Allow room initialSync for users that have left the room, returning a snapshot of how the room was when they left it

synapse/api/auth.py

@@ -104,6 +104,20 @@ class Auth(object):
 
     @defer.inlineCallbacks
     def check_joined_room(self, room_id, user_id, current_state=None):
+        """Check if the user is currently joined in the room
+        Args:
+            room_id(str): The room to check.
+            user_id(str): The user to check.
+            current_state(dict): Optional map of the current state of the room.
+                If provided then that map is used to check whether they are a
+                member of the room. Otherwise the current membership is
+                loaded from the database.
+        Raises:
+            AuthError if the user is not in the room.
+        Returns:
+            A deferred membership event for the user if the user is in
+            the room.
+        """
         if current_state:
             member = current_state.get(
                 (EventTypes.Member, user_id),
@@ -119,6 +133,41 @@ class Auth(object):
         self._check_joined_room(member, user_id, room_id)
         defer.returnValue(member)
 
+    @defer.inlineCallbacks
+    def check_user_was_in_room(self, room_id, user_id, current_state=None):
+        """Check if the user was in the room at some point.
+        Args:
+            room_id(str): The room to check.
+            user_id(str): The user to check.
+            current_state(dict): Optional map of the current state of the room.
+                If provided then that map is used to check whether they are a
+                member of the room. Otherwise the current membership is
+                loaded from the database.
+        Raises:
+            AuthError if the user was never in the room.
+        Returns:
+            A deferred membership event for the user if the user was in
+            the room.
+        """
+        if current_state:
+            member = current_state.get(
+                (EventTypes.Member, user_id),
+                None
+            )
+        else:
+            member = yield self.state.get_current_state(
+                room_id=room_id,
+                event_type=EventTypes.Member,
+                state_key=user_id
+            )
+
+        if not member:
+            raise AuthError(403, "User %s not in room %s" % (
+                user_id, room_id
+            ))
+
+        defer.returnValue(member)
+
     @defer.inlineCallbacks
     def check_host_in_room(self, room_id, host):
         curr_state = yield self.state.get_current_state(room_id)

synapse/handlers/message.py

@@ -22,7 +22,7 @@ from synapse.events.utils import serialize_event
 from synapse.events.validator import EventValidator
 from synapse.util import unwrapFirstError
 from synapse.util.logcontext import PreserveLoggingContext
-from synapse.types import UserID, RoomStreamToken
+from synapse.types import UserID, RoomStreamToken, StreamToken
 
 from ._base import BaseHandler
 
@@ -377,7 +377,6 @@ class MessageHandler(BaseHandler):
                         lambda states: states[event.event_id]
                     )
 
-
                 (messages, token), current_state = yield defer.gatherResults(
                     [
                         self.store.get_recent_events_for_room(
@@ -434,13 +433,83 @@ class MessageHandler(BaseHandler):
     @defer.inlineCallbacks
     def room_initial_sync(self, user_id, room_id, pagin_config=None,
                           feedback=False):
-        current_state = yield self.state.get_current_state(
+        """Capture the a snapshot of a room. If user is currently a member of
-            room_id=room_id,
+        the room this will be what is currently in the room. If the user left
+        the room this will be what was in the room when they left.
+
+        Args:
+            user_id(str): The user to get a snapshot for.
+            room_id(str): The room to get a snapshot of.
+            pagin_config(synapse.api.streams.PaginationConfig): The pagination
+            config used to determine how many messages to return.
+        Raises:
+            AuthError if the user wasn't in the room.
+        Returns:
+            A JSON object with the snapshot of the room.
+        """
+
+        member_event = yield self.auth.check_user_was_in_room(room_id, user_id)
+
+        if member_event.membership == Membership.JOIN:
+            result = yield self._room_initial_sync_joined(
+                user_id, room_id, pagin_config, member_event
+            )
+        elif member_event.membership == Membership.LEAVE:
+            result = yield self._room_initial_sync_parted(
+                user_id, room_id, pagin_config, member_event
+            )
+        defer.returnValue(result)
+
+    @defer.inlineCallbacks
+    def _room_initial_sync_parted(self, user_id, room_id, pagin_config,
+                                  member_event):
+        room_state = yield self.store.get_state_for_events(
+            member_event.room_id, [member_event.event_id], None
         )
 
-        yield self.auth.check_joined_room(
+        room_state = room_state[member_event.event_id]
-            room_id, user_id,
+
-            current_state=current_state
+        limit = pagin_config.limit if pagin_config else None
+        if limit is None:
+            limit = 10
+
+        stream_token = yield self.store.get_stream_token_for_event(
+            member_event.event_id
+        )
+
+        messages, token = yield self.store.get_recent_events_for_room(
+            room_id,
+            limit=limit,
+            end_token=stream_token
+        )
+
+        messages = yield self._filter_events_for_client(
+            user_id, room_id, messages
+        )
+
+        start_token = StreamToken(token[0], 0, 0, 0)
+        end_token = StreamToken(token[1], 0, 0, 0)
+
+        time_now = self.clock.time_msec()
+
+        defer.returnValue({
+            "membership": member_event.membership,
+            "room_id": room_id,
+            "messages": {
+                "chunk": [serialize_event(m, time_now) for m in messages],
+                "start": start_token.to_string(),
+                "end": end_token.to_string(),
+            },
+            "state": [serialize_event(s, time_now) for s in room_state.values()],
+            "presence": [],
+            "receipts": [],
+        })
+
+    @defer.inlineCallbacks
+    def _room_initial_sync_joined(self, user_id, room_id, pagin_config,
+                                  member_event):
+        current_state = yield self.state.get_current_state(
+            room_id=room_id,
         )
 
         # TODO(paul): I wish I was called with user objects not user_id
@@ -454,8 +523,6 @@ class MessageHandler(BaseHandler):
             for x in current_state.values()
         ]
 
-        member_event = current_state.get((EventTypes.Member, user_id,))
-
         now_token = yield self.hs.get_event_sources().get_current_token()
 
         limit = pagin_config.limit if pagin_config else None

synapse/storage/stream.py

@@ -379,6 +379,21 @@ class StreamStore(SQLBaseStore):
             )
             defer.returnValue("t%d-%d" % (topo, token))
 
+    def get_stream_token_for_event(self, event_id):
+        """The stream token for an event
+        Args:
+            event_id(str): The id of the event to look up a stream token for.
+        Raises:
+            StoreError if the event wasn't in the database.
+        Returns:
+            A deferred "s%d" stream token.
+        """
+        return self._simple_select_one_onecol(
+            table="events",
+            keyvalues={"event_id": event_id},
+            retcol="stream_ordering",
+        ).addCallback(lambda stream_ordering: "s%d" % (stream_ordering,))
+
     def _get_max_topological_txn(self, txn):
         txn.execute(
             "SELECT MAX(topological_ordering) FROM events"