[#2485] Enforce order of precedence on request handler middleware

Enforce Flask Extension > Pylons Extension > Flask Core > Pylons Core

Pylons requests are marked core=True or core=False depending on whether
they were set up in core or by an extension. This information is passed
to the handler so it can prioritize which app to use.

TODO: It's still not clear how we will mark Flask routes as core or not,
it will depend on how we end up setting up routing

ckan/config/middleware.py

@@ -252,10 +252,12 @@ def can_handle_request(self, environ):
         Returns (True, 'flask_app') if this is the case.
         '''
 
+        # TODO: identify matching urls as core or extension. This will depend
+        # on how we setup routing in Flask
+
         urls = self.url_map.bind_to_environ(environ)
         try:
             endpoint, args = urls.match()
-
             log.debug('Flask route match, endpoint: {0}, args: {1}'.format(
                 endpoint, args))
             return (True, self.app_name)
@@ -316,15 +318,29 @@ def __call__(self, environ, start_response):
 
         app_name = 'pylons_app'  # currently defaulting to pylons app
         answers = self.ask_around('can_handle_request', environ)
-        for answer in answers:
-            can_handle, asked_app = answer
-            if can_handle:
-                app_name = asked_app
-                break
-
         log.debug('Route support answers for {0} {1}: {2}'.format(
             environ.get('REQUEST_METHOD'), environ.get('PATH_INFO'),
             answers))
+        available_handlers = []
+        for answer in answers:
+            if len(answer) == 2:
+                can_handle, asked_app = answer
+                origin = 'core'
+            else:
+                can_handle, asked_app, origin = answer
+            if can_handle:
+                available_handlers.append('{0}_{1}'.format(asked_app, origin))
+
+        # Enforce order of precedence:
+        # Flask Extension > Pylons Extension > Flask Core > Pylons Core
+        if available_handlers:
+            if 'flask_app_extension' in available_handlers:
+                app_name = 'flask_app'
+            elif 'pylons_app_extension' in available_handlers:
+                app_name = 'pylons_app'
+            elif 'flask_app_core' in available_handlers:
+                app_name = 'flask_app'
+
         log.debug('Serving request via {0} app'.format(app_name))
         return self.apps[app_name](environ, start_response)
 

ckan/config/routing.py

@@ -88,16 +88,22 @@ def make_map():
 
     # The ErrorController route (handles 404/500 error pages); it should
     # likely stay at the top, ensuring it can always be resolved.
-    map.connect('/error/{action}', controller='error')
-    map.connect('/error/{action}/{id}', controller='error')
+    map.connect('/error/{action}', controller='error', core=True)
+    map.connect('/error/{action}/{id}', controller='error', core=True)
 
     map.connect('*url', controller='home', action='cors_options',
-                conditions=OPTIONS)
+                conditions=OPTIONS, core=True)
 
     # CUSTOM ROUTES HERE
     for plugin in p.PluginImplementations(p.IRoutes):
         map = plugin.before_map(map)
 
+    # Mark all routes added from extensions on the `before_map` extension point
+    # as non-core
+    for route in map.matchlist:
+        if 'core' not in route.defaults:
+            route.defaults['core'] = False
+
     map.connect('invite', '/__invite__/', controller='partyline', action='join_party')
 
     map.connect('home', '/', controller='home', action='index')
@@ -415,15 +421,26 @@ def make_map():
         m.connect('/testing/primer', action='primer')
         m.connect('/testing/markup', action='markup')
 
+    # Mark all unmarked routes added up until now as core routes
+    for route in map.matchlist:
+        if 'core' not in route.defaults:
+            route.defaults['core'] = True
+
     for plugin in p.PluginImplementations(p.IRoutes):
         map = plugin.after_map(map)
 
+    # Mark all routes added from extensions on the `after_map` extension point
+    # as non-core
+    for route in map.matchlist:
+        if 'core' not in route.defaults:
+            route.defaults['core'] = False
+
     # sometimes we get requests for favicon.ico we should redirect to
     # the real favicon location.
     map.redirect('/favicon.ico', config.get('ckan.favicon'))
 
     map.redirect('/*(url)/', '/{url}',
                  _redirect_code='301 Moved Permanently')
-    map.connect('/*url', controller='template', action='view')
+    map.connect('/*url', controller='template', action='view', core=True)
 
     return map

ckan/controllers/partyline.py

@@ -33,7 +33,10 @@ def _can_handle_request(self, environ):
         Decides whether it can handle a request with the Pylons app by
         matching the request environ against the route mapper
 
-        Returns (True, 'pylons_app') if this is the case.
+        Returns (True, 'pylons_app', origin) if this is the case.
+
+        origin can be either 'core' or 'extension' depending on where
+        the route was defined.
 
         NOTE: There is currently a catch all route for GET requests to
         point arbitrary urls to templates with the same name:
@@ -49,7 +52,8 @@ def _can_handle_request(self, environ):
         pylons_mapper = config['routes.map']
         match = pylons_mapper.match(environ=environ)
         if match:
+            origin = 'core' if match.get('core') == 'True' else 'extension'
             log.debug('Pylons route match: {0}'.format(match))
-            return (True, self.app_name)
+            return (True, self.app_name, origin)
         else:
             raise HighAndDry()