311 lines
11 KiB
Python
311 lines
11 KiB
Python
"""
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.. moduleauthor:: Fabio Manganiello <blacklight86@gmail.com>
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.. license: MIT
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"""
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import logging
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import threading
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import time
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from threading import Thread
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from typing import Optional
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from platypush.bus import Bus
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from platypush.config import Config
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from platypush.context import get_backend
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from platypush.utils import set_timeout, clear_timeout, \
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get_redis_queue_name_by_message, set_thread_name
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from platypush.event import EventGenerator
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from platypush.message import Message
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from platypush.message.event import Event, StopEvent
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from platypush.message.request import Request
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from platypush.message.response import Response
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class Backend(Thread, EventGenerator):
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"""
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Parent class for backends.
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A backend is basically a thread that checks for new events on some channel
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(e.g. a network socket, a queue, some new entries on an API endpoint or an
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RSS feed, a voice command through an assistant, a new measure from a sensor
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etc.) and propagates event messages to the main application bus whenever a
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new event happens. You can then build whichever type of custom logic you
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want on such events.
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"""
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_default_response_timeout = 5
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# Loop function, can be implemented by derived classes
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loop = None
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def __init__(self, bus: Optional[Bus] = None, poll_seconds: Optional[float] = None, **kwargs):
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"""
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:param bus: Reference to the bus object to be used in the backend
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:param poll_seconds: If the backend implements a ``loop`` method, this parameter expresses how often the
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loop should run in seconds.
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:param kwargs: Key-value configuration for the backend
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"""
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self._thread_name = self.__class__.__name__
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EventGenerator.__init__(self)
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Thread.__init__(self, name=self._thread_name)
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# If no bus is specified, create an internal queue where
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# the received messages will be pushed
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self.bus = bus or Bus()
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self.poll_seconds = float(poll_seconds) if poll_seconds else None
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self.device_id = Config.get('device_id')
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self.thread_id = None
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self._should_stop = False
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self._stop_event = threading.Event()
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self._kwargs = kwargs
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self.logger = logging.getLogger(self.__class__.__name__)
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# Internal-only, we set the request context on a backend if that
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# backend is intended to react for a response to a specific request
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self._request_context = kwargs['_req_ctx'] if '_req_ctx' in kwargs \
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else None
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if 'logging' in kwargs:
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self.logger.setLevel(getattr(logging, kwargs.get('logging').upper()))
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Thread.__init__(self)
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def on_message(self, msg):
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"""
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Callback when a message is received on the backend.
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It parses and posts the message on the main bus.
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It should be called by the derived classes whenever
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a new message should be processed.
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:param msg: Received message. It can be either a key-value dictionary, a platypush.message.Message object,
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or a string/byte UTF-8 encoded string
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"""
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msg = Message.build(msg)
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if not getattr(msg, 'target') or msg.target != self.device_id:
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return # Not for me
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self.logger.debug('Message received on the {} backend: {}'.format(
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self.__class__.__name__, msg))
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if self._is_expected_response(msg):
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# Expected response, trigger the response handler
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clear_timeout()
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self._request_context['on_response'](msg)
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self.stop()
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return
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if isinstance(msg, StopEvent) and msg.targets_me():
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self.logger.info('Received STOP event on {}'.format(self.__class__.__name__))
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self._should_stop = True
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else:
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msg.backend = self # Augment message to be able to process responses
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self.bus.post(msg)
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def _is_expected_response(self, msg):
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""" Internal only - returns true if we are expecting for a response
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and msg is that response """
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return self._request_context \
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and isinstance(msg, Response) \
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and msg.id == self._request_context['request'].id
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def _get_backend_config(self):
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config_name = 'backend.' + self.__class__.__name__.split('Backend')[0].lower()
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return Config.get(config_name)
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def _setup_response_handler(self, request, on_response, response_timeout):
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def _timeout_hndl():
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raise RuntimeError('Timed out while waiting for a response from {}'.
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format(request.target))
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req_ctx = {
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'request': request,
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'on_response': on_response,
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'response_timeout': response_timeout,
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}
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resp_backend = self.__class__(bus=self.bus, _req_ctx=req_ctx,
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**self._get_backend_config(), **self._kwargs)
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# Set the response timeout
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if response_timeout:
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set_timeout(seconds=response_timeout, on_timeout=_timeout_hndl)
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resp_backend.start()
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def send_event(self, event, **kwargs):
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"""
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Send an event message on the backend.
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:param event: Event to send. It can be a dict, a string/bytes UTF-8 JSON, or a platypush.message.event.Event
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object.
