I am building a web application.
On one of the pages there is an upload form, where user can upload a file. After the upload is done, I want to check on the server if the uploaded file is an image.
Is it possible to check this beyond simple file extension checking (i.e. not assuming that a *.png
filename is actually a PNG image)?
For example, if I edit a JPEG image adding/editing a byte in a random place to make an invalid JPEG file, I want to detect that it is not a JPEG image anymore. I used to do such type of thing via PHP some time ago, using a GD library.
I would like to know if it is possible to do with Go?
DetectContentType is way better than a manual magic number checking. The use is simple:
clientFile, _, _ := r.FormFile("img") // or get your file from a file system
defer clientFile.Close()
buff := make([]byte, 512) // docs tell that it take only first 512 bytes into consideration
if _, err = clientFile.Read(buff); err != nil {
fmt.Println(err) // do something with that error
return
}
fmt.Println(http.DetectContentType(buff)) // do something based on your detection.
Using this method you need to know that you still are not guaranteed to have a correct file. So I would recommend to do some image manipulation with that file (like resize it to make sure this is really an image).