id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
25409	Allow url and groups of urls to be easily tagged and selected	Atul Bhouraskar	Atul Bhouraskar	"== The Problem ==
Often (usually in middleware) processing has to be applied to a certain URLs only eg CORS. 

The usual way to specify this would be to create an additional set of regex patterns identifying these urls - eg. 
{{{
CORS_URLS_REGEX = r'^/api/.*$'
}}}
The middleware then typically matches the incoming request URL to the regex and determines whether it is to be selected for processing.

This approach has several limitations including:
* It violates DRY as the regexes in the settings have to be synced with the actual URL patterns
* Matching multiple patterns may require the app writer to essentially reinvent URL patterns - poorly.

== The Proposal ==
Add an optional {{{tags}}} keyword argument to {{{django.conf.urls.url}}} allowing a URL to be optionally tagged with one or more tags which can then be retrieved via {{{HttpRequest.resolver_match.tags}}} in the middleware / view etc.
{{{
urlpatterns = [
    url(r'^$', views.home, name='home'),
    url(r'^articles/$', views.show_articles, name='show-articles', tags=['require_GET']),
    url(r'^private/$', include(private_patterns), tags=['login_required']),
    url(r'^api/', include(api_patterns), tags=[
        'cors_allowed', 'nologin_forbidden', 'ajax_required'
    ]),
]
}}}

In the example above, the {{{home}}} url has no tags, the {{{show-articles}}} url is tagged {{{require_GET}}}, the urls under {{{private/}}} are all tagged {{{login_required}}} while the the urls under  {{{api/}}} have multiple tags.

This allows app middleware to selectively process urls very easily:
{{{
class LoginRequiredMiddleware(object):
    def process_view(self, request, view_func, view_args, view_kwargs):
        if 'login_required' in request.resolver_match.tags and \
                not request.user.is_authenticated():
            return redirect('login')

class RequireGETMiddleware(object):
    def process_view(self, request, view_func, view_args, view_kwargs):
        if 'require_GET' in request.resolver_match.tags and request.method != 'GET':
            return HttpResponseNotAllowed(['GET'])

class AjaxRequiredMiddleware(object):
    def process_view(self, request, view_func, view_args, view_kwargs):
        if 'ajax_required' in request.resolver_match.tags and not request.is_ajax():
            return HttpResponseForbidden()

class CorsMiddleware(object):
    def process_view(self, request, view_func, view_args, view_kwargs):
        if 'cors_allowed' in request.resolver_match.tags:
            # continue CORS processing
}}}

I am attaching a patch that implements this tagging feature to urlpatterns. It has tests (docs to be added). The change is fully backwards compatible as specifying tags is completely optional, all existing tests pass with the patch applied to master.

I'm working on my branch at https://github.com/atul-bhouraskar/django/tree/ticket_25409
 
Comments welcome!"	New feature	assigned	Core (URLs)	dev	Normal				Unreviewed	1	0	0	0	0	0