Add experimental and incomplete support for MSC4306: Thread Subscriptions. (#18674)

Implements:
[MSC4306](https://github.com/matrix-org/matrix-spec-proposals/blob/rei/msc_thread_subscriptions/proposals/4306-thread-subscriptions.md)
(partially)

What's missing:
- Changes to push rules

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>

Author: reivilibre

changelog.d/18674.feature

@@ -0,0 +1 @@
+Add experimental and incomplete support for [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-spec-proposals/blob/rei/msc_thread_subscriptions/proposals/4306-thread-subscriptions.md).

docker/configure_workers_and_start.py

@@ -327,6 +327,15 @@
         "shared_extra_conf": {},
         "worker_extra_conf": "",
     },
+    "thread_subscriptions": {
+        "app": "synapse.app.generic_worker",
+        "listener_resources": ["client", "replication"],
+        "endpoint_patterns": [
+            "^/_matrix/client/unstable/io.element.msc4306/.*",
+        ],
+        "shared_extra_conf": {},
+        "worker_extra_conf": "",
+    },
 }
 
 # Templates for sections that may be inserted multiple times in config files
@@ -427,6 +436,7 @@ def add_worker_roles_to_shared_config(
         "to_device",
         "typing",
         "push_rules",
+        "thread_subscriptions",
     }
 
     # Worker-type specific sharding config. Now a single worker can fulfill multiple

synapse/_scripts/synapse_port_db.py

@@ -136,6 +136,7 @@
         "has_known_state",
         "is_encrypted",
     ],
+    "thread_subscriptions": ["subscribed", "automatic"],
     "users": ["shadow_banned", "approved", "locked", "suspended"],
     "un_partial_stated_event_stream": ["rejection_status_changed"],
     "users_who_share_rooms": ["share_private"],

synapse/app/generic_worker.py

@@ -104,6 +104,9 @@
 from synapse.storage.databases.main.stream import StreamWorkerStore
 from synapse.storage.databases.main.tags import TagsWorkerStore
 from synapse.storage.databases.main.task_scheduler import TaskSchedulerWorkerStore
+from synapse.storage.databases.main.thread_subscriptions import (
+    ThreadSubscriptionsWorkerStore,
+)
 from synapse.storage.databases.main.transactions import TransactionWorkerStore
 from synapse.storage.databases.main.ui_auth import UIAuthWorkerStore
 from synapse.storage.databases.main.user_directory import UserDirectoryStore
@@ -132,6 +135,7 @@ class GenericWorkerStore(
     KeyStore,
     RoomWorkerStore,
     DirectoryWorkerStore,
+    ThreadSubscriptionsWorkerStore,
     PushRulesWorkerStore,
     ApplicationServiceTransactionWorkerStore,
     ApplicationServiceWorkerStore,

synapse/config/experimental.py

@@ -581,3 +581,7 @@ def read_config(
 
         # MSC4155: Invite filtering
         self.msc4155_enabled: bool = experimental.get("msc4155_enabled", False)
+
+        # MSC4306: Thread Subscriptions
+        # (and MSC4308: sliding sync extension for thread subscriptions)
+        self.msc4306_enabled: bool = experimental.get("msc4306_enabled", False)

synapse/config/workers.py

@@ -174,6 +174,10 @@ class WriterLocations:
         default=[MAIN_PROCESS_INSTANCE_NAME],
         converter=_instance_to_list_converter,
     )
+    thread_subscriptions: List[str] = attr.ib(
+        default=["master"],
+        converter=_instance_to_list_converter,
+    )
 
 
 @attr.s(auto_attribs=True)

synapse/handlers/deactivate_account.py

@@ -187,6 +187,9 @@ async def deactivate_account(
         # Remove account data (including ignored users and push rules).
         await self.store.purge_account_data_for_user(user_id)
 
+        # Remove thread subscriptions for the user
+        await self.store.purge_thread_subscription_settings_for_user(user_id)
+
         # Delete any server-side backup keys
         await self.store.bulk_delete_backup_keys_and_versions_for_user(user_id)
 

