support systemd notifications

Fixes #1733

vendor/github.com/okzk/sdnotify/util.go

@@ -0,0 +1,39 @@
+package sdnotify
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrSdNotifyNoSocket is the error returned when the NOTIFY_SOCKET does not exist.
+var ErrSdNotifyNoSocket = errors.New("No socket")
+
+// Ready sends READY=1 to the systemd notify socket.
+func Ready() error {
+	return SdNotify("READY=1")
+}
+
+// Stopping sends STOPPING=1 to the systemd notify socket.
+func Stopping() error {
+	return SdNotify("STOPPING=1")
+}
+
+// Reloading sends RELOADING=1 to the systemd notify socket.
+func Reloading() error {
+	return SdNotify("RELOADING=1")
+}
+
+// Errno sends ERRNO=? to the systemd notify socket.
+func Errno(errno int) error {
+	return SdNotify(fmt.Sprintf("ERRNO=%d", errno))
+}
+
+// Status sends STATUS=? to the systemd notify socket.
+func Status(status string) error {
+	return SdNotify("STATUS=" + status)
+}
+
+// Watchdog sends WATCHDOG=1 to the systemd notify socket.
+func Watchdog() error {
+	return SdNotify("WATCHDOG=1")
+}