Streams 允许从源读取数据或写入数据到目标对象。在Node.js中有四种 stream

• Writeable：可写
• Readable：可读
• Duplex：双向，即可用于读写
• Transform：根据输入计算输出

每种类型的stream都是EventEmitter实例，在不同的实例抛出多个事件。常用的事件：

• data：当数据可读抛出
• end：当数据读取结束
• error：当数据读取错误
• finish：在调用 stream.end() 方法之后，并且所有数据都已刷新到底层系统

读取数据

var fs = require('fs')
var data = ''

// Create a readable stream
var readerStream = fs.createReadStream('input.txt')

// Set the encoding to be utf8.
readerStream.setEncoding('UTF8')

// Handle stream events --> data, end, and error
readerStream.on('data', function (chunk) {
  data += chunk
})

readerStream.on('end', function () {
  console.log(data)
})

readerStream.on('error', function (err) {
  console.log(err.stack)
})

console.log('Program Ended') // Program Ended Tutorials Point is giving self learning content to teach the world in simple and easy way!!!!!

写入数据

var fs = require('fs')
var data = 'Simply Easy Learning'

// Create a writable stream
var writerStream = fs.createWriteStream('output.txt')

// Write the data to stream with encoding to be utf8
writerStream.write(data, 'UTF8')

// Mark the end of file
writerStream.end()

// Handle stream events --> finish, and error
writerStream.on('finish', function () {
  console.log('Write completed.')
})

writerStream.on('error', function (err) {
  console.log(err.stack)
})

console.log('Program Ended')

Pipe-管道流

pipe是一种机制，我们将一个stream的输出作为另一个stream的输入。它通常用于从一个stream中获取数据，并将该stream的输出传递给另一个stream。pipe操作没有限制。

var fs = require('fs')

var readerStream = fs.createReadStream('input.txt')
var writerStream = fs.createWriteStream('output.txt')

readerStream.pipe(writerStream)

console.log('Program Ended')

链式流

chaining是一种将一个stream的输出连接到另一个stream并创建多个stream操作链的机制，它通常用于管道操作。

var fs = require('fs')
var zlib = require('zlib')

// Compress the file input.txt to input.txt.gz
fs.createReadStream('input.txt')
  .pipe(zlib.createGzip())
  .pipe(fs.createWriteStream('input.txt.gz'))

console.log('File Compressed.')