HttpResponse的Output与OutputStream、Filter关系与区别介绍

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在网上经常看见有这样的代码

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

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首先我们来看看这3个属性的源代码吧：

复制代码代码如下:

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; 
} 
} 

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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); 
} 
}