sdk: check systemd running for socket activation

Signed-off-by: Antonio Murdaca <[email protected]>

sdk/unix_listener.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 
 	"github.com/coreos/go-systemd/activation"
+	"github.com/coreos/go-systemd/util"
 	"github.com/docker/go-connections/sockets"
 )
 
@@ -21,20 +22,15 @@ func newUnixListener(pluginName string, group string) (net.Listener, string, err
 	if err != nil {
 		return nil, "", err
 	}
-	listenFds := activation.Files(false)
-	if len(listenFds) > 1 {
-		return nil, "", fmt.Errorf("expected only one socket from systemd, got %d", len(listenFds))
+	listener, err := setupSocketActivation()
+	if err != nil {
+		return nil, "", err
 	}
-	if len(listenFds) == 1 {
-		l, err := net.FileListener(listenFds[0])
+	if listener == nil {
+		listener, err = sockets.NewUnixSocket(path, group)
 		if err != nil {
 			return nil, "", err
 		}
-		return l, path, nil
-	}
-	listener, err := sockets.NewUnixSocket(path, group)
-	if err != nil {
-		return nil, "", err
 	}
 	return listener, path, nil
 }
@@ -48,3 +44,22 @@ func fullSocketAddress(address string) (string, error) {
 	}
 	return filepath.Join(pluginSockDir, address+".sock"), nil
 }
+
+func setupSocketActivation() (net.Listener, error) {
+	if !util.IsRunningSystemd() {
+		return nil, nil
+	}
+	listenFds := activation.Files(false)
+	if len(listenFds) > 1 {
+		return nil, fmt.Errorf("expected only one socket from systemd, got %d", len(listenFds))
+	}
+	var listener net.Listener
+	if len(listenFds) == 1 {
+		l, err := net.FileListener(listenFds[0])
+		if err != nil {
+			return nil, err
+		}
+		listener = l
+	}
+	return listener, nil
+}