Wu.Country@侠缘

http://blog.joycode.com/saucer/archive/2004/03/16/16225.aspx

我们在上传大文件时都遇到过这样或那样的问题。设置很大的maxRequestLength值并不能完全解决问题，因为ASP.NET会block直到把整个文件载入内存后，再加以处理。实际上，如果文件很大的话，我们经常会见到Internet Explorer显示 "The page cannot be displayed - Cannot find server or DNS Error"，好像是怎么也catch不了这个错误。为什么？因为这是个client side错误，server side端的Application_Error是处理不到的，可以参考这个帖子研究一下产生这个错误的机理。

handling server error when upload file too large

解决的方法是利用隐含的HttpWorkerRequest，用它的GetPreloadedEntityBody 和 ReadEntityBody方法从IIS为ASP.NET建立的pipe里分块读取数据

  IServiceProvider provider = (IServiceProvider) HttpContext.Current;
  HttpWorkerRequest wr = (HttpWorkerRequest) provider.GetService(typeof(HttpWorkerRequest));
  byte[] bs = wr.GetPreloadedEntityBody();
  ....
  if (!wr.IsEntireEntityBodyIsPreloaded())
  {
        int n = 1024;
        byte[] bs2 = new byte[n];
        while (wr.ReadEntityBody(bs2,n) >0)
       {
             .....
        }
  }

Chris Hynes为我们提供了这样的一个方案(用HttpModule)，该方案除了允许你上传大文件外，还能实时显示上传进度：

ASP.NET Upload Magic Part 2

这里有他讲座的PPT文件：

Uploading with ASP.NET (part 1)

Uploading with ASP.NET (part 2)

为这个问题已经找了好几天的资料了，可是都没有解决我的问题，上面的这篇文件被我找到了三次了，还是先收下来了再说。

根据讨论的结果来看，如果要解决大文件上传问题，我必须自己处理一些底层的请求处理了。

这里也有一篇文章：

http://weblogs.asp.net/cazzu/archive/2003/12/10/42635.aspx

Sometimes you need low level information about the current request in a web application, such as the IP address of the physical network adapter the request came through (cool in clustered multi-NIC servers), or some other weird stuff you can't find in the higher-level view provided by HttpRequest, HttpResponseand friends.
Luckily, the HttpContext implements IServiceProvider, which means you can ask for services with the following code:

IServiceProvider provider = (IServiceProvider) HttpContext.Current;
// Get the request
HttpRequest util = (HttpRequest)
  provider.GetService(typeof(HttpRequest));

OK, I know... who on earth would use that instead of simply calling HttpContext.Current.Request??? Well, THE one thing you can get that there's absolutely NO other way of getting, is the current HttpWorkerRequest:

// Get the worker
HttpWorkerRequest wr = (HttpWorkerRequest)
  provider.GetService(typeof(HttpWorkerRequest));
// Get the NIC address!!!!
string addr = wr.GetLocalAddress();

Another very cool use is to retrieve known header values. Usually, you just get the header from the Request.Header collection by its name:

// Would return "Keep-Alive" if enabled.
string cn = Request.Headers["Connection"]; 
// Would return "gzip, deflate" for example.
string enc = Request.Headers["Accept-Encoding"];

but that's prone to errors, and you have to sort of guess the casing, etc. This is the cool way:

// Get the worker
HttpWorkerRequest wr = (HttpWorkerRequest)
  provider.GetService(typeof(HttpWorkerRequest));

string cn = wr.GetKnownRequestHeader(HttpWorkerRequest.HeaderConnection); 
string enc = wr.GetKnownRequestHeader(HttpWorkerRequest.HeaderAcceptEncoding);

Have a look at the class members , there are quite a few interesting things, now that you can call them ... and use them NOW, before they regret making such a beast available...