文件操作，关闭可读可写流

场景：分片上传，分片文件全部传输完毕后，将小文件进行合并：

/**
 * @method 合并文件
 * @param {array} file_path_arr 文件路径数组，注意文件路径要按照分片顺序，从小到大排列
 * @param {string} target_path 目标文件地址
 * @returns {null} 注意使用了shift方法，会将传入的数据逐步的清空
 */
exports.mergeChunks = function(file_path_arr, target_path) {
    return new Promise(async (resolve, reject) => {
        try{
            let targetStream = fs.createWriteStream(target_path);
            let readStream = function(paths_arr, targetStream) {
                let file_path = paths_arr.shift();
                let originStream = fs.createReadStream(file_path);
                originStream.pipe(targetStream, {end: false});
                originStream.on('end', async () => {
                    if(paths_arr.length > 0) {
                        readStream(paths_arr, targetStream);
                    } else {
                        resolve();
                    }
                });
            };
            readStream(file_path_arr, targetStream);
        }catch(err) {
            if(err) reject(err);
        }
    })
}

此时，突然需要删除以上传的文件，会报无权限操作：operation not permitted

通过windows任务管理器中的资源监视器，查看搜索关联的句柄，确实自身的Node进程对相关文件有占用（红色框关键字搜索）

审视代码，发现需要关闭流，即可放开进程对文件的占用：

/**
 * @method 合并文件
 * @param {array} file_path_arr 文件路径数组，注意文件路径要按照分片顺序，从小到大排列
 * @param {string} target_path 目标文件地址
 * @returns {null} 注意使用了shift方法，会将传入的数据逐步的清空
 */
exports.mergeChunks = function(file_path_arr, target_path) {
    return new Promise(async (resolve, reject) => {
        try{
            let targetStream = fs.createWriteStream(target_path);
            let readStream = function(paths_arr, targetStream) {
                let file_path = paths_arr.shift();
                let originStream = fs.createReadStream(file_path);
                originStream.pipe(targetStream, {end: false});
                originStream.on('end', async () => {
                    if(paths_arr.length > 0) {
                        readStream(paths_arr, targetStream);
                    } else {
                        // 关闭流
                        targetStream.close();
                        originStream.close();
                        resolve();
                    }
                });
            };
            readStream(file_path_arr, targetStream);
        }catch(err) {
            if(err) reject(err);
        }
    })
}
```