1 files changed, 41 insertions, 0 deletions
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index f80486102a..0425380e55 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -858,6 +858,47 @@ class FederationHandler(BaseHandler):
logger.debug("Not backfilling as no extremeties found.")
return
+ # We only want to paginate if we can actually see the events we'll get,
+ # as otherwise we'll just spend a lot of resources to get redacted
+ # events.
+ #
+ # We do this by filtering all the extremities and seeing if any remain.
+ # Given we don't have the extremity events themselves, we need to
+ # actually check the events that reference them.
+ #
+ # *Note*: the spec wants us to keep backfilling until we reach the start
+ # of the room in case we are allowed to see some of the history. However
+ # in practice that causes more issues than its worth, as a) its
+ # relatively rare for there to be any visible history and b) even when
+ # there is its often sufficiently long ago that clients would stop
+ # attempting to paginate before backfill reached the visible history.
+ #
+ # TODO: If we do do a backfill the we should filter the extremities to
+ # only include those that point to visible portions of history.
+ #
+ # TODO: Correctly handle the case where we are allowed to see the
+ # forward event but not the extremity, e.g. in the case of initial
+ # join of the server where we are allowed to see the join event but
+ # not anything before it.
+
+ forward_events = yield self.store.get_forward_events(
+ list(extremities),
+ )
+
+ extremities_events = yield self.store.get_events(
+ forward_events,
+ check_redacted=False,
+ get_prev_content=False,
+ )
+
+ filtered_extremities = yield filter_events_for_server(
+ self.store, self.server_name, list(extremities_events.values()),
+ redact=False,
+ )
+
+ if not filtered_extremities:
+ defer.returnValue(False)
+
# Check if we reached a point where we should start backfilling.
sorted_extremeties_tuple = sorted(
extremities.items(),
|
