twisted.web._auth.wrapper causes an "Unhandled error in Deferred"

[honeyman]

Whenever a deferred without any errbacks gets a Failure, the "Unhandled error in Deferred" warning is unconditionally generated.

Whenever an http.Request.notifyFinish() method is called, a new deferred is generated (rather than, eg., some common one is used). It is a duty of caller to add the proper errback to this deferred, to handle a scenario if the connection is suddenly dropped. If the errback is not added, the "Unhandled error in Deferred" warning is generated.

One of the built-in callers of notifyFinish (and in fact, at the moment, the only one) is ResourceWrapper.render() in HTTPAuthSessionWrapper._loginSucceeded() method in twisted.web._auth.wrapper module - it adds a callback to log out, but doesn't add any errbacks.

[exarkun]

(In [28869]) Call logout on notifyFinish errback, too.

refs #4411

[itamar]

1. Move common infrastructure for logout test into shared utility function.

2. That's it I guess, looks good otherwise.

[exarkun]

(In [28881]) Factor common code out of test_logout and test_logoutOnError into a helper method

refs #4411

[exarkun]

(In [28884]) Merge guard-logout-on-error-4411

Author: exarkun Reviewer: itamar Fixes: #4411

Fix a bug in twisted.web.guard.SessionWrapper which would cause it to fail to call the realm-provided logout callback if there was an error rendering the response to the request (eg the client disconnected before it was all generated).