PlayerKickEvent triggered on wrong thread

[brawaru]

Expected behavior

Bedrock Edition players can enter some characters that are considered illegal on Java Editions, so whenever player sends such characters they are supposed to be disconnected with reason multiplayer.disconnect.illegal_characters.

Observed/Actual behavior

Paper specifies the cause for disconnect — a kick. This causes it to try and fire PlayerKickEvent, however, it can only be triggered on the main thread, while the chat is handled on a separate thread, which results in an IllegalStateException. This still disconnects the player but does not show them a meaningful message, instead, they see ‘Internal Exception: java.lang.IllegalStateException: PlayerKickEvent may only be triggered synchronously.’

Steps/models to reproduce

The easiest way is to install Geyser and Floodgate plugin, then to connect to the server using Bedrock Edition and simply send § paragraph character, which is illegal on Java.

Plugin and Datapack List

Plugins (3): floodgate, Geyser-Spigot, ProtocolLib

Paper version

[19:25:52 INFO]: Checking version, please wait...
[19:25:53 INFO]: This server is running Paper version git-Paper-155 (MC: 1.18.1) (Implementing API version 1.18.1-R0.1-SNAPSHOT) (Git: 99cf01f)
You are running the latest version

Other

Related LOC: Paper-Server/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java:2070

Debug stack trace

[17:42:26 DEBUG]: Failed to sent packet
java.lang.IllegalStateException: PlayerKickEvent may only be triggered synchronously.
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:616) ~[paper-api-1.18.1-R0.1-SNAPSHOT.jar:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.disconnect(ServerGamePacketListenerImpl.java:446) ~[?:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.disconnect(ServerGamePacketListenerImpl.java:432) ~[?:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleChat(ServerGamePacketListenerImpl.java:2070) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundChatPacket.handle(ServerboundChatPacket.java:46) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundChatPacket.a(ServerboundChatPacket.java:6) ~[?:?]
        at net.minecraft.network.Connection.genericsFtw(Connection.java:281) ~[?:?]
        at net.minecraft.network.Connection.channelRead0(Connection.java:267) ~[?:?]
        at net.minecraft.network.Connection.channelRead0(Connection.java:54) ~[?:?]
        at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:302) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at com.comphenix.protocol.injector.netty.ChannelInjector$2.channelRead(ChannelInjector.java:289) ~[ProtocolLib.jar:?]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:286) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.handler.flush.FlushConsolidationHandler.channelRead(FlushConsolidationHandler.java:152) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.local.LocalChannel.readInbound(LocalChannel.java:299) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.local.LocalChannel.finishPeerRead0(LocalChannel.java:445) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.local.LocalChannel.access$400(LocalChannel.java:50) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.local.LocalChannel$5.run(LocalChannel.java:403) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.channel.DefaultEventLoop.run(DefaultEventLoop.java:54) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-all-4.1.68.Final.jar:4.1.68.Final]
        at java.lang.Thread.run(Thread.java:833) ~[?:?]

[molor]

The easiest way iirc is send Component to player that inserts command with a section sign (e.g. /§4test) into chat on click and then press [Enter]/send it. I don't know, maybe this cause has been fixed, but I encountered it in the early versions of Paper 1.18 during chat plugin testing :p