baseimage-tutorial-framework/lib/tfw/event_handler_base.py

189 lines
5.8 KiB
Python

# Copyright (C) 2018 Avatao.com Innovative Learning Kft.
# All Rights Reserved. See LICENSE file for details.
from abc import ABC, abstractmethod
from inspect import currentframe
from typing import Iterable
from tfw.networking.event_handlers import ServerConnector
from tfw.crypto import message_checksum, KeyManager, verify_message
from tfw.config.logs import logging
LOG = logging.getLogger(__name__)
class EventHandlerBase(ABC):
"""
Abstract base class for all Python based EventHandlers. Useful implementation template
for other languages.
Derived classes must implement the handle_event() method
"""
def __init__(self, key):
self.server_connector = ServerConnector()
self.keys = []
if isinstance(key, str):
self.keys.append(key)
elif isinstance(key, Iterable):
self.keys = list(key)
self.subscribe(*self.keys)
self.server_connector.register_callback(self.event_handler_callback)
@property
def key(self):
"""
Returns the oldest key this EventHandler was subscribed to.
"""
return self.keys[0]
def event_handler_callback(self, message):
"""
Callback that is invoked when receiving a message.
Dispatches messages to handler methods and sends
a response back in case the handler returned something.
This is subscribed in __init__().
"""
if not self.check_key(message):
return
response = self.dispatch_handling(message)
if response:
self.server_connector.send(response)
def check_key(self, message):
"""
Checks whether the message is intended for this
EventHandler.
This is necessary because ZMQ handles PUB - SUB
connetions with pattern matching (e.g. someone
subscribed to 'fsm' will receive 'fsm_update'
messages as well.
"""
if '' in self.keys:
return True
return message['key'] in self.keys
def dispatch_handling(self, message):
"""
Used to dispatch messages to their specific handlers.
:param message: the message received
:returns: the message to send back
"""
return self.handle_event(message)
@abstractmethod
def handle_event(self, message):
"""
Abstract method that implements the handling of messages.
:param message: the message received
:returns: the message to send back
"""
raise NotImplementedError
def subscribe(self, *keys):
"""
Subscribe this EventHandler to receive events for given keys.
Note that you can subscribe to the same key several times in which
case you will need to unsubscribe multiple times in order to stop
receiving events.
:param keys: list of keys to subscribe to
"""
for key in keys:
self.server_connector.subscribe(key)
self.keys.append(key)
def unsubscribe(self, *keys):
"""
Unsubscribe this eventhandler from the given keys.
:param keys: list of keys to unsubscribe from
"""
for key in keys:
self.server_connector.unsubscribe(key)
self.keys.remove(key)
def cleanup(self):
"""
Perform cleanup actions such as releasing database
connections and stuff like that.
"""
pass
@classmethod
def get_local_instances(cls):
frame = currentframe()
if frame is None:
raise EnvironmentError('inspect.currentframe() is not supported!')
locals_values = frame.f_back.f_locals.values()
return {
instance for instance in locals_values
if isinstance(instance, cls)
}
class FSMAwareEventHandler(EventHandlerBase, ABC):
# pylint: disable=abstract-method
"""
Abstract base class for EventHandlers which automatically
keep track of the state of the TFW FSM.
"""
def __init__(self, key):
super().__init__(key)
self.subscribe('fsm_update')
self.fsm_state = None
self.in_accepted_state = False
self._auth_key = KeyManager().auth_key
def dispatch_handling(self, message):
if message['key'] == 'fsm_update':
if verify_message(self._auth_key, message):
self._handle_fsm_update(message)
return None
return super().dispatch_handling(message)
def _handle_fsm_update(self, message):
try:
new_state = message['data']['current_state']
trigger = message['data']['last_trigger']
if self.fsm_state != new_state:
self.handle_fsm_step(self.fsm_state, new_state, trigger)
self.fsm_state = new_state
self.in_accepted_state = message['data']['in_accepted_state']
except KeyError:
LOG.error('Invalid fsm_update message received!')
def handle_fsm_step(self, from_state, to_state, trigger):
"""
Called in case the TFW FSM has stepped.
"""
pass
class BroadcastingEventHandler(EventHandlerBase, ABC):
# pylint: disable=abstract-method
"""
Abstract base class for EventHandlers which broadcast responses
and intelligently ignore their own broadcasted messages they receive.
"""
def __init__(self, key):
super().__init__(key)
self.own_message_hashes = []
def event_handler_callback(self, message):
message_hash = message_checksum(message)
if message_hash in self.own_message_hashes:
self.own_message_hashes.remove(message_hash)
return
response = self.dispatch_handling(message)
if response:
self.own_message_hashes.append(message_checksum(response))
self.server_connector.broadcast(response)