CODEWITHSUNDEEP
javascriptnode.jsmulter
lzam
lzam

Reputation: 185

How does multer determine the value of file.mimetype

Multer's file object contains a mimetype value. The documentation describes it as "Mime type of the file", but provides no other details.

How is the value of this field determined? Is it simply the Content-Type: provided by the client (which can easily be spoofed) or is the uploaded file evaluated in some way that can help determine the true file type?

Upvotes: 2

Views: 2571

Answers (1)

hankchiutw
hankchiutw

Reputation: 1662

By tracking the source code, it's come from content-type header.

Here is how I track:

make-middleware.js in Multer: Where there is a busboy stream object listening on file event and having mimetype as one of the input parameter of callback function. The mimetype is appended to req.files that the user got.

busboy: The busboy instance is created with request headers parsed by it's own parseHeaders and parseParams function. You can find it's doing something on content-type header.

Further tracking, you will find it applies the Dicer object to listen on headers event and emit file event to busboy with parsed mimeType.

Upvotes: 5

Related Questions