baseimage-tutorial-framework/lib/tfw/builtins/fsm_managing_event_handler.py

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import logging
from tfw.crypto import KeyManager, sign_message, verify_message
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from tfw.networking import Scope
from tfw.components import FSMUpdater
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from .event_handler import EventHandler
LOG = logging.getLogger(__name__)
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class FSMManagingEventHandler(EventHandler):
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"""
EventHandler responsible for managing the state machine of
the framework (TFW FSM).
tfw.networking.TFWServer instances automatically send 'trigger'
commands to the event handler listening on the 'fsm' key,
which should be an instance of this event handler.
This event handler accepts messages that have a
data['command'] key specifying a command to be executed.
An 'fsm_update' message is broadcasted after every successful
command.
"""
def __init__(self, key, fsm_type, require_signature=False):
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super().__init__(key, scope=Scope.WEBSOCKET)
self.fsm = fsm_type()
self._fsm_updater = FSMUpdater(self.fsm)
self.auth_key = KeyManager().auth_key
self._require_signature = require_signature
self.command_handlers = {
'trigger': self.handle_trigger,
'update': self.handle_update
}
def handle_event(self, message):
try:
message = self.command_handlers[message['data']['command']](message)
if message:
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fsm_update_message = self._fsm_updater.fsm_update
sign_message(self.auth_key, message)
sign_message(self.auth_key, fsm_update_message)
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self.server_connector.send_message(fsm_update_message, Scope.BROADCAST)
self.send_message(message)
except KeyError:
LOG.error('IGNORING MESSAGE: Invalid message received: %s', message)
def handle_trigger(self, message):
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"""
Attempts to step the FSM with the supplied trigger.
:param message: TFW message with a data field containing
the action to try triggering in data['value']
"""
trigger = message['data']['value']
if self._require_signature:
if not verify_message(self.auth_key, message):
LOG.error('Ignoring unsigned trigger command: %s', message)
return None
if self.fsm.step(trigger):
return message
return None
def handle_update(self, message):
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"""
Does nothing, but triggers an 'fsm_update' message.
"""
# pylint: disable=no-self-use
return message