POST 文件上传问题。

这次要做这个。post百度网盘的文件。模拟网页版的百度网盘上传文件。
有一段代码是这样的。------------Ij5ei4ae0ei4cH2ae0Ef1ei4Ij5gL6
Content-Disposition: form-data; name="Filename"1.bmp
------------Ij5ei4ae0ei4cH2ae0Ef1ei4Ij5gL6
Content-Disposition: form-data; name="Filedata"; filename="1.bmp"
Content-Type: application/octet-stream
------------Ij5ei4ae0ei4cH2ae0Ef1ei4Ij5gL6
Content-Disposition: form-data; name="Upload"Submit Query
------------Ij5ei4ae0ei4cH2ae0Ef1ei4Ij5gL6--我的代码是这样的。为什么一直无法发送出去呢？我的cookie是自己截取来的。       public bool postFile(string Url, string cookieStr, string StrPostFileName, string host, string referer,string fileName)
        {
            //1.读入一个文件。
            FileStream fs = new FileStream(StrPostFileName, FileMode.Open, FileAccess.Read);
            //2.将读入的文件保存为二进制文件。
            BinaryReader r = new BinaryReader(fs);            //3.http header头
            string strBoundary = "------------Ij5ei4ae0ei4cH2ae0Ef1ei4Ij5gL6"; //"----------" + DateTime.Now.Ticks.ToString("x");
            //byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + strBoundary + "\r\n");
            
            StringBuilder sb = new StringBuilder();
            sb.Append(strBoundary);
            sb.Append("\r\nContent-Disposition: form-data; name=\"Filename\"");
            sb.Append("\r\n");
            sb.Append(fileName);
            sb.Append("\r\n");
            sb.Append(strBoundary);
            sb.Append("\r\n");
            sb.Append("Content-Disposition: form-data; name=\"Filedata\"; filename=" + fileName + "\"");
            sb.Append("\r\nContent-Type: application/octet-stream");
            sb.Append("\r\n");
            sb.Append("\r\n");
            sb.Append("\r\n");
            sb.Append(strBoundary);
            sb.Append("\r\nContent-Disposition: form-data; name=\"Upload\"");
            sb.Append("\r\n");
            sb.Append("\r\nSubmit Query");
            sb.Append("\r\n");
            sb.Append(strBoundary);            string strPostHeader = sb.ToString();
            byte[] postHeaderBytes = Encoding.UTF8.GetBytes(strPostHeader);            //根据uri创建httpWebRequest对象
            HttpWebRequest httpReq = (HttpWebRequest)WebRequest.Create(new Uri(Url));
            httpReq.Method = "POST";
            httpReq.Accept = "*/*";
            httpReq.Timeout = 300;
            httpReq.Referer = referer;
            httpReq.ContentType = "multipart/form-data; boundary="+strBoundary;
            long length = fs.Length + postHeaderBytes.Length;
            long fileLength = fs.Length;
            httpReq.ContentLength = length;
            CookieContainer objcok = new CookieContainer();
            string[] st = cookieStr.Split(';');
            foreach (string s in st)
            {
                int i = 0;
                i = s.IndexOf('=');
                Cookie ck = new Cookie();
                ck.Name = s.Substring(0, i).Trim();
                ck.Value = s.Substring(i + 1, s.Length - i - 1).Trim();
                objcok.Add(new Uri(host), ck);
            }
            httpReq.CookieContainer = objcok;            try
            {
                //每次上传1k；
                int bufferLength = 1024;
                byte[] buffer = new byte[bufferLength];                //已上传的字节数
                long offset = 0;                //开始上传时间
                DateTime startTime = DateTime.Now;
                int size = r.Read(buffer, 0, bufferLength);
                Stream postStream = httpReq.GetRequestStream();                postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);                while (size > 0)
                {
                    postStream.Write(buffer, 0, size);
                    offset += size;
                    //Application.DoEvents();
                    size = r.Read(buffer, 0, bufferLength);
                }
                postStream.Close();
            }
            catch
            {
                return false;
            }
            finally
            {
                fs.Close();
                r.Close();            }
            return true;
        }