[gnome-flashback] screensaver: add gf_find_systemd_session

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 6ec4ffce6b7ad61ba0533f9a5743cc13a46a05d1
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Tue Dec 10 22:21:16 2019 +0200

    screensaver: add gf_find_systemd_session
    
    Will be needed by next commit, XDG_SESSION_ID is blacklisted by
    gnome-session and will not be available:
    https://gitlab.gnome.org/GNOME/gnome-session/commit/646b9bc0584d02

 configure.ac                                       |  1 +
 gnome-flashback/libscreensaver/Makefile.am         |  2 +
 .../libscreensaver/gf-screensaver-utils.c          | 74 ++++++++++++++++++++++
 .../libscreensaver/gf-screensaver-utils.h          | 29 +++++++++
 4 files changed, 106 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index 8acd621..0317836 100644
--- a/configure.ac
+++ b/configure.ac
@@ -231,6 +231,7 @@ PKG_CHECK_MODULES([SCREENSAVER], [
   glib-2.0 >= $GLIB_REQUIRED
   gnome-desktop-3.0 >= $LIBGNOME_DESKTOP_REQUIRED
   gtk+-3.0 >= $GTK_REQUIRED
+  libsystemd
 ])
 
 PKG_CHECK_MODULES([SCREENSHOT], [
diff --git a/gnome-flashback/libscreensaver/Makefile.am b/gnome-flashback/libscreensaver/Makefile.am
index acdad6d..6b2f51a 100644
--- a/gnome-flashback/libscreensaver/Makefile.am
+++ b/gnome-flashback/libscreensaver/Makefile.am
@@ -28,6 +28,8 @@ libscreensaver_la_SOURCES = \
        gf-prefs.h \
        gf-screensaver.c \
        gf-screensaver.h \
+       gf-screensaver-utils.c \
+       gf-screensaver-utils.h \
        gf-watcher.c \
        gf-watcher.h \
        $(BUILT_SOURCES) \
diff --git a/gnome-flashback/libscreensaver/gf-screensaver-utils.c 
b/gnome-flashback/libscreensaver/gf-screensaver-utils.c
new file mode 100644
index 0000000..1840496
--- /dev/null
+++ b/gnome-flashback/libscreensaver/gf-screensaver-utils.c
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2019 Alberts Muktupāvels
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+#include "gf-screensaver-utils.h"
+
+#include <systemd/sd-login.h>
+#include <unistd.h>
+
+gboolean
+gf_find_systemd_session (char **session_id)
+{
+  int n_sessions;
+  char **sessions;
+  char *session;
+  int i;
+
+  n_sessions = sd_uid_get_sessions (getuid (), 0, &sessions);
+
+  if (n_sessions < 0)
+    {
+      g_debug ("Failed to get sessions for user %d", getuid ());
+      return FALSE;
+    }
+
+  session = NULL;
+
+  for (i = 0; i < n_sessions; i++)
+    {
+      int r;
+      char *type;
+
+      r = sd_session_get_type (sessions[i], &type);
+
+      if (r < 0)
+        {
+          g_debug ("Couldn't get type for session '%s': %s",
+                   sessions[i], strerror (-r));
+          continue;
+        }
+
+      if (g_strcmp0 (type, "x11") != 0)
+        {
+          free (type);
+          continue;
+        }
+
+      session = sessions[i];
+      free (type);
+    }
+
+  if (session != NULL)
+    *session_id = g_strdup (session);
+
+  for (i = 0; i < n_sessions; i++)
+    free (sessions[i]);
+  free (sessions);
+
+  return session != NULL;
+}
diff --git a/gnome-flashback/libscreensaver/gf-screensaver-utils.h 
b/gnome-flashback/libscreensaver/gf-screensaver-utils.h
new file mode 100644
index 0000000..6e0b2ea
--- /dev/null
+++ b/gnome-flashback/libscreensaver/gf-screensaver-utils.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2019 Alberts Muktupāvels
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GF_SCREENSAVER_UTILS_H
+#define GF_SCREENSAVER_UTILS_H
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+gboolean gf_find_systemd_session (char **session_id);
+
+G_END_DECLS
+
+#endif