Stop shadow-banned users from sending non-member events. (#8142)

1 files changed, 13 insertions, 5 deletions

diff --git a/synapse/rest/client/v2_alpha/relations.py b/synapse/rest/client/v2_alpha/relations.py
index 89002ffbff..e29f49f7f5 100644
--- a/synapse/rest/client/v2_alpha/relations.py
+++ b/synapse/rest/client/v2_alpha/relations.py
@@ -22,7 +22,7 @@ any time to reflect changes in the MSC.
 import logging
 
 from synapse.api.constants import EventTypes, RelationTypes
-from synapse.api.errors import SynapseError
+from synapse.api.errors import ShadowBanError, SynapseError
 from synapse.http.servlet import (
     RestServlet,
     parse_integer,
@@ -35,6 +35,7 @@ from synapse.storage.relations import (
     PaginationChunk,
     RelationPaginationToken,
 )
+from synapse.util.stringutils import random_string
 
 from ._base import client_patterns
 
@@ -111,11 +112,18 @@ class RelationSendServlet(RestServlet):
             "sender": requester.user.to_string(),
         }
 
-        event, _ = await self.event_creation_handler.create_and_send_nonmember_event(
-            requester, event_dict=event_dict, txn_id=txn_id
-        )
+        try:
+            (
+                event,
+                _,
+            ) = await self.event_creation_handler.create_and_send_nonmember_event(
+                requester, event_dict=event_dict, txn_id=txn_id
+            )
+            event_id = event.event_id
+        except ShadowBanError:
+            event_id = "$" + random_string(43)
 
-        return 200, {"event_id": event.event_id}
+        return 200, {"event_id": event_id}
 
 
 class RelationPaginationServlet(RestServlet):