daemon: SdNotify: add support for abstract unix sockets

As per https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#

daemon/sdnotify.go

@@ -54,16 +54,29 @@ const (
 // (false, err) - notification supported, but failure happened (e.g. error connecting to NOTIFY_SOCKET or while sending data)
 // (true, nil) - notification supported, data has been sent
 func SdNotify(unsetEnvironment bool, state string) (bool, error) {
-	socketAddr := &net.UnixAddr{
-		Name: os.Getenv("NOTIFY_SOCKET"),
-		Net:  "unixgram",
-	}
+	notifySocket := os.Getenv("NOTIFY_SOCKET")
 
 	// NOTIFY_SOCKET not set
-	if socketAddr.Name == "" {
+	if notifySocket == "" {
+		return false, nil
+	}
+
+	// socket type not supported. We only support unix domain sockets
+	// but NOTIFY_SOCKET can also use vsock
+	if notifySocket[0] != '@' && notifySocket[0] != '/' {
 		return false, nil
 	}
 
+	// abstract unix socket. Start with a 0-byte
+	if notifySocket[0] == '@' {
+		notifySocket = "\x00" + notifySocket[1:]
+	}
+
+	socketAddr := &net.UnixAddr{
+		Name: notifySocket,
+		Net:  "unixgram",
+	}
+
 	if unsetEnvironment {
 		if err := os.Unsetenv("NOTIFY_SOCKET"); err != nil {
 			return false, err

daemon/sdnotify_test.go

@@ -41,6 +41,14 @@ func TestSdNotify(t *testing.T) {
 		panic(e)
 	}
 
+	abstractLAddr := net.UnixAddr{
+		Name: "\x00" + notifySocket,
+	}
+	_, e = net.ListenUnixgram("unixgram", &abstractLAddr)
+	if e != nil {
+		panic(e)
+	}
+
 	tests := []struct {
 		unsetEnv  bool
 		envSocket string
@@ -50,10 +58,14 @@ func TestSdNotify(t *testing.T) {
 	}{
 		// (true, nil) - notification supported, data has been sent
 		{false, notifySocket, true, false},
+		{false, "@" + notifySocket, true, false},
+
 		// (false, err) - notification supported, but failure happened
 		{true, testDir + "/missing.sock", false, true},
 		// (false, nil) - notification not supported
 		{true, "", false, false},
+
+		// (true, nil) - notification supported, data has been sent
 	}
 
 	for i, tt := range tests {