Send a binary file as content in http:response, I need help

I tested it using the class external file, but my file is a wbxml type, so in order to retrieve the content I'm using the next command

 

 

set ::xbxml_content [lindex $::answer_403 0]

 

 

but the length is zero , This is because it is a binary file (the options that I have on the class menu for file content type are string,integer,ip) so I choosed string, is it possible to hardcoded the binary content to a plain text? basically the file contains several binary characters like: NUL, SOH,ETX

 

 

Thanks