203 lines
6.8 KiB
Python
203 lines
6.8 KiB
Python
import importlib
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import logging
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import sys
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import threading
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from threading import Thread
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from platypush.bus import Bus
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from platypush.config import Config
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from platypush.utils import get_message_class_by_type, set_timeout, clear_timeout
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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):
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""" Parent class for backends """
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_default_response_timeout = 5
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def __init__(self, bus=None, **kwargs):
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"""
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Params:
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bus -- Reference to the Platypush bus where the requests and the
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responses will be posted [Bus]
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kwargs -- key-value configuration for this backend [Dict]
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"""
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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.device_id = Config.get('device_id')
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self.thread_id = None
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self._stop = False
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self._kwargs = kwargs
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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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Thread.__init__(self)
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logging.basicConfig(stream=sys.stdout, level=Config.get('logging')
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if 'logging' not in kwargs
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else getattr(logging, kwargs['logging']))
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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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Params:
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msg -- The message. It can be either a key-value
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dictionary, a platypush.message.Message
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object, 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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logging.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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logging.info('Received STOP event on {}'.format(self.__class__.__name__))
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self._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_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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Params:
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request -- The request, either a dict, a string/bytes UTF-8 JSON,
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or a platypush.message.request.Request object.
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on_response -- Response handler, takes a platypush.message.response.Response
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as argument. If set, the method will wait for a
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response before exiting (default: None)
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response_timeout -- If on_response is set, the backend will raise
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an exception if the response isn't received
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within this number of seconds (default: 5)
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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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Params:
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response -- The response, either a dict, a string/bytes UTF-8 JSON,
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or a platypush.message.response.Response object
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request -- Associated request, used to set the response parameters
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that will link them
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"""
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response = Response.build(response)
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assert isinstance(response, Response)
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assert isinstance(request, Request)
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response.id = request.id
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response.target = request.origin
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response.origin = self.device_id
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self.send_message(response, **kwargs)
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def send_message(self, msg, **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.
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Always call send_request or send_response instead of send_message directly
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Param:
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msg -- The message
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"""
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raise NotImplementedError("send_message should be implemented in a derived class")
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def run(self):
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""" Starts the backend thread. To be implemented in the derived classes """
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self.thread_id = threading.get_ident()
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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.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._stop
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# vim:sw=4:ts=4:et:
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