1 files changed, 82 insertions, 0 deletions
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
new file mode 100644
index 0000000000..412f690f08
--- /dev/null
+++ b/synapse/events/utils.py
@@ -0,0 +1,82 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.api.constants import EventTypes
+
+
+def prune_event(event):
+    """ Returns a pruned version of the given event, which removes all keys we
+    don't know about or think could potentially be dodgy.
+
+    This is used when we "redact" an event. We want to remove all fields that
+    the user has specified, but we do want to keep necessary information like
+    type, state_key etc.
+    """
+    event_type = event.type
+
+    allowed_keys = [
+        "event_id",
+        "sender",
+        "room_id",
+        "hashes",
+        "signatures",
+        "content",
+        "type",
+        "state_key",
+        "depth",
+        "prev_events",
+        "prev_state",
+        "auth_events",
+        "origin",
+        "origin_server_ts",
+    ]
+
+    new_content = {}
+
+    def add_fields(*fields):
+        for field in fields:
+            if field in event.content:
+                new_content[field] = event.content[field]
+
+    if event_type == EventTypes.Member:
+        add_fields("membership")
+    elif event_type == EventTypes.Create:
+        add_fields("creator")
+    elif event_type == EventTypes.JoinRules:
+        add_fields("join_rule")
+    elif event_type == EventTypes.PowerLevels:
+        add_fields(
+            "users",
+            "users_default",
+            "events",
+            "events_default",
+            "events_default",
+            "state_default",
+            "ban",
+            "kick",
+            "redact",
+        )
+    elif event_type == EventTypes.Aliases:
+        add_fields("aliases")
+
+    allowed_fields = {
+        k: v
+        for k, v in event.get_dict().items()
+        if k in allowed_keys
+    }
+
+    allowed_fields["content"] = new_content
+
+    return type(event)(allowed_fields)