Merge pull request #94 from Harvard-ATG/bugfix/launch-invalidation

Fixes issue with launch invalidation

annotationsx/middleware.py

@@ -262,6 +262,7 @@ def _update_session(self, request):
         max_launches = getattr(settings, 'LTI_MAX_LAUNCHES', 10)
         self.logger.info("LTI launches in session: %s [max=%s]" % (lti_launches.keys(), max_launches))
         if len(lti_launches.keys()) >= max_launches:
+            self.logger.info("Invalidating oldest LTI launch (FIFO)")
             invalidated_launch = lti_launches.popitem(last=False)
             self.logger.info("LTI launch invalidated: %s", json.dumps(invalidated_launch, indent=4))
 
@@ -355,4 +356,4 @@ def __contains__(self, item):
 
     def __repr__(self):
         self.assert_valid()
-        return repr(self.session['LTI_LAUNCH'][self.resource_link_id])
+        return repr(self.session['LTI_LAUNCH'][self.resource_link_id])

annotationsx/serializers.py

@@ -0,0 +1,12 @@
+from collections import OrderedDict
+import json
+
+class JsonOrderedDictSerializer(object):
+    """
+    Simple wrapper around JSON serializer that decodes dicts as ordered dicts.
+    """
+    def dumps(self, obj):
+        return json.dumps(obj, separators=(',', ':')).encode('latin-1')
+
+    def loads(self, data):
+        return json.loads(data.decode('latin-1'), object_pairs_hook=OrderedDict)

annotationsx/settings/base.py

@@ -245,6 +245,11 @@
     SESSION_COOKIE_SECURE = True
     SESSION_EXPIRE_AT_BROWSER_CLOSE = True
 
+# Instead of using the default JSON serializer, we need to modify it slightly so that
+# session dicts stored in JSON are de-serialized with their order preserved. This functionality
+# is used in particular by the MultiLTILaunchMiddleware.
+SESSION_SERIALIZER = 'annotationsx.serializers.JsonOrderedDictSerializer'
+
 # Organization-specific configuration
 # Try to minimize this as much as possible in favor of configuration
 if ORGANIZATION == "ATG":