code: func (c *Context) FileAttachment(filepath, filename string) {
  	c.Writer.Header().Set("content-disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
  	http.ServeFile(c.Writer, c.Request, filepath)
  }
docs: // FileAttachment writes the specified file into the body stream in an efficient way
  // On the client side, the file will typically be downloaded with the given filename