第37篇 Asp.Net源码解析(二)--详解HttpApplication

这篇文章花了点时间,差点成烂到电脑里面，写的过程中有好几次修改，最终的这个版本也不是很满意，东西说的不够细，还需要认真的去看下源码才能有所体会，先这样吧，后面有时间把细节慢慢的再修改。顺便对于开发的学习，个人是觉得源码的阅读是最快的提高方式，当然阅读不是走马观花，应该多次阅读。

上次说到获得HttpApplication对象的创建，创建完成后调用InitInternal方法，这个方法任务比较多，也比较长，这里就不贴全码了，一个一个过程的去说：

初始化HttpModule

对于HttpModule的认识，首先应该看下HttpModule的使用情况，下面通过一个简单的例子展示：

httpModule使用实例

新建一个项目，添加一个webform的窗体default.aspx，使用IIS添加到网站，应用程序池使用集成模式。
添加一个MyModule.cs,继承自IHttpModule。

在IHttpMoudule中有两个方法，在MyModule中必须要实现：

public void Init(HttpApplication context)
{
   throw new System.NotImplementedException();
}

public void Dispose()
{
   throw new System.NotImplementedException();
}

在Init方法中，有一个HttpApplication类型的对象context，这里可以对其中的响应的内容进行更改，修改如下：

public void Init(HttpApplication context)
{
   context.EndRequest += Context_EndRequest;
}

private void Context_EndRequest(object sender, System.EventArgs e)
{
  var context = (HttpApplication) sender;
  context.Response.Write("<h1>Hello MyModule</h1>");
}

添加web.config文件如下(在 system.webServer下 modules节点下面):
```
<add name="MyModule" type="Application.MyModule,Application"/>
```
运行结果：
在上面的例子中，使用的是集成模式，当改成经典模式的时候，module又不起作用了。对于经典模式的配置文件与集成模式不同。经典模式的配置文件如下：
```
<httpModules>
   <add name="MyModule" type="IISIntegratedPipeline.MyModule,IISIntegratedPipeline"/>
</httpModules>
```
对于 module的使用，有了一个简单的认识，在asp.net中module是一个灵活的配置，可以对请求进行自定义的处理，对于Asp.net如何处理的，在下面详细解说。

asp.net中HttpModule的处理

结合上面例子，HttpModule在Asp.net中有重要的作用，可以HttpApplication的事件进行订阅，也可以修改对应的响应的内容

对于HttpModule的初始化,asp.Net中会根据当前应用程序池的类型进行初始化，核心代码如下：

if (HttpRuntime.UseIntegratedPipeline) {
    try {
    context.HideRequestResponse = true;
    _hideRequestResponse = true;
    InitIntegratedModules();
}
finally {
    context.HideRequestResponse = false;
    _hideRequestResponse = false;
   }
}
else {
    InitModules();
 }

对于Module的理解，需要根据应用程序池的模式来处理（经典和集成）。

对于集成模式，获得所有Modules的方法是调用非托管的方法的进行获得，具体获得的代码如下:

InitIntegratedModules的方法

private void InitIntegratedModules()
{
    _moduleCollection = BuildIntegratedModuleCollection(_moduleConfigInfo);
    InitModulesCommon();
}

_moduleConfigInfo 的来源
这个_moduleConfigInfo的来源，还需要追到上篇 HttpApplication中三个方法的调用（EnsureAppStartCalled 第二个方法的调用）具体调用步骤如下：

     [DllImport(_IIS_NATIVE_DLL)]
        internal static extern int MgdGetModuleCollection(
        IntPtr pConfigSystem,
        IntPtr appContext,
        out IntPtr pModuleCollection,
        out int count);

对于经典模式获得Modules简单的多，直接获得是调用配置文件

private void InitModules()
{
    HttpModulesSection pconfig = RuntimeConfig.GetAppConfig().HttpModules;

    // get the static list, then add the dynamic members
    HttpModuleCollection moduleCollection = pconfig.CreateModules();
    HttpModuleCollection dynamicModules = CreateDynamicModules();

    moduleCollection.AppendCollection(dynamicModules);
    _moduleCollection = moduleCollection; // don't assign until all ops have succeeded

    InitModulesCommon();
}

最终会调用 InitModulesCommon方法,循环调用Modules中的方法

 private void InitModulesCommon()
 {
        int n = _moduleCollection.Count;

        ; i < n; i++) {

        _currentModuleCollectionKey = _moduleCollection.GetKey(i);
         _moduleCollection[i].Init(this);
        }

        _currentModuleCollectionKey = null;
        InitAppLevelCulture();
 }

Global内的方法调用

对于Global方法的调用，是调用HookupEventHandlersForApplicationAndModules(handlers);方法，这里的Handlers的收集和创建来源于上篇讲HttpAplication的三个方法调用的第一个方法。具体的看下上次的代码，这里不多叙述。对于方法的handlers的调用的核心代码如下,其实也是一个循环加上判断：

