Do not add `origin` field to LPDUs.

Synapse has a bad habit of adding `origin` to the top-level of event content.

The Linearized Matrix spec does not include `origin`, and in fact cannot as that will cause the content hashes and signatures computed by the participant server to differ from Synapse's own results.

So, we perform a hack here to drop `origin` from any event derived from an LPDU event. Other DAG homeserver implementations might be sad however.

2 files changed, 8 insertions, 1 deletions

diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index d93ed095cc..e3b2569f91 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -276,7 +276,10 @@ def create_local_event_from_event_dict(
     if format_version == EventFormatVersions.ROOM_V1_V2:
         event_dict["event_id"] = _create_event_id(clock, hostname)
 
-    event_dict["origin"] = hostname
+    if "hub_server" not in event_dict:
+        # Do not add "origin" field to LPDUs.
+        event_dict["origin"] = hostname
+
     event_dict.setdefault("origin_server_ts", time_now)
 
     event_dict.setdefault("unsigned", {})
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index 9278f1a1aa..e3c33d922d 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -66,6 +66,10 @@ class EventValidator:
             "type",
         ]
 
+        if event.hub_server is not None:
+            # Do not add the "origin" field to LPDUs.
+            required.remove("origin")
+
         for k in required:
             if k not in event:
                 raise SynapseError(400, "Event does not have key %s" % (k,))