Catch bad comment links to prevent server errors

[ayleph]

While debugging #5376, we noticed that attempting to access a comment which doesn't exist causes a server error. Ideally, we'd catch this and throw a 404 or just show the media page instead.

Here's an example to illustrate the issue, but these links may go away soon :)

There's an actual comment at this link. Following it works as expected.

​http://pumpdev.goblinrefuge.com/u/ayleph/m/doge/c/23/#comment

Here I fat-fingered manually typing in the link, and I get a server error.

​http://pumpdev.goblinrefuge.com/u/ayleph/m/doge/c/123/#comment

Here's what the error looks like.

Error - <type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'id'
URL: http://pumpdev.goblinrefuge.com/u/ayleph/m/doge/c/28/
File '/path/to/mediagoblin/lib/python2.7/site-packages/Paste-1.7.5.1-py2.7.egg/paste/exceptions/errormiddleware.py', line 144 in __call__
  app_iter = self.application(environ, sr_checker)
File '/path/to/mediagoblin/mediagoblin/app.py', line 342 in __call__
  return self.call_backend(environ, start_response)
File '/path/to/mediagoblin/lib/python2.7/site-packages/Werkzeug-0.9.6-py2.7.egg/werkzeug/wsgi.py', line 588 in __call__
  return self.app(environ, start_response)
File '/path/to/mediagoblin/mediagoblin/app.py', line 276 in call_backend
  return self._finish_call_backend(request, environ, start_response)
File '/path/to/mediagoblin/mediagoblin/app.py', line 318 in _finish_call_backend
  response = controller(request)
File '/path/to/mediagoblin/mediagoblin/decorators.py', line 47 in wrapper
  return controller(request, *args, **kwargs)
File '/path/to/mediagoblin/mediagoblin/decorators.py', line 210 in wrapper
  return controller(request, media=media, *args, **kwargs)
File '/path/to/mediagoblin/mediagoblin/decorators.py', line 170 in wrapper
  return controller(request, page=page, *args, **kwargs)
File '/path/to/mediagoblin/mediagoblin/user_pages/views.py', line 135 in media_home
  mark_comment_notification_seen(comment_id, request.user)
File '/path/to/mediagoblin/mediagoblin/notifications/__init__.py', line 75 in mark_comment_notification_seen
  obj_pk=comment.id,
AttributeError: 'NoneType' object has no attribute 'id'

[ayleph]

If instead of typing in a comment ID which doesn't exist you type in a comment ID which does exist but isn't attached to this media, the media page is displayed with no comment highlighted. This seems acceptable to me. Here's a patch which replicates that behaviour when a non-existent comment ID is passed.

diff --git a/mediagoblin/notifications/__init__.py b/mediagoblin/notifications/__init__.py
index 9d2f2b7..d554de2 100644
--- a/mediagoblin/notifications/__init__.py
+++ b/mediagoblin/notifications/__init__.py
@@ -71,6 +71,11 @@ def mark_notification_seen(notification):

 def mark_comment_notification_seen(comment_id, user):
     comment = Comment.query.get(comment_id)
+
+    # If there is no comment, there is no notification
+    if comment == None:
+        return
+
     comment_gmr = GenericModelReference.query.filter_by(
         obj_pk=comment.id,
         model_type=comment.__tablename__

[ayleph]

Fixed as of ​289826d