上一篇文章提到了,最近做一个基于 File System/IndexedDB的应用,上一篇是定额和使用的查询。

因为LocalFileSystem只有chrome支持,有点尴尬,如果按需加载又何来尴尬。

这一篇是关于文件和目录的操作的,怕陷入回调陷阱,基于promise和ES7的await。

首先介绍两个函数:

第一个是 :toPromise,把那种带成功失败回调的函数转化为Promise,因为File API的File System里面很多方法都是这种格式的。
/**
 * 转为promise,主要是把 a.b(param1,param2,successCallback,errorCall) 转为promise
 * @param {*期待的是函数} obj 
 * @param {*上下文} ctx 
 * @param {*参数} args 
 */
function toPromise(obj, ctx = window, ...args) {
    if (!obj) return obj

    //如果已经是Promise对象
    if ('function' == typeof obj.then) return obj

    //若obj是函数直接转换
    if ('function' == typeof obj) return _toPromise(obj)

    return obj;

    //函数转成 promise
    function _toPromise(fn) {
        return new Promise((resolve, reject) => {

            fn.call(ctx, ...args, (...ags) => {
                //多个参数返回数组,单个直接返回对象
                resolve(ags && ags.length > 1 ? ags : ags[0] || null)
            }, (err) => {
                reject(err)
            })

        })
    }
}

 第二个是 promiseForEach,顺序的执行多个Promise,思想也就是then的拼接

/**
 * https://segmentfault.com/q/1010000007499416
 * Promise for forEach
 * @param {*数组} arr 
 * @param {*回调} cb(val)返回的应该是Promise 
 * @param {*是否需要执行结果集} needResults
 */
function promiseForEach(arr, cb, needResults) {
    let realResult = [], lastResult //lastResult参数暂无用
    let result = Promise.resolve()
    Array.from(arr).forEach((val, index) => {
        result = result.then(() => {
            return cb(val, index).then((res) => {
                lastResult = res
                needResults && realResult.push(res)
            })
        })
    })

    return needResults ? result.then(() => realResult) : result
}

 

这两个方法完毕后,就直接上主体代码了, hold on。

/**
 * 参考的API:
 * http://w3c.github.io/quota-api/
 * 
 */

if (!window.location.origin) {
    window.location.origin = window.location.protocol + "//" + window.location.hostname + (window.location.port ? ':' + window.location.port : '');
}
//文件系统请求标识 
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem
//根据URL取得文件的读取权限 
window.resolveLocalFileSystemURL = window.resolveLocalFileSystemURL || window.webkitResolveLocalFileSystemURL

//临时储存和永久存储
navigator.temporaryStorage = navigator.temporaryStorage || navigator.webkitTemporaryStorage;
navigator.persistentStorage = navigator.persistentStorage || navigator.webkitPersistentStorage;

//常量
const _TEMPORARY = 'temporary',
    _PERSISTENT = 'persistent',
    FS_SCHEME = 'filesystem:'


class LocalFileSystem {

    constructor(fs) {
        this._fs = fs       //文件系统
        this._root = fs.root //文件系统的根Entry
        this._instance = null //示例对象
        this._type = null //类型,window.TEMPORAR| window.PERSISTENT
        this._fsBaseUrl = null //文件系统的基础地址
    }


    /**
       * 
       * @param {* window.TEMPORAR(0) |window.PERSISTENT(1)} type
       * @param {* 申请空间大小,单位为M } size
       */
    static getInstance(type = window.TEMPORARY, size = 1) {

        if (this._instance) {
            return Promise.resolve(this._instance)
        }
        //类型
        let typeValue = type,
            //文件系统基础地址
            fsBaseUrl = FS_SCHEME + location.origin + '/' + (type == 1 ? _PERSISTENT : _TEMPORARY) + '/'
        return new Promise((resolve, reject) => {
            window.requestFileSystem(type, size * 1024 * 1024, fs => {
                this._instance = new LocalFileSystem(fs)
                this._instance._type = typeValue;
                this._instance._fsBaseUrl = fsBaseUrl
                return resolve(this._instance)
            }, (err) => reject(err))
        })

    }

    /**
     * 获得FileEntry
     * @param {*文件路径} path  
     */
    _getFileEntry(path, create = false) {
        return toPromise(this._root.getFile, this._root, path, { create, exclusive: false })
    }

