怎么把stream转成MemoryStream
public static Stream sss(Stream inStream)
{
//把instream转成MemoryStream

}

[解决办法]
不可能直接转的，需要从Stream把数据读出来，写入MemoryStream。

MemoryStream ms = new MemoryStream();
byte[] buffer = new byte[1024];

while(true) {
int sz = inStream.Read(buffer, 0, 1024);
if (sz == 0) break;
ms.Write(buffer, 0, sz);
}
ms.Position = 0;
return ms;