I'm developping an app using a `UIDocumentPickerViewController` to choose file to send to a server.

I have to retrieve the `Mime Type` of this file in order to correctly send this file with `Amalofire` :

```
Alamofire.upload(.POST, url, headers: headers, multipartFormData: { multipartFormData in
    if let url = attachment as? NSURL, let data = NSData(contentsOfURL: url) {
        multipartFormData.appendBodyPart(data: data, name :"File\(i)",  fileName: "file\(i).\(url.pathExtension)", mimeType: "???")
    }
}

```

Is there any method able to get the mime type from extension or NSURL ?