code: func (d *ClientDigestsFile) ClientRef(plat string) (ref *api.ObjectRef) {
  	for _, e := range d.entries {
  		if e.plat == plat && (ref == nil || e.ref.HashAlgo > ref.HashAlgo) {
  			ref = e.ref
  		}
  	}
  	return
  }
docs: // ClientRef returns an expected client ObjectRef for the given platform.
  //
  // Returns the best hash (higher algo number) or nil if there are no digests
  // for this platform at all.