On connection timeout, POP3 grabber fails with an unhandled AttributeError

[Jean-Paul Calderone]

This traceback shows up in my logs sometimes:

2012-05-10 14:40:57-0400 [ControlledPOP3GrabberProtocol (BandwidthMeasuringProtocol) (TLSMemoryBIOProtocol),client] Unhandled Error
        Traceback (most recent call last):
          File "/home/quotient/.local/lib/python2.7/site-packages/epsilon/hotfixes/deferredgenerator_tfailure.py", line 44, in gotResult
            _deferGenerator(g, deferred)
          File "/home/quotient/.local/lib/python2.7/site-packages/epsilon/hotfixes/deferredgenerator_tfailure.py", line 25, in _deferGenerator
            deferred.errback()
          File "/home/quotient/.local/lib/python2.7/site-packages/Twisted-11.1.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 391, in errback
            self._startRunCallbacks(fail)
          File "/home/quotient/.local/lib/python2.7/site-packages/Twisted-11.1.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 458, in _start File "/home/quotient/.local/lib/python2.7/site-packages/Twisted-11.1.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 458, in _start
RunCallbacks
            self._runCallbacks()
          File "/home/quotient/.local/lib/python2.7/site-packages/Twisted-11.1.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 545, in _runCa
llbacks
            current.result = callback(current.result, *args, **kw)
          File "/home/quotient/.local/lib/python2.7/site-packages/epsilon/hotfixes/deferredgenerator_tfailure.py", line 44, in gotResult
            _deferGenerator(g, deferred)
        --- <exception caught here> ---
          File "/home/quotient/.local/lib/python2.7/site-packages/epsilon/hotfixes/deferredgenerator_tfailure.py", line 20, in _deferGenerator
            result = g.next()
          File "/home/quotient/.local/lib/python2.7/site-packages/xquotient/grabber.py", line 501, in _grab
            self.setStatus(u"Connection lost", False)
          File "/home/quotient/.local/lib/python2.7/site-packages/xquotient/grabber.py", line 596, in setStatus
            self._transact(self.grabber.status.setStatus, msg, success)
        exceptions.AttributeError: 'NoneType' object has no attribute 'status'

Looking at the code, it seems the likely explanation is that the connection times out (a frequent occurrence on my net connection/server). `timeoutConnection` calls `stoppedRunning`. `stoppedRunning` sets `self.grabber` to `None` (a recent improvement, as previously it would choke on a scheduler problem before getting there, now fixed). `timeoutConnection` then calls `loseConnection` which eventually causes the connection to be lost, resulting in `connectionLost`, causing one of the Deferreds waited on in `_grab` to fail. This leads to a `setStatus` call which fails because the `grabber` attribute was discarded already.