node通过multer上传文件获取不到

APP.JS

var fs = require('fs');
var express = require('express');
var multer  = require('multer')

var app = express();
var upload = multer({ dest: 'upload/' });

// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
    var file = req.file;

    console.log('文件类型：%s', file.mimetype);
    console.log('原始文件名：%s', file.originalname);
    console.log('文件大小：%s', file.size);
    console.log('文件保存路径：%s', file.path);

    res.send({ret_code: '0'});
});

app.get('/form', function(req, res, next){
    var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
    res.send(form);
});

app.listen(3000);

<form action="/upload" method="post" enctype="multipart/form-data">
    <h2>单图上传</h2>
    <input type="file" name="logo">
    <input type="submit" value="提交">
</form>

注意后台接收的file名称要一致：都是logo，你看看你的name是否一致