[#552] Add sdnotify package

To avoid using third-party dependencies.

Signed-off-by: Ekaterina Lebedeva <ekaterina.lebedeva@yadro.com>

pkg/util/sdnotify/sdnotify.go

@@ -0,0 +1,59 @@
+package sdnotify
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"strings"
+)
+
+const (
+	ReadyEnabled     = "READY=1"
+	StoppingEnabled  = "STOPPING=1"
+	ReloadingEnabled = "RELOADING=1"
+)
+
+var socket *net.UnixAddr
+
+// Initializes socket with provided name of
+// environment variable.
+func InitSocket() error {
+	notifySocket := os.Getenv("NOTIFY_SOCKET")
+	if notifySocket == "" {
+		return fmt.Errorf("\"NOTIFY_SOCKET\" environment variable is not present")
+	}
+	socket = &net.UnixAddr{
+		Name: notifySocket,
+		Net:  "unixgram",
+	}
+	return nil
+}
+
+// FlagAndStatus sends systemd a combination of a
+// well-known status and STATUS=%s{status}, separated by newline.
+func FlagAndStatus(status string) error {
+	status += "\nSTATUS=" + strings.TrimSuffix(status, "=1")
+	return Send(status)
+}
+
+// Status sends systemd notify STATUS=%s{status}.
+func Status(status string) error {
+	return Send(fmt.Sprintf("STATUS=%s", status))
+}
+
+// Send state through the notify socket if any.
+// If the notify socket was not detected, it returns an error.
+func Send(state string) error {
+	if socket == nil {
+		return fmt.Errorf("socket is not initialized")
+	}
+	conn, err := net.DialUnix(socket.Net, nil, socket)
+	if err != nil {
+		return fmt.Errorf("can't open unix socket: %v", err)
+	}
+	defer conn.Close()
+	if _, err = conn.Write([]byte(state)); err != nil {
+		return fmt.Errorf("can't write into the unix socket: %v", err)
+	}
+	return nil
+}