+ more accurate implementation for BIsAppInstalled, it now rejects uint32_max

+ allow behavior customizization via installed_app_ids.txt config file

+ limit/lock list of installed apps on an empty file (similar to dlc.txt)

dll/settings.cpp

@@ -280,3 +280,14 @@ int Settings::add_image(std::string data, uint32 width, uint32 height)
     images[last] = dt;
     return last;
 }
+
+bool Settings::appIsInstalled(AppId_t appID)
+{
+    if (this->assume_any_app_installed) return true;
+
+    auto f = std::find_if(installed_app_ids.begin(), installed_app_ids.end(), [&appID](AppId_t const& item) { return item == appID; });
+    if (installed_app_ids.end() == f)
+        return false;
+
+    return true;
+}

dll/settings.h

@@ -206,6 +206,11 @@ public:
     int add_image(std::string data, uint32 width, uint32 height);
     bool disable_account_avatar = false;
 
+    //installed app ids, Steam_Apps::BIsAppInstalled()
+    std::set<AppId_t> installed_app_ids;
+    bool assume_any_app_installed = true;
+    bool appIsInstalled(AppId_t appID);
+
     //controller
     struct Controller_Settings controller_settings;
     std::string glyphs_directory;

dll/settings_parser.cpp

@@ -805,6 +805,37 @@ uint32 create_localstorage_settings(Settings **settings_client_out, Settings **s
         }
     }
 
+    {
+        std::string installed_apps_list_path = Local_Storage::get_game_settings_path() + "installed_app_ids.txt";
+        std::ifstream input( utf8_decode(installed_apps_list_path) );
+        if (input.is_open()) {
+            settings_client->assume_any_app_installed = false;
+            settings_server->assume_any_app_installed = false;
+            PRINT_DEBUG("Limiting/Locking installed apps\n");
+            consume_bom(input);
+            for( std::string line; getline( input, line ); ) {
+                if (!line.empty() && line[line.length()-1] == '\n') {
+                    line.pop_back();
+                }
+
+                if (!line.empty() && line[line.length()-1] == '\r') {
+                    line.pop_back();
+                }
+
+                try {
+                    AppId_t app_id = std::stoul(line);
+                    settings_client->installed_app_ids.insert(app_id);
+                    settings_server->installed_app_ids.insert(app_id);
+                    PRINT_DEBUG("Added installed app with ID %u\n", app_id);
+                } catch (...) {}
+            }
+        } else {
+            settings_client->assume_any_app_installed = true;
+            settings_server->assume_any_app_installed = true;
+            PRINT_DEBUG("Assuming any app is installed\n");
+        }
+    }
+
     load_subscribed_groups_clans(local_storage->get_global_settings_path() + "subscribed_groups_clans.txt", settings_client, settings_server);
     load_subscribed_groups_clans(Local_Storage::get_game_settings_path() + "subscribed_groups_clans.txt", settings_client, settings_server);
 

dll/steam_apps.cpp

@@ -240,10 +240,18 @@ uint32 Steam_Apps::GetAppInstallDir( AppId_t appID, char *pchFolder, uint32 cchF
 }
 
 // returns true if that app is installed (not necessarily owned)
+// "This only works for base applications, not Downloadable Content (DLC). Use BIsDlcInstalled for DLC instead"
+// https://partner.steamgames.com/doc/api/ISteamApps
 bool Steam_Apps::BIsAppInstalled( AppId_t appID )
 {
     PRINT_DEBUG("BIsAppInstalled %u\n", appID);
-    return true;
+    // is this true? it seems to indicate a non-steam game
+    if (appID == 0) return true;
+    // game LEGO® 2K Drive (app id 1451810) checks for a proper steam behavior by sending uint32_max and expects false in return
+    if (appID == UINT32_MAX) return false;
+    if (appID == settings->get_local_game_id().AppID()) return true;
+
+    return settings->appIsInstalled(appID);
 }
 
 // returns the SteamID of the original owner. If different from current user, it's borrowed

files_example/steam_settings.EXAMPLE/installed_app_ids.EXAMPLE.txt

@@ -0,0 +1,8 @@
+1. Rename this to: installed_app_ids.txt
+2. Add all apps IDs (each on a separate line) that should be reported as insatlled, they could be NOT owned, that is allowed
+3. Or, remove the file installed_app_ids.txt if it exists to:
+    * Allow app ID 0, this seems to be a special denotation to "non-steam apps"
+    * Allow app ID of the current game (you must create the file steam_appid.txt)
+    * Allow anything else
+
+In all cases app ID 4294967295 is disallowed