From 8120a238a465de576ad4d171e3072b28e5df32ac Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Wed, 11 Mar 2020 18:49:41 +0000
Subject: [PATCH] Refactor a bit

---
 synapse/visibility.py | 58 ++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 28 deletions(-)

diff --git a/synapse/visibility.py b/synapse/visibility.py
index 56603eb276b9..bab41182b9a0 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -118,34 +118,36 @@ def allowed(event):
 
                the original event if they can see it as normal.
         """
-        if event.type == "org.matrix.dummy_event" and filter_send_to_client:
-            return None
-
-        if (
-            not event.is_state()
-            and event.sender in ignore_list
-            and filter_send_to_client
-        ):
-            return None
-
-        # Until MSC2261 has landed we can't redact malicious alias events, so for
-        # now we temporarily filter out m.room.aliases entirely to mitigate
-        # abuse, while we spec a better solution to advertising aliases
-        # on rooms.
-        if event.type == EventTypes.Aliases and filter_send_to_client:
-            return None
-
-        # Don't try to apply the room's retention policy if the event is a state event, as
-        # MSC1763 states that retention is only considered for non-state events.
-        if filter_send_to_client and not event.is_state():
-            retention_policy = retention_policies[event.room_id]
-            max_lifetime = retention_policy.get("max_lifetime")
-
-            if max_lifetime is not None:
-                oldest_allowed_ts = storage.main.clock.time_msec() - max_lifetime
-
-                if event.origin_server_ts < oldest_allowed_ts:
-                    return None
+        # Only run some checks if these events aren't about to be sent to clients. This is
+        # because, if this is not the case, we're probably only checking if the users can
+        # see events in the room at that point in the DAG, and that shouldn't be decided
+        # on those checks.
+        if filter_send_to_client:
+            if event.type == "org.matrix.dummy_event":
+                return None
+
+            if not event.is_state() and event.sender in ignore_list:
+                return None
+
+            # Until MSC2261 has landed we can't redact malicious alias events, so for
+            # now we temporarily filter out m.room.aliases entirely to mitigate
+            # abuse, while we spec a better solution to advertising aliases
+            # on rooms.
+            if event.type == EventTypes.Aliases:
+                return None
+
+            # Don't try to apply the room's retention policy if the event is a state
+            # event, as MSC1763 states that retention is only considered for non-state
+            # events.
+            if not event.is_state():
+                retention_policy = retention_policies[event.room_id]
+                max_lifetime = retention_policy.get("max_lifetime")
+
+                if max_lifetime is not None:
+                    oldest_allowed_ts = storage.main.clock.time_msec() - max_lifetime
+
+                    if event.origin_server_ts < oldest_allowed_ts:
+                        return None
 
         if event.event_id in always_include_ids:
             return event