c# post body文件上传 并下载文件

        /// 使用Post方法上传文件
        /// </summary>
        /// <param name="url"></param>
        /// <param name="files">需要上传的文件，Key：对应要上传的Name，Value：本地文件名</param>
        public void Upload(string url, Dictionary<string, string> files)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";

            Stream postStream = new MemoryStream();
            var doUpload = files != null && files.Count > 0;//是否用Form
            if (doUpload)
            {
                //通过表单上传文件
                string boundary = "----" + DateTime.Now.Ticks.ToString("x");
                string formdataTemplate = "\r\n--" + boundary + "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: application/octet-stream\r\n\r\n";

                foreach (var file in files)
                {
                    try
                    {
                        var fileName = file.Value;
                        using (var fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read))
                        {
                            var formdata = string.Format(formdataTemplate, file.Key, fileName /*Path.GetFileName(fileName)*/);
                            var formdataBytes = Encoding.ASCII.GetBytes(postStream.Length == 0 ? formdata.Substring(2, formdata.Length - 2) : formdata);//第一行不需要换行
                            postStream.Write(formdataBytes, 0, formdataBytes.Length);

                            byte[] buffer = new byte[1024];
                            int bytesRead = 0;
                            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                            {
                                postStream.Write(buffer, 0, bytesRead);
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        throw ex;
                    }
                }
                //结尾
                var footer = Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
                postStream.Write(footer, 0, footer.Length);
                request.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
            }

            request.ContentLength = postStream != null ? postStream.Length : 0;
            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
            request.KeepAlive = true;
            request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36";

            if (postStream != null)
            {
                postStream.Position = 0;

                //直接写入流
                Stream requestStream = request.GetRequestStream();

                byte[] buffer = new byte[1024];
                int bytesRead = 0;
                while ((bytesRead = postStream.Read(buffer, 0, buffer.Length)) != 0)
                {
                    requestStream.Write(buffer, 0, bytesRead);
                }

                postStream.Close();
            }

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            using (Stream responseStream = response.GetResponseStream())
            {
                using (var fs = File.Create(@"d:\xx.png"))
                {
                    int buffer_count = 65536;
                    byte[] buffer2 = new byte[buffer_count];
                    int size = 0;
                    while ((size = responseStream.Read(buffer2, 0, buffer_count)) > 0)
                    {
                        fs.Write(buffer2, 0, size);
                    }
                    fs.Flush();
                }
            }
        }