Cant see traceback

class FooConsumer(SyncConsumer):
    def connect(self):
        assert False

    ...

produces

WebSocket HANDSHAKING /foo/ [127.0.0.1:00000]
WebSocket DISCONNECT /foo/ [127.0.0.1:00000]

With no traceback

python==3.6.8
django==1.11.16
channels==2.2.0
daphne==2.1.0
channels-redis==2.1.1
asgi-redis==1.4.3
asgiref==2.2.0

macOS Mojave 10.14.1

When I try to reproduce this with a minimal setup, it gives traceback

Exception inside application: 
  File "/path/to/django_sandbox/venv/lib/python3.6/site-packages/channels/sessions.py", line 183, in __call__
 ... 
  File "/path/to/django_sandbox/foo/consumers.py", line 7, in connect
    assert False

as expected.

Adding a print

logger.error("Exception inside application: %s", exception_output)
print(exception_output)

inside daphne.server.Server.application_checker allows me to see the output, so it seems daphne swallows the errors somehow.

[Ivo-Donchev]

Hey guys 🙂 ,

I think I found what’s the issue 🔥 🎉

So, what I did:

1. I created a super basic django project (as @carltongibson suggested) and start reproducing the bug - https://github.com/HackSoftware/django-channels-playground
2. I couldn’t reproduce in this clean state ❌
3. So I reproduce it in the project we first hit it and started slicing things from the code
4. I turned out that django-debug-toolbar was causing the issue in our case 😦 So it’s not a channels issue

I searched in the other issues and found this - https://github.com/django/channels/issues/1193 (there’s a suggested quickfix there)

I started debugging the django-debug-toolbar code to find the root of the problem and turned out that this class is causing it - https://github.com/jazzband/django-debug-toolbar/blob/87eb27ffb2d0aea60b8b139360ece4d9fc91b47e/debug_toolbar/utils.py#L222

It’s used by a code hooked to the python logging module and collects only the logs from the current thread (which channels is not part from) 😞

https://github.com/django/channels/issues/1340#issuecomment-539957522 - this was solving the problem because the print is forcing a message to the standart output rather than using the python logging module

Hope this will help someone ^

[Wrufesh]

Same here

backend:

WebSocket HANDSHAKING /webrtc/ [127.0.0.1:38882]
WebSocket DISCONNECT /webrtc/ [127.0.0.1:38882]
WebSocket HANDSHAKING /webrtc/ [127.0.0.1:39086]
WebSocket DISCONNECT /webrtc/ [127.0.0.1:39086]
WebSocket HANDSHAKING /webrtc/ [127.0.0.1:39114]
WebSocket DISCONNECT /webrtc/ [127.0.0.1:39114]
WebSocket HANDSHAKING /webrtc/ [127.0.0.1:39208]
WebSocket DISCONNECT /webrtc/ [127.0.0.1:39208]

frontend:

WebSocket connection to 'ws://localhost:8000/webrtc/' failed: Error during WebSocket handshake: Unexpected response code: 500