Handle to-device extensions to Sliding Sync (#17416)

Implements MSC3885

---------

Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>

1 files changed, 16 insertions, 1 deletions

diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index 13aed1dc85..94d5faf9f7 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -942,7 +942,9 @@ class SlidingSyncRestServlet(RestServlet):
         response["rooms"] = await self.encode_rooms(
             requester, sliding_sync_result.rooms
         )
-        response["extensions"] = {}  # TODO: sliding_sync_result.extensions
+        response["extensions"] = await self.encode_extensions(
+            requester, sliding_sync_result.extensions
+        )
 
         return response
 
@@ -1054,6 +1056,19 @@ class SlidingSyncRestServlet(RestServlet):
 
         return serialized_rooms
 
+    async def encode_extensions(
+        self, requester: Requester, extensions: SlidingSyncResult.Extensions
+    ) -> JsonDict:
+        result = {}
+
+        if extensions.to_device is not None:
+            result["to_device"] = {
+                "next_batch": extensions.to_device.next_batch,
+                "events": extensions.to_device.events,
+            }
+
+        return result
+
 
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     SyncRestServlet(hs).register(http_server)