Stream

const fs = require('fs')
const s = fs.createReadStream('./file.txt')
console.log(s)
Terminal run//
node --inspect-brk main.js
在打开浏览器开发者模式 -> 打开node调试模式
ReadStream.__proto__ = Readable.prototype
Readable.__proto__ = Stream.prototype
Stream.__protp__ = EventEmitter.prototype
EventEmitter.__proto__ = Object.prototype
每一层原型都继承上一个构造函数

const fs = require('fs');
const stream = fs.createWriteStream('./file.txt');
for(let i=0;i<1000000;i++){
    stream.write(`这是第${i}行内容，我还要写更多继续写\n`)
}
stream.end();
console.log('done')

stream 流 chunk 块 pipe 管道链接 sink 池 source 源 每次传递的 chunk 都是一个 Buffer // 一个16进制的01数据 Readable 可读 Writable 可写 Duplex 可读可写（双向）
Transform 可读可写（变化） 类似babel -> es6+ > es5 // sass -> css

const http = require('http')
const fs = require('fs')
const serve = http.createServer()
serve.on('request',(request,response)=>{
  fs.readFile('./file.txt',(error,data)=>{
    if(error)throw error
    response.end(data)
    console.log('done')
  })
})
serve.listen('8999')
//文件内容一下全部读取 ，占用很高的内存 ， 速度快

const http = require('http')
const fs = require('fs')
const serve = http.createServer()
serve.on('request',(request,response)=>{
  fs.readFile('./file.txt',(error,data)=>{
    if(error)throw error
    response.end(data)
    console.log('done')
  })
})
serve.listen('8999')
//用Stream 的方式 ， 数据一块一块的读取 每次读到一定程度就释放内存在重新开始
// 内存占用小  速度偏慢

const http = require('http')
const fs = require('fs')
const serve = http.createServer()
serve.on('request',(request,response)=>{
  const stream = fs.createReadStream('./file.txt')
  stream.on('data',(chunk)=>{
    console.log('停一下')
    console.log(chunk)
  })
  stream.pipe(response)  //暂停
  stream.pause()
  setTimeout(()=>{stream.resume},1000)  // 1秒后继续
 })
serve.listen('8000')
console.log('done')

// Readable stream

分两种状态 pasused（静止状态） 和 flowing（流动状态）
默认处于 paused 状态下
添加 data 事件监听就变成flowing状态
删掉 data 事件监听就变成paused状态了
pause() 可以变成 paused状态
resume() 可以变成 flowing 状态

const fs = require('fs')
function writeOneMillionTimes(writer, data) {
  let i = 10000;
  write();
  function write() {
    let ok = true;
    do {
      i--;
      if (i === 0) {
        // Last time!
        writer.write(data);
      } else {
        // See if we should continue, or wait.
        // Don't pass the callback, because we're not done yet.
        ok = writer.write(data);
        if(ok===false){
          console.log('别写了')
        }
      }
    } while (i > 0 && ok);
    if (i > 0) {
      // Had to stop early!
      // Write some more once it drains.
      writer.once('drain', ()=>{
        console.log('lets go')
          write()
      });
    }
  }
}
const writer = fs.createWriteStream('./big.txt');
writeOneMillionTimes(writer,'hello')
// https://nodejs.org/api/stream.html#stream_event_drain

drain官方文档

drain 事件 ， 写入太快了会堵塞 ， 当疏通后 drain事件会继续往下写