# Buggy code
def on_message(self, prepare, message):
    _type = message.delivery_info["routing_key"]

    # For redis when `fanout_patterns=False` (See Issue #1882)
    if _type.split(".", 1)[0] == "task":
        return
    try:
        handler = self.event_handlers[_type]
    except KeyError:
        pass
    else:
        return handler(message.payload)

    # proto2: hostname in header; proto1: in body
    hostname = message.headers.get("hostname") or message.payload["hostname"]
    if hostname != self.hostname:
        _, event = prepare(message.payload)
        self.update_state(event)
    else:
        self.clock.forward()


# Traceback (kombu.exceptions.ContentDisallowed)
[2018-09-10 02:33:07,446: CRITICAL/MainProcess] Unrecoverable error: ContentDisallowed('Refusing to deserialize disabled content of type json (application/json)',)
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/celery/worker/worker.py", line 205, in start
self.blueprint.start(self)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
step.start(parent)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 369, in start
return self.obj.start()
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 317, in start
blueprint.start(self)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
step.start(parent)
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 593, in start
c.loop(*c.loop_args())
File "/usr/lib/python3.6/site-packages/celery/worker/loops.py", line 91, in asynloop
next(loop)
File "/usr/lib/python3.6/site-packages/kombu/asynchronous/hub.py", line 354, in create_loop
cb(*cbargs)
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 1040, in on_readable
self.cycle.on_readable(fileno)
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 337, in on_readable
chan.handlers[type]()
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 667, in _receive
ret.append(self._receive_one(c))
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 697, in _receive_one
message, self._fanout_to_queue[exchange])
File "/usr/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 983, in _deliver
callback(message)
File "/usr/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 633, in _callback
return callback(message)
File "/usr/lib/python3.6/site-packages/kombu/messaging.py", line 624, in _receive_callback
return on_m(message) if on_m else self.receive(decoded, message)
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/gossip.py", line 201, in on_message
_, event = prepare(message.payload)
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 207, in payload
return self._decoded_cache if self._decoded_cache else self.decode()
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 192, in decode
self._decoded_cache = self._decode()
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 197, in _decode
self.content_encoding, accept=self.accept)
File "/usr/lib/python3.6/site-packages/kombu/serialization.py", line 256, in loads
raise self._for_untrusted_content(content_type, 'disabled')
kombu.exceptions.ContentDisallowed: Refusing to deserialize disabled content of type json (application/json)

# Fixed code
def on_message(self, prepare, message):
    _type = message.delivery_info["routing_key"]

    # For redis when `fanout_patterns=False` (See Issue #1882)
    if _type.split(".", 1)[0] == "task":
        return
    try:
        handler = self.event_handlers[_type]
    except KeyError:
        pass
    else:
        return handler(message.payload)

    # proto2: hostname in header; proto1: in body
    hostname = message.headers.get("hostname") or message.payload["hostname"]
    if hostname != self.hostname:
        try:
            _, event = prepare(message.payload)
            self.update_state(event)
        except (DecodeError, ContentDisallowed, TypeError) as exc:
            logger.error(exc)
    else:
        self.clock.forward()