Refactor event signing to work on dicts

This is in preparation for making EventBuilder format agnostic, which
means event signing should be done against the event dict rather than
the EventBuilder object.

1 files changed, 35 insertions, 12 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 652941ca0d..63f693f259 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -38,8 +38,31 @@ def prune_event(event):
     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.
+
+    Args:
+        event (FrozenEvent)
+
+    Returns:
+        FrozenEvent
+    """
+    pruned_event_dict = prune_event_dict(event.get_dict())
+
+    from . import event_type_from_format_version
+    return event_type_from_format_version(event.format_version)(
+        pruned_event_dict, event.internal_metadata.get_dict()
+    )
+
+
+def prune_event_dict(event_dict):
+    """Redacts the event_dict in the same way as `prune_event`, except it
+    operates on dicts rather than event objects
+
+    Args:
+        event_dict (dict)
+
+    Returns:
+        dict: A copy of the pruned event dict
     """
-    event_type = event.type
 
     allowed_keys = [
         "event_id",
@@ -59,13 +82,13 @@ def prune_event(event):
         "membership",
     ]
 
-    event_dict = event.get_dict()
+    event_type = event_dict["type"]
 
     new_content = {}
 
     def add_fields(*fields):
         for field in fields:
-            if field in event.content:
+            if field in event_dict["content"]:
                 new_content[field] = event_dict["content"][field]
 
     if event_type == EventTypes.Member:
@@ -98,17 +121,17 @@ def prune_event(event):
 
     allowed_fields["content"] = new_content
 
-    allowed_fields["unsigned"] = {}
+    unsigned = {}
+    allowed_fields["unsigned"] = unsigned
 
-    if "age_ts" in event.unsigned:
-        allowed_fields["unsigned"]["age_ts"] = event.unsigned["age_ts"]
-    if "replaces_state" in event.unsigned:
-        allowed_fields["unsigned"]["replaces_state"] = event.unsigned["replaces_state"]
+    event_unsigned = event_dict.get("unsigned", {})
 
-    return type(event)(
-        allowed_fields,
-        internal_metadata_dict=event.internal_metadata.get_dict()
-    )
+    if "age_ts" in event_unsigned:
+        unsigned["age_ts"] = event_unsigned["age_ts"]
+    if "replaces_state" in event_unsigned:
+        unsigned["replaces_state"] = event_unsigned["replaces_state"]
+
+    return allowed_fields
 
 
 def _copy_field(src, dst, field):