Ensure we don't mutate state cache entries

1 files changed, 4 insertions, 0 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 8a1038c44a..f7cb3c1bb2 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1585,10 +1585,12 @@ class FederationHandler(BaseHandler):
                 current_state = set(e.event_id for e in auth_events.values())
                 different_auth = event_auth_events - current_state
 
+                context.current_state_ids = dict(context.current_state_ids)
                 context.current_state_ids.update({
                     k: a.event_id for k, a in auth_events.items()
                     if k != event_key
                 })
+                context.prev_state_ids = dict(context.prev_state_ids)
                 context.prev_state_ids.update({
                     k: a.event_id for k, a in auth_events.items()
                 })
@@ -1670,10 +1672,12 @@ class FederationHandler(BaseHandler):
                 # 4. Look at rejects and their proofs.
                 # TODO.
 
+                context.current_state_ids = dict(context.current_state_ids)
                 context.current_state_ids.update({
                     k: a.event_id for k, a in auth_events.items()
                     if k != event_key
                 })
+                context.prev_state_ids = dict(context.prev_state_ids)
                 context.prev_state_ids.update({
                     k: a.event_id for k, a in auth_events.items()
                 })