add ALLOW_PLAYER_CHANGE_WORLD

fabric-entity-events-v1/src/main/java/net/fabricmc/fabric/api/entity/event/v1/ServerEntityWorldChangeEvents.java

@@ -45,6 +45,19 @@ public final class ServerEntityWorldChangeEvents {
 		}
 	});
 
+	/**
+	 * Called before a player is being moved to a different world.
+	 */
+	public static final Event<AllowPlayerChange> ALLOW_PLAYER_CHANGE_WORLD = EventFactory.createArrayBacked(AllowPlayerChange.class, callbacks -> (player, origin, destination) -> {
+		for (AllowPlayerChange callback : callbacks) {
+			if (!callback.allowChangeWorld(player, origin, destination)) {
+				return false;
+			}
+		}
+
+		return true;
+	});
+
 	/**
 	 * An event which is called after a player has been moved to a different world.
 	 *
@@ -75,6 +88,19 @@ public interface AfterEntityChange {
 		void afterChangeWorld(Entity originalEntity, Entity newEntity, ServerWorld origin, ServerWorld destination);
 	}
 
+	@FunctionalInterface
+	public interface AllowPlayerChange {
+		/**
+		 * Called before a player is being moved to a different world.
+		 *
+		 * @param player the player
+		 * @param origin the original world the player is in
+		 * @param destination the new world the player is moving to
+		 * @return true if the player is allowed to change worlds, false otherwise
+		 */
+		boolean allowChangeWorld(ServerPlayerEntity player, ServerWorld origin, ServerWorld destination);
+	}
+
 	@FunctionalInterface
 	public interface AfterPlayerChange {
 		/**

fabric-entity-events-v1/src/main/java/net/fabricmc/fabric/mixin/entity/event/ServerPlayerEntityMixin.java

@@ -20,6 +20,7 @@
 
 import com.mojang.datafixers.util.Either;
 import org.jetbrains.annotations.Nullable;
+import org.objectweb.asm.Opcodes;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;
@@ -43,6 +44,7 @@
 import net.minecraft.util.Unit;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.Direction;
+import net.minecraft.world.TeleportTarget;
 import net.minecraft.world.World;
 
 import net.fabricmc.fabric.api.entity.event.v1.EntitySleepEvents;
@@ -77,6 +79,16 @@ private void notifyDeath(DamageSource source, CallbackInfo ci) {
 		ServerLivingEntityEvents.AFTER_DEATH.invoker().afterDeath((ServerPlayerEntity) (Object) this, source);
 	}
 
+	@Inject(method = "teleportTo", at = @At(value = "FIELD", target = "Lnet/minecraft/server/network/ServerPlayerEntity;inTeleportationState:Z", opcode = Opcodes.PUTFIELD), cancellable = true)
+	private void beforeWorldChanged(TeleportTarget teleportTarget, CallbackInfoReturnable<Entity> cir) {
+		ServerPlayerEntity player = (ServerPlayerEntity) (Object) this;
+		boolean allowed = ServerEntityWorldChangeEvents.ALLOW_PLAYER_CHANGE_WORLD.invoker().allowChangeWorld(player, player.getServerWorld(), teleportTarget.world());
+
+		if (!allowed) {
+			cir.setReturnValue(null);
+		}
+	}
+
 	/**
 	 * This is called by {@code teleportTo}.
 	 */

fabric-entity-events-v1/src/testmod/java/net/fabricmc/fabric/test/entity/event/EntityEventTests.java

@@ -64,6 +64,16 @@ public void onInitialize() {
 			LOGGER.info("Entity {} Killed: {}", entity, killed);
 		});
 
+		ServerEntityWorldChangeEvents.ALLOW_PLAYER_CHANGE_WORLD.register((player, origin, destination) -> {
+			if (player.getMainHandStack().isOf(Items.END_ROD)) {
+				LOGGER.info("Player {} failed to change world because of handing an end rod", player.getGameProfile().getName());
+				return false;
+			}
+
+			LOGGER.info("Allow Moving player {}: [{} -> {}]", player, origin.getRegistryKey().getValue(), destination.getRegistryKey().getValue());
+			return true;
+		});
+
 		ServerEntityWorldChangeEvents.AFTER_PLAYER_CHANGE_WORLD.register((player, origin, destination) -> {
 			LOGGER.info("Moved player {}: [{} -> {}]", player, origin.getRegistryKey().getValue(), destination.getRegistryKey().getValue());
 		});