还是前天的那个encoding的问题。今天坐车的时候我突然想到，HttpWebResponse的对象应该有保存了Encoding相关的信息，回来一查 HttpWebResponse 对象的 ContentEncoding Property似乎与此有关，msdn上这样说：
Gets the method used to encode the body of the response.
public string ContentEncoding {get;}
Property Value
A string describing the method used to encode the body of the response.
Remarks
The ContentEncoding property contains the value of the Content-Encoding header returned with the response.
然而，我试了几个网站，这个属性都返回空字符串，这是怎么回事呀？