Lua: fix: ReadOnlyTable, existing keys could be written

server/src/lua/console.cpp

@@ -54,7 +54,7 @@ void Console::push(lua_State* L)
   lua_pushcfunction(L, fatal);
   lua_setfield(L, -2, "fatal");
 
-  ReadOnlyTable::setMetatable(L, -1);
+  ReadOnlyTable::wrap(L, -1);
 }
 
 void Console::log(lua_State* L, ::Console::Level level, const std::string& message)

server/src/lua/enum.hpp

@@ -98,7 +98,7 @@ struct Enum
       push(L, it.first);
       lua_setfield(L, -2, toUpper(it.second).c_str());
     }
-    ReadOnlyTable::setMetatable(L, -1);
+    ReadOnlyTable::wrap(L, -1);
     lua_setfield(L, -2, EnumName<T>::value);
   }
 };

server/src/lua/readonlytable.hpp

@@ -3,7 +3,7 @@
  *
  * This file is part of the traintastic source code.
  *
- * Copyright (C) 2019-2020 Reinder Feenstra
+ * Copyright (C) 2019-2021 Reinder Feenstra
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -29,29 +29,33 @@
 
 namespace Lua {
 
-struct ReadOnlyTable
+class ReadOnlyTable
 {
-  static constexpr const char* metatableName = "read_only_table";
+  private:
+    static int __newindex(lua_State* L)
+    {
+      errorTableIsReadOnly(L);
+    }
 
-  static void setMetatable(lua_State* L, int index)
-  {
-    luaL_getmetatable(L, metatableName);
-    assert(lua_istable(L, -1)); // is type registered?
-    lua_setmetatable(L, index < 0 ? index - 1 : index);
-  }
-
-  static int __newindex(lua_State* L)
-  {
-    errorTableIsReadOnly(L);
-  }
-
-  static void registerType(lua_State* L)
-  {
-    luaL_newmetatable(L, metatableName);
-    lua_pushcfunction(L, __newindex);
-    lua_setfield(L, -2, "__newindex");
-    lua_pop(L, 1);
-  }
+  public:
+    static void wrap(lua_State* L, int index)
+    {
+      assert(lua_istable(L, index));
+      lua_newtable(L); // create wrapper table
+      lua_newtable(L); // metatable for wrapper table
+      if(index < 0)
+        index -= 2; // correct index if relative
+      lua_pushvalue(L, index); // copy source table (ref)
+      lua_setfield(L, -2, "__index");
+      lua_pushcfunction(L, __newindex);
+      lua_setfield(L, -2, "__newindex");
+      lua_pushboolean(L, 0);
+      lua_setfield(L, -2, "__metatable");
+      lua_setmetatable(L, -2); // set metatable @ wrapper table
+      if(index < 0)
+        index++; // correct index if relative
+      lua_replace(L, index); // replace source table by wrapper table
+    }
 };
 
 }

server/src/lua/sandbox.cpp

@@ -98,13 +98,13 @@ SandboxPtr Sandbox::create(Script& script)
   Enum<DecoderProtocol>::registerValues(L);
   Enum<Direction>::registerValues(L);
   Enum<WorldEvent>::registerValues(L);
-  ReadOnlyTable::setMetatable(L, -1);
+  ReadOnlyTable::wrap(L, -1);
   lua_setfield(L, -2, "enum");
 
   // add set values:
   lua_newtable(L);
   Set<WorldState>::registerValues(L);
-  ReadOnlyTable::setMetatable(L, -1);
+  ReadOnlyTable::wrap(L, -1);
   lua_setfield(L, -2, "set");
 
   // let global _G point to itself:

server/src/lua/set.hpp

@@ -174,7 +174,7 @@ struct Set
       push(L, it.first);
       lua_setfield(L, -2, it.second);
     }
-    ReadOnlyTable::setMetatable(L, -1);
+    ReadOnlyTable::wrap(L, -1);
     lua_setfield(L, -2, set_name_v<T>);
   }
 };

server/test/lua/enum.cpp

@@ -37,7 +37,6 @@ static lua_State* createState()
 {
   lua_State* L = newStateWithProtect();
 
-  Lua::ReadOnlyTable::registerType(L);
   Lua::Enum<T>::registerType(L);
 
   lua_createtable(L, 0, 1);

server/test/lua/set.cpp

@@ -35,7 +35,6 @@ static lua_State* createState()
 {
   lua_State* L = newStateWithProtect();
 
-  Lua::ReadOnlyTable::registerType(L);
   Lua::Set<T>::registerType(L);
 
   lua_createtable(L, 0, 1);