Implement CanNTP property

data/org.freedesktop.timedate1.xml

@@ -5,6 +5,7 @@
   <property name="Timezone" type="s" access="read"/>
   <property name="LocalRTC" type="b" access="read"/>
   <property name="NTP" type="b" access="read"/>
+  <property name="CanNTP" type="b" access="read"/>
   <method name="SetTime">
    <arg name="usec_utc" type="x" direction="in"/>
    <arg name="relative" type="b" direction="in"/>

src/timedate.cpp

@@ -18,6 +18,7 @@
 #include <cstring>
 #include <filesystem>
 #include <fstream>
+#include <iostream>
 #include <string>
 
 #include "timedate.h"
@@ -116,6 +117,10 @@ static void slack_get_property(Glib::VariantBase& result, const Glib::RefPtr<Gio
     {
         result = Glib::Variant<bool>::create(dlackware::timedate::ntp());
     }
+    else if (prop_name == "CanNTP")
+    {
+        result = Glib::Variant<bool>::create(dlackware::timedate::can_ntp());
+    }
 }
 
 namespace dlackware::timedate
@@ -265,6 +270,24 @@ namespace dlackware::timedate
         return Glib::file_test("/etc/rc.d/rc.ntpd", Glib::FileTest::FILE_TEST_IS_EXECUTABLE);
     }
 
+    bool can_ntp()
+    {
+        std::string standard_output;
+        int wait_status{-1};
+
+        try
+        {
+            Glib::spawn_sync("", std::vector<std::string>{ "s6-rc-db", "type", "ntpd" },
+                    Glib::SpawnFlags::SPAWN_SEARCH_PATH | Glib::SpawnFlags::SPAWN_STDERR_TO_DEV_NULL,
+                    {}, &standard_output, nullptr, &wait_status);
+        }
+        catch (const Glib::SpawnError& spawn_error)
+        {
+            return std::filesystem::exists("/etc/rc.d/rc.ntpd");
+        }
+        return wait_status == 0 && standard_output == "bundle\n";
+    }
+
     void set_time(gint64 seconds_since_epoch, bool relative, bool)
     {
         timespec ts;

src/timedate.h

@@ -34,9 +34,12 @@ namespace dlackware::timedate
     // Returns if the hardware clock is set to local time or not
     bool local_rtc();
 
-    // Returns if NTP is enabled
+    // Returns whether NTP is enabled.
     bool ntp();
 
+    // Returns whether NTP is available.
+    bool can_ntp();
+
     // Returns the timezones available on the system.
     std::vector<Glib::ustring> list_timezones();