// Encode as JSON string.
					b, err := json.Marshal(string(data))
					if err == nil {
						s += `, "data_string": ` + string(b)
					}
				}
				// Base64 encode.
				s += `, "data_base64": "` + base64.StdEncoding.EncodeToString(data) + `"`
			}
			s += "}"
		}
		res = append(res, []byte(s)...)
	}
	res = append(res, '}')
	return res, nil
}

// files returns files as callback.