Implement group_expiry on database channel backend

channels/database_layer.py

@@ -27,8 +27,9 @@ class DatabaseChannelLayer(object):
     it's not a valid Unicode character, so it should be safe enough.
     """
 
-    def __init__(self, db_alias=DEFAULT_DB_ALIAS, expiry=60):
+    def __init__(self, db_alias=DEFAULT_DB_ALIAS, expiry=60, group_expiry=86400):
         self.expiry = expiry
+        self.group_expiry = group_expiry
         self.db_alias = db_alias
 
     # ASGI API
@@ -165,13 +166,14 @@ class DatabaseChannelLayer(object):
         class Group(models.Model):
             group = models.CharField(max_length=200)
             channel = models.CharField(max_length=200)
+            created = models.DateTimeField(db_index=True, auto_now_add=True)
 
             class Meta:
                 apps = Apps()
                 app_label = "channels"
                 db_table = "django_channel_groups"
                 unique_together = [["group", "channel"]]
-        # Ensure its table exists
+        # Ensure its table exists with the right schema
         if Group._meta.db_table not in self.connection.introspection.table_names(self.connection.cursor()):
             with self.connection.schema_editor() as editor:
                 editor.create_model(Group)
@@ -187,8 +189,11 @@ class DatabaseChannelLayer(object):
         old_messages = self.channel_model.objects.filter(expiry__lt=target)
         channels_to_ungroup = old_messages.values_list("channel", flat=True).distinct()
         old_messages.delete()
-        # Now, remove channel membership from channels that expired
-        self.group_model.objects.filter(channel__in=channels_to_ungroup).delete()
+        # Now, remove channel membership from channels that expired and ones that just expired
+        self.group_model.objects.filter(
+            models.Q(channel__in=channels_to_ungroup) |
+            models.Q(created__lte=target - datetime.timedelta(seconds=self.group_expiry))
+        ).delete()
 
     def __str__(self):
         return "%s(alias=%s)" % (self.__class__.__name__, self.connection.alias)

channels/tests/test_database_layer.py

@@ -1,6 +1,8 @@
 from __future__ import unicode_literals
-from asgiref.conformance import make_tests
+from asgiref.conformance import ConformanceTestCase
 from ..database_layer import DatabaseChannelLayer
 
-channel_layer = DatabaseChannelLayer(expiry=1)
-DatabaseLayerTests = make_tests(channel_layer, expiry_delay=2.1)
+
+class DatabaseLayerTests(ConformanceTestCase):
+    channel_layer = DatabaseChannelLayer(expiry=1, group_expiry=3)
+    expiry_delay = 2.1