1 files changed, 20 insertions, 2 deletions
diff --git a/server/src/luaquerymapper.cc b/server/src/luaquerymapper.cc
index b698fe9..2de1d3c 100644
--- a/server/src/luaquerymapper.cc
+++ b/server/src/luaquerymapper.cc
@@ -78,6 +78,8 @@ LUAQueryMapper::LUAQueryMapper(QueryResult &res)
 
   // Run program (init)
   lua_pcall(L, 0, LUA_MULTRET, 0);
+
+  clean_top = lua_gettop(L);
 }
 
 LUAQueryMapper::~LUAQueryMapper()
@@ -87,6 +89,14 @@ LUAQueryMapper::~LUAQueryMapper()
 
 Value LUAQueryMapper::map(const std::string &mapper)
 {
+  Value v;
+
+  if(mapper == "") {
+    printf("Empty LUA mapper detected!\n");
+    v.timestamp = 0;
+    v.value = "";
+  }
+
   int s = luaL_loadbuffer(L, mapper.c_str(), mapper.size(), "mapper");
   switch(s) {
   case 0: //no errors;
@@ -104,8 +114,16 @@ Value LUAQueryMapper::map(const std::string &mapper)
   // Run the loaded code
   lua_pcall(L, 0, LUA_MULTRET, 0);
 
-  Value v;
-  
+  // Check if app messed up the stack.
+  if(lua_gettop(L) != clean_top) {
+    printf("LUA mapper messed up the stack (wrong number of return values)!\n");
+    lua_pop(L, lua_gettop(L) - clean_top);
+    Value v;
+    v.timestamp = 0;
+    v.value = "";
+    return v;
+  }
+
   v.timestamp = lua_tointeger(L, lua_gettop(L));
   lua_pop(L, 1);
   v.value = lua_tostring(L, lua_gettop(L));