PaperMC/paper-server/nms-patches/net/minecraft/world/item/ItemBucket.patch

--- a/net/minecraft/world/item/ItemBucket.java
+++ b/net/minecraft/world/item/ItemBucket.java
@@ -29,6 +29,16 @@
 import net.minecraft.world.phys.MovingObjectPosition;
 import net.minecraft.world.phys.MovingObjectPositionBlock;
 
+// CraftBukkit start
+import net.minecraft.network.protocol.game.PacketPlayOutBlockChange;
+import net.minecraft.server.level.WorldServer;
+import org.bukkit.craftbukkit.event.CraftEventFactory;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.craftbukkit.util.DummyGeneratorAccess;
+import org.bukkit.event.player.PlayerBucketEmptyEvent;
+import org.bukkit.event.player.PlayerBucketFillEvent;
+// CraftBukkit end
+
 public class ItemBucket extends Item implements DispensibleContainerItem {
 
     public final FluidType content;
@@ -59,6 +69,17 @@
                     iblockdata = world.getBlockState(blockposition);
                     if (iblockdata.getBlock() instanceof IFluidSource) {
                         IFluidSource ifluidsource = (IFluidSource) iblockdata.getBlock();
+                        // CraftBukkit start
+                        ItemStack dummyFluid = ifluidsource.pickupBlock(DummyGeneratorAccess.INSTANCE, blockposition, iblockdata);
+                        if (dummyFluid.isEmpty()) return InteractionResultWrapper.fail(itemstack); // Don't fire event if the bucket won't be filled.
+                        PlayerBucketFillEvent event = CraftEventFactory.callPlayerBucketFillEvent((WorldServer) world, entityhuman, blockposition, blockposition, movingobjectpositionblock.getDirection(), itemstack, dummyFluid.getItem());
+
+                        if (event.isCancelled()) {
+                            ((EntityPlayer) entityhuman).connection.send(new PacketPlayOutBlockChange(world, blockposition)); // SPIGOT-5163 (see PlayerInteractManager)
+                            ((EntityPlayer) entityhuman).getBukkitEntity().updateInventory(); // SPIGOT-4541
+                            return InteractionResultWrapper.fail(itemstack);
+                        }
+                        // CraftBukkit end
                         ItemStack itemstack1 = ifluidsource.pickupBlock(world, blockposition, iblockdata);
 
                         if (!itemstack1.isEmpty()) {
@@ -67,7 +88,7 @@
                                 entityhuman.playSound(soundeffect, 1.0F, 1.0F);
                             });
                             world.gameEvent(entityhuman, GameEvent.FLUID_PICKUP, blockposition);
-                            ItemStack itemstack2 = ItemLiquidUtil.createFilledResult(itemstack, entityhuman, itemstack1);
+                            ItemStack itemstack2 = ItemLiquidUtil.createFilledResult(itemstack, entityhuman, CraftItemStack.asNMSCopy(event.getItemStack())); // CraftBukkit
 
                             if (!world.isClientSide) {
                                 CriterionTriggers.FILLED_BUCKET.trigger((EntityPlayer) entityhuman, itemstack1);
@@ -82,7 +103,7 @@
                     iblockdata = world.getBlockState(blockposition);
                     BlockPosition blockposition2 = iblockdata.getBlock() instanceof IFluidContainer && this.content == FluidTypes.WATER ? blockposition : blockposition1;
 
-                    if (this.emptyContents(entityhuman, world, blockposition2, movingobjectpositionblock)) {
+                    if (this.emptyContents(entityhuman, world, blockposition2, movingobjectpositionblock, movingobjectpositionblock.getDirection(), blockposition, itemstack)) { // CraftBukkit
                         this.checkExtraContent(entityhuman, world, itemstack, blockposition2);
                         if (entityhuman instanceof EntityPlayer) {
                             CriterionTriggers.PLACED_BLOCK.trigger((EntityPlayer) entityhuman, blockposition2, itemstack);
@@ -109,6 +130,11 @@
 
     @Override
     public boolean emptyContents(@Nullable EntityHuman entityhuman, World world, BlockPosition blockposition, @Nullable MovingObjectPositionBlock movingobjectpositionblock) {
+        return emptyContents(entityhuman, world, blockposition, movingobjectpositionblock, null, null, null);
+    }
+
+    public boolean emptyContents(EntityHuman entityhuman, World world, BlockPosition blockposition, @Nullable MovingObjectPositionBlock movingobjectpositionblock, EnumDirection enumdirection, BlockPosition clicked, ItemStack itemstack) {
+        // CraftBukkit end
         if (!(this.content instanceof FluidTypeFlowing)) {
             return false;
         } else {
@@ -118,8 +144,18 @@
             boolean flag = iblockdata.canBeReplaced(this.content);
             boolean flag1 = iblockdata.isAir() || flag || block instanceof IFluidContainer && ((IFluidContainer) block).canPlaceLiquid(world, blockposition, iblockdata, this.content);
 
+            // CraftBukkit start
+            if (flag1 && entityhuman != null) {
+                PlayerBucketEmptyEvent event = CraftEventFactory.callPlayerBucketEmptyEvent((WorldServer) world, entityhuman, blockposition, clicked, enumdirection, itemstack);
+                if (event.isCancelled()) {
+                    ((EntityPlayer) entityhuman).connection.send(new PacketPlayOutBlockChange(world, blockposition)); // SPIGOT-4238: needed when looking through entity
+                    ((EntityPlayer) entityhuman).getBukkitEntity().updateInventory(); // SPIGOT-4541
+                    return false;
+                }
+            }
+            // CraftBukkit end
             if (!flag1) {
-                return movingobjectpositionblock != null && this.emptyContents(entityhuman, world, movingobjectpositionblock.getBlockPos().relative(movingobjectpositionblock.getDirection()), (MovingObjectPositionBlock) null);
+                return movingobjectpositionblock != null && this.emptyContents(entityhuman, world, movingobjectpositionblock.getBlockPos().relative(movingobjectpositionblock.getDirection()), (MovingObjectPositionBlock) null, enumdirection, clicked, itemstack); // CraftBukkit
             } else if (world.dimensionType().ultraWarm() && this.content.is(TagsFluid.WATER)) {
                 int i = blockposition.getX();
                 int j = blockposition.getY();