Denying a PotionApplicable event and attempting to apply a "replacement" potion with a weaker effect/duration causes a ticking player entity crash, likely because it is triggering the event handler infinitely.

Is there any way to modify an incoming potion effect, as well as determine whether the potion was applied through drinking/splash?

Code:

Spoiler

@SubscribeEvent
public static void potionApplied(PotionEvent.PotionApplicableEvent event) {
	if (!(event.getEntity() instanceof LivingEntity entity)) return;
	if (entity.getLevel().isClientSide()) return;

	List<ItemStack> armor = (List<ItemStack>) entity.getArmorSlots();
	int i = 0;
	for (ItemStack is : armor) {
		if (is.getItem() instanceof LeatherArmor) {
			i++;
		}
	}

	MobEffectInstance effect = event.getPotionEffect();
	int duration = effect.getDuration();

	if (i > 0) {
		event.setResult(Event.Result.DENY);
		duration = (int)(duration * (1 - (0.25 * i)));
		// Crash occurs in below method
		entity.addEffect(new MobEffectInstance(effect.getEffect(), duration, 0, true, true));
	}
}

 

Crash log:

Spoiler

net.minecraft.ReportedException: Ticking player
	at net.minecraft.server.network.ServerConnectionListener.tick(ServerConnectionListener.java:145) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:916) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:842) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.client.server.IntegratedServer.tickServer(IntegratedServer.java:84) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:685) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:261) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at java.lang.Thread.run(Thread.java:833) [?:?]
Caused by: java.lang.BootstrapMethodError: java.util.regex.PatternSyntaxException: Stack overflow during pattern compilation near index 12
(?:\Q/\E)+(?=(?:\Q/\E))
            ^
	at net.minecraftforge.eventbus.EventBus.handleException(EventBus.java:316) ~[eventbus-5.0.7.jar%239!/:?]
	at net.minecraftforge.eventbus.EventBus.post(EventBus.java:307) ~[eventbus-5.0.7.jar%239!/:?]
	at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-5.0.7.jar%239!/:?]
	at net.minecraft.world.entity.LivingEntity.canBeAffected(LivingEntity.java:908) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.addEffect(LivingEntity.java:888) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.addEffect(LivingEntity.java:884) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.item.PotionItem.finishUsingItem(PotionItem.java:44) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.item.ItemStack.finishUsingItem(ItemStack.java:256) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.completeUsingItem(LivingEntity.java:2962) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.level.ServerPlayer.completeUsingItem(ServerPlayer.java:1094) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.updateUsingItem(LivingEntity.java:2845) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.level.ServerPlayer.updateUsingItem(ServerPlayer.java:1567) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.updatingUsingItem(LivingEntity.java:2830) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.LivingEntity.tick(LivingEntity.java:2216) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.world.entity.player.Player.tick(Player.java:235) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.level.ServerPlayer.doTick(ServerPlayer.java:439) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.network.ServerGamePacketListenerImpl.tick(ServerGamePacketListenerImpl.java:207) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.network.Connection.tick(Connection.java:245) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]
	at net.minecraft.server.network.ServerConnectionListener.tick(ServerConnectionListener.java:142) ~[forge-1.18.2-40.1.48_mapped_official_1.18.2-recomp.jar%2376!/:?]

 

 

Edited July 29, 20223 yr by CrackedScreen
Marked thread as solved

This is indeed recursive death. That method is meant to decide if you want to block a potion effect.

Possible fixes include;

* A hack with a ThreadLocal to spot the call is your addEffect() invocation.

* Instead of applying the effect directly, defer the addition by remembering some flag for the player and doing it in a player tick handler on the next tick. 

1 hour ago, warjort said:

Instead of applying the effect directly, defer the addition by remembering some flag for the player and doing it in a player tick handler on the next tick. 

This will cause the same issue:
Event is fired -> store MobEffectInstance -> add MobEffectInstance in next tick -> Event is fired -> StackOverflowError

you need modify the MobEffectInstance before adding it, for example you add a CurativeItem via MobEffectInstance#addCurativeItem (e.g. Items#BARRIER)
then you need to check if the given MobEffectInstance of the Event has your CurativeItem if the MobEffectInstance has your CurativeItem you need to ignore it if not you can contine with the your logic

Note: the CurativeItem should be a creative only item (e.g. Items#BARRIER, Items#BEDROCK), to make sure you do not have unwanted side effects
you also can create a custom Item for this usage, to avoid conflict with other Mods

Quote

This will cause the same issue:
Event is fired -> store MobEffectInstance -> add MobEffectInstance in next tick -> Event is fired -> StackOverflowError

A naive implementation yes. 🙂

You just make the flag on the player something like NOTHING, NEEDS_ADDING, BEING_ADDED

Adding a Tag to the player and removing it after the new effect is applied, then checking for it at the beginning of the event handler prevents the crash from occurring. I still need a way to check if the potion was applied through drinking/splash effect, I think getPotionSource() is supposed to handle this but it isn't part of PotionApplicableEvent.

Are there any cleaner implementations for this aside from using event handler?

49 minutes ago, CrackedScreen said:

Are there any cleaner implementations for this aside from using event handler?

As far as i know that's not possible with Events

On 7/27/2022 at 11:46 AM, Luis_ST said:

As far as i know that's not possible with Events

Is this referring to separation of drank/splashed potions? I was asking about moving the entire implementation where all the needed information is accessible. If possible, I'd prefer to avoid doing something drastic like overriding/extending entity classes.

You can try to use PotionEvent.PotionAddedEvent in the Event you have #getPotionSource
if the source is not null and does not equal the Player which the MobEffectInstance  should be applied,
you can assume that the potion was thrown, but this is not 100% the case.

Marking this thread as solved, seeing as how Forge doesn't seem to have a clean solution for this.

You can create a PR for Forge 1.19 and port it then back to 1.18, which fix this.