[1.19] Implementing event handler for server side code only

[Adil Yilan]

I want to prevent monster from despawning.

Idea is to use AllowDespawn event from Forge.

However, since event requires for Result to be set, I am not sure what result to set when code is executing on logical client side...

To fix that, I thought that I might set event handler to Dist.DEDICATED_SERVER but I am not really sure if that is proper way:

// Option 1: Set Dist.DEDICATED.SERVER? But what will then happen in single player?
@EventBusSubscriber(modid = ExperimentalMod.MODID, bus = Bus.MOD, value = Dist.DEDICATED_SERVER)
public class AllowDespawnEventHandler {
	
	@SubscribeEvent()
	public static void onAllowDespawn(final AllowDespawn event) {
		
		// Option 2: Check if it is logical client side in event handler.
		if(event.getLevel().isClientSide())
		{
			// But I don't know what to set for event.setResult(...) ?
			return;
		}
		

	}
}

 

So the question is what should I use to avoid duplicate code execution / messing up the single player mode:

1) Use Dist.DEDICATED_SERVER

2) Use level.isClientSide()

3) Use something else?

 

I hope code snippet above illustrates my doubts / question.

Thanks for any assistance.

 

 

Edited July 24, 2022 by Adil Yilan

[Luis_ST]

12 minutes ago, Adil Yilan said:

2) Use level.isClientSide()

use this, if you're playing on a DedictaedServer you have the Dist DEDICATED_SERVER,
if you're playing in Singleplayer you also have a Server an IntegratedServer which has not the Dist DEDICATED_SERVER

14 minutes ago, Adil Yilan said:

// But I don't know what to set for event.setResult(...) ?

read the javadoc of the Event

[Adil Yilan]

Thanks @Luis_ST !

I did check event comments but is still not entirely clear what to do with this check:

    /**
     * This event is fired for a {@link Mob} that can despawn <i>each mob tick</i>.
     * This event only fires if a mob can be allowed to despawn and will not
     * otherwise fire if a despawn is certain.
     * <p>
     * This event is not {@linkplain Cancelable cancellable}, but does {@linkplain HasResult have a result}.
     * {@link Result#DEFAULT} indicates that default despawn mechanics should be used.
     * {@link Result#ALLOW} indicates that the mob should forcefully despawn.
     * {@link Result#DENY} indicates that the mob should forcefully stay spawned.
     * <p>
     * This event is fired on the {@linkplain MinecraftForge#EVENT_BUS main Forge event bus},
     * only on the {@linkplain LogicalSide#SERVER logical server}.
     *
     * @see LivingEntity#checkDespawn()
     * @author cpw
     */

Comment mentiona that event is fired only on the LogicalSide.SERVER.

Is .isClientSide() check then necessary if Forge ensures that event is never fired on logical client?

This is what I have now in code:

		// IF: Code is executing on the logical client.
		if(event.getLevel().isClientSide())
		{
			// Do not change anything, do regular behavior.
			event.setResult(Result.DEFAULT);

			return;
		}

Should I:

1) Set result to DEFAUT?

2) Don't set result at all?

3) Regarding the comment, just remove isClientSide() check entirely?

Thanks again!

[warjort]

As the javadoc says, this event is only ever fired on the (logical) server.

So the isClientSide() check is redundant, it's always false.

Edited July 24, 2022 by warjort

[Luis_ST]

12 minutes ago, Adil Yilan said:

This is what I have now in code:

This code is only called on client, if you want to execute the code on server only you need to check:

!event.getLevel().isClientSide()

I Personally, keep this side check, since if there are changes in Forge or the Event is called by another mod somewhere you don't get any issues.

16 minutes ago, Adil Yilan said:

Should I:

do not execute any code on client just ignore it:

if (!event.getLevel().isClientSide()) {
	// do your stuff here
}

[Adil Yilan]

@Luis_ST @warjort Thank you both for your answers!

 

This is final version of code, in case someone else ends up looking for the same thing:

 

@EventBusSubscriber(modid = ExperimentalMod.MODID, bus = Bus.FORGE)
public final class AllowDespawnEventHandler {
	
	@SubscribeEvent()
	public static void onAllowDespawn(final AllowDespawn event) {
		
		// IF: Code is executing on the logical client.
		if(event.getLevel().isClientSide())
		{
			// Do not change anything, do regular behavior.
			event.setResult(Result.DEFAULT);

			return;
		}

		// Get reference to entity that is about to despawn.
		Mob mob = event.getEntity();

		// IF: Entity is instance of GoblinEntity class.
		if(mob instanceof GoblinEntity) {
			
			// Prevent Goblins from despawning.
			event.setResult(Result.DENY);
			
			// Stop execution.
			return;
		}
		
		// For other entities, we don't want to change regular logic, so we set result to be DEFAULT which means
		// whatever should happen otherwise, continue with it.
		event.setResult(Result.DEFAULT);
	}
}

 

It works as expected.