public static void FillFormDataStream(this Dictionary<string, string> formData, Stream stream)
{
string dataString = GetQueryString(formData);
var formDataBytes = formData == null ? new byte[0] : Encoding.UTF8.GetBytes(dataString);
stream.Write(formDataBytes, 0, formDataBytes.Length);
stream.Seek(0, SeekOrigin.Begin);//设置指针读取位置
}