fix incorrect next item ID during game join

src/ReceiveCommands.cc

@@ -4203,6 +4203,17 @@ static void on_0C_C1_E7_EC(shared_ptr<Client> c, uint16_t command, uint32_t, str
   if (game) {
     s->change_client_lobby(c, game);
     c->config.set_flag(Client::Flag::LOADING);
+
+    // There is a bug in DC NTE and 11/2000 that causes them to assign item IDs
+    // twice when joining a game. If there are other players in the game, this
+    // isn't an issue because the equivalent of the 6x6D command resets the next
+    // item ID before the second assignment, so the item IDs stay in sync with
+    // the server. If there was no one else in the game, however (as in this
+    // case, when it was just created), we need to artificially change the next
+    // item IDs during the client's loading procedure.
+    if (is_pre_v1(c->version())) {
+      c->config.set_flag(Client::Flag::SHOULD_SEND_ARTIFICIAL_ITEM_STATE);
+    }
   }
 }
 

src/ReceiveSubcommands.cc

@@ -905,12 +905,9 @@ static void on_change_floor_6x1F(shared_ptr<Client> c, uint8_t command, uint8_t
   if (is_pre_v1(c->version())) {
     check_size_t<G_SetPlayerFloor_DCNTE_6x1F>(data, size);
     // DC NTE and 11/2000 don't send 6F when they're done loading, so we clear
-    // the loading flag here instead. On these versions, it also seems to be
-    // necessary to assign item IDs again here.
+    // the loading flag here instead.
     if (c->config.check_flag(Client::Flag::LOADING)) {
       c->config.clear_flag(Client::Flag::LOADING);
-      auto l = c->require_lobby();
-      l->assign_inventory_and_bank_item_ids(c);
     }
 
   } else {

src/SendCommands.cc

@@ -2360,8 +2360,25 @@ void send_game_item_state(shared_ptr<Client> c) {
 
   G_SyncItemState_6x6D_Decompressed decompressed_header;
   for (size_t z = 0; z < 12; z++) {
-    decompressed_header.next_item_id_per_player[z] = l->next_item_id_for_client[z];
+    if (z == c->lobby_client_id) {
+      // If the player is joining, adjust the next item ID to use the value
+      // before inventory item IDs are assigned
+      size_t num_items = c->character()->inventory.num_items;
+      uint32_t next_id = l->next_item_id_for_client[z] - num_items;
+      if ((next_id & 0xFFE00000) != (l->next_item_id_for_client[z] & 0xFFE00000)) {
+        throw runtime_error("next item ID underflow during joining player item state generation");
+      }
+      decompressed_header.next_item_id_per_player[z] = next_id;
+    } else {
+      decompressed_header.next_item_id_per_player[z] = l->next_item_id_for_client[z];
+    }
   }
+  l->log.info("Sending next item IDs to client: %08" PRIX32 " %08" PRIX32 " %08" PRIX32 " %08" PRIX32,
+      decompressed_header.next_item_id_per_player[0].load(),
+      decompressed_header.next_item_id_per_player[1].load(),
+      decompressed_header.next_item_id_per_player[2].load(),
+      decompressed_header.next_item_id_per_player[3].load());
+
   for (size_t floor = 0; floor < 0x10; floor++) {
     const auto& m = l->floor_item_managers.at(floor);
     for (const auto& it : m.queue_for_client.at(c->lobby_client_id)) {