Introduce vanguards-lite subsystem and some of its entry points

Co-authored-by: Mike Perry <mikeperry-git@torproject.org>

src/core/mainloop/mainloop.c

@@ -1293,6 +1293,7 @@ signewnym_impl(time_t now)
   circuit_mark_all_dirty_circs_as_unusable();
   addressmap_clear_transient();
   hs_client_purge_state();
+  purge_vanguards_lite();
   time_of_last_signewnym = now;
   signewnym_is_pending = 0;
 
@@ -1370,6 +1371,7 @@ CALLBACK(save_state);
 CALLBACK(write_stats_file);
 CALLBACK(control_per_second_events);
 CALLBACK(second_elapsed);
+CALLBACK(manage_vglite);
 
 #undef CALLBACK
 
@@ -1392,6 +1394,9 @@ STATIC periodic_event_item_t mainloop_periodic_events[] = {
   CALLBACK(second_elapsed, NET_PARTICIPANT,
            FL(RUN_ON_DISABLE)),
 
+  /* Update vanguards-lite once per hour, if we have networking */
+  CALLBACK(manage_vglite, NET_PARTICIPANT, FL(NEED_NET)),
+
   /* XXXX Do we have a reason to do this on a callback? Does it do any good at
    * all?  For now, if we're dormant, we can let our listeners decay. */
   CALLBACK(retry_listeners, NET_PARTICIPANT, FL(NEED_NET)),
@@ -1662,6 +1667,21 @@ mainloop_schedule_shutdown(int delay_sec)
   mainloop_event_schedule(scheduled_shutdown_ev, &delay_tv);
 }
 
+/**
+ * Update vanguards-lite layer2 nodes, once per hour
+ */
+static int
+manage_vglite_callback(time_t now, const or_options_t *options)
+{
+ (void)now;
+ (void)options;
+#define VANGUARDS_LITE_INTERVAL (60*60)
+
+  maintain_layer2_guards();
+
+  return VANGUARDS_LITE_INTERVAL;
+}
+
 /** Perform regular maintenance tasks.  This function gets run once per
  * second.
  */