code: func (d *ClientDigestsFile) Contains(plat string, ref *api.ObjectRef) bool {
  	for _, e := range d.entries {
  		if e.plat == plat && proto.Equal(ref, e.ref) {
  			return true
  		}
  	}
  	return false
  }
docs: // Contains returns true if the given ref is among refs for the given platform.
  //
  // Compares 'ref' to all hashes corresponding to 'plat', not only the best one.