xlate/openconfig: add cache datastore option

This change adds a runtime option for the OpenConfig translator to
use a cache datastore. It may improve the response speed to retrieve
operational states of OpenConfig models. However, it also introduces
differences between the operational states and actual states of the
device as a side effect.

src/xlate/openconfig/README.md

@@ -47,7 +47,7 @@ sudo pip3 install .
 
 ```sh
 $ gsxlated-openconfig -h
-usage: gsxlated-openconfig [-h] [-v] operational-modes-file
+usage: gsxlated-openconfig [-h] [-v] [-c {none,in-memory}] operational-modes-file
 
 positional arguments:
   operational-modes-file
@@ -56,10 +56,12 @@ positional arguments:
 options:
   -h, --help            show this help message and exit
   -v, --verbose         enable detailed output
+  -c {none,in-memory}, --cache-datastore {none,in-memory}
+                        select cache datastore
 ```
 
 Example:
 
 ```sh
-gsxlated-openconfig operational-modes.json
+gsxlated-openconfig -c none operational-modes.json
 ```

src/xlate/openconfig/goldstone/xlate/openconfig/cache.py

@@ -0,0 +1,67 @@
+"""Cache datastore for OpenConfig translators."""
+
+
+from abc import abstractmethod
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class CacheDataNotExistError(Exception):
+    pass
+
+
+class Cache:
+    """Base for cache datastore.
+
+    It is an abstract class. You should implement a subclass for each datastore type.
+    """
+
+    @abstractmethod
+    def get(self, module):
+        """Get operational state data of a module from the cache datastore.
+
+        Args:
+            module (str): Module name.
+
+        Returns:
+            dict: Operational state data of a module.
+
+        Raises:
+            CacheDataNotExistError: Data for the module does not exist in the cache datastore.
+        """
+        pass
+
+    @abstractmethod
+    def set(self, module, data):
+        """Set operational state data of an OpenConfig model to the cache datastore.
+
+        Args:
+            module (str): Module name.
+            data (dict): Operational state data of a model.
+        """
+        pass
+
+
+class InMemoryCache(Cache):
+    """In-memory cache datastore.
+
+    Attribute:
+        _data (dict): Operational state data for modules. A key is a module name.
+    """
+
+    def __init__(self):
+        self._data = {}
+
+    def get(self, module):
+        try:
+            return self._data[module]
+        except KeyError as e:
+            logger.error("%s is not cached.", module)
+            raise CacheDataNotExistError(
+                f"Cache data for {module} does not exist in the cache datastore"
+            ) from e
+
+    def set(self, module, data):
+        self._data[module] = data

src/xlate/openconfig/goldstone/xlate/openconfig/cache_updater.py

@@ -0,0 +1,88 @@
+"""Cache data updater for OpenConfig translators."""
+
+import asyncio
+import logging
+from .interfaces import InterfacesObjectTree
+from .platform import PlatformObjectTree
+from .terminal_device import TerminalDeviceObjectTree
+from goldstone.lib.errors import Error as ConnectorError
+from goldstone.lib.connector.sysrepo import Connector
+
+
+logger = logging.getLogger(__name__)
+
+
+DEFAULT_UPDATE_INTERVAL = 5
+
+
+class CacheUpdater:
+    """Cache data updater for OpenConfig translators.
+
+    Args:
+        cache (Cache): Cache datastore instance to use.
+        operational_modes (dict): Supported operational-modes.
+        update_interval (int): Interval seconds between executions of the update task.
+    """
+
+    def __init__(
+        self, cache, operational_modes, update_interval=DEFAULT_UPDATE_INTERVAL
+    ):
+        self._cache = cache
+        self._operational_modes = operational_modes
+        self._update_interval = update_interval
+        self._connector = Connector()
+        self._required_data = []
+        self._object_trees = {
+            "openconfig-interfaces": InterfacesObjectTree(),
+            "openconfig-platform": PlatformObjectTree(self._operational_modes),
+            "openconfig-terminal-device": TerminalDeviceObjectTree(
+                self._operational_modes
+            ),
+        }
+        for _, object_tree in self._object_trees.items():
+            for data in object_tree.required_data():
+                if not data in self._required_data:
+                    self._required_data.append(data)
+
+    def _get_gs(self):
+        """Get operational state data of Goldstone primitive models from the central datastore.
+
+        Returns:
+            dict: Operational state data of Goldstone primitive models.
+        """
+        gs = {}
+        for d in self._required_data:
+            try:
+                gs[d["name"]] = self._connector.get_operational(
+                    d["xpath"], d["default"]
+                )
+            except ConnectorError as e:
+                logger.error("Failed to get source data from %s. %s", d["name"], e)
+        return gs
+
+    async def _update(self):
+        """Update cache datastore."""
+        gs = self._get_gs()
+        for module, object_tree in self._object_trees.items():
+            try:
+                self._cache.set(module, object_tree.create(gs))
+            except Exception as e:
+                logger.error("Failed to update cache data for %s. %s", module, e)
+
+    async def _update_loop(self):
+        """Update task coroutine."""
+        while True:
+            await asyncio.sleep(self._update_interval)
+            await self._update()
+
+    async def start(self):
+        """Start a service.
+
+        Returns:
+            list: List of coroutine objects.
+        """
+        return [self._update_loop()]
+
+    async def stop(self):
+        """Stop a service."""
+        pass

src/xlate/openconfig/goldstone/xlate/openconfig/interfaces.py

@@ -15,6 +15,7 @@
 from .lib import (
     OpenConfigChangeHandler,
     OpenConfigObjectFactory,
+    OpenConfigObjectTree,
     OpenConfigServer,
 )
 from .platform import ComponentNameResolver
@@ -471,11 +472,24 @@ def create(self, gs):
         return result
 
 
+class InterfacesObjectTree(OpenConfigObjectTree):
+    """OpenConfigObjectTree for the openconfig-interfaces module.
+
+    It creates an operational state tree of the openconfig-interfaces module.
+    """
+
+    def __init__(self):
+        super().__init__()
+        self.objects = {
+            "interfaces": {"interface": InterfaceFactory(ComponentNameResolver())}
+        }
+
+
 class InterfaceServer(OpenConfigServer):
     """InterfaceServer provides a service for the openconfig-interfaces module to central datastore."""
 
-    def __init__(self, conn, reconciliation_interval=10):
-        super().__init__(conn, "openconfig-interfaces", reconciliation_interval)
+    def __init__(self, conn, cache, reconciliation_interval=10):
+        super().__init__(conn, "openconfig-interfaces", cache, reconciliation_interval)
         self.handlers = {
             "interfaces": {
                 "interface": {
@@ -498,9 +512,7 @@ def __init__(self, conn, reconciliation_interval=10):
                 }
             }
         }
-        self.objects = {
-            "interfaces": {"interface": InterfaceFactory(ComponentNameResolver())}
-        }
+        self._object_tree = InterfacesObjectTree()
 
     async def reconcile(self):
         # NOTE: This should be implemented as a separated class of function to remove the dependency from the