from functools import partial import uuid from engineio import json import pickle from .base_manager import BaseManager class PubSubManager(BaseManager): """Manage a client list attached to a pub/sub backend. This is a base class that enables multiple servers to share the list of clients, with the servers communicating events through a pub/sub backend. The use of a pub/sub backend also allows any client connected to the backend to emit events addressed to Socket.IO clients. The actual backends must be implemented by subclasses, this class only provides a pub/sub generic framework. :param channel: The channel name on which the server sends and receives notifications. """ name = 'pubsub' def __init__(self, channel='socketio', write_only=False, logger=None): super(PubSubManager, self).__init__() self.channel = channel self.write_only = write_only self.host_id = uuid.uuid4().hex self.logger = logger def initialize(self): super(PubSubManager, self).initialize() if not self.write_only: self.thread = self.server.start_background_task(self._thread) self._get_logger().info(self.name + ' backend initialized.') def emit(self, event, data, namespace=None, room=None, skip_sid=None, callback=None, **kwargs): """Emit a message to a single client, a room, or all the clients connected to the namespace. This method takes care or propagating the message to all the servers that are connected through the message queue. The parameters are the same as in :meth:`.Server.emit`. """ if kwargs.get('ignore_queue'): return super(PubSubManager, self).emit( event, data, namespace=namespace, room=room, skip_sid=skip_sid, callback=callback) namespace = namespace or '/' if callback is not None: if self.server is None: raise RuntimeError('Callbacks can only be issued from the ' 'context of a server.') if room is None: raise ValueError('Cannot use callback without a room set.') id = self._generate_ack_id(room, callback) callback = (room, namespace, id) else: callback = None self._publish({'method': 'emit', 'event': event, 'data': data, 'namespace': namespace, 'room': room, 'skip_sid': skip_sid, 'callback': callback, 'host_id': self.host_id}) def can_disconnect(self, sid, namespace): if self.is_connected(sid, namespace): # client is in this server, so we can disconnect directly return super().can_disconnect(sid, namespace) else: # client is in another server, so we post request to the queue self._publish({'method': 'disconnect', 'sid': sid, 'namespace': namespace or '/'}) def disconnect(self, sid, namespace=None): self._publish({'method': 'disconnect', 'sid': sid, 'namespace': namespace or '/'}) def close_room(self, room, namespace=None): self._publish({'method': 'close_room', 'room': room, 'namespace': namespace or '/'}) def _publish(self, data): """Publish a message on the Socket.IO channel. This method needs to be implemented by the different subclasses that support pub/sub backends. """ raise NotImplementedError('This method must be implemented in a ' 'subclass.') # pragma: no cover def _listen(self): """Return the next message published on the Socket.IO channel, blocking until a message is available. This method needs to be implemented by the different subclasses that support pub/sub backends. """ raise NotImplementedError('This method must be implemented in a ' 'subclass.') # pragma: no cover def _handle_emit(self, message): # Events with callbacks are very tricky to handle across hosts # Here in the receiving end we set up a local callback that preserves # the callback host and id from the sender remote_callback = message.get('callback') remote_host_id = message.get('host_id') if remote_callback is not None and len(remote_callback) == 3: callback = partial(self._return_callback, remote_host_id, *remote_callback) else: callback = None super(PubSubManager, self).emit(message['event'], message['data'], namespace=message.get('namespace'), room=message.get('room'), skip_sid=message.get('skip_sid'), callback=callback) def _handle_callback(self, message): if self.host_id == message.get('host_id'): try: sid = message['sid'] id = message['id'] args = message['args'] except KeyError: return self.trigger_callback(sid, id, args) def _return_callback(self, host_id, sid, namespace, callback_id, *args): # When an event callback is received, the callback is returned back # to the sender, which is identified by the host_id self._publish({'method': 'callback', 'host_id': host_id, 'sid': sid, 'namespace': namespace, 'id': callback_id, 'args': args}) def _handle_disconnect(self, message): self.server.disconnect(sid=message.get('sid'), namespace=message.get('namespace'), ignore_queue=True) def _handle_close_room(self, message): super(PubSubManager, self).close_room( room=message.get('room'), namespace=message.get('namespace')) def _thread(self): for message in self._listen(): data = None if isinstance(message, dict): data = message else: if isinstance(message, bytes): # pragma: no cover try: data = pickle.loads(message) except: pass if data is None: try: data = json.loads(message) except: pass if data and 'method' in data: self._get_logger().info('pubsub message: {}'.format( data['method'])) if data['method'] == 'emit': self._handle_emit(data) elif data['method'] == 'callback': self._handle_callback(data) elif data['method'] == 'disconnect': self._handle_disconnect(data) elif data['method'] == 'close_room': self._handle_close_room(data)