dbus: Use xdg-desktop-portal Inhibit when running under Flatpak or Snap

In order to inhibit the screen saver, SDL currently uses
`org.freedesktop.ScreenSaver.Inhibit()` and, as a fallback, a protocol
specific method for X11 or Wayland.

Accessing `org.freedesktop.ScreenSaver` is usually not allowed when
inside a sandbox like Flatpak, unless the permission has been explicitly
granted to the application.

Another issue is that the Wayland protocol "Idle inhibit" is relatively
new and not yet widely adopted. For example Mutter still doesn't support
it.

For those reasons, when running under Flatpak or Snap, we should try to
inhibit the screen saver by using xdg-desktop-portal instead. This
should give us an higher chance of success.

Fixes: https://github.com/libsdl-org/SDL/issues/6075

Signed-off-by: Ludovico de Nittis <ludovico.denittis@collabora.com>

src/core/linux/SDL_dbus.c

@@ -22,6 +22,7 @@
 #include "SDL_hints.h"
 #include "SDL_dbus.h"
 #include "SDL_atomic.h"
+#include "SDL_sandbox.h"
 #include "../../stdlib/SDL_vacopy.h"
 
 #if SDL_USE_LIBDBUS
@@ -29,6 +30,7 @@
 #include "SDL_loadso.h"
 static const char *dbus_library = "libdbus-1.so.3";
 static void *dbus_handle = NULL;
+static char *inhibit_handle = NULL;
 static unsigned int screensaver_cookie = 0;
 static SDL_DBusContext dbus;
 
@@ -192,6 +194,8 @@ SDL_DBus_Quit(void)
 #endif
     SDL_zero(dbus);
     UnloadDBUSLibrary();
+    SDL_free(inhibit_handle);
+    inhibit_handle = NULL;
 }
 
 SDL_DBusContext *
@@ -363,20 +367,108 @@ SDL_DBus_QueryProperty(const char *node, const char *path, const char *interface
 void
 SDL_DBus_ScreensaverTickle(void)
 {
-    if (screensaver_cookie == 0) {  /* no need to tickle if we're inhibiting. */
+    if (screensaver_cookie == 0 && inhibit_handle == NULL) {  /* no need to tickle if we're inhibiting. */
         /* org.gnome.ScreenSaver is the legacy interface, but it'll either do nothing or just be a second harmless tickle on newer systems, so we leave it for now. */
         SDL_DBus_CallVoidMethod("org.gnome.ScreenSaver", "/org/gnome/ScreenSaver", "org.gnome.ScreenSaver", "SimulateUserActivity", DBUS_TYPE_INVALID);
         SDL_DBus_CallVoidMethod("org.freedesktop.ScreenSaver", "/org/freedesktop/ScreenSaver", "org.freedesktop.ScreenSaver", "SimulateUserActivity", DBUS_TYPE_INVALID);
     }
 }
 
