此流不支持查找操作

1、  解决思路:

           1.将获取的网络流转化成内存流

           2.内存流位置指向0     

2、具体操作：

 var request = (HttpWebRequest)WebRequest.Create(originTripImageUrl);
request.Timeout = 30000;
WebResponse response = request.GetResponse();
Stream stream = response.GetResponseStream();

var memoryStream = new MemoryStream();
 //将基础流写入内存流
 const int bufferLength = 1024;
byte[] buffer = new byte[bufferLength];
 int actual = stream.Read(buffer, 0, bufferLength);
if (actual > 0)
 {
       memoryStream.Write(buffer, 0, actual);
 }
memoryStream.Position = 0;