Fix splash potions turning into drinkable potions when re-sent by the…

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/rewriter/BlockItemPacketRewriter1_9.java

@@ -332,7 +332,8 @@ public Item handleItemToServer(UserConnection connection, Item item) {
             item.setData((short) 0);
         }
 
-        if (item.identifier() == 373 && (tag == null || !tag.contains("Potion"))) { // Potions
+        if (item.identifier() == 373) { // Potions
+            // Restore the splash id even when a Potion tag is present (e.g. items re-sent by a creative mode client)
             if (item.data() >= 16384) {
                 item.setIdentifier(438);
                 item.setData((short) (item.data() - 8192));

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/rewriter/EntityPacketRewriter1_9.java

@@ -138,6 +138,16 @@ public void register() {
                         wrapper.passthrough(Types.SHORT); // Velocity x
                         wrapper.passthrough(Types.SHORT); // Velocity y
                         wrapper.passthrough(Types.SHORT); // Velocity z
+                        if (type.is(EntityTypes1_9.EntityType.POTION)) {
+                            // 1.8 clients read the potion type from the object data, but newer versions only
+                            // send it in the entity data - the next packet. Held until then, see handleEntityData
+                            wrapper.cancel();
+                            final EntityTracker1_9 entityTracker = tracker(wrapper.user());
+                            entityTracker.getPendingPotionSpawns().put(entityId, new EntityTracker1_9.PotionSpawn(
+                                wrapper.get(Types.INT, 0), wrapper.get(Types.INT, 1), wrapper.get(Types.INT, 2),
+                                wrapper.get(Types.BYTE, 1), wrapper.get(Types.BYTE, 2),
+                                wrapper.get(Types.SHORT, 0), wrapper.get(Types.SHORT, 1), wrapper.get(Types.SHORT, 2)));
+                        }
                     } else {
                         final short velocityX = wrapper.read(Types.SHORT);
                         final short velocityY = wrapper.read(Types.SHORT);
@@ -541,8 +551,40 @@ protected void registerRewrites() {
         filter().handler(this::handleEntityData);
     }
 
+    private void sendDelayedPotionSpawn(EntityDataHandlerEvent event, EntityTracker1_9 tracker, Item item) {
+        final EntityTracker1_9.PotionSpawn spawn = tracker.getPendingPotionSpawns().remove(event.entityId());
+        if (spawn == null) {
+            return;
+        }
+        final Item converted = protocol.getItemRewriter().handleItemToClient(event.user(), item);
+        short data = converted == null ? 0 : converted.data();
+        if (data <= 0) {
+            data = 16384; // Unmapped potion, at least display a splash bottle
+        }
+
+        final PacketWrapper addEntity = PacketWrapper.create(ClientboundPackets1_8.ADD_ENTITY, event.user());
+        addEntity.write(Types.VAR_INT, event.entityId());
+        addEntity.write(Types.BYTE, (byte) EntityTypes1_9.ObjectType.POTION.getId());
+        addEntity.write(Types.INT, spawn.x());
+        addEntity.write(Types.INT, spawn.y());
+        addEntity.write(Types.INT, spawn.z());
+        addEntity.write(Types.BYTE, spawn.pitch());
+        addEntity.write(Types.BYTE, spawn.yaw());
+        addEntity.write(Types.INT, (int) data);
+        addEntity.write(Types.SHORT, spawn.velocityX());
+        addEntity.write(Types.SHORT, spawn.velocityY());
+        addEntity.write(Types.SHORT, spawn.velocityZ());
+        addEntity.send(Protocol1_9To1_8.class); // Before the entity data is sent
+    }
+
     private void handleEntityData(EntityDataHandlerEvent event, EntityData entityData) {
         final EntityTracker1_9 tracker = tracker(event.user());
+        if (event.entityType() == EntityTypes1_9.EntityType.POTION && entityData.value() instanceof Item potionItem) {
+            // No 1.8 equivalent; supplies the object data of the held-back spawn. Matched by value type as the index is version dependent
+            sendDelayedPotionSpawn(event, tracker, potionItem);
+            event.cancel();
+            return;
+        }
         if (entityData.id() == EntityDataIndex1_9.ENTITY_STATUS.getIndex()) {
             tracker.getStatus().put(event.entityId(), (Byte) entityData.value());
         }

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/storage/EntityTracker1_9.java

@@ -35,6 +35,7 @@ public class EntityTracker1_9 extends EntityTrackerBase {
     private final Int2ObjectMap<IntList> vehicles = new Int2ObjectOpenHashMap<>();
     private final Int2ObjectMap<Vector> offsets = new Int2ObjectOpenHashMap<>();
     private final Int2IntMap status = new Int2IntOpenHashMap();
+    private final Int2ObjectMap<PotionSpawn> pendingPotionSpawns = new Int2ObjectOpenHashMap<>();
 
     public EntityTracker1_9(UserConnection connection) {
         super(connection, EntityTypes1_9.EntityType.PLAYER);
@@ -45,6 +46,7 @@ public void removeEntity(int id) {
         vehicles.remove(id);
         offsets.remove(id);
         status.remove(id);
+        pendingPotionSpawns.remove(id);
 
         vehicles.forEach((vehicle, passengers) -> passengers.rem(id));
         vehicles.int2ObjectEntrySet().removeIf(entry -> entry.getValue().isEmpty());
@@ -88,4 +90,12 @@ public Integer getVehicle(final int passenger) {
     public Int2IntMap getStatus() {
         return status;
     }
+
+    public Int2ObjectMap<PotionSpawn> getPendingPotionSpawns() {
+        return pendingPotionSpawns;
+    }
+
+    /** Spawn packet values of a thrown potion, held until its item entity data supplies the 1.8 object data. */
+    public record PotionSpawn(int x, int y, int z, byte pitch, byte yaw, short velocityX, short velocityY, short velocityZ) {
+    }
 }