HttpWebRequest 上传图片

 public string HttpUploadFile()
        {
            string url = "http://localhost:50380/WebForm1.aspx";
            string filepath = "C:\\Users\\lei2.wang\\Desktop\\Capture.PNG";
            string fileformname = "Capture.PNG";
            string poststr = "";
            // 这个可以是改变的，也可以是下面这个固定的字符串
            string boundary = "------WebKitFormBoundarylAiKcuBRGd1pRVJI";

            // 创建request对象
            HttpWebRequest webrequest = (HttpWebRequest)WebRequest.Create(url);
            webrequest.ContentType = " multipart/form-data; boundary=----WebKitFormBoundarylAiKcuBRGd1pRVJI";
            webrequest.Method = "POST";
            webrequest.Headers.Add("Cookie: SGSRev_Order_ReportUser=billy-wp_li; SGSBlackClientListUser=seven_jiang; SGSCNComplaintCaseUser=Jiang_Seven; CtsisUserCode=apac\\Seven_Jiang; CNZZDATA1996164=cnzz_eid%3D798484094-1479962914-http%253A%252F%252Flocalhost%253A35708%252F%26ntime%3D1479974059 ");
            webrequest.Referer = "http://localhost:50380/WebForm1.aspx";

            //webrequest.Proxy = new WebProxy("127.0.0.1", 8888); // new WebProxy("127.0.0.1", "8888");//:8888

            // 构造发送数据
            StringBuilder sb = new StringBuilder();

            // 文本域的数据，将user=eking&pass=123456  格式的文本域拆分 ，然后构造 

            sb.Append("\r\n");
            sb.Append("\r\n");
            sb.Append("------WebKitFormBoundarylAiKcuBRGd1pRVJI");
            sb.Append("\r\n");
            sb.Append("Content-Disposition: form-data; name=\"__VIEWSTATE\"");
            sb.Append("\r\n");
            sb.Append("\r\n");
            sb.Append("revyQ+TvGvOWCVIQshKUEnHeGf0ftCH92iHWuRYVAct4lnXANDjVJUFuMPHDleYjIQfcrEsDhwzGYtRqw+fVLeUPs6OhI7/w2gubieoS4RQ=");
            sb.Append("\r\n");

            // 文件域的数据
            sb.Append("------WebKitFormBoundarylAiKcuBRGd1pRVJI");
            sb.Append("\r\n");
            sb.Append("Content-Disposition: form-data; name=\"aaab\"; filename=\"" + fileformname + "\"");
            sb.Append("\r\n");
            sb.Append("Content-Type: image/jpeg");
            sb.Append("\r\n");
            sb.Append("\r\n");

            string postHeader = sb.ToString();
            byte[] postHeaderBytes = Encoding.UTF8.GetBytes(postHeader);

            //构造尾部数据
            StringBuilder sb1 = new StringBuilder();
            sb1.Append("------WebKitFormBoundarylAiKcuBRGd1pRVJI");
            sb1.Append("\r\n");
            sb1.Append("Content-Disposition: form-data; name=\"__VIEWSTATEGENERATOR\"");
            sb1.Append("\r\n");
            sb1.Append("\r\n");
            sb1.Append("C687F31A");
            sb1.Append("\r\n");
            sb1.Append("------WebKitFormBoundarylAiKcuBRGd1pRVJI--");
            sb1.Append("\r\n");
            sb1.Append("\r\n");
            byte[] boundaryBytes = Encoding.ASCII.GetBytes(sb1.ToString());
            var cc = sb1.ToString();

            FileStream fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
            long length = postHeaderBytes.Length + fileStream.Length + boundaryBytes.Length;
            webrequest.ContentLength = length;

            Stream requestStream = webrequest.GetRequestStream();

            // 输入头部数据
            requestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);

            // 输入文件流数据
            byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)fileStream.Length))];
            int bytesRead = 0;
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                requestStream.Write(buffer, 0, bytesRead);

            // 输入尾部数据
            requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);
            WebResponse responce = webrequest.GetResponse();
            Stream s = responce.GetResponseStream();
            StreamReader sr = new StreamReader(s);

            // 返回数据流(源码)
            return sr.ReadToEnd();
        }

 protected void Page_Load(object sender, EventArgs e)
        {
             var aa=   Request.Files[0];
                HttpFileCollection hfc = HttpContext.Current.Request.Files;  //获取文件,保存图片
                HttpPostedFile hpf = hfc[0];
                int extIndex = hpf.FileName.LastIndexOf(‘.‘);
                string ext = hpf.FileName.Substring(extIndex);
                string fileName = Guid.NewGuid().ToString();
                string dir = HttpContext.Current.Server.MapPath("photos/buildings/");
                hpf.SaveAs(dir + fileName + ext);
        }