Multer文件过滤器无法正常工作NodeJS

Question

所以我想做的就是让用户仅上传jpg jpeg或png文件。但是，我现在拥有的代码仍然让我上载gif个文件。代码如下：

let storage = multer.diskStorage({
    destination: function (req, file, cb) {
        cb(null, '/public/images')
    },
    filename: function (req, file, cb) {
        crypto.pseudoRandomBytes(16, function (err, raw) {
            cb(null, raw.toString('hex') + Date.now() + '.' + mime.getExtension(file.mimetype));
        });
    }
});
let upload = multer({
    limits: {
        fileSize: 1000000
    },
    fileFilter: function(req, file, cb) {
        if(!file.originalname.match(/\.(jpg|jpeg|png)$/)){
            return cb('File must be an image.');
        }
        cb(undefined, true);
    },
    storage: storage
});

路线：

app.post('/post', upload.any(), recaptcha.middleware.verify, (req, res) => {
    img: req.files[0].filename,
});

为什么验证无效？