Fix bug where we incorrectly removed a remote host from the list of hosts in a room when any user from that host left that room even if they weren't the last user from that host in that room

synapse/storage/roommember.py

@@ -18,6 +18,7 @@ from twisted.internet import defer
 from ._base import SQLBaseStore
 
 from synapse.api.constants import Membership
+from synapse.util.logutils import log_function
 
 import logging
 
@@ -29,8 +30,18 @@ class RoomMemberStore(SQLBaseStore):
     def _store_room_member_txn(self, txn, event):
         """Store a room member in the database.
         """
+        try:
             target_user_id = event.state_key
             domain = self.hs.parse_userid(target_user_id).domain
+        except:
+            logger.exception("Failed to parse target_user_id=%s", target_user_id)
+            raise
+
+        logger.debug(
+            "_store_room_member_txn: target_user_id=%s, membership=%s",
+            target_user_id,
+            event.membership,
+        )
 
         self._simple_insert_txn(
             txn,
@@ -51,7 +62,25 @@ class RoomMemberStore(SQLBaseStore):
                 "VALUES (?, ?)"
             )
             txn.execute(sql, (event.room_id, domain))
-        else:
+        elif event.membership != Membership.INVITE:
+            # Check if this was the last person to have left.
+            member_events = self._get_members_query_txn(
+                txn,
+                where_clause="c.room_id = ? AND m.membership = ?",
+                where_values=(event.room_id, Membership.JOIN,)
+            )
+
+            joined_domains = set()
+            for e in member_events:
+                try:
+                    joined_domains.add(
+                        self.hs.parse_userid(e.state_key).domain
+                    )
+                except:
+                    # FIXME: How do we deal with invalid user ids in the db?
+                    logger.exception("Invalid user_id: %s", event.state_key)
+
+            if domain not in joined_domains:
                 sql = (
                     "DELETE FROM room_hosts WHERE room_id = ? AND host = ?"
                 )
@@ -146,8 +175,13 @@ class RoomMemberStore(SQLBaseStore):
         vals = where_dict.values()
         return self._get_members_query(clause, vals)
 
-    @defer.inlineCallbacks
     def _get_members_query(self, where_clause, where_values):
+        return self._db_pool.runInteraction(
+            self._get_members_query_txn,
+            where_clause, where_values
+        )
+
+    def _get_members_query_txn(self, txn, where_clause, where_values):
         sql = (
             "SELECT e.* FROM events as e "
             "INNER JOIN room_memberships as m "
@@ -157,12 +191,11 @@ class RoomMemberStore(SQLBaseStore):
             "WHERE %s "
         ) % (where_clause,)
 
-        rows = yield self._execute_and_decode(sql, *where_values)
+        txn.execute(sql, where_values)
+        rows = self.cursor_to_dict(txn)
 
-        # logger.debug("_get_members_query Got rows %s", rows)
-
-        results = yield self._parse_events(rows)
-        defer.returnValue(results)
+        results = self._parse_events_txn(txn, rows)
+        return results
 
     @defer.inlineCallbacks
     def user_rooms_intersect(self, user_list):