detect stale persisted cm list and update

steam/client/__init__.py

@@ -128,7 +128,20 @@ class SteamClient(CMClient, BuiltinBase):
         if self.credential_location:
             filepath = os.path.join(self.credential_location, 'cm_servers.json')
 
-            if not os.path.exists(filepath):
+            if os.path.exists(filepath):
+                try:
+                    with open(filepath, 'r') as f:
+                        data = json.load(f)
+                except ValueError:
+                    self._LOG.error("Failed parsing %s", repr(filepath))
+                except IOError as e:
+                    self._LOG.error("Failed reading %s (%s)", repr(filepath), str(e))
+                else:
+                    if data.get('last_updated', 0) + 3600*24 > time():
+                        return
+
+                self._LOG.debug("Persisted CM server list is stale")
+
             data = {
                 'cell_id': self.cm_servers.cell_id,
                 'last_updated': self.cm_servers.last_updated,