code: func (f *Function) ZipBytes() ([]byte, error) {
  	if f.Zip == "" {
  		f.Log.Debug("building zip")
  		return f.BuildBytes()
  	}
  
  	f.Log.Debugf("reading zip %q", f.Zip)
  	return ioutil.ReadFile(f.Zip)
  }
docs: // ZipBytes builds the in-memory zip, or reads
  // the .Zip from disk if specified.