cloudbridge/test/test_middleware_system.py

import unittest

from cloudbridge.cloud.base.events import SimpleEventDispatcher
from cloudbridge.cloud.base.middleware import BaseMiddleware
from cloudbridge.cloud.base.middleware import ExceptionWrappingMiddleware
from cloudbridge.cloud.base.middleware import SimpleMiddlewareManager
from cloudbridge.cloud.base.middleware import implement
from cloudbridge.cloud.base.middleware import intercept
from cloudbridge.cloud.base.middleware import observe
from cloudbridge.cloud.interfaces.exceptions import CloudBridgeBaseException
from cloudbridge.cloud.interfaces.exceptions import \
    InvalidConfigurationException
from cloudbridge.cloud.interfaces.middleware import Middleware


class MiddlewareSystemTestCase(unittest.TestCase):

    def test_basic_middleware(self):

        class DummyMiddleWare(Middleware):

            def __init__(self):
                self.invocation_order = ""

            def install(self, event_manager):
                self.event_manager = event_manager
                self.invocation_order += "install_"

            def uninstall(self):
                self.invocation_order += "uninstall"

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        middleware = DummyMiddleWare()
        manager.add(middleware)

        self.assertEqual(middleware.invocation_order, "install_",
                         "install should be called when adding new middleware")

        manager.remove(middleware)
        self.assertEqual(middleware.invocation_order, "install_uninstall",
                         "uninstall should be called when removing middleware")

    def test_base_middleware(self):
        EVENT_NAME = "some.event.occurred"

        class DummyMiddleWare(BaseMiddleware):

            def __init__(self):
                self.invocation_order = ""

            @intercept(event_pattern="some.event.*", priority=900)
            def my_callback_intcpt(self, event_args, *args, **kwargs):
                self.invocation_order += "intcpt_"
                assert 'first_pos_arg' in args
                assert kwargs.get('a_keyword_arg') == "something"
                next_handler = event_args.get('next_handler')
                return next_handler.invoke(event_args, *args, **kwargs)

            @implement(event_pattern="some.event.*", priority=950)
            def my_callback_impl(self, *args, **kwargs):
                self.invocation_order += "impl_"
                assert 'first_pos_arg' in args
                assert kwargs.get('a_keyword_arg') == "something"
                return "hello"

            @observe(event_pattern="some.event.*", priority=1000)
            def my_callback_obs(self, event_args, *args, **kwargs):
                self.invocation_order += "obs"
                assert 'first_pos_arg' in args
                assert event_args['result'] == "hello"
                assert kwargs.get('a_keyword_arg') == "something"

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        middleware = DummyMiddleWare()
        manager.add(middleware)
        dispatcher.dispatch(self, EVENT_NAME, 'first_pos_arg',
                            a_keyword_arg='something')

        self.assertEqual(middleware.invocation_order, "intcpt_impl_obs")
        self.assertListEqual(
            [middleware.my_callback_intcpt, middleware.my_callback_impl,
             middleware.my_callback_obs],
            [handler.callback for handler
             in dispatcher.get_handlers_for_event(EVENT_NAME)])

        manager.remove(middleware)

        self.assertListEqual([], dispatcher.get_handlers_for_event(EVENT_NAME))

    def test_multiple_middleware(self):
        EVENT_NAME = "some.really.interesting.event.occurred"

        class DummyMiddleWare1(BaseMiddleware):

            @observe(event_pattern="some.really.*", priority=1000)
            def my_obs1_3(self, *args, **kwargs):
                pass

            @implement(event_pattern="some.*", priority=970)
            def my_impl1_2(self, *args, **kwargs):
                return "hello"

            @intercept(event_pattern="some.*", priority=900)
            def my_intcpt1_1(self, event_args, *args, **kwargs):
                next_handler = event_args.get('next_handler')
                return next_handler.invoke(event_args, *args, **kwargs)

        class DummyMiddleWare2(BaseMiddleware):

            @observe(event_pattern="some.really.*", priority=1050)
            def my_obs2_3(self, *args, **kwargs):
                pass

            @intercept(event_pattern="*", priority=950)
            def my_intcpt2_2(self, event_args, *args, **kwargs):
                next_handler = event_args.get('next_handler')
                return next_handler.invoke(event_args, *args, **kwargs)

            @implement(event_pattern="some.really.*", priority=920)
            def my_impl2_1(self, *args, **kwargs):
                pass

