Purge old announcements

README.md

@@ -96,6 +96,12 @@ If the latest announcement has been cleared or there are no announcements yet, a
 There's a hook in the configuration that lets you add a custom message above all the annoucements.
 A good use for this message would be to include a link to a more general system status or message of the day (MOTD) page.
 
+## Announcement Lifetime
+
+Announcements are retained in the queue for up to some configurable lifetime in days.
+After that they are purged automatically.
+By default announcements stay in the queue for a week.
+
 ## Persisted Announcements
 
 By default the service does nothing to persist announcements.
@@ -106,7 +112,3 @@ On update, the file is over-written to reflect the current state of the queue.
 This way if the service is restarted, those old announcements aren't lost.
 The persistence file is just JSON.
 **BE CERTAIN** access to this file is protected! 
-
-## Things That Could Use Work
-
-We should put a cap on the size of the announcement queue, or expire them after some time period.

announcement_config.py

@@ -49,6 +49,12 @@
 # AnnouncementQueue(LoggingConfigurable) configuration
 #------------------------------------------------------------------------------
 
+## Number of days to retain announcements.
+#  
+#  Announcements that have been in the queue for this many days are purged from
+#  the queue.
+#c.AnnouncementQueue.lifetime_days = 7.0
+
 ## File path where announcements persist as JSON.
 #  
 #  For a persistent announcement queue, this parameter must be set to a non-empty

jupyterhub_announcement/announcement.py

@@ -12,7 +12,7 @@
 from tornado import escape, gen, ioloop, web
 
 from traitlets.config import Application, LoggingConfigurable
-from traitlets import Bool, Dict, Integer, List, Unicode, default
+from traitlets import Bool, Dict, Float, Integer, List, Unicode, default
 
 
 class _JSONEncoder(json.JSONEncoder):
@@ -56,6 +56,13 @@ class AnnouncementQueue(LoggingConfigurable):
             announcements will not be persisted on updates to the queue."""
     ).tag(config=True)
 
+    lifetime_days = Float(7.0,
+            help="""Number of days to retain announcements.
+
+            Announcements that have been in the queue for this many days are
+            purged from the queue."""
+    ).tag(config=True)
+
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
 
@@ -96,6 +103,16 @@ def _persist(self):
         with open(self.persist_path, "w") as stream:
             json.dump(self.announcements, stream, cls=_JSONEncoder, indent=2)
 
+    def purge(self):
+        max_age = datetime.timedelta(days=self.lifetime_days)
+        now = datetime.datetime.now()
+        old_count = len(self.announcements)
+        self.announcements = [a for a in self.announcements 
+                if now - a["timestamp"] < max_age]
+        if self.persist_path and len(self.announcements) < old_count:
+            self.log.info(f"persisting queue to {self.persist_path}")
+            self._handle_persist()
+
 
 class AnnouncementHandler(HubAuthenticated, web.RequestHandler):
 
@@ -261,6 +278,10 @@ def init_queue(self):
 
     def start(self):
         self.app.listen(self.port)
+        def purge_callback():
+            self.queue.purge()
+        c = ioloop.PeriodicCallback(purge_callback, 300000)
+        c.start()
         ioloop.IOLoop.current().start()
 
 

setup.py

@@ -4,7 +4,7 @@
 
 setup(
         name='jupyterhub-announcement',
-        version='0.2.0',
+        version='0.3.0',
         description='JupyterHub Announcement Service',
         author='R. C. Thomas',
         author_email='[email protected]',