 ; i < handlers.Length; i++) {
        MethodInfo appMethod = handlers[i];
        String appMethodName = appMethod.Name;
        int namePosIndex = appMethodName.IndexOf('_');
        String targetName = appMethodName.Substring(, namePosIndex);

        ...
        ParameterInfo[] addMethodParams = addMethod.GetParameters();

        )
        continue;
        Delegate handlerDelegate = null;

        ParameterInfo[] appMethodParams = appMethod.GetParameters();

        ...
        try {
            addMethod.Invoke(target, ]{handlerDelegate});
        }
        catch {
            if (HttpRuntime.UseIntegratedPipeline) {
                throw;
            }
        }

    if (eventName != null) {
        if (_pipelineEventMasks.ContainsKey(eventName)) {
            if (!StringUtil.StringStartsWith(eventName, "Post")) {
            _appRequestNotifications |= _pipelineEventMasks[eventName];
            }
            else {
                _appPostNotifications |= _pipelineEventMasks[eventName];
            }
        }
    }
}

根据应用程序池的类型创建不同的_stepManager

这里很简单，直接看代码：

// Construct the execution steps array
if (HttpRuntime.UseIntegratedPipeline) {
  _stepManager = new PipelineStepManager(this);
}
else {
 _stepManager = new ApplicationStepManager(this);
}

执行BuildStep

BuildStep与ResumeStep是Asp.net的核心运行环节。同样，在经典模式与集成模式下原理和过程也有所不一样。

集成模式

下面先讨论集成模式下是如何进行的。

internal override void BuildSteps(WaitCallback stepCallback)
    {
        HttpApplication app = _application;

        IExecutionStep materializeStep = new MaterializeHandlerExecutionStep(app);

        app.AddEventMapping(
        HttpApplication.IMPLICIT_HANDLER,
        RequestNotification.MapRequestHandler,
        false, materializeStep);

        app.AddEventMapping(
        HttpApplication.IMPLICIT_HANDLER,
        RequestNotification.ExecuteRequestHandler,
        false, app.CreateImplicitAsyncPreloadExecutionStep());

        IExecutionStep handlerStep = new CallHandlerExecutionStep(app);

        app.AddEventMapping(
        HttpApplication.IMPLICIT_HANDLER,
        RequestNotification.ExecuteRequestHandler,
        false, handlerStep);

        IExecutionStep webSocketsStep = new TransitionToWebSocketsExecutionStep(app);

        app.AddEventMapping(
        HttpApplication.IMPLICIT_HANDLER,
        RequestNotification.EndRequest,
        true /* isPostNotification */, webSocketsStep);

        IExecutionStep filterStep = new CallFilterExecutionStep(app);
        app.AddEventMapping(
        HttpApplication.IMPLICIT_FILTER_MODULE,
        RequestNotification.UpdateRequestCache,
        false, filterStep);

        app.AddEventMapping(
        HttpApplication.IMPLICIT_FILTER_MODULE,
        RequestNotification.LogRequest,
        false, filterStep);

        _resumeStepsWaitCallback = stepCallback;
    }

上面的代码是核心是AddEventMapping方法，把相关的步骤添加到一个PipelineModuleStepContainer.

private void AddEventMapping(string moduleName,RequestNotification requestNotification,bool isPostNotification, IExecutionStep step)
{

    ThrowIfEventBindingDisallowed();
    if (!IsContainerInitalizationAllowed) {
        return;
    }
    PipelineModuleStepContainer container = GetModuleContainer(moduleName);
    if (container != null) {
        container.AddEvent(requestNotification, isPostNotification, step);
    }
}

经典模式

1.看下代码：

internal override void BuildSteps(WaitCallback stepCallback ) {
        ArrayList steps = new ArrayList();
        HttpApplication app = _application;

        bool urlMappingsEnabled = false;
        UrlMappingsSection urlMappings = RuntimeConfig.GetConfig().UrlMappings;
        urlMappingsEnabled = urlMappings.IsEnabled && ( urlMappings.UrlMappings.Count >  );

        steps.Add(new ValidateRequestExecutionStep(app));
        steps.Add(new ValidatePathExecutionStep(app));

        if (urlMappingsEnabled)
        steps.Add(new UrlMappingsExecutionStep(app)); // url mappings

