code: func GetACLs(m *api.PrefixMetadata) map[api.Role]stringset.Set {
  	out := map[api.Role]stringset.Set{}
  	for _, acl := range m.Acls {
  		if len(acl.Principals) == 0 {
  			continue
  		}
  		set := out[acl.Role]
  		if set == nil {
  			set = stringset.New(len(acl.Principals))
  			out[acl.Role] = set
  		}
  		for _, p := range acl.Principals {
  			set.Add(p)
  		}
  	}
  	return out
  }
docs: // GetACLs returns ACLs in the metadata as a map: role -> set of principals.