Attempted to load class LocalPlayer for invalid dist DEDICATED_SERVER

[Synthesyzer]

Hello,

I'm trying to spawn some particles and play some sound ones a block has been broken (particles and sounds must be observable for all players)
I have it setup that when a breakevent is emitted and some criteria has been met, I send out a packet to the client of all players:

	@SubscribeEvent
    public static void onBreakPowerCrystal(BlockEvent.BreakEvent event) {
        var world = event.getWorld();
        var block = event.getWorld().getBlockState(event.getPos()).getBlock();

        if (world.isClientSide())) {
          	// calling anything here seems to not work. looks like this event happens on the server side only
            return;
        }
  
  		if (!block.equals(ModBlocks.POWER_CRYSTAL_BLOCK.get()) {
            return;
        }

        event.setCanceled(true);
        Player player = event.getPlayer();

        KingdomManager manager = KingdomManager.get(player.level);
        getKingdom(player).ifPresentOrElse(
                kingdomOfPlayer -> {
                    manager.getKingdom(event.getPos()).ifPresentOrElse(
                            kingdomOfBlock -> {
                                if (!kingdomOfBlock.equals(kingdomOfPlayer)) {
                                    manager.decrementLives(kingdomOfBlock, 1);
                                  
                                    sendPacketToAllPlayers(player.getLevel(), new SPacketCrystalBreak(
                                      kingdomOfBlock.getName(), 
                                      event.getPos(), 																
                                      kingdomOfBlock.getLives()
                                    ));

                                    if (kingdomOfBlock.isDead()) {
                                        event.setCanceled(false);
                                    }

                                } else {
                                    // not important logic
                                }
                            },
                            () -> event.setCanceled(false)
                    );
                },
                () -> Messenger.sendClientError(player, "You are not in a kingdom"));
    }
            
    
	private static void sendPacketToAllPlayers(Level level, Object packet) {
        level.players().forEach(player -> {
            if (player instanceof ServerPlayer serverPlayer) {
                PacketHandler.sendToPlayer(packet, serverPlayer);
            }
        });
    }

Now this packet gets handled with the following code

   public boolean handle(Supplier<NetworkEvent.Context> supplier) {
        NetworkEvent.Context context = supplier.get();

        context.enqueueWork(() -> {
            DistExecutor.unsafeCallWhenOn(Dist.CLIENT, () -> () -> {
                Player player = Minecraft.getInstance().player;

                float randomSoundPitch = ((float) Math.random() / 10f) + 0.9f;

                // Adding this line crashes multiplayer servers on startup
                player.playSound(SoundEvents.ANVIL_PLACE, 1f, randomSoundPitch);
                return 0;
            });
        });

        return true;
    }

This will work fine on singleplayer. However, when trying to boot up a multiplayer server, it will refuse to start, giving the following error:

Caused by 0: java.lang.BootstrapMethodError: java.lang.RuntimeException: Attempted to load class net/minecraft/client/player/LocalPlayer for invalid dist DEDICATED_SERVER
		at org.daan.kingdomclash.common.network.PacketHandler.register(PacketHandler.java:37) ~[%2380!/:?] {re:classloading}
		at org.daan.kingdomclash.common.KingdomClash.setup(KingdomClash.java:62) ~[%2380!/:?] {re:classloading}
		at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-5.0.7.jar%239!/:?] {}
		at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-5.0.7.jar%239!/:?] {}
		at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-5.0.7.jar%239!/:?] {}
		at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-5.0.7.jar%239!/:?] {}
		at net.minecraftforge.fml.javafmlmod.FMLModContainer.acceptEvent(FMLModContainer.java:106) ~[javafmllanguage-1.18.2-40.1.0.jar%2377!/:?] {}
		at net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$4(ModContainer.java:107) ~[fmlcore-1.18.2-40.1.0.jar%2379!/:?] {}
		at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804) ~[?:?] {}
		at java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796) ~[?:?] {}
		at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373) ~[?:?] {}
		at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182) ~[?:?] {}
		at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655) ~[?:?] {}
		at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622) ~[?:?] {}
		at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165) ~[?:?] {}

