Stream 长度问题
http://topic.csdn.net/u/20091221/09/63662f0e-87fd-49ec-a1f8-8f229189f12f.html
System.Net.WebRequest request = WebRequest.Create("http://xxx.xxx/prog1.exe");
request.Credentials = CredentialCache.DefaultCredentials;
System.Net.HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream dataStream = response.GetResponseStream();
想得到 dataStream 长度 用于做滚动条 复制时候显示
dataStream.Length 无法使用,得到一个不支持的错误