On-air issue: packet queue is empty

[raffaellof]

First Check

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Example Code

from nicegui import ui

ui.label('Hello')

ui.run(on_air=True, frameless=True, reload=False, window_size=(1200,700))

Description

I'm facing an issue using NiceGUI on air (i think not related to my code), sometimes on-air mode stop working with this message on console:

packet queue is empty, aborting

this error appears from the log:

2025-06-25 18:38:06,812 - ERROR: engineio.client packet queue is empty, aborting

subsequently the on-air service tries to restart several times (every time with a different address, of course):

NiceGUI is on air at https://europe.on-air.io/devices/.../
NiceGUI is on air at https://europe.on-air.io/devices/.../
NiceGUI is on air at https://europe.on-air.io/devices/.../
NiceGUI is on air at https://europe.on-air.io/devices/.../
NiceGUI is on air at https://europe.on-air.io/devices/.../
NiceGUI is on air at https://europe.on-air.io/devices/.../

but from the log it always shows an error:

2025-06-25 18:40:42,976 - WARNING: nicegui.air Connection error: Unable to connect
2025-06-25 18:41:05,343 - WARNING: nicegui.air Connection error: Unable to connect

The app on localhost still working as expected. I couldn't figure out how or when the error occurs, most of the time it works fine. Has anyone else encountered this problem?

NiceGUI Version

2.20.0 - 2.18.0

Python Version

3.10.11

Browser

Other

Operating System

Windows

Additional Context

[evnchn]

Do you have access to VPN? Can you try it with VPN on, then it'll direct you to another server. See if it works.

• if it does, maybe only Europe affected, likely some deployment issue (we seen it in On-Air between Brazil and Poland not working #4740)
• if it doesn't, either there's a bug in NiceGUI on air, or maybe there's some network firewall / software incompatibility on your machine (at select computers at my university, somehow WebSocket is unreliable for some reason)

[raffaellof]

I haven't tried with VPN, I noticed that sometimes instead of an "europe.on-air.io" address (my area) an "us-west.on-air.io" address is generated, but that error still occurs.

[rodja]

The error ERROR: engineio.client packet queue is empty, aborting occurs when Engine.IO/Socket.IO heartbeat fails. The error typically happens due to network issues. Or server-side issues like much load, infrastructure failures or bugs in the application.

It would be interesting to check:

1. Can you still ping europe.on-air.io when the error happens
2. Can you reproduce the problem in the next 1-2 days and share the device tokens you got? We will closely monitor the server logs to see what might cause problems.

[raffaellof]

I'm in Italy, the domain is reachable at dns level, but it is not responding...

nslookup europe.on-air.io

Non-authoritative answer:
Nome:    europe.on-air.io
Addresses:  2a09:8280:5d::e:3232:0
          213.188.204.130

[rodja]

Can you try pinging 213.188.204.130 explicitly. Many residential ISPs still advertise IPv6 but silently black-hole large MTU or fragmented ICMP/TCP packets. If your OS prefers the v6 address, the ping might fail.

[raffaellof]

Explicit ping to ipv4 works, implicit also works when there is no error, now my app works regularly via onair. The problem is that I could not understand how and why sometimes the error appears, I think that if it was a network configuration problem it should always work or never. I tried in different network configurations (different places), can't it depend on my code in any way?

p.s. I repeat: it is not a continuous error, it happens rarely, but I wanted to investigate to find bugs in my code

PS C:\Users\raffa> ping -w 5000 213.188.204.130

Esecuzione di Ping 213.188.204.130 con 32 byte di dati:
Risposta da 213.188.204.130: byte=32 durata=40ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=42ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=47ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=38ms TTL=57

Statistiche Ping per 213.188.204.130:
    Pacchetti: Trasmessi = 4, Ricevuti = 4,
    Persi = 0 (0% persi),
Tempo approssimativo percorsi andata/ritorno in millisecondi:
    Minimo = 38ms, Massimo =  47ms, Medio =  41ms

[evnchn]

Likely it's half-baked IPv6 from your ISP. If the On Air works for an hour or half after you turn off IPv4, call up your ISP's customer support, then.

Also I personally recommend turning off IPv6 in your router entirely. Never had a use for it.

[rodja]

We just removed the v6 DNS entries. @raffaellof might not be the only one experiencing these issues.

[ffilotto]

I am based in Switzerland, connecting to europe.on-air and currently experiencing the same issues.

I got "packet queue is empty, aborting" but I can ping on-air.io, europe.on-air.io, nicegui.io.

[rodja]

That's super strange. I can create a On Air connection without any issues. Have you tested with a minimal hello world example?

[ffilotto]

That's super strange. I can create a On Air connection without any issues. Have you tested with a minimal hello world example?

I have not. But it has now been 2 days straight without showing this issue. I'll keep you posted if it comes back.

[ffilotto]

I called it. It just happened, here the logs:

2025-07-02 12:47:36 - engineio.client - ERROR - packet queue is empty, aborting
2025-07-02 12:47:43 - nicegui.air - WARNING - Connection error: Unable to connect
2025-07-02 12:54:37 - engineio.client - ERROR - packet queue is empty, aborting
2025-07-02 12:54:57 - nicegui - WARNING - On Air host "https://on-air.nicegui.io/" is not reachable. Please check your internet connection.

It happened only after some activity on the page, while before there was no activity in those two days, besides refreshing pages.

I will run a hello world example on on-air and report back if there is any long term instability.

[raffaellof]

Sometimes (rarely) the problem happens again to me too. I share the tokens, if it should be useful for investigation:

NiceGUI ready to go on http://127.0.0.1:8000
NiceGUI is on air at https://europe.on-air.io/devices/tkhDuhaN/
packet queue is empty, aborting
NiceGUI is on air at https://europe.on-air.io/devices/TWLZiWIy/
NiceGUI is on air at https://europe.on-air.io/devices/z4pOjoxk/

2025-07-02 22:03:07,694 - ERROR: engineio.client packet queue is empty, aborting
2025-07-02 22:04:12,913 - WARNING: nicegui.air Connection error: Unable to connect
2025-07-02 22:04:35,866 - WARNING: nicegui.air Connection error: Unable to connect

ping ok:

PS C:\Users\raffa> ping -w 5000 europe.on-air.io

Esecuzione di Ping europe.on-air.io [213.188.204.130] con 32 byte di dati:
Risposta da 213.188.204.130: byte=32 durata=40ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=39ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=40ms TTL=57
Risposta da 213.188.204.130: byte=32 durata=40ms TTL=57

Statistiche Ping per 213.188.204.130:
    Pacchetti: Trasmessi = 4, Ricevuti = 4,
    Persi = 0 (0% persi),
Tempo approssimativo percorsi andata/ritorno in millisecondi:
    Minimo = 39ms, Massimo =  40ms, Medio =  39ms

Thanks for support @rodja and @evnchn