node爬虫下载图片0字节

又是我，新的一天新的爬虫问题。 运行结果，程序能跑起来但是下载率实在没法看，是因为什么问题导致这样，有解决方法吗 贴一下拙劣的代码。

var cheerio = require("cheerio");
	http = require("http"),
	https = require("https"),
	request = require("request");
	fs =require("fs"),
	path =require("path"),
	util = require('util');

var	url = 'http://www.ivsky.com/tupian/';
	dir = 'D:/download/',
	dir = mkdirSync(dir);

function main(){
	for(i=0;i<5;i++){
		if(i!=0){
			var index = 'index_' + i + '.html';
		}else{
			var index = '';
		}
		_url = url + index;
			//console.log(_url);
			downHtml(_url);
	}
	
}

// 获取html
function downHtml(url){
	http.get(url, function(res){
		var data="";
		res.setEncoding("utf-8");
		res.on('data', function(chunk){
			data += chunk;
		});
		res.on("end", function(){
			var $ = cheerio.load(data);
			var allhref=[];
			$('.il_img a').each(function(i, e){
				allhref[i] = 'http://www.ivsky.com' + $(e).attr('href');
				for(i=0;i<allhref.length;i++){
					str = encodeURI(allhref[i]);
					download(str);
				}
			})
		});
	}).on("error", function(){
		return null;
	});
}

//遍历图片
function download(url){
	http.get(url, function(res){
		var data="";
		res.setEncoding("utf-8");
		res.on('data', function(chunk){
			data += chunk;
		});
		res.on("end", function(){
			var $ = cheerio.load(data);
			$('img').each(function(i, e){
				downImg($(e).attr('src'), dir);
			})
		});
	}).on("error", function(){
		return null;
	});
}
//包装了模块就函数进行复写
/*server.download(url, function(data){
	if(data){
		//console.log(data);
		var $= cheerio.load(data);
		$('img').each(function(i, e){
			//console.log($(e).attr('src'));
			downImg($(e).attr("src"), dir)
		})
	}
});*/


//创建目录
function mkdirSync(dir){
	fs.existsSync(dir) || fs.mkdirSync(dir);
	return dir;
}

//下载图片
function downImg(url, dir){
	var startTime = new Date().getTime();
	url = encodeURI(url);
	var fileName = url.split('/').pop();
	//var img_name = $('il_img a').attr('title').trim() + '.jpg';
	request(url).on('response', function(){
		var endTime = new Date().getTime();
		console.log('downloading..%s..%ss', url, (endTime-startTime)/1000);
	})
	.pipe(fs.createWriteStream(dir + fileName)
		)
	.on('error', function(){console.log('failed to download');});
}



main();//执行主函数