Paper/nms-patches/BlockFlowing.patch

--- a/net/minecraft/server/BlockFlowing.java
+++ b/net/minecraft/server/BlockFlowing.java
@@ -5,6 +5,11 @@
 import java.util.Random;
 import java.util.Set;
 
+// CraftBukkit start
+import org.bukkit.block.BlockFace;
+import org.bukkit.event.block.BlockFromToEvent;
+// CraftBukkit end
+
 public class BlockFlowing extends BlockFluids {
 
     int a;
@@ -18,6 +23,11 @@
     }
 
     public void b(World world, BlockPosition blockposition, IBlockData iblockdata, Random random) {
+        // CraftBukkit start
+        org.bukkit.World bworld = world.getWorld();
+        org.bukkit.Server server = world.getServer();
+        org.bukkit.block.Block source = bworld == null ? null : bworld.getBlockAt(blockposition.getX(), blockposition.getY(), blockposition.getZ());
+        // CraftBukkit end
         int i = ((Integer) iblockdata.get(BlockFlowing.LEVEL)).intValue();
         byte b0 = 1;
 
@@ -88,6 +98,12 @@
         IBlockData iblockdata2 = world.getType(blockposition.down());
 
         if (this.h(world, blockposition.down(), iblockdata2)) {
+            // CraftBukkit start - Send "down" to the server
+            BlockFromToEvent event = new BlockFromToEvent(source, BlockFace.DOWN);
+            if (server != null) {
+                server.getPluginManager().callEvent(event);
+            }
+            if (!event.isCancelled()) {
             if (this.material == Material.LAVA && world.getType(blockposition.down()).getMaterial() == Material.WATER) {
                 world.setTypeUpdate(blockposition.down(), Blocks.STONE.getBlockData());
                 this.fizz(world, blockposition.down());
@@ -99,6 +115,8 @@
             } else {
                 this.flow(world, blockposition.down(), iblockdata2, i + 8);
             }
+            }
+            // CraftBukkit end
         } else if (i >= 0 && (i == 0 || this.g(world, blockposition.down(), iblockdata2))) {
             Set set = this.c(world, blockposition);
 
@@ -116,14 +134,23 @@
             while (iterator1.hasNext()) {
                 EnumDirection enumdirection1 = (EnumDirection) iterator1.next();
 
-                this.flow(world, blockposition.shift(enumdirection1), world.getType(blockposition.shift(enumdirection1)), k);
+                // CraftBukkit start
+                BlockFromToEvent event = new BlockFromToEvent(source, org.bukkit.craftbukkit.block.CraftBlock.notchToBlockFace(enumdirection1));
+                if (server != null) {
+                    server.getPluginManager().callEvent(event);
+                }
+
+                if (!event.isCancelled()) {
+                    this.flow(world, blockposition.shift(enumdirection1), world.getType(blockposition.shift(enumdirection1)), k);
+                }
+                // CraftBukkit end
             }
         }
 
     }
 
     private void flow(World world, BlockPosition blockposition, IBlockData iblockdata, int i) {
-        if (this.h(world, blockposition, iblockdata)) {
+        if (world.isLoaded(blockposition) && this.h(world, blockposition, iblockdata)) { // CraftBukkit - add isLoaded check
             if (iblockdata.getBlock() != Blocks.AIR) {
                 if (this.material == Material.LAVA) {
                     this.fizz(world, blockposition);