component pubsub: implement default configuration:

rel 476

libervia/backend/plugins/plugin_comp_pubsub/__init__.py

@@ -564,7 +564,34 @@ class PubsubResource(pubsub.PubSubResource):
         return defer.ensureDeferred(self._default(request))
 
     async def _default(self, request: pubsub.PubSubRequest) -> dict[str, object]:
-        raise pubsub.Unsupported("retrieve-default")
+        """Return default node configuration.
+
+        @param request: Default configuration request.
+        @return: Default configuration values.
+        """
+        node_type = request.nodeType or "leaf"
+
+        if node_type != "leaf":
+            raise error.StanzaError(
+                "not-acceptable", text=f"Unknown node type: {node_type!r}"
+            )
+
+        # we build from PubsubNodeConfig defaults
+        config = PubsubNodeConfig()
+
+        default_config: dict[str, object] = {}
+
+        for field_name, value in config.__dict__.items():
+            try:
+                pubsub_var = PubsubNodeConfig._field_var_mapping[field_name]
+            except KeyError:
+                log.error(f"Missing field mapping for {field_name!r}, ignoring.")
+                continue
+
+            if value is not None:
+                default_config[pubsub_var] = str(value)
+
+        return default_config
 
     def configureGet(self, request: pubsub.PubSubRequest) -> defer.Deferred[dict]:
         return defer.ensureDeferred(self._configureGet(request))