1 files changed, 32 insertions, 0 deletions
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 457ca288d0..cb0791e591 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -533,6 +533,38 @@ class RoomMemberStore(SQLBaseStore):
 
         defer.returnValue(True)
 
+    @cachedInlineCallbacks()
+    def was_host_joined(self, room_id, host):
+        """Check whether the server is or ever was in the room.
+        """
+        if '%' in host or '_' in host:
+            raise Exception("Invalid host name")
+
+        sql = """
+            SELECT user_id FROM room_memberships
+            WHERE room_id = ?
+                AND user_id LIKE ?
+                AND membership = 'join'
+            LIMIT 1
+        """
+
+        # We do need to be careful to ensure that host doesn't have any wild cards
+        # in it, but we checked above for known ones and we'll check below that
+        # the returned user actually has the correct domain.
+        like_clause = "%:" + host
+
+        rows = yield self._execute("was_host_joined", None, sql, room_id, like_clause)
+
+        if not rows:
+            defer.returnValue(False)
+
+        user_id = rows[0][0]
+        if get_domain_from_id(user_id) != host:
+            # This can only happen if the host name has something funky in it
+            raise Exception("Invalid host name")
+
+        defer.returnValue(True)
+
     def get_joined_hosts(self, room_id, state_entry):
         state_group = state_entry.state_group
         if not state_group: