guess_mime.m

NSString* guessMIMETypeFromFileName(NSString* fileName) {
    NSString* fileExtension = [[fileName pathExtension] lowercaseString];
    CFStringRef uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge CFStringRef)fileExtension, NULL);
    CFStringRef mimeType = UTTypeCopyPreferredTagWithClass(uti, kUTTagClassMIMEType);
    CFRelease(uti);

    if (mimeType == nil) {
        return @"application/octet-stream";
    }

    return (__bridge NSString*)mimeType;
}