C上传文件不成功

c# 桌面开发上传文件不成功：代码如下

private string HttpPostData(string url, int timeOut, string fileKeyName,string filePath)
        {
            string responseContent;
            var memStream = new MemoryStream();
            var webRequest = (HttpWebRequest)WebRequest.Create(url);
            // 边界符
            var boundary = "---------------" + DateTime.Now.Ticks.ToString("x");
            // 边界符
            var beginBoundary = Encoding.UTF8.GetBytes("--" + boundary + "\r\n");      //用ASCII编码方式也不成功
            var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
            // 最后的结束符
            var endBoundary = Encoding.UTF8.GetBytes("--" + boundary + "--\r\n");      //用ASCII编码方式也不成功


            // 设置属性
            webRequest.Method = "POST";
            webRequest.Timeout = timeOut;
            webRequest.ContentType = " multipart/form-data; boundary=" + boundary;


            // 写入文件
            string filePartHeader = boundary + "\r\n" +
                "Content-Disposition:form-data; name=\"{0}\"; filename=\"{1}\"\r\n" +
                 "Content-Type:application/octet-stream\r\n\r\n";
            var header = string.Format(filePartHeader, fileKeyName, filePath);
            var headerbytes = Encoding.UTF8.GetBytes(header);                           //用ASCII编码方式也不成功


            memStream.Write(headerbytes, 0, headerbytes.Length);


            var buffer = new byte[1024];
            int bytesRead; // =0


            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                memStream.Write(buffer, 0, bytesRead);
            }


            // 写入结束边界符
            memStream.Write(endBoundary, 0, endBoundary.Length);


            webRequest.ContentLength = memStream.Length;


            var requestStream = webRequest.GetRequestStream();


            memStream.Position = 0;
            var tempBuffer = new byte[memStream.Length];
            memStream.Read(tempBuffer, 0, tempBuffer.Length);
            memStream.Close();


            requestStream.Write(tempBuffer, 0, tempBuffer.Length);
            requestStream.Close();


            var httpWebResponse = (HttpWebResponse)webRequest.GetResponse();


            using (var httpStreamReader = new StreamReader(httpWebResponse.GetResponseStream(),Encoding.GetEncoding("utf-8")))
            {
                responseContent = httpStreamReader.ReadToEnd();
            }


            fileStream.Close();
            httpWebResponse.Close();
            webRequest.Abort();


            return responseContent;                                   //返回的结果：{"errcode":-1,"errmsg":"系统繁忙"}
        }


有C#上传文件的例子吗？谢谢了