Properly generate traceback in lua_error_handler() avoiding the first…

… line showing the manual call to debug.traceback() itself

Signed-off-by: DL6ER <[email protected]>

src/webserver/civetweb/mod_lua.inl

@@ -2798,23 +2798,34 @@ lua_error_handler(lua_State *L)
 {
 	const char *error_msg = lua_isstring(L, -1) ? lua_tostring(L, -1) : "?\n";
 
-	/* Log error message */
-	lua_cry(NULL, 0, L, error_msg, "error");
-
 	lua_getglobal(L, "mg");
 	if (!lua_isnil(L, -1)) {
-		lua_getfield(L, -1, "write"); /* call mg.write() */
+		/* Write the error message to the error log */
+		lua_getfield(L, -1, "write");
 		lua_pushstring(L, error_msg);
 		lua_pushliteral(L, "\n");
-		lua_call(L, 2, 0);
-		IGNORE_UNUSED_RESULT(
-		    luaL_dostring(L, "mg.write(debug.traceback(), '\\n')"));
+		lua_call(L, 2, 0); /* call mg.write(error_msg + \n) */
+		lua_pop(L, 1); /* pop mg */
+
+		/* Get Lua traceback */
+		lua_getglobal(L, "debug");
+		lua_getfield(L, -1, "traceback");
+		lua_call(L, 0, 1);	/* call debug.traceback() */
+		lua_remove(L, -2);	/* remove debug */
+
+		/* Write the Lua traceback to the error log */
+		lua_getglobal(L, "mg");
+		lua_getfield(L, -1, "write");
+		lua_pushvalue(L, -3);	/* copy the traceback */
+		lua_pushliteral(L, "\n"); /* append a newline */
+		lua_call(L, 2, 0); /* call mg.write(traceback + \n) */
+		lua_pop(L, 2); /* pop mg and traceback */
 	} else {
 		printf("Lua error: [%s]\n", error_msg);
 		IGNORE_UNUSED_RESULT(
 		    luaL_dostring(L, "print(debug.traceback(), '\\n')"));
 	}
-	/* TODO(lsm, low): leave the stack balanced */
+	lua_pop(L, 1); /* pop error message */
 
 	return 0;
 }