    /**
     * 获取目录
     * @param {*路径} path 
     * @param {*不存在的时候是否创建} create 
     */
    _getDirectory(path = '', create = false) {
        return toPromise(this._root.getDirectory, this._root, path, { create, exclusive: false })
    }

    async _readEntriesRecursively(rootEntry, refResults) {

        if (rootEntry.isFile) {
            return Promise.resolve(rootEntry)
        }
        let reader = rootEntry.createReader()
        let entries = await toPromise(reader.readEntries, reader)
        refResults.push(...entries)
        let psEntries = entries.map(entry => this._readEntriesRecursively(entry, refResults))
        return Promise.all(psEntries)
    }

    /**
     * 获得Entry
     * @param {*路径} path 
     */
    resolveLocalFileSystemURL(path) {
        return toPromise(window.resolveLocalFileSystemURL, window, `${this._fsBaseUrl}${path.startsWith('\/') ? path.substr(1) : path}`)
    }

    /**
     * 获得文件
     * @param {*文件路径} path 
     */
    async getFile(path) {
        let fe = await this._getFileEntry(path)
        return toPromise(fe.file, fe)
    }

    /**
     * 往文件写入内容
     * @param {*文件路径} path 
     * @param {*写入的内容} content 
     * @param {*数据类型} type 
     * @param {*是否是append} append 
     */
    async writeToFile(path, content, type = 'text/plain', append = false) {

        let fe = await this._getFileEntry(path, true)
        let writer = await toPromise(fe.createWriter, fe);
        let data = content;

        //不是blob,转为blob
        if (content instanceof ArrayBuffer) {
            data = new Blob([new Uint8Array(content)], { type })
        } else if (typeof content == 'string') {
            data = new Blob([content], { type: 'text/plain' })
        } else {
            data = new Blob([content])
        }

        if (append) {
            writer.seek(writer.length)
        }

        return new Promise((resolve, reject) => {
            //写入成功
            writer.onwriteend = () => {
                resolve(true)
            }

            //写入失败
            writer.onerror = (err) => {
                reject(err)
            }

            writer.write(data)
        })
    }

    /**
     * 获取指定目录下的文件和文件夹
     * @param {*路径} path 
     */
    async readEntries(path = '') {
        let entry = null
        if (!path) {
            entry = this._root
        } else {
            entry = await this.resolveLocalFileSystemURL(path)
        }
        let reader = entry.createReader()
        return toPromise(reader.readEntries, reader);
    }

    /**
     * 获取所有的文件和文件夹,按照路径排序
     */
    async readAllEntries() {
        let refResults = []
        let entries = await this._readEntriesRecursively(this._root, refResults)
        refResults.sort((a, b) => a.fullPath > b.fullPath)
        return refResults

    }


    /**
     * 确认目录存在,递归检查,没有会自动创建
     * @param {*} directory 
     */
    async ensureDirectory(directory = '') {
        //过滤空的目录,比如 '/music/' => ['','music','']
        let _dirs = directory.split('/').filter(v => !!v)

        if (!_dirs || _dirs.length == 0) {
            return Promise.resolve(true)
        }

        return promiseForEach(_dirs, (dir, index) => {
            return this._getDirectory(_dirs.slice(0, index + 1).join('/'), true)
        }, true).then((rs) => {
            console.log(rs)
            return true
        })
    }



    /**
     * 清除所有的文件和文件夹
     */
    async clear() {
        let entries = await this.readEntries()
        let ps_entries = entries.map(e => e.isFile ? toPromise(e.remove, e) : toPromise(e.removeRecursively, e))
        return Promise.all(ps_entries)
    }

    /**
    * Promise里面的错误处理
    * @param {*reject}  
    */
    errorHandler(reject) {
        return (error) => {
            reject(error)
        }
    }

}


// 测试语句
//读取某个目录的子目录和文件:  LocalFileSystem.getInstance().then(fs=>fs.readEntries()).then(f=>console.log(f))
//写文件         LocalFileSystem.getInstance().then(fs=>fs.writeToFile('music/txt.txt','爱死你')).then(f=>console.log(f))
//获取文件:     LocalFileSystem.getInstance().then(fs=>fs.getFile('music/txt.txt')).then(f=>console.log(f))
//递归创建目录:  LocalFileSystem.getInstance().then(fs=>fs.ensureDirectory('music/vbox')).then(r=>console.log('r:' + r))
//递归获取:     LocalFileSystem.getInstance().then(fs=>fs.readAllEntries()).then(f=>console.log(f))
//删除所有:     LocalFileSystem.getInstance().then(fs=>fs.clear()).then(f=>console.log(f)).catch(err=>console.log(err)) 

  

当然测试语句也在上面了,因为用了 await,那么大家自然知道了。需要 chrome://flags开启javascript的特性。

如果你有兴趣,代码地址:https://github.com/xiangwenhu/BlogCodes/tree/master/client/FileSystem,下载下来

npm install 之后, node server/app.js就可以查询demo了

 
 
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