Don't clear AppleUpdates.plist if we cannot (currently) reach the softwareupdate server. Prevents UpdateNotificationTracking.plist from losing track of Apple updates when an internal softwareupdate replica is not always available (for example, when available only via VPN)

code/client/munkilib/appleupdates/au.py

@@ -166,7 +166,7 @@ class AppleUpdates(object):
         if retcode:  # there was an error
             display.display_error('softwareupdate error: %s', retcode)
             return False
-        # not sure all older OS X versions set LastSessionSuccessful, so
+        # not sure all older macOS versions set LastSessionSuccessful, so
         # react only if it's explicitly set to False
         last_session_successful = su_prefs.pref('LastSessionSuccessful')
         if last_session_successful is False:
@@ -283,7 +283,8 @@ class AppleUpdates(object):
           force_check: Boolean. If True, forces a check, otherwise only checks
               if the last check is deemed outdated.
         Returns:
-          Boolean. True if there are updates, False otherwise.
+          Integer. -1 if there was an error, otherwise the number of available
+            updates.
         """
         before_hash = munkihash.getsha256hash(
             self.applesync.apple_download_catalog_path)
@@ -293,20 +294,20 @@ class AppleUpdates(object):
         try:
             self.applesync.cache_apple_catalog()
         except sync.CatalogNotFoundError:
-            return False
+            return -1
         except (sync.ReplicationError, fetch.Error) as err:
             display.display_warning(
                 'Could not download Apple SUS catalog:')
             display.display_warning(u'\t%s', err)
-            return False
+            return -1
 
         if not force_check and not self._force_check_necessary(before_hash):
             display.display_info(
                 'Skipping Apple Software Update check '
                 'because sucatalog is unchanged, installed Apple packages are '
                 'unchanged and we recently did a full check.')
-            # return True if we have cached updates; False otherwise
-            return bool(self.software_update_info())
+            # return count of cached updates
+            return len(self.software_update_info())
 
         if self.download_available_updates():  # Success; ready to install.
             prefs.set_pref('LastAppleSoftwareUpdateCheck', NSDate.date())
@@ -314,21 +315,21 @@ class AppleUpdates(object):
             if not product_ids:
                 # No updates found
                 self.applesync.clean_up_cache()
-                return False
+                return 0
             try:
                 self.applesync.cache_update_metadata(product_ids)
             except sync.ReplicationError as err:
                 display.display_warning(
                     'Could not replicate software update metadata:')
                 display.display_warning(u'\t%s', err)
-                return False
-            return True
+                return -1
+            return len(product_ids)
         else:
             # Download error, allow check again soon.
             display.display_error(
                 'Could not download all available Apple updates.')
             prefs.set_pref('LastAppleSoftwareUpdateCheck', None)
-            return False
+            return 0
 
     def update_downloaded(self, product_key):
         """Verifies that a given update appears to be downloaded.
@@ -443,7 +444,7 @@ class AppleUpdates(object):
         """Returns:
           List of dictionaries describing available Apple updates.
         """
-        if self.apple_updates is not None:
+        if self.apple_updates is None:
             self.apple_updates = self.get_apple_updates()
         return self.apple_updates
 
@@ -737,6 +738,16 @@ class AppleUpdates(object):
 
         return restart_action
 
+    def cached_update_count(self):
+        """Returns the count of updates in the cached AppleUpdates.plist"""
+        if not os.path.exists(self.apple_updates_plist):
+            return 0
+        try:
+            plist = FoundationPlist.readPlist(self.apple_updates_plist)
+        except FoundationPlist.FoundationPlistException:
+            plist = {}
+        return len(plist.get('AppleUpdates', []))
+
     def software_updates_available(
             self, force_check=False, suppress_check=False):
         """Checks for available Apple Software Updates, trying not to hit the
@@ -753,17 +764,11 @@ class AppleUpdates(object):
             # don't check at all --
             # typically because we are doing a logout install
             # just return any AppleUpdates info we already have
-            if not os.path.exists(self.apple_updates_plist):
-                return 0
-            try:
-                plist = FoundationPlist.readPlist(self.apple_updates_plist)
-            except FoundationPlist.FoundationPlistException:
-                plist = {}
-            return len(plist.get('AppleUpdates', []))
+            return self.cached_update_count()
         if force_check:
             # typically because user initiated the check from
             # Managed Software Update.app
-            success = self.check_for_software_updates(force_check=True)
+            updatecount = self.check_for_software_updates(force_check=True)
         else:
             # have we checked recently?  Don't want to check with
             # Apple Software Update server too frequently
@@ -790,12 +795,15 @@ class AppleUpdates(object):
                 success = self.check_for_software_updates(force_check=False)
         display.display_debug1(
             'CheckForSoftwareUpdates result: %s' % success)
-        if success:
-            count = self.write_appleupdates_file()
-        else:
+        if updatecount == -1:
+            # some (transient?) communications error with the su server; return
+            # cached AppleInfo
+            return self.cached_update_count()
+        elif updatecount == 0:
             self.clear_apple_update_info()
-            return 0
-        return count
+        else:
+            _ = self.write_appleupdates_file()
+        return updatecount
 
     def copy_update_metadata(self, item, metadata):
         """Applies metadata to Apple update item restricted