        app.CreateEventExecutionSteps(HttpApplication.EventBeginRequest, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventAuthenticateRequest, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventDefaultAuthentication, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostAuthenticateRequest, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventAuthorizeRequest, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostAuthorizeRequest, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventResolveRequestCache, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostResolveRequestCache, steps);
        steps.Add(new MapHandlerExecutionStep(app)); // map handler
        app.CreateEventExecutionSteps(HttpApplication.EventPostMapRequestHandler, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventAcquireRequestState, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostAcquireRequestState, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPreRequestHandlerExecute, steps);
        steps.Add(app.CreateImplicitAsyncPreloadExecutionStep()); // implict async preload step
        steps.Add(new CallHandlerExecutionStep(app)); // execute handler
        app.CreateEventExecutionSteps(HttpApplication.EventPostRequestHandlerExecute, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventReleaseRequestState, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostReleaseRequestState, steps);
        steps.Add(new CallFilterExecutionStep(app)); // filtering
        app.CreateEventExecutionSteps(HttpApplication.EventUpdateRequestCache, steps);
        app.CreateEventExecutionSteps(HttpApplication.EventPostUpdateRequestCache, steps);
        _endRequestStepIndex = steps.Count;
        app.CreateEventExecutionSteps(HttpApplication.EventEndRequest, steps);
        steps.Add(new NoopExecutionStep()); // the last is always there

        _execSteps = new IExecutionStep[steps.Count];
        steps.CopyTo(_execSteps);

        _resumeStepsWaitCallback = stepCallback;
    }

对于上面的代码，可以看出都调用了 CreateEventExecutionSteps 方法，这个方法的详细如下：

 private void CreateEventExecutionSteps(Object eventIndex, ArrayList steps) {
            // async
            AsyncAppEventHandler asyncHandler = AsyncEvents[eventIndex];
            if (asyncHandler != null) {
                asyncHandler.CreateExecutionSteps(this, steps);
            }
            EventHandler handler = (EventHandler)Events[eventIndex];

            if (handler != null) {
                Delegate[] handlers = handler.GetInvocationList();
                ; i < handlers.Length; i++) {
                steps.Add(new SyncEventExecutionStep(this, (EventHandler)handlers[i]));
            }
        }
    }

可以看出， CreateEventExecutionSteps是把注册的步骤都转换成了SyncEventExecutionStep，最终会被按顺序进行调用。

执行BeginProcessRequest

HttpApplication在完成BuildSteps的时候，把生成的App经过层层返回到HttpRuntime,前面几篇文章提到，在HttpRuntime里面有对app的类型进行判断，如果是IHttpAsyncHandler直接调用BeginProcessRequest方法，具体的代码如下：

 if (app is IHttpAsyncHandler) {
            IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)app;
            context.AsyncAppHandler = asyncHandler;
            asyncHandler.BeginProcessRequest(context, _handlerCompletionCallback, context);
        }
        else {
            // synchronous handler
            app.ProcessRequest(context);
            FinishRequest(context.WorkerRequest, context, null);
        }

BeginProcessRequest 方法：

IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) {
        HttpAsyncResult result;

        _context = context;
        _context.ApplicationInstance = this;

        _stepManager.InitRequest();

        _context.Root();

        result = new HttpAsyncResult(cb, extraData);

        AsyncResult = result;

        if (_context.TraceIsEnabled)
        HttpRuntime.Profile.StartRequest(_context);

        ResumeSteps(null);
        return result;
    }

其中最核心的方法是ResumeSteps方法，具体如下：

internal override void ResumeSteps(Exception error)
{

    for (; ; ) {

        // ...

        IExecutionStep step = _application.CurrentModuleContainer.GetNextEvent(context.CurrentNotification, context.IsPostNotification,context.CurrentModuleEventIndex);

        context.SyncContext.Enable();

        stepCompletedSynchronously = false;

        //*******
        error = _application.ExecuteStep(step, ref stepCompletedSynchronously);
        //*********
        ...

        if (!stepCompletedSynchronously) {
            _application.AcquireNotifcationContextLock(ref locked);
            context.NotificationContext.PendingAsyncCompletion = true;
            break;
        }
        else {
            context.Response.SyncStatusIntegrated();
        }
    }
}

BeginProcessRequest 方法：

IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) {
    HttpAsyncResult result;

    _context = context;
    _context.ApplicationInstance = this;

    _stepManager.InitRequest();

    _context.Root();

    result = new HttpAsyncResult(cb, extraData);

    AsyncResult = result;

    if (_context.TraceIsEnabled)
    HttpRuntime.Profile.StartRequest(_context);

    ResumeSteps(null);
    return result;
}

其中最核心的方法是ResumeSteps方法，具体如下：

internal override void ResumeSteps(Exception error)
    {
        ...
        for (; ; ) {

        // ...

        IExecutionStep step = _application.CurrentModuleContainer.GetNextEvent(context.CurrentNotification, context.IsPostNotification,context.CurrentModuleEventIndex);

        context.SyncContext.Enable();

        stepCompletedSynchronously = false;

        //*******
        error = _application.ExecuteStep(step, ref stepCompletedSynchronously);
        //*********
        ...

        if (!stepCompletedSynchronously) {
            _application.AcquireNotifcationContextLock(ref locked);
            context.NotificationContext.PendingAsyncCompletion = true;
            break;
        }
        else {
            context.Response.SyncStatusIntegrated();
            }
        }
    }

对于上面的内容总结原理为：

写于 2017.03.21