今天测试文件下载程序中发现的文件名过长的问题

居然发现文件名编码后长度超过155就会不能正确显示和下载，最后只好找了这样一个折中的方法，截短了
下面是那里的代码
/// <summary>
  /// 下载附件。
  /// </summary>
  /// <param name="filename">文件名</param>
  /// <param name="path">文件路径</param>
  public static void downloadfileattachment(string filename , string path)
  {
   if (system.io.file.exists(path))
   {
    try
    {
     filename  = filename.trim();

     for (int  i = 0 ; i < system.io.path.invalidpathchars.length ; i ++)
     {
      filename = filename.trim().replace(system.io.path.invalidpathchars[i].tostring() , string.empty);
     }

     filename  = filename.replace(system.io.path.pathseparator.tostring() , string.empty);
     
     int maxlength = 155;

     int length  = httputility.urlencode(filename).length;
     while (length > maxlength)
     {
      int index = filename.lastindexof(".");
      if (index > 0)
      {
       filename = filename.substring(0 , index - 1) + filename.substring(index);
      }
      else
      {
       filename = filename.substring(0 , filename.length - 1);
      }
      length  = httputility.urlencode(filename).length;
     }

     system.io.fileinfo file = new system.io.fileinfo(path);
     httpcontext.current.response.clear();
     httpcontext.current.response.appendheader("content-disposition", "attachment; filename=" + httputility.urlencode(filename));
     httpcontext.current.response.appendheader("content-length", file.length.tostring());
     httpcontext.current.response.contenttype = "application/octet-stream";
     httpcontext.current.response.writefile(file.fullname);
     httpcontext.current.response.end();
    }
    catch
    {
    }
   }
   else
   {
    httpcontext.current.response.clear();
    displaynofilemessage();
    httpcontext.current.response.end();
   }
  }