// after
static int output_json_one_sensor(
    bool first, const sensor_data_t* data,
    char* buffer, size_t size, int offset)
{
    // 中略
    new_offset += snprintf(
        buffer + new_offset, size - new_offset,
        "{\"name\":\"%s\",\"value\":%.2f}",
        data->name, data->value);
    // 中略
}
