fix misshandling mau reaping where reserved users are present

synapse/storage/monthly_active_users.py

@@ -97,6 +97,7 @@ class MonthlyActiveUsersStore(SQLBaseStore):
 
             txn.execute(sql, query_args)
 
+            max_mau_value = self.hs.config.max_mau_value
             if self.hs.config.limit_usage_by_mau:
                 # If MAU user count still exceeds the MAU threshold, then delete on
                 # a least recently active basis.
@@ -106,29 +107,44 @@ class MonthlyActiveUsersStore(SQLBaseStore):
                 # While Postgres does not require 'LIMIT', but also does not support
                 # negative LIMIT values. So there is no way to write it that both can
                 # support
-                safe_guard = self.hs.config.max_mau_value - len(self.reserved_users)
-                # Must be greater than zero for postgres
-                safe_guard = safe_guard if safe_guard > 0 else 0
-                query_args = [safe_guard]
-
-                base_sql = """
-                    DELETE FROM monthly_active_users
-                    WHERE user_id NOT IN (
-                        SELECT user_id FROM monthly_active_users
-                        ORDER BY timestamp DESC
-                        LIMIT ?
+                if len(self.reserved_users) == 0:
+                    sql = """
+                        DELETE FROM monthly_active_users
+                        WHERE user_id NOT IN (
+                            SELECT user_id FROM monthly_active_users
+                            ORDER BY timestamp DESC
+                            LIMIT ?
                         )
-                    """
+                        """
+                    txn.execute(sql, (max_mau_value,))
                 # Need if/else since 'AND user_id NOT IN ({})' fails on Postgres
                 # when len(reserved_users) == 0. Works fine on sqlite.
-                if len(self.reserved_users) > 0:
-                    query_args.extend(self.reserved_users)
-                    sql = base_sql + """ AND user_id NOT IN ({})""".format(
+                else:
+                    safe_guard = max_mau_value - len(self.reserved_users)
+                    # Must be greater than zero for postgres
+                    safe_guard = safe_guard if safe_guard > 0 else 0
+                    # It is important to filter reserved users twice to guard
+                    # against the case where the reserved user is present in the
+                    # SELECT, meaning that a legitmate mau is deleted.
+                    sql = """
+                        DELETE FROM monthly_active_users
+                        WHERE user_id NOT IN (
+                            SELECT user_id FROM monthly_active_users
+                            WHERE user_id NOT IN ({})""".format(
+                        ",".join(questionmarks)
+                    ) + """
+                            ORDER BY timestamp DESC
+                            LIMIT ?
+                        )
+                        AND user_id NOT IN ({})""".format(
                         ",".join(questionmarks)
                     )
-                else:
-                    sql = base_sql
-                txn.execute(sql, query_args)
+                    query_args = []
+                    query_args.extend(self.reserved_users)
+                    query_args.append(safe_guard)
+                    query_args.extend(self.reserved_users)
+
+                    txn.execute(sql, query_args)
 
         yield self.runInteraction("reap_monthly_active_users", _reap_users)
         # It seems poor to invalidate the whole cache, Postgres supports
@@ -167,12 +183,18 @@ class MonthlyActiveUsersStore(SQLBaseStore):
             Defered[int]: Number of real reserved users
         """
         count = 0
+        users = ()
         for tp in self.hs.config.mau_limits_reserved_threepids:
             user_id = yield self.hs.get_datastore().get_user_id_by_threepid(
                 tp["medium"], tp["address"]
             )
             if user_id:
                 count = count + 1
+                users = users + (user_id,)
+
+        # Update reserved_users to ensure it stays in sync, this is important
+        # for reaping.
+        self.reserved_users = users
         return count
 
     @defer.inlineCallbacks

tests/storage/test_monthly_active_users.py

@@ -158,6 +158,54 @@ class MonthlyActiveUsersTestCase(unittest.HomeserverTestCase):
         count = self.store.get_monthly_active_count()
         self.assertEquals(self.get_success(count), 0)
 
+    def test_reap_monthly_active_users_reserved_users(self):
+        """ Tests that reaping correctly handles reaping where reserved users are
+        present"""
+
+        self.hs.config.max_mau_value = 5
+        initial_users = 5
+        reserved_user_number = initial_users - 1
+        threepids = []
+        for i in range(initial_users):
+            user = "@user%d:server" % i
+            email = "user%d@example.com" % i
+            self.store.upsert_monthly_active_user(user)
+            threepids.append({"medium": "email", "address": email},)
+            # Need to ensure that the most recent entries in the
+            # monthly_active_users table are reserved
+            now = int(self.hs.get_clock().time_msec())
+            if i != 0:
+                self.store.register_user(user_id=user, password_hash=None)
+                self.pump()
+                self.store.user_add_threepid(user, "email", email, now, now)
+
+        self.hs.config.mau_limits_reserved_threepids = threepids
+        self.store.runInteraction(
+            "initialise", self.store._initialise_reserved_users, threepids
+        )
+        self.pump()
+        count = self.store.get_monthly_active_count()
+        self.assertTrue(self.get_success(count), initial_users)
+
+        count = self.store.get_registered_reserved_users_count()
+        self.assertEquals(self.get_success(count), reserved_user_number)
+
+        self.store.reap_monthly_active_users()
+        self.pump()
+        count = self.store.get_monthly_active_count()
+        self.assertEquals(
+            self.get_success(count), self.hs.config.max_mau_value
+        )
+
+    def _populate_reserved_users(self, user, email):
+        """Helper function that registers userpopulates reserved users"""
+        # Test reserved registed users
+        self.store.register_user(user_id=user, password_hash=None)
+        self.pump()
+
+        now = int(self.hs.get_clock().time_msec())
+        self.store.user_add_threepid(user, "email", email, now, now)
+
     def test_populate_monthly_users_is_guest(self):
         # Test that guest users are not added to mau list
         user_id = "@user_id:host"
@@ -198,6 +246,7 @@ class MonthlyActiveUsersTestCase(unittest.HomeserverTestCase):
 
         user1 = "@user1:example.com"
         user2 = "@user2:example.com"
+
         user1_email = "user1@example.com"
         user2_email = "user2@example.com"
         threepids = [