Internal Exception: io.netty.handler.codec.DecoderException: java.io.IOException: Bad packet id 118 #661
Description
/viaversion dump Output
https://dump.viaversion.com/d77418c8191f4b09e1e2c9c5b8c136820adf3775de39e8dbd77caecb7454aa35
Server/Client Error
[19:09:14 INFO]: Tester[/x.x.x.x:xxxxx] logged in with entity id 134 at ([world]0.5, 72.0, 0.5)
[19:09:15 WARN]: [ViaBackwards] (1.13->1.12.2) Ignoring plugin channel in serverbound REGISTER: FML
[19:09:15 WARN]: [ViaBackwards] (1.13->1.12.2) Ignoring plugin channel in serverbound REGISTER: FORGE
[19:09:15 WARN]: [ViaBackwards] (1.13->1.12.2) Ignoring plugin channel in serverbound REGISTER: FML
[19:09:15 WARN]: [ViaBackwards] (1.13->1.12.2) Ignoring plugin channel in serverbound REGISTER: FML
[19:09:15 WARN]: [ViaBackwards] (1.13->1.12.2) Ignoring plugin channel in serverbound REGISTER: FORGE
[19:09:15 INFO]: Tester lost connection: Disconnected
Bug Description
I am reporting a very specific behavior that happens only with 1.8.9 clients after updating ViaVersion, ViaBackwards and ViaRewind to the latest builds.
Network setup:
- Proxy: FlameCord - Ultimate Anti-Bot Solution v2.5.4
- 3 identical Purpur 1.21.11 lobby servers
- Same plugins, same configuration, same Java version
- ViaVersion, ViaBackwards and ViaRewind installed only on backend servers (not on proxy)
Observed behavior:
If a 1.8.9 player connects DIRECTLY to a lobby running the latest Via* builds, the player is immediately kicked with:
"Bad packet id 118"
However, if the player:
- First connects to another lobby running older Via versions (ViaBackwards 5.7.0 / ViaRewind 4.0.13)
- Then switches servers using the proxy (/server lobbyX)
The player can join the updated lobby without any issue.
This proves that:
- This is NOT a general server compatibility issue
- This is NOT a plugin conflict
- The problem happens specifically during the LOGIN / handshake phase for 1.8.9 clients
- Once the player is already online and switches servers, everything works perfectly
Tests performed:
- Tested with only Purpur + Via* (no ProtocolLib or other plugins)
- Deleted Via config folders
- Tested on identical servers
- Confirmed only the updated server has the problem
- Downgrading to ViaBackwards 5.7.0 + ViaRewind 4.0.13 immediately fixes it
Conclusion:
This appears to be a recent regression in the packet transformation pipeline during the LOGIN state for 1.8.9 clients when connecting through FlameCord.
Steps to Reproduce
-
Environment:
- Proxy: FlameCord v2.5.4
- 3 identical Purpur 1.21.11 lobby servers (Lobby1, Lobby2, Lobby3)
- Same plugins, same configuration, same Java version
- ViaVersion, ViaBackwards and ViaRewind installed only on backends
-
Update only one lobby to the latest ViaVersion, ViaBackwards and ViaRewind builds.
Keep the other two running:- ViaBackwards 5.7.0
- ViaRewind 4.0.13
- ViaRewind Legacy Support 1.5.5
-
Using a Minecraft 1.8.9 client:
CASE A (error happens):
- Connect DIRECTLY to the lobby running the latest Via builds
- The player is immediately kicked with:
"Bad packet id 118"
CASE B (error does NOT happen):
- First connect to a lobby running the older Via builds
- Then switch servers through the proxy (/server updatedLobby)
- The player joins the updated lobby without any issue
-
Result:
- The error only occurs when the 1.8.9 player directly joins the updated server
- It does not occur when the player is already online and switches servers
This indicates the problem happens specifically during the LOGIN/handshake state for 1.8.9 clients through FlameCord.
Additional Server Info
Proxy: FlameCord - Ultimate Anti-Bot Solution v2.5.4
Backend software: Purpur 1.21.11
Via plugins are installed ONLY on backend servers.
There are NO Via plugins installed on the proxy.
Plugins present during testing:
- ViaVersion
- ViaBackwards
- ViaRewind
- ViaRewind Legacy Support
For testing, all other plugins were removed to eliminate any packet/pipeline interference.
No ProtocolLib, no anti-cheat, no packet manipulation plugins.
All three lobby servers are identical in configuration, plugins and Java version.
The ONLY difference is the Via plugin versions.
Downgrading to:
- ViaBackwards 5.7.0
- ViaRewind 4.0.13
- ViaRewind Legacy Support 1.5.5
immediately fixes the issue for 1.8.9 clients.
Checklist
- Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), not on both.
- I have included a ViaVersion dump.
- If applicable, I have included a paste (not a screenshot) of the error.
- I have tried the latest build(s) from https://ci.viaversion.com/ and the issue still persists.