C# 上传文件（防止内存溢出）

上传文件，之前使用WebClient的上传方法，UploadFile方法容易造成内存溢出，UploadData方法又一直没搞定，所以借鉴下网友的方法
文章主要内容源自（http://blogs.msdn.com/b/johan/archive/2006/11/15/are-you-getting-outofmemoryexceptions-when-uploading-large-files.aspx），本文做些修改，使其可直接使用：

public static string MyUploader(string strFileToUpload, string strUrl，Action<double,double> uploading)
{
   string strFileFormName = "file";
   Uri oUri = new Uri(strUrl);
   string strBoundary = "----------" + DateTime.Now.Ticks.ToString("x");

   // The trailing boundary string
   byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + strBoundary + "--\r\n");
  //**注意此处的 strBoundary后的换行前加上--，不然会异常**
   // The post message header
   StringBuilder sb = new StringBuilder();
   sb.Append("--");
   sb.Append(strBoundary);
   sb.Append("\r\n");
   sb.Append("Content-Disposition: form-data; name=\"");
   sb.Append(strFileFormName);
   sb.Append("\"; filename=\"");
   sb.Append(Path.GetFileName(strFileToUpload));
   sb.Append("\"");
   sb.Append("\r\n");
   sb.Append("Content-Type: ");
   sb.Append("application/octet-stream");
   sb.Append("\r\n");
   sb.Append("\r\n");
   string strPostHeader = sb.ToString();
   byte[] postHeaderBytes = Encoding.UTF8.GetBytes(strPostHeader);

   // The WebRequest
   HttpWebRequest oWebrequest = (HttpWebRequest)WebRequest.Create(oUri);
   oWebrequest.ContentType = "multipart/form-data; boundary=" + strBoundary;
   oWebrequest.Method = "POST";

   // This is important, otherwise the whole file will be read to memory anyway...
   oWebrequest.AllowWriteStreamBuffering = false;

   // Get a FileStream and set the final properties of the WebRequest
   FileStream oFileStream = new FileStream(strFileToUpload, FileMode.Open, FileAccess.Read);
   long length = postHeaderBytes.Length + oFileStream.Length + boundaryBytes.Length;
   oWebrequest.ContentLength = length;
   Stream oRequestStream = oWebrequest.GetRequestStream();

   // Write the post header
   oRequestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);

   // Stream the file contents in small pieces (4096 bytes, max).
   byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)oFileStream.Length))];
   int bytesRead = 0;
   double size=0;
   while ((bytesRead = oFileStream.Read(buffer, 0, buffer.Length)) != 0)
      {
       oRequestStream.Write(buffer, 0, bytesRead);
       size+=bytesRead;
       if(uploading!=null)uploading(length ,size);
      }
    oFileStream.Close();

    // Add the trailing boundary
   oRequestStream.Write(boundaryBytes, 0, boundaryBytes.Length);
   WebResponse oWResponse = oWebrequest.GetResponse();
   Stream s = oWResponse.GetResponseStream();
   StreamReader sr = new StreamReader(s);
   String sReturnString = sr.ReadToEnd();

    // Clean up
    oFileStream.Close();
    oRequestStream.Close();
    s.Close();
    sr.Close();

    return sReturnString;
}

如果有增加取消功能，可以调用oWebrequest的Abort方法取消上传请求。