Merge pull request #249 from Pylons/fix/avoid-touching-session

avoid touching the session except when the user already touched it

CHANGES.txt

@@ -27,6 +27,12 @@ unreleased
   3. Mako reformatted into "defs" for simpler reorganization in the future
   See https://github.com/Pylons/pyramid_debugtoolbar/pull/241
 
+- Fix to prevent the toolbar from loading the session until it is actually
+  accessed by the user. This avoids unnecessary parsing of the session object
+  as well as waiting to parse it until later in the request which may meet
+  more expectations of the session factory.
+  See https://github.com/Pylons/pyramid_debugtoolbar/pull/249
+
 2.4.2 (2015-10-28)
 ------------------
 

pyramid_debugtoolbar/panels/request_vars.py

@@ -10,30 +10,30 @@
 # extractable_request_attributes allow us to programmatically pull data
 # the format is ( attr_, is_dict)
 extractable_request_attributes = (
-    ('accept_charset', None),
-    ('accept_encoding', None),
-    ('accept_language', None),
-    ('application_url', None),
-    ('authenticated_userid', None),
-    ('authorization', None),
-    ('cache_control', None),
-    ('context', None),
-    ('effective_principals', None),
-    ('exc_info', None),
-    ('exception', None),
-    ('locale_name', None),
-    ('matchdict', None),
+    ('accept_charset', False),
+    ('accept_encoding', False),
+    ('accept_language', False),
+    ('application_url', False),
+    ('authenticated_userid', False),
+    ('authorization', False),
+    ('cache_control', False),
+    ('context', False),
+    ('effective_principals', False),
+    ('exc_info', False),
+    ('exception', False),
+    ('locale_name', False),
+    ('matchdict', False),
     ('matched_route', True),
-    ('path', None),
-    # ('registry', None),  # see "Note1"
-    ('root', None),
-    ('subpath', None),
-    ('traversed', None),
-    ('unauthenticated_userid', None),
-    ('url', None),
-    ('view_name', None),
-    ('virtual_root_path', None),
-    ('virtual_root', None),
+    ('path', False),
+    # ('registry', False),  # see "Note1"
+    ('root', False),
+    ('subpath', False),
+    ('traversed', False),
+    ('unauthenticated_userid', False),
+    ('url', False),
+    ('view_name', False),
+    ('virtual_root_path', False),
+    ('virtual_root', False),
 )
 # Note1: accessed as a 'string', `registry` be the python package name;
 #        accessed as a dict, will be the contents of the registry
@@ -78,27 +78,51 @@ class RequestVarsDebugPanel(DebugPanel):
     def __init__(self, request):
         self.request = request
         self.data = data = {}
-        attr_dict = request.__dict__.copy()
+        attrs = request.__dict__.copy()
         # environ is displayed separately
-        del attr_dict['environ']
-        if 'response' in attr_dict:
-            attr_dict['response'] = repr(attr_dict['response'])
+        del attrs['environ']
+
+        if 'response' in attrs:
+            attrs['response'] = repr(attrs['response'])
+
+        if 'session' in attrs:
+            self.process_session_attr(self, attrs['session'])
+            del attrs['session']
+        else:
+            # only process the session if it's accessed
+            callback_on_load(request, 'session', self.process_session_attr)
+
         data.update({
             'get': [(k, request.GET.getall(k)) for k in request.GET],
             'post': [(k, saferepr(v)) for k, v in request.POST.items()],
             'cookies': [(k, request.cookies.get(k)) for k in request.cookies],
-            'attrs': dictrepr(attr_dict),
             'environ': dictrepr(request.environ),
             'extracted_attributes': {},
+            'attrs': dictrepr(attrs),
+            'session': None,
+        })
+
+    def process_session_attr(self, session):
+        self.data.update({
+            'session': dictrepr(session),
         })
-        if hasattr(request, 'session'):
-            data.update({
-                'session': dictrepr(request.session),
-            })
+        return session
 
     def process_response(self, response):
         extracted_attributes = extract_request_attributes(self.request)
         self.data['extracted_attributes'] = extracted_attributes
 
         # stop hanging onto the request after the response is processed
         del self.request
+
+def callback_on_load(obj, name, cb):
+    """ Callback when a property is accessed.
+
+    This currently only works for reified properties that are called once.
+
+    """
+    orig_property = getattr(obj.__class__, name)
+    def wrapper(self):
+        val = orig_property.__get__(obj)
+        return cb(val)
+    obj.set_property(wrapper, name=name, reify=True)

pyramid_debugtoolbar/panels/templates/request_vars.dbtmako

@@ -203,6 +203,8 @@
 				% endfor
 			</tbody>
 		</table>
+	% elif session is None:
+		<p>Session was not accessed</p>
 	% else:
 		<p>No session data</p>
 	% endif