HttpResponse的Output与OutputStream、Filter关系

来源：互联网发布：网络安全法实施方案编辑：程序博客网时间：2024/06/06 10:06

在网上经常看见有这样的代码

HttpResponse response = HttpContext.Current.Response;
response.Filter = new PageFilter(response.Filter);

来拦截输出流，自己也做个类似的东东，如asp.net中 js 合并压缩，现在我也来说说这几个东东是什么吧，需要大家对asp.net的生命周期比较熟悉，如不熟悉的朋友建议先看看ASP.NET 请求处理流程 ASP.NET管线与应用程序生命周期

首先我们来看看这3个属性的源代码吧：

public TextWriter Output{    get    {        return this._writer;    }    set    {        this._writer = value;    }}public Stream OutputStream{    get    {        if (!this.UsingHttpWriter)        {            throw new HttpException(SR.GetString("OutputStream_NotAvail"));        }        return this._httpWriter.OutputStream;    }}public Stream Filter{     get      {          if (this.UsingHttpWriter)          {              return this._httpWriter.GetCurrentFilter();          }          return null;      }      set      {          if (!this.UsingHttpWriter)          {             throw new HttpException(SR.GetString("Filtering_not_allowed"));          }          this._httpWriter.InstallFilter(value);          IIS7WorkerRequest request = this._wr as IIS7WorkerRequest;          if (request != null)          {             request.ResponseFilterInstalled();          }      } }

我们看到Filter和OutputStream都用到了一个属性UsingHttpWriter，那这个属性是怎么定义的了

 private bool UsingHttpWriter    {        get        {            return ((this._httpWriter != null) && (this._writer == this._httpWriter));        }    }

从这个属性我们可以知道_writer 、_httpWriter实际上是同一个东东，它们的类型是HttpWriter ，而HttpWriter 又继承与TextWriter。现在我们可以解释Output就是_httpWriter，而OutputStream是_httpWriter的OutputStream属性。类HttpWriter 主要代码如下

public Stream OutputStream{    get    {        return this._stream;    }}internal HttpWriter(HttpResponse response) : base(null){    this._response = response;    this._stream = new HttpResponseStream(this);    this._buffers = new ArrayList();    this._lastBuffer = null;    this._charBuffer = (char[]) s_Allocator.GetBuffer();    this._charBufferLength = this._charBuffer.Length;    this._charBufferFree = this._charBufferLength;    this.UpdateResponseBuffering();}internal HttpResponseStream(HttpWriter writer){    this._writer = writer;}

HttpResponse 在Filter属性设置调用了HttpWriter类的InstallFilter方法，而获取调用了该类的GetCurrentFilter

internal void InstallFilter(Stream filter){    if (this._filterSink == null)    {        throw new HttpException(SR.GetString("Invalid_response_filter"));    }    this._installedFilter = filter;}internal Stream GetCurrentFilter() {     if (this._installedFilter != null)     {         return this._installedFilter;     }     if (this._filterSink == null)     {        this._filterSink = new HttpResponseStreamFilterSink(this);     }   return this._filterSink;}

由以上代码我们可以得知HttpResponse的输出流就是Filter属性设置的流,即HttpResponse的Output和OutputStream属性的输出流都是来自Filter中的流。我们来看看_writer 、_httpWriter它们是在什么时候初始化的了？在HttpResonse中有一个方法
internal void InitResponseWriter()
{
if (this._httpWriter == null)
{
this._httpWriter = new HttpWriter(this);
this._writer = this._httpWriter;
}
}

该方法是由HttpRuntime的ProcessRequestInternal来调用

private void ProcessRequestInternal(HttpWorkerRequest wr){    HttpContext context;    try    {        context = new HttpContext(wr, false);    }    catch    {        wr.SendStatus(400, "Bad Request");        wr.SendKnownResponseHeader(12, "text/html; charset=utf-8");        byte[] bytes = Encoding.ASCII.GetBytes("<html><body>Bad Request</body></html>");        wr.SendResponseFromMemory(bytes, bytes.Length);        wr.FlushResponse(true);        wr.EndOfRequest();        return;    }    wr.SetEndOfSendNotification(this._asyncEndOfSendCallback, context);    Interlocked.Increment(ref this._activeRequestCount);    HostingEnvironment.IncrementBusyCount();    try    {        try        {            this.EnsureFirstRequestInit(context);        }        catch        {            if (!context.Request.IsDebuggingRequest)            {                throw;            }        }        context.Response.InitResponseWriter();        IHttpHandler applicationInstance = HttpApplicationFactory.GetApplicationInstance(context);        if (applicationInstance == null)        {            throw new HttpException(SR.GetString("Unable_create_app_object"));        }        if (EtwTrace.IsTraceEnabled(5, 1))        {            EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, context.WorkerRequest, applicationInstance.GetType().FullName, "Start");        }        if (applicationInstance is IHttpAsyncHandler)        {            IHttpAsyncHandler handler2 = (IHttpAsyncHandler) applicationInstance;            context.AsyncAppHandler = handler2;            handler2.BeginProcessRequest(context, this._handlerCompletionCallback, context);        }        else        {            applicationInstance.ProcessRequest(context);            this.FinishRequest(context.WorkerRequest, context, null);        }    }    catch (Exception exception)    {        context.Response.InitResponseWriter();        this.FinishRequest(wr, context, exception);    }}