On this page:
bytes+ false?
ensure-bytes

2 Bytes utilities

 (require (planet untyped/unlib/bytes))
Useful bytes utilities.

(bytes+false? item)  boolean?
  item : any
Returns #t if item is a bytes and #f otherwise.

(ensure-bytes item)  any
  item : any
Converts string arguments to bytes: passes all other arguments straight through.