fix cache: the cache each time was replacing the original metadata ev…

…en if the metadata request was just for a subset of topics, this pr tries to address this by updating only partially the metadata object

karapace/kafka_rest_apis/__init__.py

@@ -429,7 +429,9 @@ def __init__(
         self.serializer = serializer
         self._cluster_metadata = None
         self._cluster_metadata_complete = False
-        self._metadata_birth = None
+        # birth of all the metadata (when the request was requiring all the metadata available in the cluster)
+        self._global_metadata_birth = None
+        self._cluster_metadata_topic_birth: dict[str, float] = {}
         self.metadata_max_age = self.config["admin_metadata_max_age"]
         self.admin_client = None
         self.admin_lock = asyncio.Lock()
@@ -607,28 +609,55 @@ async def get_topic_config(self, topic: str) -> dict:
         async with self.admin_lock:
             return self.admin_client.get_topic_config(topic)
 
-    async def cluster_metadata(self, topics: Optional[List[str]] = None) -> dict:
-        async with self.admin_lock:
-            if self._metadata_birth is None or time.monotonic() - self._metadata_birth > self.metadata_max_age:
-                self._cluster_metadata = None
 
-            if self._cluster_metadata:
-                # Return from metadata only if all queried topics have cached metadata
-                if topics is None:
-                    if self._cluster_metadata_complete:
-                        return self._cluster_metadata
-                elif all(topic in self._cluster_metadata["topics"] for topic in topics):
-                    return {
-                        **self._cluster_metadata,
-                        "topics": {topic: self._cluster_metadata["topics"][topic] for topic in topics},
-                    }
+    def is_global_metadata_old(self) -> bool:
+        return self._global_metadata_birth is None or (time.monotonic() - self._global_metadata_birth) > self.metadata_max_age
+
+    def is_metadata_of_topics_old(self, topics: list[str]) -> bool:
+        # Return from metadata only if all queried topics have cached metadata
+        are_all_topic_queried_at_least_once = all(topic in self._cluster_metadata_topic_birth for topic in topics)
+        oldest_requested_topic_udpate_timestamp = min(self._cluster_metadata_topic_birth[topic] for topic in topics)
+        return are_all_topic_queried_at_least_once and (time.monotonic() - oldest_requested_topic_udpate_timestamp) > self.metadata_max_age
+
+    async def _update_all_metadata(self) -> dict:
+        if not self.is_global_metadata_old() and self._cluster_metadata_complete:
+            return self._cluster_metadata
+
+        metadata_birth = time.monotonic()
+        metadata = self.admin_client.cluster_metadata(None)
+        for topic in metadata["topics"]:
+            self._cluster_metadata_topic_birth[topic] = metadata_birth
+
+        self._global_metadata_birth = metadata_birth
+        self._cluster_metadata = metadata
+        self._cluster_metadata_complete = True
+
+    async def _update_metadata_for_topics(self, topics: list[str]) -> dict:
+        if self.is_metadata_of_topics_old(topics):
+            return {
+                **self._cluster_metadata,
+                "topics": {topic: self._cluster_metadata["topics"][topic] for topic in topics},
+            }
 
+        metadata_birth = time.monotonic()
+        metadata = self.admin_client.cluster_metadata(topics)
+        for topic in metadata["topics"]:
+            self._cluster_metadata_topic_birth[topic] = metadata_birth
+
+        for topic in metadata["topics"]:
+            self._cluster_metadata[topic] = metadata["topics"][topic]
+
+        self._cluster_metadata = metadata
+        self._cluster_metadata_complete = False
+
+
+    async def cluster_metadata(self, topics: Optional[List[str]] = None) -> dict:
+        async with self.admin_lock:
             try:
-                metadata_birth = time.monotonic()
-                metadata = self.admin_client.cluster_metadata(topics)
-                self._metadata_birth = metadata_birth
-                self._cluster_metadata = metadata
-                self._cluster_metadata_complete = topics is None
+                if topics is None:
+                    metadata = await self._update_all_metadata()
+                else:
+                    metadata = await self._update_metadata_for_topics(topics)
             except KafkaException:
                 log.warning("Could not refresh cluster metadata")
                 KafkaRest.r(