Stop update from being sent to the player when the player places a block on themselves (#939)

src/main/java/net/minestom/server/collision/BlockCollision.java

@@ -329,7 +329,7 @@ final class BlockCollision {
                 Vec.ZERO, finalResult.collidedShapePosition, finalResult.blockType);
     }
 
-    static boolean canPlaceBlockAt(Instance instance, Point blockPos, Block b) {
+    static Entity canPlaceBlockAt(Instance instance, Point blockPos, Block b) {
         for (Entity entity : instance.getNearbyEntities(blockPos, 3)) {
             final EntityType type = entity.getEntityType();
             if (type == EntityType.ITEM)
@@ -348,9 +348,9 @@ final class BlockCollision {
             } else {
                 intersects = b.registry().collisionShape().intersectBox(entity.getPosition().sub(blockPos), entity.getBoundingBox());
             }
-            if (intersects) return false;
+            if (intersects) return entity;
         }
-        return true;
+        return null;
     }
 
     /**

src/main/java/net/minestom/server/collision/CollisionUtils.java

@@ -80,7 +80,7 @@ public final class CollisionUtils {
         return handlePhysics(entity, entityVelocity, null);
     }
 
-    public static boolean canPlaceBlockAt(Instance instance, Point blockPos, Block b) {
+    public static Entity canPlaceBlockAt(Instance instance, Point blockPos, Block b) {
         return BlockCollision.canPlaceBlockAt(instance, blockPos, b);
     }
 

src/main/java/net/minestom/server/listener/BlockPlacementListener.java

@@ -3,6 +3,7 @@ package net.minestom.server.listener;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.collision.CollisionUtils;
 import net.minestom.server.coordinate.Point;
+import net.minestom.server.entity.Entity;
 import net.minestom.server.entity.GameMode;
 import net.minestom.server.entity.Player;
 import net.minestom.server.event.EventDispatcher;
@@ -105,9 +106,18 @@ public class BlockPlacementListener {
         }
 
         final Block placedBlock = useMaterial.block();
-        if (!CollisionUtils.canPlaceBlockAt(instance, placementPosition, placedBlock)) {
+        Entity collisionEntity = CollisionUtils.canPlaceBlockAt(instance, placementPosition, placedBlock);
+        if (collisionEntity != null) {
+            // If a player is trying to place a block on themselves, the client will send a block change but will not set the block on the client
+            // For this reason, the block doesn't need to be updated for the client
+
+            // Client also doesn't predict placement of blocks on entities, but we need to refresh for cases where bounding boxes on the server don't match the client
+            if (collisionEntity != player)
+                refresh(player, chunk);
+            
             return;
         }
+
         // BlockPlaceEvent check
         PlayerBlockPlaceEvent playerBlockPlaceEvent = new PlayerBlockPlaceEvent(player, placedBlock, blockFace, placementPosition, packet.hand());
         playerBlockPlaceEvent.consumeBlock(player.getGameMode() != GameMode.CREATIVE);

src/test/java/net/minestom/server/collision/PlacementCollisionIntegrationTest.java

@@ -9,8 +9,7 @@ import net.minestom.server.entity.EntityType;
 import net.minestom.server.instance.block.Block;
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.*;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 @EnvTest
 public class PlacementCollisionIntegrationTest {
@@ -18,27 +17,27 @@ public class PlacementCollisionIntegrationTest {
     @Test
     public void empty(Env env) {
         var instance = env.createFlatInstance();
-        assertTrue(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE));
+        assertNull(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE));
     }
 
     @Test
     public void entityBlock(Env env) {
         var instance = env.createFlatInstance();
         new Entity(EntityType.ZOMBIE).setInstance(instance, new Pos(0, 40, 0)).join();
-        assertFalse(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE));
+        assertNotNull(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE));
     }
 
     @Test
     public void slab(Env env) {
         var instance = env.createFlatInstance();
         new Entity(EntityType.ZOMBIE).setInstance(instance, new Pos(0, 40.75, 0)).join();
-        assertTrue(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE_SLAB));
+        assertNull(BlockCollision.canPlaceBlockAt(instance, new Vec(0, 40, 0), Block.STONE_SLAB));
     }
 
     @Test
     public void belowPlayer(Env env) {
         var instance = env.createFlatInstance();
         env.createPlayer(instance, new Pos(5.7, -8, 6.389));
-        assertTrue(BlockCollision.canPlaceBlockAt(instance, new Vec(5, -9, 6), Block.STONE));
+        assertNull(BlockCollision.canPlaceBlockAt(instance, new Vec(5, -9, 6), Block.STONE));
     }
 }