how to block uploading gif images in multer? - node.js

Question

This multer configuration lets me upload images with '.gif' format. How to solve this ? I want it to only upload png, jpg, jpeg
This is my code:
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
});
Route:
app.post('/upload-ad', upload.any(), recaptcha.middleware.verify, (req, res)

Answer 1

If I test your code like below, I get the correct response, e.g. "File must be an image." if I try to upload a .gif file.
const request = require("request");
const fs = require("fs");
const options = {
method: "POST",
url: "http://localhost:3300/upload-ad",
headers: {
"Content-Type": "multipart/form-data"
},
formData : {
"image" : fs.createReadStream("./test.gif")
}
};
request(options, function (err, res, body) {
if(err) console.log(err);
console.log(body);
});
This works because we're setting the Content-Disposition field in this case. I suspect that what's happening to you is that maybe the client is not setting this header, or it was set incorrectly. For example if we changed a filename from "test.gif" to "test.jpg" this would upload successfully despite the fact it is actually a GIF image.
In my case the start of the upload looks like so:
----------------------------321622124424983663382061
Content-Disposition: form-data; name="image"; filename="test.gif"
Content-Type: image/gif
And everything works as it is supposed to.
I'd recommend maybe not trusting the filename field in the POST and actually check what the image really is by looking at the uploaded buffer.