Add first experiment with websockets, for datasync status page

tailbone/app.py

@@ -129,6 +129,9 @@ def make_pyramid_config(settings, configure_csrf=True):
         settings.setdefault('pyramid_deform.template_search_path', 'tailbone:templates/deform')
         config = Configurator(settings=settings, root_factory=Root)
 
+    # add rattail config directly to registry
+    config.registry['rattail_config'] = rattail_config
+
     # configure user authorization / authentication
     config.set_authorization_policy(TailboneAuthorizationPolicy())
     config.set_authentication_policy(SessionAuthenticationPolicy())
@@ -175,9 +178,45 @@ def make_pyramid_config(settings, configure_csrf=True):
     config.add_directive('add_tailbone_index_page', 'tailbone.app.add_index_page')
     config.add_directive('add_tailbone_config_page', 'tailbone.app.add_config_page')
 
+    config.add_directive('add_tailbone_websocket', 'tailbone.app.add_websocket')
+
     return config
 
 
+def add_websocket(config, name, view, attr=None):
+    """
+    Register a websocket entry point for the app.
+    """
+    def action():
+        rattail_config = config.registry.settings['rattail_config']
+        rattail_app = rattail_config.get_app()
+
+        if isinstance(view, six.string_types):
+            view_callable = rattail_app.load_object(view)
+        else:
+            view_callable = view
+        view_callable = view_callable(config.registry)
+        if attr:
+            view_callable = getattr(view_callable, attr)
+
+        path = '/ws/{}'.format(name)
+
+        # register route
+        config.add_route('ws.{}'.format(name),
+                         path,
+                         static=True)
+
+        # register view callable
+        websockets = config.registry.setdefault('tailbone_websockets', {})
+        websockets[path] = view_callable
+
+    config.action('tailbone-add-websocket', action,
+                  # nb. since this action adds routes, it must happen
+                  # sooner in the order than it normally would, hence
+                  # we declare that
+                  order=-20)
+
+
 def add_index_page(config, route_name, label, permission):
     """
     Register a config page for the app.