Unable to emit after rabbitmq channel.start_consuming() call in flask-socketio handler - rabbitmq

Question

I'm trying to listen to a rabbitmq queue from within a flask-socketio event handler so I can send realtime notifications to a web app. My setup so far:
Server
import pika
import sys
from flask import Flask, request
from flask_socketio import SocketIO, emit, disconnect
app = Flask(__name__)
app.config['SECRET_KEY'] = 'not-so-secret'
socketio = SocketIO(app)
def is_authenticated():
return True
def rabbit_callback(ch, method, properties, body):
socketio.emit('connect', {'data': 'yes'})
print "body: ", body
#socketio.on('connect')
def connected():
emit('notification', {'data': 'Connected'})
creds = pika.PlainCredentials(
username="username",
password="password")
params = pika.ConnectionParameters(
host="localhost",
credentials=creds,
virtual_host="/")
connection = pika.BlockingConnection(params)
# This is one channel inside the connection
channel = connection.channel()
# Declare the exchange we're going to use
exchange_name = 'user'
channel.exchange_declare(exchange=exchange_name,
type='topic')
channel.queue_declare(queue='notifications')
channel.queue_bind(exchange='user',
queue='notifications',
routing_key='#')
channel.basic_consume(rabbit_callback,
queue='notifications',
no_ack=True)
channel.start_consuming()
if __name__ == '__main__':
socketio.run(app, port=8082)
Browser
<script type="text/javascript" charset="utf-8">
var socket = io.connect('http://' + document.domain + ':8082');
socket.on('connect', function(resp) {
console.log(resp);
});
socket.on('disconnect', function(resp) {
console.log(resp);
});
socket.on('error', function(resp) {
console.log(resp);
});
socket.on('notification', function(resp) {
console.log(resp);
});
</script>
If I comment out the "channel.start_consuming()" line at the bottom of the server code and load the browser page, I connect successfully to flask-socketio and I see {data: "Connected"} in my console.
When I uncomment the line, I do not see {data: "Connected"} in my console. Nevertheless, when I send a message to the notifications queue, the rabbit_callback function fires. I see my message printed to the server console, but the emit call doesn't seem to work. There are no errors on the server or in the browser. Any advice is much appreciated.
Thanks!

Answer 1

I had the same problem using eventlet and I just solved adding:
import eventlet
eventlet.monkey_patch()
,at the beginning of my source code.
Anyway my code is a bit different and using the start_background_task method:
import pika
from threading import Lock
from flask import Flask, render_template, session, request, copy_current_request_context
from flask_socketio import SocketIO, emit, join_room, leave_room, \
close_room, rooms, disconnect
app = Flask(__name__, static_url_path='/static')
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app, async_mode=async_mode)
thread = None
thread_lock = Lock()
#socketio.on('connect', namespace='/test')
def test_connect():
global thread
with thread_lock:
if thread is None:
thread = socketio.start_background_task(target=get_messages)
emit('my_response', {'data': 'Connected', 'count': 0})
print('connected')
def get_messages():
channel = connect_rabbitmq()
channel.start_consuming()
def connect_rabbitmq():
cred = pika.credentials.PlainCredentials('username', 'password')
conn_param = pika.ConnectionParameters(host='yourhostname',
credentials=cred)
connection = pika.BlockingConnection(conn_param)
channel = connection.channel()
channel.exchange_declare(exchange='ncs', exchange_type='fanout')
result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue
channel.queue_bind(exchange='myexchangename', queue=queue_name)
channel.basic_consume(callback, queue=queue_name, no_ack=True)
return channel
Hope this helps...