Setting response statuses using Multer in Express? - node.js

Question

I'm using Multer as Express middleware. In my example I'm checking that the file extension and mimetype are correct (for a wave file), and I want to respond with 415 if they aren't. However I don't know how to do this with Multer's fileFilter, so I'm checking if the file exists in router handler's request object, which feels a bit awkward. Also maybe I want to implement different fileFilter's and error codes in the future. Is there a recommended pattern for setting response statuses with Multer in Express?
const upload = multer(
{
dest: UPLOAD_PATH,
fileFilter: function(req, file, cb) {
const filetypes = /wave|wav/;
const mimetype = filetypes.test(file.mimetype);
const extname = filetypes.test(
path.extname(file.originalname).toLowerCase());
cb(null, (mimetype && extname));
},
}
);
router.post('/', upload.single('wave'), (req, res) => {
const file = req.file;
if (!file) {
return res.status(415).send('Only audio/wav files are supported.');
}
// Do some async task with file
return res.sendStatus(200);
});

Answer 1

You can do it like this:
const upload = multer({
dest: 'uploads/',
fileFilter: function (req, file, cb) {
const filetypes = /wave|wav/;
const mimetype = filetypes.test(file.mimetype);
const extname = filetypes.test(
path.extname(file.originalname).toLowerCase());
if (mimetype && extname) {
cb(undefined, true);
} else {
req.notWAVEMimeType = 'Only audio/wav files are supported.';
return cb(undefined, false);
}
}
});
router.post('/', upload.single('wave'), (req, res) => {
if (req.notWAVEMimeType) {
return res.status(415).end(req.notWAVEMimeType);
}
// Do some async task with file
return res.sendStatus(200);
});
The notWAVEMimeType property on the request object allows you to return the error message to the POST method. According to this you can add other mime types and check the existence of the related property of req afterwards.