app_manager: add a function to request to load the server application

this is similar to handler.register_service but for client-server
style applications.  register_service is not appropriate for such
applications becuase normally the client does not consume
(in the sense of set_ev_cls) asynchronous events from the server.

note: this automatically load the server only if "api" module is
directly loaded from the module defining the client application.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

ryu/base/app_manager.py

@@ -1,4 +1,4 @@
-# Copyright (C) 2011, 2012 Nippon Telegraph and Telephone Corporation.
+# Copyright (C) 2011-2014 Nippon Telegraph and Telephone Corporation.
 # Copyright (C) 2011 Isaku Yamahata <yamahata at valinux co jp>
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -48,6 +48,19 @@ def unregister_app(app):
     SERVICE_BRICKS.pop(app.name)
 
 
+def require_app(app_name):
+    """
+    Request the application to be loaded.
+
+    This is used for "api" style modules, which is imported by a client
+    application, to automatically load the corresponding server application.
+    """
+    frm = inspect.stack()[2]  # skip a frame for "api" module
+    m = inspect.getmodule(frm[0])  # client module
+    m._REQUIRED_APP = getattr(m, '_REQUIRED_APP', [])
+    m._REQUIRED_APP.append(app_name)
+
+
 class RyuApp(object):
     """
     The base class for Ryu applications.

ryu/controller/handler.py

@@ -90,6 +90,8 @@ def get_dependent_services(cls):
                     if cls.__module__ != service:
                         services.append(service)
 
+    m = sys.modules[cls.__module__]
+    services.extend(getattr(m, '_REQUIRED_APP', []))
     services = list(set(services))
     return services