synapse/handlers/thread_subscriptions.py

@@ -0,0 +1,126 @@
+import logging
+from typing import TYPE_CHECKING, Optional
+
+from synapse.api.errors import AuthError, NotFoundError
+from synapse.storage.databases.main.thread_subscriptions import ThreadSubscription
+from synapse.types import UserID
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class ThreadSubscriptionsHandler:
+    def __init__(self, hs: "HomeServer"):
+        self.store = hs.get_datastores().main
+        self.event_handler = hs.get_event_handler()
+        self.auth = hs.get_auth()
+
+    async def get_thread_subscription_settings(
+        self,
+        user_id: UserID,
+        room_id: str,
+        thread_root_event_id: str,
+    ) -> Optional[ThreadSubscription]:
+        """Get thread subscription settings for a specific thread and user.
+        Checks that the thread root is both a real event and also that it is visible
+        to the user.
+
+        Args:
+            user_id: The ID of the user
+            thread_root_event_id: The event ID of the thread root
+
+        Returns:
+            A `ThreadSubscription` containing the active subscription settings or None if not set
+        """
+        # First check that the user can access the thread root event
+        # and that it exists
+        try:
+            event = await self.event_handler.get_event(
+                user_id, room_id, thread_root_event_id
+            )
+            if event is None:
+                raise NotFoundError("No such thread root")
+        except AuthError:
+            raise NotFoundError("No such thread root")
+
+        return await self.store.get_subscription_for_thread(
+            user_id.to_string(), event.room_id, thread_root_event_id
+        )
+
+    async def subscribe_user_to_thread(
+        self,
+        user_id: UserID,
+        room_id: str,
+        thread_root_event_id: str,
+        *,
+        automatic: bool,
+    ) -> Optional[int]:
+        """Sets or updates a user's subscription settings for a specific thread root.
+
+        Args:
+            requester_user_id: The ID of the user whose settings are being updated.
+            thread_root_event_id: The event ID of the thread root.
+            automatic: whether the user was subscribed by an automatic decision by
+                their client.
+
+        Returns:
+            The stream ID for this update, if the update isn't no-opped.
+
+        Raises:
+            NotFoundError if the user cannot access the thread root event, or it isn't
+            known to this homeserver.
+        """
+        # First check that the user can access the thread root event
+        # and that it exists
+        try:
+            event = await self.event_handler.get_event(
+                user_id, room_id, thread_root_event_id
+            )
+            if event is None:
+                raise NotFoundError("No such thread root")
+        except AuthError:
+            logger.info("rejecting thread subscriptions change (thread not accessible)")
+            raise NotFoundError("No such thread root")
+
+        return await self.store.subscribe_user_to_thread(
+            user_id.to_string(),
+            event.room_id,
+            thread_root_event_id,
+            automatic=automatic,
+        )
+
+    async def unsubscribe_user_from_thread(
+        self, user_id: UserID, room_id: str, thread_root_event_id: str
+    ) -> Optional[int]:
+        """Clears a user's subscription settings for a specific thread root.
+
+        Args:
+            requester_user_id: The ID of the user whose settings are being updated.
+            thread_root_event_id: The event ID of the thread root.
+
+        Returns:
+            The stream ID for this update, if the update isn't no-opped.
+
+        Raises:
+            NotFoundError if the user cannot access the thread root event, or it isn't
+            known to this homeserver.
+        """
+        # First check that the user can access the thread root event
+        # and that it exists
+        try:
+            event = await self.event_handler.get_event(
+                user_id, room_id, thread_root_event_id
+            )
+            if event is None:
+                raise NotFoundError("No such thread root")
+        except AuthError:
+            logger.info("rejecting thread subscriptions change (thread not accessible)")
+            raise NotFoundError("No such thread root")
+
+        return await self.store.unsubscribe_user_from_thread(
+            user_id.to_string(),
+            event.room_id,
+            thread_root_event_id,
+        )

synapse/replication/tcp/handler.py

@@ -72,7 +72,10 @@
     ToDeviceStream,
     TypingStream,
 )
-from synapse.replication.tcp.streams._base import DeviceListsStream
+from synapse.replication.tcp.streams._base import (
+    DeviceListsStream,
+    ThreadSubscriptionsStream,
+)
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -186,6 +189,15 @@ def __init__(self, hs: "HomeServer"):
 
                 continue
 
+            if isinstance(stream, ThreadSubscriptionsStream):
+                if (
+                    hs.get_instance_name()
+                    in hs.config.worker.writers.thread_subscriptions
+                ):
+                    self._streams_to_replicate.append(stream)
+
+                continue
+
             if isinstance(stream, DeviceListsStream):
                 if hs.get_instance_name() in hs.config.worker.writers.device_lists:
                     self._streams_to_replicate.append(stream)

synapse/replication/tcp/streams/__init__.py

@@ -41,6 +41,7 @@
     PushRulesStream,
     ReceiptsStream,
     Stream,
+    ThreadSubscriptionsStream,
     ToDeviceStream,
     TypingStream,
 )
@@ -67,6 +68,7 @@
         ToDeviceStream,
         FederationStream,
         AccountDataStream,
+        ThreadSubscriptionsStream,
         UnPartialStatedRoomStream,
         UnPartialStatedEventStream,
     )
@@ -86,6 +88,7 @@
     "DeviceListsStream",
     "ToDeviceStream",
     "AccountDataStream",
+    "ThreadSubscriptionsStream",
     "UnPartialStatedRoomStream",
     "UnPartialStatedEventStream",
 ]