Leave out optional keys from /sync (#9919)

This leaves out all optional keys from /sync. This should be fine for all clients tested against conduit already, but it may break some clients, as such we should check, that at least most of them don't break horribly and maybe back out some of the individual changes. (We can probably always leave out groups for example, while the others may cause more issues.)

Signed-off-by: Nicolas Werner <nicolas.werner@hotmail.de>

1 files changed, 44 insertions, 18 deletions

diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 95ee3f1b84..5f85653330 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -14,6 +14,7 @@
 
 import itertools
 import logging
+from collections import defaultdict
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.constants import PresenceState
@@ -229,24 +230,49 @@ class SyncRestServlet(RestServlet):
         )
 
         logger.debug("building sync response dict")
-        return {
-            "account_data": {"events": sync_result.account_data},
-            "to_device": {"events": sync_result.to_device},
-            "device_lists": {
-                "changed": list(sync_result.device_lists.changed),
-                "left": list(sync_result.device_lists.left),
-            },
-            "presence": SyncRestServlet.encode_presence(sync_result.presence, time_now),
-            "rooms": {"join": joined, "invite": invited, "leave": archived},
-            "groups": {
-                "join": sync_result.groups.join,
-                "invite": sync_result.groups.invite,
-                "leave": sync_result.groups.leave,
-            },
-            "device_one_time_keys_count": sync_result.device_one_time_keys_count,
-            "org.matrix.msc2732.device_unused_fallback_key_types": sync_result.device_unused_fallback_key_types,
-            "next_batch": await sync_result.next_batch.to_string(self.store),
-        }
+
+        response: dict = defaultdict(dict)
+        response["next_batch"] = await sync_result.next_batch.to_string(self.store)
+
+        if sync_result.account_data:
+            response["account_data"] = {"events": sync_result.account_data}
+        if sync_result.presence:
+            response["presence"] = SyncRestServlet.encode_presence(
+                sync_result.presence, time_now
+            )
+
+        if sync_result.to_device:
+            response["to_device"] = {"events": sync_result.to_device}
+
+        if sync_result.device_lists.changed:
+            response["device_lists"]["changed"] = list(sync_result.device_lists.changed)
+        if sync_result.device_lists.left:
+            response["device_lists"]["left"] = list(sync_result.device_lists.left)
+
+        if sync_result.device_one_time_keys_count:
+            response[
+                "device_one_time_keys_count"
+            ] = sync_result.device_one_time_keys_count
+        if sync_result.device_unused_fallback_key_types:
+            response[
+                "org.matrix.msc2732.device_unused_fallback_key_types"
+            ] = sync_result.device_unused_fallback_key_types
+
+        if joined:
+            response["rooms"]["join"] = joined
+        if invited:
+            response["rooms"]["invite"] = invited
+        if archived:
+            response["rooms"]["leave"] = archived
+
+        if sync_result.groups.join:
+            response["groups"]["join"] = sync_result.groups.join
+        if sync_result.groups.invite:
+            response["groups"]["invite"] = sync_result.groups.invite
+        if sync_result.groups.leave:
+            response["groups"]["leave"] = sync_result.groups.leave
+
+        return response
 
     @staticmethod
     def encode_presence(events, time_now):