之一：IIS到路由表

关于IIS的介绍，可以参考Introduction to IIS Architecture 。IIS到托管代码的入口点是位于System.Web dll中

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1	`public sealed class ISAPIRuntime : MarshalByRefObject, IISAPIRuntime, IISAPIRuntime2, IRegisteredObject`

的方法

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35	`public` `int` `ProcessRequest(IntPtr ecb,` `int` `iWRType)` `{` `IntPtr intPtr = IntPtr.Zero;` `if` `(iWRType == 2)` `{` `intPtr = ecb;` `ecb = UnsafeNativeMethods.GetEcb(intPtr);` `}` `ISAPIWorkerRequest iSAPIWorkerRequest =` `null;` `int` `result;` `try` `{` `bool` `useOOP = iWRType == 1;` `iSAPIWorkerRequest = ISAPIWorkerRequest.CreateWorkerRequest(ecb, useOOP);` `iSAPIWorkerRequest.Initialize();` `string` `appPathTranslated = iSAPIWorkerRequest.GetAppPathTranslated();` `string` `appDomainAppPathInternal = HttpRuntime.AppDomainAppPathInternal;` `if` `(appDomainAppPathInternal ==` `null` `\|\| StringUtil.EqualsIgnoreCase(appPathTranslated, appDomainAppPathInternal))` `{` `HttpRuntime.ProcessRequestNoDemand(iSAPIWorkerRequest);` `result = 0;` `}` `else` `{` `//……` `}` `}` `catch` `(Exception ex)` `{` `//……` `}` `return` `result;` `}`

（注:IIS7 的入口似乎是PipeLineRuntime.InitializeApplication(IntPtr appContext)，过程有所不同，但是不影响后面的流程）其中ecb是一个指向httprequest的信息的指针，由IIS提供。 CreateWorkerRequest根据ecb提供的信息，比如IIS的版本、模式等，创建一个ISAPIWorkerRequest对象，ISAPIWorkerReuqeuest是一个http请求的.NET封装。创建好WorkerRequest之后，调用 HttpRuntime.ProcessRequestNoDemand(iSAPIWorkerRequest);开始执行请求，这个方法是会从 httpRuntime对象中的一个队列中获取一个workerrequest进行处理，最终调用的是HttpRuntime类中的ProcessRequestInternal（代码有删节）:

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51	`private` `void` `ProcessRequestInternal(HttpWorkerRequest wr)` `{` `Interlocked.Increment(ref` `this._activeRequestCount);` `if` `(this._disposingHttpRuntime)` `wr.SendStatus(503,` `"Server Too Busy");` `HttpContext httpContext;` `try` `{` `httpContext =` `new` `HttpContext(wr,` `false);` `}` `catch` `{` `try` `{` `wr.SendStatus(400,` `"Bad Request");` `//…….` `}` `finally` `{` `Interlocked.Decrement(ref` `this._activeRequestCount);` `}` `}` `wr.SetEndOfSendNotification(this._asyncEndOfSendCallback, httpContext);` `HostingEnvironment.IncrementBusyCount();` `try` `{` `httpContext.Response.InitResponseWriter();` `IHttpHandler applicationInstance = HttpApplicationFactory.GetApplicationInstance(httpContext);` `if` `(applicationInstance ==` `null)` `{` `throw` `new` `HttpException(SR.GetString("Unable_create_app_object"));` `}` `if` `(applicationInstance` `is` `IHttpAsyncHandler)` `{` `IHttpAsyncHandler httpAsyncHandler = (IHttpAsyncHandler)applicationInstance;` `httpContext.AsyncAppHandler = httpAsyncHandler;` `httpAsyncHandler.BeginProcessRequest(httpContext,` `this._handlerCompletionCallback, httpContext);` `}` `else` `{` `applicationInstance.ProcessRequest(httpContext);` `this.FinishRequest(httpContext.WorkerRequest, httpContext,` `null);` `}` `}` `catch` `(Exception e)` `{` `httpContext.Response.InitResponseWriter();` `this.FinishRequest(wr, httpContext, e);` `}` `}`

在这段代码中，HttpRuntime可以根据当前服务器的状况回送不同的Http状态码。如果一切正常，首先根据WorkerRequest创建了 HttpContext，HttpApplication根据HttpContext创建了一个IHttpHandler对象,这是一个比较复杂的过程。先看代码：

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1 2 3 4 5 6 7 8 9 10 11 12 13 14	`internal` `static` `IHttpHandler GetApplicationInstance(HttpContext context)` `{` `if` `(HttpApplicationFactory._customApplication !=` `null)` `{` `return` `HttpApplicationFactory._customApplication;` `}` `if` `(context.Request.IsDebuggingRequest)` `{` `return` `new` `HttpDebugHandler();` `}` `HttpApplicationFactory._theApplicationFactory.EnsureInited();` `HttpApplicationFactory._theApplicationFactory.EnsureAppStartCalled(context);` `return` `HttpApplicationFactory._theApplicationFactory.GetNormalApplicationInstance(context);` `}`

customApplication 应该是使用 ASP.NET State Service的时候的情况，DebugHandler应该是调试状态下的情况，不作深究，除此以外，一共有三大步骤，首先要确保调用且仅调用了一次 ApplicationFactory的Init方法，在这个方法中，主要完成了以下工作（代码有删节）：