Comment 7 for bug 1765748

Glance doesn't have any specific q-value tests broken at this point (we have broken tests, just not those). Like Nova, we have a glance Request object that relies on the best_match() that is being eliminated by webob. Using the webob replacement lookup() method doesn't make our tests pass out of the box. The different behavior has to do with the circumstances under which None is returned by the glance Request object's best_match_language() method.

The webob lookup() takes two optional arguments, default_tag and default, and both cannot be none. The difference is if there's no match by the algorithm, default is returned. If default_tag has a value, then *it* will be returned ... unless it is specifically ruled out in the header string by being mentioned with q=0 (in which case, default (which could be None in this case) is returned).

So we can't use lookup() without specifying a value for one of default_tag or default, which is going to mean there will be circumstances under which None is not returned for lookup() whereas it was for best_match(). We could do some monkeying around in best_match_language() to preserve current behavior, e.g., use a sentinel value for default and then return None if lookup() returns the sentinel. Not sure what the best course of action is here. Just making notes so I don't forget I thought about this.