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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, **kwargs):
if kwargs.get('ignore_queue'):
return super(PubSubManager, self).disconnect(
sid, namespace=namespace)
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']))
try:
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)
except:
self.server.logger.exception(
'Unknown error in pubsub listening thread')
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