nixos/syncthing: support syncthing gui and api over unix sockets (#247343)

  settingsFormat = pkgs.formats.json { };

  cleanedConfig = converge (filterAttrsRecursive (_: v: v != null && v != {})) cfg.settings;

  isUnixGui = (builtins.substring 0 1 cfg.guiAddress) == "/";

  # Syncthing supports serving the GUI over Unix sockets. If that happens, the

  # API is served over the Unix socket as well.  This function returns the correct

  # curl arguments for the address portion of the curl command for both network

  # and Unix socket addresses.

  curlAddressArgs = path: if isUnixGui

    # if cfg.guiAddress is a unix socket, tell curl explicitly about it

    # note that the dot in front of `${path}` is the hostname, which is

    # required.

    then "--unix-socket ${cfg.guiAddress} http://.${path}"

    # no adjustements are needed if cfg.guiAddress is a network address

    else "${cfg.guiAddress}${path}"

    ;

  devices = mapAttrsToList (_: device: device // {

    deviceID = device.id;

  }) cfg.settings.devices;

      GET_IdAttrName = "deviceID";

      override = cfg.overrideDevices;

      conf = devices;

      baseAddress = "${cfg.guiAddress}/rest/config/devices";

      baseAddress = curlAddressArgs "/rest/config/devices";

    };

    dirs = {

      new_conf_IDs = map (v: v.id) folders;

      GET_IdAttrName = "id";

      override = cfg.overrideFolders;

      conf = folders;

      baseAddress = "${cfg.guiAddress}/rest/config/folders";

      baseAddress = curlAddressArgs "/rest/config/folders";

    };

  } [

    # Now for each of these attributes, write the curl commands that are

    builtins.attrNames

    (lib.subtractLists ["folders" "devices"])

    (map (subOption: ''

      curl -X PUT -d ${lib.escapeShellArg (builtins.toJSON cleanedConfig.${subOption})} \

        ${cfg.guiAddress}/rest/config/${subOption}

      curl -X PUT -d ${lib.escapeShellArg (builtins.toJSON cleanedConfig.${subOption})} ${curlAddressArgs "/rest/config/${subOption}"}

    ''))

    (lib.concatStringsSep "\n")

  ]) + ''

    # restart Syncthing if required

    if curl ${cfg.guiAddress}/rest/config/restart-required |

    if curl ${curlAddressArgs "/rest/config/restart-required"} |

       ${jq} -e .requiresRestart > /dev/null; then

        curl -X POST ${cfg.guiAddress}/rest/system/restart

        curl -X POST ${curlAddressArgs "/rest/system/restart"}

    fi

  '');

in {

          ExecStart = ''

            ${cfg.package}/bin/syncthing \

              -no-browser \

              -gui-address=${cfg.guiAddress} \

              -gui-address=${if isUnixGui then "unix://" else ""}${cfg.guiAddress} \

              -home=${cfg.configDir} ${escapeShellArgs cfg.extraFlags}

          '';

          MemoryDenyWriteExecute = true;