core程序实现文件下载

已知本地文件名，返回给前台流

string filepath = path +“/” + filename +".txt";
if(System.IO.File.Exists(filepath))
{
byte[] bytes;
  using (Stream stream = new Filestream(FilePath,FileMode.Open))
  {
      bytes = new byte[stream.Length];
      stream.Read(bytes,0,bytes.length);
      stream.Close();
  }
  return File(bytes,"application/octet-stream",filename+".txt");
//字段说明第一个字节流，第二个返回方式，第三个，返给前台的文件名
}