how to make Swift app download a binary file through app's dropbox api from my dropbox account to some type of Swift var.?

Question

Presently, it downloads text files okay, with this...

    client!.files.download(  path: access_pathname )    /////////////////////////////    R E S U L T   C A L L     B A C K
    .response 
    { 
        response, error in                                          
            if let response = response 
            {                               
                        let responseMetadata = response.0
                        let fileContents = response.1               // TEXT CONTENTS

But now I need to know how to download a binary file from dropbox to a Swift var