Fix `failures` property in `/keys/query` (#17499)

Fixes: https://github.com/element-hq/synapse/issues/17498
Fixes: https://github.com/element-hq/element-web/issues/27867

1 files changed, 56 insertions, 3 deletions

diff --git a/tests/handlers/test_e2e_keys.py b/tests/handlers/test_e2e_keys.py
index 0e6352ff4b..8a3dfdcf75 100644
--- a/tests/handlers/test_e2e_keys.py
+++ b/tests/handlers/test_e2e_keys.py
@@ -43,9 +43,7 @@ from tests.unittest import override_config
 class E2eKeysHandlerTestCase(unittest.HomeserverTestCase):
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.appservice_api = mock.AsyncMock()
-        return self.setup_test_homeserver(
-            federation_client=mock.Mock(), application_service_api=self.appservice_api
-        )
+        return self.setup_test_homeserver(application_service_api=self.appservice_api)
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.handler = hs.get_e2e_keys_handler()
@@ -1224,6 +1222,61 @@ class E2eKeysHandlerTestCase(unittest.HomeserverTestCase):
             },
         )
 
+    def test_query_devices_remote_down(self) -> None:
+        """Tests that querying keys for a remote user on an unreachable server returns
+        results in the "failures" property
+        """
+
+        remote_user_id = "@test:other"
+        local_user_id = "@test:test"
+
+        # The backoff code treats time zero as special
+        self.reactor.advance(5)
+
+        self.hs.get_federation_http_client().agent.request = mock.AsyncMock(  # type: ignore[method-assign]
+            side_effect=Exception("boop")
+        )
+
+        e2e_handler = self.hs.get_e2e_keys_handler()
+
+        query_result = self.get_success(
+            e2e_handler.query_devices(
+                {
+                    "device_keys": {remote_user_id: []},
+                },
+                timeout=10,
+                from_user_id=local_user_id,
+                from_device_id="some_device_id",
+            )
+        )
+
+        self.assertEqual(
+            query_result["failures"],
+            {
+                "other": {
+                    "message": "Failed to send request: Exception: boop",
+                    "status": 503,
+                }
+            },
+        )
+
+        # Do it again: we should hit the backoff
+        query_result = self.get_success(
+            e2e_handler.query_devices(
+                {
+                    "device_keys": {remote_user_id: []},
+                },
+                timeout=10,
+                from_user_id=local_user_id,
+                from_device_id="some_device_id",
+            )
+        )
+
+        self.assertEqual(
+            query_result["failures"],
+            {"other": {"message": "Not ready for retry", "status": 503}},
+        )
+
     @parameterized.expand(
         [
             # The remote homeserver's response indicates that this user has 0/1/2 devices.