Add experimental support for MSC4308: Thread Subscriptions extension to Sliding Sync when MSC4306 and MSC4186 are enabled.

synapse/rest/client/sync.py

@@ -23,6 +23,8 @@
 from collections import defaultdict
 from typing import TYPE_CHECKING, Any, Dict, List, Mapping, Optional, Tuple, Union
 
+import attrs
+
 from synapse.api.constants import AccountDataTypes, EduTypes, Membership, PresenceState
 from synapse.api.errors import Codes, StoreError, SynapseError
 from synapse.api.filtering import FilterCollection
@@ -1256,6 +1258,17 @@ async def encode_extensions(
                 "rooms": extensions.typing.room_id_to_typing_map,
             }
 
+        if (
+            extensions.thread_subscriptions is not None
+            and extensions.thread_subscriptions.changed is not None
+        ):
+            serialized_extensions["thread_subscriptions"] = {
+                "changes": [
+                    attrs.asdict(change, filter=lambda _attr, v: v is not None)
+                    for change in extensions.thread_subscriptions.changed
+                ]
+            }
+
         return serialized_extensions
 
 

synapse/types/handlers/sliding_sync.py

@@ -357,11 +357,34 @@ class TypingExtension:
             def __bool__(self) -> bool:
                 return bool(self.room_id_to_typing_map)
 
+        @attr.s(slots=True, frozen=True, auto_attribs=True)
+        class ThreadSubscriptionsExtension:
+            """The Thread Subscriptions extension (MSC4308)
+
+            Attributes:
+                changes: list of changes to thread subscriptions
+            """
+
+            @attr.s(slots=True, frozen=True, auto_attribs=True)
+            class ThreadSubscriptionChange:
+                room_id: str
+                root_event_id: str
+                subscribed: bool
+
+                # always present when `subscribed`
+                automatic: Optional[bool]
+
+            changed: Optional[List[ThreadSubscriptionChange]]
+
+            def __bool__(self) -> bool:
+                return bool(self.changed)
+
         to_device: Optional[ToDeviceExtension] = None
         e2ee: Optional[E2eeExtension] = None
         account_data: Optional[AccountDataExtension] = None
         receipts: Optional[ReceiptsExtension] = None
         typing: Optional[TypingExtension] = None
+        thread_subscriptions: Optional[ThreadSubscriptionsExtension] = None
 
         def __bool__(self) -> bool:
             return bool(
@@ -370,6 +393,7 @@ def __bool__(self) -> bool:
                 or self.account_data
                 or self.receipts
                 or self.typing
+                or self.thread_subscriptions
             )
 
     next_pos: SlidingSyncStreamToken

synapse/types/rest/client/__init__.py

@@ -364,11 +364,23 @@ class TypingExtension(RequestBodyModel):
             # Process all room subscriptions defined in the Room Subscription API. (This is the default.)
             rooms: Optional[List[StrictStr]] = ["*"]
 
+        class ThreadSubscriptionsExtension(RequestBodyModel):
+            """The Thread Subscriptions extension (MSC4308)
+
+            Attributes:
+                enabled
+                limit: maximum number of subscription changes to return (default 100)
+            """
+
+            enabled: Optional[StrictBool] = False
+            limit: StrictInt = 100
+
         to_device: Optional[ToDeviceExtension] = None
         e2ee: Optional[E2eeExtension] = None
         account_data: Optional[AccountDataExtension] = None
         receipts: Optional[ReceiptsExtension] = None
         typing: Optional[TypingExtension] = None
+        thread_subscriptions: Optional[ThreadSubscriptionsExtension] = None
 
     conn_id: Optional[StrictStr]