+static SDL_bool
+SDL_DBus_AppendDictWithKeyValue(DBusMessageIter *iterInit, const char *key, const char *value)
+{
+    DBusMessageIter iterDict, iterEntry, iterValue;
+
+    if (!dbus.message_iter_open_container(iterInit, DBUS_TYPE_ARRAY, "{sv}", &iterDict))
+        goto failed;
+
+    if (!dbus.message_iter_open_container(&iterDict, DBUS_TYPE_DICT_ENTRY, NULL, &iterEntry))
+        goto failed;
+
+    if (!dbus.message_iter_append_basic(&iterEntry, DBUS_TYPE_STRING, &key))
+        goto failed;
+
+    if (!dbus.message_iter_open_container(&iterEntry, DBUS_TYPE_VARIANT, DBUS_TYPE_STRING_AS_STRING, &iterValue))
+        goto failed;
+
+    if (!dbus.message_iter_append_basic(&iterValue, DBUS_TYPE_STRING, &value))
+        goto failed;
+
+    if (!dbus.message_iter_close_container(&iterEntry, &iterValue)
+        || !dbus.message_iter_close_container(&iterDict, &iterEntry)
+        || !dbus.message_iter_close_container(iterInit, &iterDict)) {
+        goto failed;
+    }
+
+    return SDL_TRUE;
+
+failed:
+    /* message_iter_abandon_container_if_open() and message_iter_abandon_container() might be
+     * missing if libdbus is too old. Instead, we just return without cleaning up any eventual
+     * open container */
+    return SDL_FALSE;
+}
+
 SDL_bool
 SDL_DBus_ScreensaverInhibit(SDL_bool inhibit)
 {
-    if ( (inhibit && (screensaver_cookie != 0)) || (!inhibit && (screensaver_cookie == 0)) ) {
+    const char *default_inhibit_reason = "Playing a game";
+
+    if ( (inhibit && (screensaver_cookie != 0 || inhibit_handle != NULL))
+        || (!inhibit && (screensaver_cookie == 0 && inhibit_handle == NULL)) ) {
         return SDL_TRUE;
+    }
+
+    if (SDL_DetectSandbox() != SDL_SANDBOX_NONE) {
+        const char *bus_name = "org.freedesktop.portal.Desktop";
+        const char *path = "/org/freedesktop/portal/desktop";
+        const char *interface = "org.freedesktop.portal.Inhibit";
+        const char *window = ""; /* As a future improvement we could gather the X11 XID or Wayland surface identifier */
+        static const unsigned int INHIBIT_IDLE = 8; /* Taken from the portal API reference */
+        DBusMessageIter iterInit;
+
+        if (inhibit) {
+            DBusMessage *msg;
+            SDL_bool retval = SDL_FALSE;
+            const char *key = "reason";
+            const char *reply = NULL;
+            const char *reason = SDL_GetHint(SDL_HINT_SCREENSAVER_INHIBIT_ACTIVITY_NAME);
+            if (!reason || !reason[0]) {
+                reason = default_inhibit_reason;
+            }
+
+            msg = dbus.message_new_method_call(bus_name, path, interface, "Inhibit");
+            if (!msg) {
+                return SDL_FALSE;
+            }
+
+            if (!dbus.message_append_args(msg, DBUS_TYPE_STRING, &window, DBUS_TYPE_UINT32, &INHIBIT_IDLE, DBUS_TYPE_INVALID)) {
+                dbus.message_unref(msg);
+                return SDL_FALSE;
+            }
+
+            dbus.message_iter_init_append(msg, &iterInit);
+            if (!SDL_DBus_AppendDictWithKeyValue(&iterInit, key, reason)) {
+                dbus.message_unref(msg);
+                return SDL_FALSE;
+            }
+
+            if (SDL_DBus_CallWithBasicReply(dbus.session_conn, msg, DBUS_TYPE_OBJECT_PATH, &reply)) {
+                inhibit_handle = SDL_strdup(reply);
+                retval = SDL_TRUE;
+            }
+
+            dbus.message_unref(msg);
+            return retval;
+        } else {
+            if (!SDL_DBus_CallVoidMethod(bus_name, inhibit_handle, "org.freedesktop.portal.Request", "Close", DBUS_TYPE_INVALID)) {
+                return SDL_FALSE;
+            }
+            SDL_free(inhibit_handle);
+            inhibit_handle = NULL;
+        }
     } else {
-        const char *node = "org.freedesktop.ScreenSaver";
+        const char *bus_name = "org.freedesktop.ScreenSaver";
         const char *path = "/org/freedesktop/ScreenSaver";
         const char *interface = "org.freedesktop.ScreenSaver";
 
@@ -387,17 +479,17 @@ SDL_DBus_ScreensaverInhibit(SDL_bool inhibit)
                app  = "My SDL application";
             }
             if (!reason || !reason[0]) {
-                reason = "Playing a game";
+                reason = default_inhibit_reason;
             }
 
-            if (!SDL_DBus_CallMethod(node, path, interface, "Inhibit",
+            if (!SDL_DBus_CallMethod(bus_name, path, interface, "Inhibit",
                     DBUS_TYPE_STRING, &app, DBUS_TYPE_STRING, &reason, DBUS_TYPE_INVALID,
                     DBUS_TYPE_UINT32, &screensaver_cookie, DBUS_TYPE_INVALID)) {
                 return SDL_FALSE;
             }
             return (screensaver_cookie != 0) ? SDL_TRUE : SDL_FALSE;
         } else {
-            if (!SDL_DBus_CallVoidMethod(node, path, interface, "UnInhibit", DBUS_TYPE_UINT32, &screensaver_cookie, DBUS_TYPE_INVALID)) {
+            if (!SDL_DBus_CallVoidMethod(bus_name, path, interface, "UnInhibit", DBUS_TYPE_UINT32, &screensaver_cookie, DBUS_TYPE_INVALID)) {
                 return SDL_FALSE;
             }
             screensaver_cookie = 0;