fix: Do not integrate an invalid relation (#509)

lib/charms/mongodb/v1/mongodb_provider.py

@@ -16,7 +16,13 @@
 from charms.data_platform_libs.v0.data_interfaces import DatabaseProvides
 from charms.mongodb.v0.mongo import MongoConfiguration, MongoConnection
 from charms.mongodb.v1.helpers import generate_password
-from ops.charm import CharmBase, EventBase, RelationBrokenEvent, RelationChangedEvent
+from ops.charm import (
+    CharmBase,
+    EventBase,
+    RelationBrokenEvent,
+    RelationChangedEvent,
+    RelationEvent,
+)
 from ops.framework import Object
 from ops.model import Relation
 from pymongo.errors import PyMongoError
@@ -31,7 +37,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 14
+LIBPATCH = 15
 
 logger = logging.getLogger(__name__)
 REL_NAME = "database"
@@ -88,6 +94,11 @@ def pass_sanity_hook_checks(self) -> bool:
         if not self.charm.db_initialised:
             return False
 
+        # Warning: the sanity_hook_checks can pass when the call is
+        # issued by a config-sever because the config-server is allowed to manage the users
+        # in MongoDB. This is not well named and does not protect integration of a config-server
+        # to a client application. The mongos charm however doesn't care
+        # because it supports only one integration that uses MongoDBProvider.
         if not self.charm.is_role(Config.Role.MONGOS) and not self.charm.is_relation_feasible(
             self.get_relation_name()
         ):
@@ -99,8 +110,14 @@ def pass_sanity_hook_checks(self) -> bool:
 
         return True
 
-    def pass_hook_checks(self, event: EventBase) -> bool:
+    def pass_hook_checks(self, event: RelationEvent) -> bool:
         """Runs the pre-hooks checks for MongoDBProvider, returns True if all pass."""
+        # First, ensure that the relation is valid, useless to do anything else otherwise
+        if not self.charm.is_role(Config.Role.MONGOS) and not self.charm.is_relation_feasible(
+            event.relation.name
+        ):
+            return False
+
         if not self.pass_sanity_hook_checks():
             return False
 

tests/unit/test_mongodb_provider.py

@@ -6,6 +6,7 @@
 from unittest import mock
 from unittest.mock import patch
 
+from ops import BlockedStatus
 from ops.charm import RelationEvent
 from ops.testing import Harness
 from parameterized import parameterized
@@ -36,9 +37,32 @@ def setUp(self, *unused):
         self.charm = self.harness.charm
         self.addCleanup(self.harness.cleanup)
 
+    @parameterized.expand([["config-server"], ["shard"]])
+    @patch("charms.mongodb.v0.set_status.get_charm_revision")
+    @patch("charm.MongoDBProvider.oversee_users")
+    def test_relation_event_relation_not_feasible(self, role: str, oversee_users, *unused):
+        """Tests that relating with a wrong role sets a blocked status."""
+
+        def is_config_server_role(role_name: str):
+            return role_name == role
+
+        self.harness.charm.is_role = is_config_server_role
+
+        relation_id = self.harness.add_relation("database", "consumer")
+        self.harness.add_relation_unit(relation_id, "consumer/0")
+        self.harness.update_relation_data(relation_id, "consumer/0", PEER_ADDR)
+
+        assert self.harness.charm.unit.status == BlockedStatus(
+            "Sharding roles do not support database interface."
+        )
+        oversee_users.assert_not_called()
+
+    @patch("charms.mongodb.v0.set_status.get_charm_revision")
+    @patch("charm.CrossAppVersionChecker.is_local_charm")
+    @patch("charm.CrossAppVersionChecker.is_integrated_to_locally_built_charm")
     @patch("ops.framework.EventBase.defer")
     @patch("charm.MongoDBProvider.oversee_users")
-    def test_relation_event_db_not_initialised(self, oversee_users, defer):
+    def test_relation_event_db_not_initialised(self, oversee_users, defer, *unused):
         """Tests no database relations are handled until the database is initialised.
 
         Users should not be "overseen" until the database has been initialised, no matter the