Fix device list update stream ids going backward (#7158)

Occasionally we could get a federation device list update transaction which
looked like:

```
[
    {'edu_type': 'm.device_list_update', 'content': {'user_id': '@user:test', 'device_id': 'D2', 'prev_id': [], 'stream_id': 12, 'deleted': True}},
    {'edu_type': 'm.device_list_update', 'content': {'user_id': '@user:test', 'device_id': 'D1', 'prev_id': [12], 'stream_id': 11, 'deleted': True}},
    {'edu_type': 'm.device_list_update', 'content': {'user_id': '@user:test', 'device_id': 'D3', 'prev_id': [11], 'stream_id': 13, 'deleted': True}}
]
```

Having `stream_ids` which are lower than `prev_ids` looks odd. It might work
(I'm not actually sure), but in any case it doesn't seem like a reasonable
thing to expect other implementations to support.

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index a5fe5c6880..33105576af 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -297,6 +297,7 @@ class FederationSenderDevicesTestCases(HomeserverTestCase):
             c = edu["content"]
             if stream_id is not None:
                 self.assertEqual(c["prev_id"], [stream_id])
+                self.assertGreaterEqual(c["stream_id"], stream_id)
             stream_id = c["stream_id"]
         devices = {edu["content"]["device_id"] for edu in self.edus}
         self.assertEqual({"D1", "D2"}, devices)
@@ -330,6 +331,7 @@ class FederationSenderDevicesTestCases(HomeserverTestCase):
                 c.items(),
                 {"user_id": u1, "prev_id": [stream_id], "deleted": True}.items(),
             )
+            self.assertGreaterEqual(c["stream_id"], stream_id)
             stream_id = c["stream_id"]
         devices = {edu["content"]["device_id"] for edu in self.edus}
         self.assertEqual({"D1", "D2", "D3"}, devices)
@@ -366,6 +368,8 @@ class FederationSenderDevicesTestCases(HomeserverTestCase):
             self.assertEqual(edu["edu_type"], "m.device_list_update")
             c = edu["content"]
             self.assertEqual(c["prev_id"], [stream_id] if stream_id is not None else [])
+            if stream_id is not None:
+                self.assertGreaterEqual(c["stream_id"], stream_id)
             stream_id = c["stream_id"]
         devices = {edu["content"]["device_id"] for edu in self.edus}
         self.assertEqual({"D1", "D2", "D3"}, devices)
@@ -482,6 +486,8 @@ class FederationSenderDevicesTestCases(HomeserverTestCase):
         }
 
         self.assertLessEqual(expected.items(), content.items())
+        if prev_stream_id is not None:
+            self.assertGreaterEqual(content["stream_id"], prev_stream_id)
         return content["stream_id"]
 
     def check_signing_key_update_txn(self, txn: JsonDict,) -> None: