江苏网站集约化建设,做爰全过程免费狐狸网站,北京国际化品牌设计,徐州网站建设外包pipe 是异步的#xff0c;可以实现读一点写一点#xff0c;管道的优势#xff1a;不会淹没可用内存#xff0c;但是在导入的过程中无法获取到内容
const fs require(fs);
const path require(path);fs.createReadStream(path.resolve(__dirname…pipe 是异步的可以实现读一点写一点管道的优势不会淹没可用内存但是在导入的过程中无法获取到内容
const fs require(fs);
const path require(path);fs.createReadStream(path.resolve(__dirname, ./56/name.txt)).pipe(fs.createWriteStream(path.resolve(__dirname, ./56/copy_name.txt)));我们新建文件 name.txt 里面添加文本
kaimo123456789下面在我们的可读流里添加 pipe 方法上一节实现的可写流直接拿过来用即可 const EventEmitter require(events);
const fs require(fs);class KaimoReadStream extends EventEmitter {constructor(path, opts {}) {super();this.path path;this.flags opts.flags || r;this.mode opts.mode || 0o666;this.autoClose opts.autoClose || true;this.start opts.start || 0;this.end opts.end;// 读取的数量默认是 64k 如果文件大于 64k 就可以采用流的方式this.highWaterMark opts.highWaterMark || 64 * 1024;// 记录读取的偏移量this.pos this.start;// 默认创建一个可读流是非流动模式不会触发 data 事件如果用户监听了 data 事件后需要变为流动模式// 是否是流动模式this.flowing false;this.on(newListener, (type) {// 如果用户监听了 dataif (type data) {this.flowing true;this.read();}});// 打开文件this.open();}open() {fs.open(this.path, this.flags, this.mode, (err, fd) {if (err) {return this.emit(error, err);}// 将 fd 保存到实例上用于稍后的读取操作this.fd fd;this.emit(open, fd);});}// 利用发布订阅来实现延迟执行read() {// 读取必须要等待文件打开完毕如果打开了会触发 open 事件if (typeof this.fd ! number) {// 如果没有 fd 就返回一个 open 的一次性事件再去回调 read 方法return this.once(open, () this.read());}console.log(KaimoReadStream----, this.fd);// 真正开始读取const buffer Buffer.alloc(this.highWaterMark);// 每次理论上应该读取 highWaterMark 个但是用户能指定读取的位置// 应该读几个不要读超了let howMuchToRead this.end ? Math.min(this.end - this.pos 1, this.highWaterMark) : this.highWaterMark;fs.read(this.fd, buffer, 0, howMuchToRead, this.pos, (err, bytesRead) {if (bytesRead) {this.pos bytesRead;this.emit(data, buffer.slice(0, bytesRead));if (this.flowing) {this.read();}} else {this.emit(end);if (this.autoClose) {fs.close(this.fd, () {this.emit(close);});}}});}pause() {this.flowing false;}resume() {this.flowing true;this.read();}// 管道pipe(dest) {this.on(data, (data) {let flag dest.write(data);console.log(pipe--flag--, flag, data.toString());if (!flag) {this.pause();}});dest.on(drain, () {this.resume();});}
}module.exports KaimoReadStream;测试一下
const path require(path);// 默认读 4 写 1
const KaimoReadStream require(./56/KaimoReadStream); // 64k
const KaimoWriteStream require(./56/KaimoWriteStream); // 16klet rs new KaimoReadStream(path.resolve(__dirname, ./56/name.txt), {highWaterMark: 4
});
// 先写1个3个放缓存
let ws new KaimoWriteStream(path.resolve(__dirname, ./56/copy_name2.txt), {highWaterMark: 1
});
rs.pipe(ws);
