Question about unexpected "connection closed" behavior

[daya0576]

Question

Hi I ran into a weird issue with iOS web app (PWA)

Here are the logs of this problem: the connection was closed after being re-established

# Close the app (move back to homescreen) and the connection closed after a few seconds ✅
2024-10-08T07:15:13Z nrt [info]INFO:     connection closed

# Reopen the web app and the connection was re-established ✅
2024-10-08T07:18:19Z nrt [info]INFO:     ('***', ***) - "WebSocket /socket.io/?client_id=***&EIO=4&transport=websocket" [accepted]
2024-10-08T07:18:19Z nrt [info]INFO:     connection open
2024-10-08T07:18:21Z nrt [info]INFO:     Getting user timezone...
2024-10-08T07:18:21Z nrt [info]INFO:     User timezone from storage: Asia/Shanghai
2024-10-08T07:18:21Z nrt [info]INFO:     Getting user habit list
2024-10-08T07:18:21Z nrt [info]INFO:     [CRUD] User be1dbc01-*** habit list query
2024-10-08T07:18:22Z nrt [info]INFO:     *** - "GET /gui HTTP/1.1" 200 OK

# The connection was closed after being re-established  ❌
# Note: "⚠️ Connection lost" error message popped up in the bottom left corner.
2024-10-08T07:18:22Z nrt [info]INFO:     connection closed
2024-10-08T07:18:22Z nrt [info]INFO:     *** - "GET /_nicegui/1.4.37/static/fonts.css HTTP/1.1" 304 Not Modified
...
2024-10-08T07:18:23Z nrt [info]INFO:     *** - "GET /_nicegui/1.4.37/static/fonts/e62204447c1ed92a.woff2 HTTP/1.1" 304 Not Modified
2024-10-08T07:18:24Z nrt [info]INFO:     *** - "WebSocket /socket.io/?client_id=***&EIO=4&transport=websocket" [accepted]
2024-10-08T07:18:24Z nrt [info]INFO:     connection open

I tested the nicegui main page with the same steps above but failed to reproduce the issue. So there must be something wrong with my code.

However, troubleshooting this problem without a reproduction case is challenging... Could you provide any possible root cause or debugging tips? thanks!

[daya0576]

I tried the aysncio debugging from the wiki but had no luck.

def startup():
    loop = asyncio.get_running_loop()
    loop.set_debug(True)
    loop.slow_callback_duration = 0.05

app.on_startup(startup)

[rodja]

Are you running multiple instances of the server?

[daya0576]

Actually not, I started the service with only one instance and one worker:

uvicorn beaverhabits.main:app --workers 1 --log-level info --port 8080 --host 0.0.0.0

[rodja]

Well.. I think we need a minimal reproducible example. Otherwise we can not help out.

[daya0576]

Sure, a minimal reproducible repo was created: https://github.com/daya0576/nicegui_websocket_mre

---

Here are the steps and logs corresponding to the clips in the repo:

# Step1: start service with `python main.py`
...

# Step2: move to the home screen and wait for a few seconds
INFO:     connection closed

# Step3: reopen the app
## 3.1. connection opened 
INFO:     ('10.200.1.182', 65064) - "WebSocket /socket.io/?client_id=bb3ff808-70a0-4b91-bbc1-ccb092b66881&EIO=4&transport=websocket" [accepted]
INFO:     connection open
INFO:     10.200.1.182:65065 - "GET /demo HTTP/1.1" 200 OK
## 3.2. connection closed because page refreshed?
INFO:     connection closed
INFO:     10.200.1.182:65065 - "GET /_nicegui/2.3.0/static/nicegui.css HTTP/1.1" 304 Not Modified
INFO:     10.200.1.182:65067 - "GET /_nicegui/2.3.0/static/fonts.css HTTP/1.1" 304 Not Modified
...
INFO:     10.200.1.182:65065 - "GET /_nicegui/2.3.0/static/fonts/62873223be6b39e0.woff2 HTTP/1.1" 304 Not Modified
INFO:     10.200.1.182:65065 - "GET /_nicegui/2.3.0/static/fonts/01d40c9fd448face.woff2 HTTP/1.1" 304 Not Modified
INFO:     ('10.200.1.182', 65071) - "WebSocket /socket.io/?client_id=06155faa-7e20-4223-a64b-c81939965e34&EIO=4&transport=websocket" [accepted]
INFO:     connection open

I guess in 3.2, the connection was closed because the page was reloaded. Do you have any idea:

• Why does the page refresh after the WebSocket connection is successfully established?
• Is it possible to refresh the page directly instead (to avoid establishing the connection twice)?

[daya0576]

With more tests, I found this is the side effect of standalone mode. If I disable it, the page will not be reloaded after the connection is re-established:

INFO:     connection closed

INFO:     10.200.1.182:65192 - "GET /demo HTTP/1.1" 200 OK
INFO:     ('10.200.1.182', 65193) - "WebSocket /socket.io/?client_id=ee6dd602-4d47-401e-992f-0e074fa43cbb&EIO=4&transport=websocket" [accepted]
INFO:     connection open

[daya0576]

Since this is an issue related to iOS instead of nicegui, I will do some research and update a solution if one is found.

Thank you anyway, @rodja.