11慕课网《进击Node.js基础（一）》Buffer和Stream

Buffer

用来保存原始数据

(logo.png)

以下代码读取logo.png为buffer类型
然后将buffer转化为string，新建png
可以将字符串配置： data:image/png;Base64,Buffer.toString()

var fs = require('fs')

fs.readFile('logo.png',function(err,origin_buffer){
	console.log('origin_buffer是否Buffer格式：'+Buffer.isBuffer(origin_buffer))
	//console.log('读取到origin_buffer:' + origin_buffer)
	//创建文件
	fs.writeFile('log_buffer.png',origin_buffer,function(err){
		if(err) console.log(err)
	})

	//var base84Image = new Buffer(origin_buffer).toString('base64')
	//转为字符串
	var base64Image = origin_buffer.toString('base64')

	console.log('字符串base64Image:' + base64Image)

	var decodedImage = new Buffer(base64Image, 'base64')

	//console.log('编码decodedImage:'+decodedImage)
	//console.log('比较origin_buffer和decodedImage：' + Buffer.compare(origin_buffer,decodedImage))

	fs.writeFile('logo_decoded.png',decodedImage,function(err){
		if(err) console.log(err)
	})

})

Stream

暂存和移动数据

通过stream直接copy图片

var fs  =  require('fs')
var source = fs.readFileSync('../buffer/logo.png')

fs.writeFileSync('stream_copy.png',source)

stream读操作触发事件

stream的读取会触发事件,通过监听可以实现许多功能
stream事件每次传输 64kb

var fs = require('fs')

var readStream = fs.createReadStream('xpg.mp3')
var n=0

//数据传递过程中触发,监听data事件
readStream
 .on('data', function(chunk){
 	n++
	console.log('data emits')
	console.log('是否以Buffer格式传递？：'+Buffer.isBuffer(chunk))
	//console.log(chunk.toString('utf8'))
	//
	readStream.pause()//暂停
	console.log('data pause')
	setTimeout(function(){
		console.log('data pause end')
		readStream.resume()//重新启动
	},10)
 })
 .on('readable',function(){
 	//文件可读
 	console.log('data readable')
 })
 .on('end', function(){
 	console.log(n)
 	//数据传递事件，同时触发目标不可写
 	console.log('data end')
 })
 .on('close',function(){
 	//整个stream关闭结束
 	console.log('data close')
 })
 .on('error',function(e){
 	console.log('data read error'+e)
 })

stream的读写

//文件copy
var fs = require('fs')

var readStream = fs.createReadStream('xpg.mp3')

var writeStream = fs.createWriteStream('copy-xpg.mp3')


readStream.on('data',function(chunk){
	//数据还在缓冲区，未写完
	if(writeStream.write(chunk) === false){
		console.log('still cached')
		//暂停读入，防止缓冲区爆掉
		readStream.pause()
	}

})


readStream.on('end',function(){
	writeStream.end()
})

//drain方法，数据被消费完，全部写入目标
writeStream.on('drain', function(){
	console.log('data drain')

	//重新启动读操作
	readStream.resume()
})

Stream种类

• Readable 可读流，读取外部数据，将数据缓冲到内部的buffer数组
• Writeable 可写流，消费buffer数组中的数据，写目标
• Duplex 双工流
• Transform 转换、双工

使用pipe

var http = require('http')
var fs = require('fs')
//需要安装 npm install request
var request = require('request')

http
  .createServer(function(req,res){
  	//通俗的做法
  	// fs.readFile('../buffer/logo.png', function(err,data){
  	// 	if(err){
  	// 		res.end('file not exist!')
  	// 	}else{
  	// 		res.writeHeader(200,{'Context-Type':'text/html'})
  	// 		res.end(data)
  	// 	}
  	// })
  	
  	//简洁的方案
  	//fs.createReadStream('../buffer/logo.png').pipe(res)
  	
  	//爬取网络中的图片
  	request('http://img2.mukewang.com/szimg/5a67ebf50001b6d005400300-228-128.jpg')
  	  .pipe(res)

  })
  .listen(8090)

  console.log('run on 8090')

使用pipe重写stream的直接读写

var fs = require('fs')

fs.createReadStream('xpg.mp3').pipe(fs.createWriteStream('xpg-pipe.mp3'))

pipe连接Readable和Writabel

//文件copy
var fs = require('fs')

var readStream = fs.createReadStream('xpg.mp3')

var writeStream = fs.createWriteStream('copy-xpg.mp3')


readStream.on('data',function(chunk){
	//数据还在缓冲区，未写完
	if(writeStream.write(chunk) === false){
		console.log('still cached')
		//暂停读入，防止缓冲区爆掉
		readStream.pause()
	}

})


readStream.on('end',function(){
	writeStream.end()
})

//drain方法，数据被消费完，全部写入目标
writeStream.on('drain', function(){
	console.log('data drain')

	//重新启动读操作
	readStream.resume()
})

自己定制的Readable Write

var stream = require('stream')
var util = require('util')


//定制可读流
function ReadStream(){
	stream.Readable.call(this)
}
//使ReadStream 继承stream.Readable的原型
util.inherits(ReadStream,stream.Readable)

ReadStream.prototype._read = function(){
	this.push('I')
	this.push('Love')
	this.push('You')
	//null结束
	this.push(null)
}
//===定制可写流 
function WriteStream(){
	stream.Writable.call(this)
	this._cached = new Buffer('')
}

util.inherits(WriteStream,stream.Writable)

WriteStream.prototype._write = function(chunk, encode, cb){
	console.log(chunk.toString())
	cb()
}

//定制转换流
function TransformStream(){
	stream.Transform.call(this)
}

util.inherits(TransformStream,stream.Transform)

TransformStream.prototype._transform = function(chunk, encode, cb){
	this.push(chunk)
	cb()
}

TransformStream.prototype._flush = function(cb){
	this.push('OK')
	cb()
}


var rs = new ReadStream()
var ws = new WriteStream()
var ts = new TransformStream()

rs.pipe(ts).pipe(ws)