nodejs使用superangent下载图像，检查文件大小

...
superagent
            .get(req.body.img)
            .set('User-Agent', 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.99 Safari/537.36')
            .pipe(fs.createWriteStream(filePath));
console.log(fs.statSync(filePath));
...
...
superagent
            .get(req.body.img)