let
  common = import ./common.nix;
in
rec {
  getTrustedServers = serviceData:
    let
      matrix =
        if serviceData ? matrix then
          common.ensureAttrset "config/services.nix matrix" serviceData.matrix
        else
          throw "config/services.nix must define matrix attrset.";

      trustedServers =
        if matrix ? trusted_servers then
          common.ensureList "config/services.nix matrix.trusted_servers" matrix.trusted_servers
        else
          throw "config/services.nix matrix.trusted_servers must exist.";
    in
      trustedServers;
}