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"""
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event = Event.build(event)
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assert isinstance(event, Event)
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event.origin = self.device_id
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if not hasattr(event, 'target'):
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event.target = self.device_id
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self.send_message(event, **kwargs)
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def send_request(self, request, on_response=None,
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response_timeout=_default_response_timeout, **kwargs):
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"""
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Send a request message on the backend.
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:param request: The request, either a dict, a string/bytes UTF-8 JSON, or a platypush.message.request.Request
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object.
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:param on_response: Optional callback that will be called when a response is received. If set, this method will
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synchronously wait for a response before exiting.
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:type on_response: function
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:param response_timeout: If on_response is set, the backend will raise an exception if the response isn't
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received within this number of seconds (default: None)
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:type response_timeout: float
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"""
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request = Request.build(request)
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assert isinstance(request, Request)
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request.origin = self.device_id
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if on_response and response_timeout != 0:
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self._setup_response_handler(request, on_response, response_timeout)
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self.send_message(request, **kwargs)
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def send_response(self, response, request, **kwargs):
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"""
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Send a response message on the backend.
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:param response: The response, either a dict, a string/bytes UTF-8 JSON, or a
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:class:`platypush.message.response.Response` object.
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:param request: Associated request, used to set the response parameters that will link them
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"""
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assert isinstance(response, Response)
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assert isinstance(request, Request)
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self.send_message(response, **kwargs)
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def send_message(self, msg, queue_name=None, **kwargs):
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"""
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Sends a platypush.message.Message to a node.
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To be implemented in the derived classes. By default, if the Redis
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backend is configured then it will try to deliver the message to
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other consumers through the configured Redis main queue.
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:param msg: The message to send
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:param queue_name: Send the message on a specific queue (default: the queue_name configured on the Redis
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backend)
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"""
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try:
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redis = get_backend('redis')
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if not redis:
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raise KeyError()
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except KeyError:
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self.logger.warning("Backend {} does not implement send_message " +
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"and the fallback Redis backend isn't configured")
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return
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redis.send_message(msg, queue_name=queue_name)
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def run(self):
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""" Starts the backend thread. To be implemented in the derived classes if the loop method isn't defined. """
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self.thread_id = threading.get_ident()
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set_thread_name(self._thread_name)
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if not callable(self.loop):
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return
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while not self.should_stop():
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try:
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with self:
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has_error = False
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while not self.should_stop() and not has_error:
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try:
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self.loop()
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except Exception as e:
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has_error = True
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self.logger.error(str(e))
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self.logger.exception(e)
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finally:
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if self.poll_seconds:
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time.sleep(self.poll_seconds)
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elif has_error:
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time.sleep(5)
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except Exception as e:
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self.logger.error('{} initialization error: {}'.format(self.__class__.__name__, str(e)))
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self.logger.exception(e)
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time.sleep(self.poll_seconds or 5)
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def __enter__(self):
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""" Invoked when the backend is initialized, if the main logic is within a ``loop()`` function """
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self.logger.info('Initialized backend {}'.format(self.__class__.__name__))
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def __exit__(self, exc_type, exc_val, exc_tb):
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""" Invoked when the backend is terminated, if the main logic is within a ``loop()`` function """
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self.on_stop()
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self.logger.info('Terminated backend {}'.format(self.__class__.__name__))
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def on_stop(self):
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""" Callback invoked when the process stops """
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pass
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def stop(self):
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""" Stops the backend thread by sending a STOP event on its bus """
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def _async_stop():
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evt = StopEvent(target=self.device_id, origin=self.device_id,
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thread_id=self.thread_id)
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self.send_message(evt)
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self._stop_event.set()
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self.on_stop()
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Thread(target=_async_stop).start()
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def should_stop(self):
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return self._should_stop
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def wait_stop(self, timeout=None):
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self._stop_event.wait(timeout)
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def _get_redis(self):
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import redis
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redis_backend = get_backend('redis')
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if not redis_backend:
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self.logger.warning('Redis backend not configured - some ' +
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'web server features may not be working properly')
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redis_args = {}
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else:
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redis_args = redis_backend.redis_args
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redis = redis.Redis(**redis_args)
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return redis
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def get_message_response(self, msg):
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try:
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redis = self._get_redis()
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response = redis.blpop(get_redis_queue_name_by_message(msg), timeout=60)
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if response and len(response) > 1:
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response = Message.build(response[1])
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else:
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response = None
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return response
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except Exception as e:
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self.logger.error('Error while processing response to {}: {}'.format(msg, str(e)))
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# vim:sw=4:ts=4:et:
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