Endless loop on missing Request.callbacks attribute

[tomek@…]

Trac uses the following code to resolve missing attribute:

    def __getattr__(self, name):
        """Performs lazy attribute lookup by delegating to the functions in the
        callbacks dictionary."""
        if name in self.callbacks:
            value = self.callbacks[name](self)
            setattr(self, name, value)
            return value
        raise AttributeError(name)

The problem is, that if the self.callbacks itself is missing, it ends with endless loop like:

Traceback (most recent call last):
  File "/var/trac/trac/trac/web/api.py", line 339, in send_error
    'text/html')
  File "/var/trac/trac/trac/web/chrome.py", line 652, in render_template
    data = self.populate_data(req, data)
  File "/var/trac/trac/trac/web/chrome.py", line 560, in populate_data
    d['chrome'].update(req.chrome)
  File "/var/trac/trac/trac/web/api.py", line 167, in __getattr__
    if name in self.callbacks:
  File "/var/trac/trac/trac/web/api.py", line 167, in __getattr__
    if name in self.callbacks:
  File "/var/trac/trac/trac/web/api.py", line 167, in __getattr__
    if name in self.callbacks:
  File "/var/trac/trac/trac/web/api.py", line 167, in __getattr__
    if name in self.callbacks:
[...]

We need to check for this condition, like:

trac/trac/web/api.py

@@ -164 +164 @@
     def __getattr__(self, name):
         """Performs lazy attribute lookup by delegating to the functions in the
         callbacks dictionary."""
-        if name in self.callbacks:
+        if name != 'callbacks' and name in self.callbacks:
             value = self.callbacks[name](self)
             setattr(self, name, value)
             return value

[osimons]

As the self.callbacks dict is created inside Request.__init__(), I can't quite see a situation where it would be missing? And, if it actually is missing somewhere due to perhaps sub-classing that does not call back the main init, that might well be worth looking into.

Could you provide some way to reproduce the error you get?

[tomek@…]

The error is related to TracForge plugin that replaces the Request.init().

The problem I got is indeed TracForge error, but occurs inside Trac itself.

[osimons]

Ah. In that case you need to file a ticket with the plugin over at Trac-Hacks. It is not really a Trac issue, and it will have to be the responsibility of that plugin to make sure everything works as it should.

Closing as invalid.

[Noah Kantrowitz]

The term "giant flaming hack" doesn't even begin to describe the code in question. However you can try to isolate the problem by looking for the line "Using patched init" in your log. TracForge is monkey-patching chunks of the 0.11 codebase into 0.10, hilarity ensues.

[tomek@…]

I do agree that this is a Trac Forge issue.

But with a change mentioned, I got a meaningfull error message, that allowed me to find the real cause. Without it, I got the loop and needed to fight the loop problem first. That's why I suggested the change. It could help in any situation, that we have a broken Request object.

Reffering to attribute in attribute-handler without the sanity check if we're reffering to ourself is a bug in my opinion.