今天在做一个图片上传的功能，在用formidable的时候遇到一个问题，查了很多资料，但是渣渣的我还是找不到原因，求大神解答解答。

下面是我的报错的提示：

而我的代码如下：

入口文件 blog.js

   var express=require('express'),
       mongoose=require('mongoose'),
       mongoStore=require('connect-mongo')(express),
       blog=module.export=express(),
       ejs=require('ejs'),
       dbUrl='mongodb://localhost/myblog', 
       SessionStore=require('session-mongoose')(express),
       db; 
   mongoose.connect(dbUrl);
   db=mongoose.connection; 
   var store=new SessionStore({
       url:dbUrl,
       interval:120000
   })  
   blog.configure(function(){
       blog.set('views',__dirname+'/blog/views');
       blog.engine('.html',ejs.__express);
       blog.set('view engine','.html');
       blog.set("view options",{
           layout:false
       })
       blog.use(express.bodyParser());
       blog.use(express.methodOverride());
       blog.use(express.cookieParser());
       blog.use(express.cookieSession({
           key:'user',
           secret:'myblog',
           store:store,
           cookie:{maxAge:1200000}
       }));
       blog.use(express.static(__dirname+'/public'));
       
   });
   db.on('error',function(err){
       console.log("link to database error!");
   })  
   db.once('open',function(){
       require('./config/route')(blog);
   })  
   blog.listen(4000)

路由文件 route.js

             var coverApi=require('../blog/controllers/cover');      
           module.exports=function(blog){        
             blog.use(function(req,res,next){
                 var _user=req.session.user;
                 blog.locals.user=_user;
                 next();
             })              
            blog.post('/manage/addCover.html',coverApi.addCover);    
         }

控制器文件 cover.js

        var fs=require('fs'),
       path=require('path'),
       formidable=require('formidable'),
       Article=require('../models/article'),
       coverApi={},
       util = require('util'); 
   module.exports=coverApi;    
   coverApi.addCover=function(req,res){ 
   
       var form = new formidable.IncomingForm({uploadDir:'./sources/'});
       form.parse(req, function(err, fields, files) {
           if(err) console.log(err);//这里报错了
         res.writeHead(200, {'content-type': 'text/plain'});
         res.write('received upload:\n\n');
         res.end(util.inspect({fields: fields, files: files}));
       });
       
   }   
   coverApi.show=function(req,res){
       var id=req.params.id;
       res.render('cover',{
           id:id
       }); 
   }

视图文件 cover.html

    <div class="container">
        <h1>添加图片</h1>
        <form action="/manage/addCover.html" method='post' enctype="multipart/form-data">
            <div class="form-group">
                <input type="text" class='hidden' value="<%= id%>" name='id'>
                <label for="">图片</label>
                <input type="file"  name='cover'>
                <button type='submit' class='btn btn-lg btn-primary'>add</button>
            </div>
        </form>
    </div>

package.json 文件

项目目录结构

现在那个问题还是解决不了，求大神帮忙解答