Node.js Stream 学习笔记

此为慕课网 两小时学会 Node.js stream 学习笔记。stream 的思想在各个语言中都是相通的，不限于Cpp、Java、Golang等，可以大大减少内存的消耗，提高代码的运行效率。

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主要组成部分

• data 事件，用来监听 stream 数据的输入
• end 事件，用来监听 stream 数据输入完成
• fs.createReadStream 方法，返回一个文件读取的 stream 对象
• fs.createWriteStream 方法，返回一个文件写入的 stream 对象
• pipe 方法，用来做数据流转

const http = require('http');
const fs = require('fs');
const path = require('path');
const PORT = 8000;
const server = http.createServer((req, res) => {
  const fileName = path.resolve(__dirname, 'data.txt');
  const stream = fs.createReadStream(fileName);
  stream.pipe(res);
});
server.listen(PORT);

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从哪里来

• 控制台输入
• http请求中的request
• 读取文件

控制台输入

process.stdin.on('data', (chunk) => {
  console.log(chunk.toString())
});

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http的request

const http = require('http');
const PORT = 8000;
const server = http.createServer((req, res) => {
  let data = '';
  req.on('data', chunk => { // 收到数据
    data += chunk.toString();
  });
  req.on('end', () => { // 数据传输结束
    res.end(data);
  });
});
server.listen(PORT);

---

从文件中读取

const fs = require('fs');
const path = require('path');
const readStream = fs.createReadStream(path.join(__dirname, 'data.txt'));
let length = 0;
readStream.on('data', (chunk) => {
  length += chunk.toString().length
});
readStream.on('end', () => {
  console.log(length)
});

---

到哪儿去

• 控制台
• http请求的response
• 写入文件

几个示例代码

// console
process.stdin.pipe(process.stdout)

// http
const fs = require('fs');
var stream = fs.createReadStream('....');
stream.path(res);

// fs
const fs = require('fs');
const rs = fs.createReadStream('....');
const ws = fs.createWriteStream('....');
rs.pipe(ws)

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建立WebServer

const http = require('http'),
      fs = require('fs'),
      path = require('path');
const PORT = 8000;
const fileName = path.join(__dirname, 'data.txt');
const server = http.createServer((req, res) => {
  switch (req.method) {
    case 'GET': // 处理 GET 方法
        const rs = fs.createReadStream(fileName);
        rs.pipe(res);
      break;
    case 'POST': // 处理 POST 方法
        let len = 0;
        req.on('data', (chunk) => {
          len += chunk.toString().length;
          console.log('chunk ', len);
        });
        req.on('end', () => {
          console.log('chunk end');
          res.end(len+'')
        });
      break;
    default:
      res.end('method not support')
  }
});
server.listen(PORT, () => {
  console.log(`Server is listening at port ${PORT}`)
});

---

按行读取

const fs = require('fs');
const path = require('path');
const readline = require('readline');
const fileName = path.join(__dirname, 'data.txt');
const rs = fs.createReadStream(fileName);
const rl = readline.createInterface({
  input: rs
});

rl.on('line', (lineData) => { // 按行读取事件
  console.log(lineData);
  console.log('----this line read----');
});
rl.on('close', () => { // 按行读取结束
  console.log('readline end')
});

---

stream流动的单位

8个二进制单位为一个存储单元，成为字节（byte），能存储的最整数位2^8=258

常常用两位16进制数代表一个字节，如 #CCCCCC 为三字节

const str = '学习 nodejs stream';
const buf = Buffer.from(str, 'utf-8');
console.log(buf); // // <Buffer e5 ad a6 e4 b9 a0 20 6e 6f 64 65 6a 73 20 73 74 72 65 61 6d>
console.log(buf.toString('utf-8'));

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流的种类

read stream

const Readable = require('stream').Readable;
const rs = new Readable;
rs.push('学习 ');
rs.push('nodejs ');
rs.push('stream\n');
rs.push(null);
rs.pipe(process.stdout);

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write stream

const Writable = require('stream').Writable;
const ws = new Writable;
ws._write = function (chunk, encoding, next) {
  console.log(chunk.toString());
  next();
};
process.stdin.pipe(ws);

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duplex stream

const fs = require('fs');
const zlib = require('zlib');
const readStream = fs.createReadStream('./file1.txt');
const writeStream = fs.createWriteStream('./file1.txt.gz');
readStream.pipe(zlib.createGzip())
          .pipe(writeStream);

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更多教程

Nodejs 中的 Stream