Flask: Unable to access current_app from within socket.io listener

Question

I am trying to access current_app from within the listener so that I can use app config values for which channel to subscribe to. However I receive "RuntimeError: working outside of application context".

Here is the code in question:

from flask import Blueprint, Response, request, current_app
from socketio import socketio_manage
from socketio.namespace import BaseNamespace
from redis import StrictRedis
import pprint

socketapp = Blueprint('socketapp', __name__)


class MessageNamespace(BaseNamespace):
    def listener(self):
        pprint.pprint(current_app.config)
        r = StrictRedis()
        p = r.pubsub()
        p.subscribe('message-channel')

        messages = r.lrange('message', 0, -1)
        self.emit('message-message', ''.join(messages))

        for m in p.listen():
            if m['type'] == 'message':
                self.emit('message-message', m['data'])

    def on_subscribe(self):
        self.spawn(self.listener)


@socketapp.route('/socket.io/<path:remaining>')
def socketio(remaining):
    try:
        socketio_manage(request.environ, {'/messages': MessageNamespace}, request)
    except BaseException:
        pass
    return Response()


@socketapp.route('/message', methods=['GET'])
def say():
    msg = request.args.get('msg', None)
    if msg:
        r = StrictRedis(host=current_app.config['REDIS_HOST'])
        r.rpush('message', msg)
        r.publish('message-channel', msg)

        return Response('Message sent!')
    else:
        return Response('Please specify your message in the "msg" parameter')

Answer 1

current_app is only valid while an HTTP request is being processed (it's a proxy that transiently points to the actual app object). You'll need to either get access to the actual app object from this module or steal a reference to it via current_app._get_current_object().

Answer 2

Sean's snippet does not work for me. I wrote following hack based on it:

@bp.route('/<path:remaining>')
def socketio(remaining):
    app = current_app._get_current_object()
    try:
        # Hack: set app instead of request to make it available in the namespace.
        socketio_manage(request.environ, {'': ChatNamespace}, app)
    except:
        app.logger.error("Exception while handling socket.io connection", exc_info=True)
    return Response()


class ChatNamespace(BaseNamespace, RoomsMixin, BroadcastMixin):
    def __init__(self, environ, ns_name, request=None):
        self.context = None
        if request:
            # Hack: initialize context with app that was set instead of request. Then miss it in parent constructor call.
            app = request
            self.context = app.request_context(environ)
            self.context.push()
            app.preprocess_request()
        super(ChatNamespace, self).__init__(environ, ns_name)

def log(self, message):
        # Now we can access app and other goodies.
        self.context.app.logger.info("[{0}] {1}".format(self.socket.sessid, message))

def disconnect(self, *args, **kwargs):
        if self.context:
            self.context.pop()
        super(ChatNamespace, self).disconnect(*args, **kwargs)