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        middleware1 = DummyMiddleWare1()
        middleware2 = DummyMiddleWare2()
        manager.add(middleware1)
        manager.add(middleware2)
        dispatcher.dispatch(self, EVENT_NAME)

        # Callbacks in both middleware classes should be registered
        self.assertListEqual(
            [middleware1.my_intcpt1_1, middleware2.my_impl2_1,
             middleware2.my_intcpt2_2, middleware1.my_impl1_2,
             middleware1.my_obs1_3, middleware2.my_obs2_3],
            [handler.callback for handler
             in dispatcher.get_handlers_for_event(EVENT_NAME)])

        manager.remove(middleware1)

        # Only middleware2 callbacks should be registered
        self.assertListEqual(
            [middleware2.my_impl2_1, middleware2.my_intcpt2_2,
             middleware2.my_obs2_3],
            [handler.callback for handler in
             dispatcher.get_handlers_for_event(EVENT_NAME)])

        # add middleware back to check that internal state is properly handled
        manager.add(middleware1)

        # should one again equal original list
        self.assertListEqual(
            [middleware1.my_intcpt1_1, middleware2.my_impl2_1,
             middleware2.my_intcpt2_2, middleware1.my_impl1_2,
             middleware1.my_obs1_3, middleware2.my_obs2_3],
            [handler.callback for handler
             in dispatcher.get_handlers_for_event(EVENT_NAME)])

    def test_automatic_middleware(self):
        EVENT_NAME = "another.interesting.event.occurred"

        class SomeDummyClass(object):

            @observe(event_pattern="another.really.*", priority=1000)
            def not_a_match(self, *args, **kwargs):
                pass

            @intercept(event_pattern="another.*", priority=900)
            def my_callback_intcpt2(self, *args, **kwargs):
                pass

            def not_an_event_handler(self, *args, **kwargs):
                pass

            @observe(event_pattern="another.interesting.*", priority=1000)
            def my_callback_obs1(self, *args, **kwargs):
                pass

            @implement(event_pattern="another.interesting.*", priority=1050)
            def my_callback_impl(self, *args, **kwargs):
                pass

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        some_obj = SomeDummyClass()
        middleware = manager.add(some_obj)
        dispatcher.dispatch(self, EVENT_NAME)

        # Middleware should be discovered even if class containing interceptors
        # doesn't inherit from Middleware
        self.assertListEqual(
            [some_obj.my_callback_intcpt2, some_obj.my_callback_obs1,
             some_obj.my_callback_impl],
            [handler.callback for handler
             in dispatcher.get_handlers_for_event(EVENT_NAME)])

        manager.remove(middleware)

        # Callbacks should be correctly removed
        self.assertListEqual(
            [],
            [handler.callback for handler in
             dispatcher.get_handlers_for_event(EVENT_NAME)])


class ExceptionWrappingMiddlewareTestCase(unittest.TestCase):

    def test_unknown_exception_is_wrapped(self):
        EVENT_NAME = "an.exceptional.event"

        class SomeDummyClass(object):

            @implement(event_pattern=EVENT_NAME, priority=2500)
            def raise_a_non_cloudbridge_exception(self, *args, **kwargs):
                raise Exception("Some unhandled exception")

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        middleware = ExceptionWrappingMiddleware()
        manager.add(middleware)

        # no exception should be raised when there's no next handler
        dispatcher.dispatch(self, EVENT_NAME)

        some_obj = SomeDummyClass()
        manager.add(some_obj)

        with self.assertRaises(CloudBridgeBaseException):
            dispatcher.dispatch(self, EVENT_NAME)

    def test_cloudbridge_exception_is_passed_through(self):
        EVENT_NAME = "an.exceptional.event"

        class SomeDummyClass(object):

            @implement(event_pattern=EVENT_NAME, priority=2500)
            def raise_a_cloudbridge_exception(self, *args, **kwargs):
                raise InvalidConfigurationException()

        dispatcher = SimpleEventDispatcher()
        manager = SimpleMiddlewareManager(dispatcher)
        some_obj = SomeDummyClass()
        manager.add(some_obj)
        middleware = ExceptionWrappingMiddleware()
        manager.add(middleware)

        with self.assertRaises(InvalidConfigurationException):
            dispatcher.dispatch(self, EVENT_NAME)