Reload metadata in-place

Metadata reloading was previously implemented by loading the metadata,
then replacing references to the old metadata with the new metadata. A
bug in the implementation caused the previous version of the metadata to
be indirectly referenced by the new version of the metadata, resulting
in a steady climb in memory usage.

In fixing the memory leak, I have also changed how metadata is reloaded
to avoid having to replace all existing references, which is prone to
errors and could cause confusing behaviour.

Author: James-REANNZ

src/saml2/entity.py

@@ -218,19 +218,11 @@ def reload_metadata(self, metadata_conf):
         """
         logger.debug("Loading new metadata")
         try:
-            new_metadata = self.config.load_metadata(metadata_conf)
+            self.metadata.reload(metadata_conf)
         except Exception as ex:
             logger.error("Loading metadata failed", exc_info=ex)
             return False
 
-        logger.debug("Applying new metadata to main config")
-        ( self.metadata, self.sec.metadata, self.config.metadata ) = [new_metadata]*3
-        policy = getattr(self.config, "_%s_policy" % self.entity_type, None)
-        if policy and policy.metadata_store:
-            logger.debug("Applying new metadata to %s policy", self.entity_type)
-            policy.metadata_store = self.metadata
-
-        logger.debug("Applying new metadata source_id")
         self.sourceid = self.metadata.construct_source_id()
 
         return True

src/saml2/mdstore.py

@@ -1110,6 +1110,15 @@ def load(self, *args, **kwargs):
         _md.load()
         self.metadata[key] = _md
 
+    def reload(self, spec):
+        old_metadata = self.metadata
+        self.metadata = {}
+        try:
+            self.imp(spec)
+        except Exception as e:
+            self.metadata = old_metadata
+            raise e
+
     def imp(self, spec):
         # This serves as a backwards compatibility
         if type(spec) is dict: