b.Handle("GET", "/captcha/{captcha_id}", "CaptchaImage"). if c.Ctx.URLParam("t") != "" {. w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate"). w.Header().Set("Content-Type", "application/octet-stream"). http.ServeContent(w, r, id+ext, time.Time{}, bytes.NewReader(content.Bytes()))