Limit the number of devices we delete at once (#14649)

tests/handlers/test_device.py

@@ -20,6 +20,8 @@ from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.errors import NotFoundError, SynapseError
 from synapse.handlers.device import MAX_DEVICE_DISPLAY_NAME_LEN, DeviceHandler
+from synapse.rest import admin
+from synapse.rest.client import account, login
 from synapse.server import HomeServer
 from synapse.util import Clock
 
@@ -30,6 +32,12 @@ user2 = "@theresa:bbb"
 
 
 class DeviceTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        login.register_servlets,
+        admin.register_servlets,
+        account.register_servlets,
+    ]
+
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         hs = self.setup_test_homeserver("server", federation_http_client=None)
         handler = hs.get_device_handler()
@@ -229,6 +237,29 @@ class DeviceTestCase(unittest.HomeserverTestCase):
             NotFoundError,
         )
 
+    def test_login_delete_old_devices(self) -> None:
+        """Delete old devices if the user already has too many."""
+
+        user_id = self.register_user("user", "pass")
+
+        # Create a bunch of devices
+        for _ in range(50):
+            self.login("user", "pass")
+            self.reactor.advance(1)
+
+        # Advance the clock for ages (as we only delete old devices)
+        self.reactor.advance(60 * 60 * 24 * 300)
+
+        # Log in again to start the pruning
+        self.login("user", "pass")
+
+        # Give the background job time to do its thing
+        self.reactor.pump([1.0] * 100)
+
+        # We should now only have the most recent device.
+        devices = self.get_success(self.handler.get_devices_by_user(user_id))
+        self.assertEqual(len(devices), 1)
+
     def _record_users(self) -> None:
         # check this works for both devices which have a recorded client_ip,
         # and those which don't.