	Mod File: main
	Failure message: Kingdom Clash (kingdomclash) encountered an error during the common_setup event phase
		java.lang.BootstrapMethodError: java.lang.RuntimeException: Attempted to load class net/minecraft/client/player/LocalPlayer for invalid dist DEDICATED_SERVER
	Mod Version: 0.0NONE
	Mod Issue URL: NOT PROVIDED
	Exception message: java.lang.RuntimeException: Attempted to load class net/minecraft/client/player/LocalPlayer for invalid dist DEDICATED_SERVER
Stacktrace:
	at net.minecraftforge.fml.loading.RuntimeDistCleaner.processClassWithFlags(RuntimeDistCleaner.java:57) ~[fmlloader-1.18.2-40.1.0.jar:1.0] {}
	at cpw.mods.modlauncher.LaunchPluginHandler.offerClassNodeToPlugins(LaunchPluginHandler.java:88) ~[modlauncher-9.1.3.jar:?] {}
	at cpw.mods.modlauncher.ClassTransformer.transform(ClassTransformer.java:120) ~[modlauncher-9.1.3.jar:?] {}
	at cpw.mods.modlauncher.TransformingClassLoader.maybeTransformClassBytes(TransformingClassLoader.java:50) ~[modlauncher-9.1.3.jar:?] {}
	at cpw.mods.cl.ModuleClassLoader.readerToClass(ModuleClassLoader.java:110) ~[securejarhandler-1.0.3.jar:?] {}
	at cpw.mods.cl.ModuleClassLoader.lambda$findClass$16(ModuleClassLoader.java:216) ~[securejarhandler-1.0.3.jar:?] {}
	at cpw.mods.cl.ModuleClassLoader.loadFromModule(ModuleClassLoader.java:226) ~[securejarhandler-1.0.3.jar:?] {}
	at cpw.mods.cl.ModuleClassLoader.findClass(ModuleClassLoader.java:216) ~[securejarhandler-1.0.3.jar:?] {}
	at cpw.mods.cl.ModuleClassLoader.loadClass(ModuleClassLoader.java:132) ~[securejarhandler-1.0.3.jar:?] {}
	at java.lang.ClassLoader.loadClass(ClassLoader.java:520) ~[?:?] {}
	at org.daan.kingdomclash.common.network.PacketHandler.register(PacketHandler.java:37) ~[%2380!/:?] {re:classloading}
	at org.daan.kingdomclash.common.KingdomClash.setup(KingdomClash.java:62) ~[%2380!/:?] {re:classloading}
	at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-5.0.7.jar%239!/:?] {}
	at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-5.0.7.jar%239!/:?] {}
	at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-5.0.7.jar%239!/:?] {}
	at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-5.0.7.jar%239!/:?] {}
	at net.minecraftforge.fml.javafmlmod.FMLModContainer.acceptEvent(FMLModContainer.java:106) ~[javafmllanguage-1.18.2-40.1.0.jar%2377!/:?] {}
	at net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$4(ModContainer.java:107) ~[fmlcore-1.18.2-40.1.0.jar%2379!/:?] {}
	at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804) ~[?:?] {}
	at java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796) ~[?:?] {}
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373) ~[?:?] {}
	at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182) ~[?:?] {}
	at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655) ~[?:?] {}
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622) ~[?:?] {}
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165) ~[?:?] {}

Swapping player to equal context.getSender() will make the server boot again, but won't make it so that the player hears the sound, because from my understanding, it will then not be called on the client side.
How do i access the player from the client side in a packet without upsetting the multiplayer server?

[warjort]

The short answer to your question is you shouldn't have client only classes in code that gets loaded during common setup.

See the example of ClientPacketHandlerClass here: https://forge.gemwire.uk/wiki/SimpleChannel

 

Edited September 16, 2022 by warjort

[Synthesyzer]

Maybe my understanding is incorrect, but isn't DistExecutor there to shield it from that?

[warjort]

That stops the code getting executed, it doesn't stop the classloader from loading the code where forge will check the classes referenced are for the correct side.

By using a separate class for the client code you will avoid that class getting loaded until it is executed (which is never on the server).

.

[Synthesyzer]

Thank you for the insight!

I've moved code that uses any class with @OnlyIn(Dist.CLIENT) into a seperate "proxy" class and just call that class instead, as you've suggested.