During my first hours of reckoning working on chad I came down with a problem.
Since we try to exploit the model of monorepo we’ve decided that we’ll have our frontend served by the backend. It is generally a very bad idea and an anti-pattern, but since we’ll be building the backend and frontend from the same repository into one single Docker image, this has been found as a sane compromise.
Namely, I would like to handle all (previously unhandled) calls to backend that requires no prefix (ie. if I queried for
/.gitkeep I’d get
.gitkeep) get the static file server, which takes a URL path, navigates the filesystem that tends to find the offending file, however problem was found in it’s constructor:
def static(prefix, view=serve, **kwargs): """ Return a URL pattern for serving files in debug mode. from django.conf import settings from django.conf.urls.static import static urlpatterns = [ # ... the rest of your URLconf goes here ... ] + static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT) """ if not prefix: raise ImproperlyConfigured("Empty static prefix not permitted") elif not settings.DEBUG or urlsplit(prefix).netloc: # No-op if not in debug mode or a non-local prefix. return  return [ re_path(r'^%s(?P<path>.*)$' % re.escape(prefix.lstrip('/')), view, kwargs=kwargs), ]
It clearly accepts a prefix that cannot be equal to False, so if we were limited to expressing ourselves with empty strings which natively are equal to False is a way nowhere. A closer inspection of the source code reveals that an empty prefix is indeed a distinct possiblity.
Note how the check here is performed. There is no
in '' syntax. There’s no checking equality to a specific value. Empty string, being a static would have been interned anyway by the Python interpreter itself. We need a particular piece of code to defeat it. We need advanced cheese, namely – empty strings that evaluate to True:
class TrueString(str): def __bool__(self): return True #: which conforms to the specification of: emptystring = TrueString('') assert emptystring assert bool(emptystring) assert len(emptystring) == 0 assert emptystring == ''
Thanks to the Python nature of everything-can-be-extended class system. So naturally being a case of static I handled it like this:
... path(r'swagger-ui/', SpectacularSwaggerView.as_view(url_name='schema'), name='swagger-ui'), ] + static(TrueString(''), document_root=settings.STATIC_ROOT)
Me and the interpreter parted ways in best of the moods.
Now it’s time for your advanced cheese stories.