pkg/updateengine: rewrite tests and code to use new dbus package

This is a safe step before moving creation of D-Bus connection to agent
and eventually agent CLI code, which however requires development of
tests on the agent code itself.

Signed-off-by: Mateusz Gozdek <mgozdek@microsoft.com>

pkg/agent/agent.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/klog/v2"
 
 	"github.com/flatcar-linux/flatcar-linux-update-operator/pkg/constants"
+	"github.com/flatcar-linux/flatcar-linux-update-operator/pkg/dbus"
 	"github.com/flatcar-linux/flatcar-linux-update-operator/pkg/k8sutil"
 	"github.com/flatcar-linux/flatcar-linux-update-operator/pkg/updateengine"
 )
@@ -67,7 +68,7 @@ func New(node string, reapTimeout time.Duration) (*Klocksmith, error) {
 	nc := kc.CoreV1().Nodes()
 
 	// Set up update_engine client.
-	updateEngineClient, err := updateengine.New(updateengine.DBusSystemPrivateConnector)
+	updateEngineClient, err := updateengine.New(dbus.SystemPrivateConnector)
 	if err != nil {
 		return nil, fmt.Errorf("establishing connection to update_engine dbus: %w", err)
 	}

pkg/updateengine/client.go

@@ -16,10 +16,10 @@ package updateengine
 
 import (
 	"fmt"
-	"os"
-	"strconv"
 
 	godbus "github.com/godbus/dbus/v5"
+
+	"github.com/flatcar-linux/flatcar-linux-update-operator/pkg/dbus"
 )
 
 const (
@@ -52,49 +52,27 @@ type Client interface {
 
 // DBusConnection is set of methods which client expects D-Bus connection to implement.
 type DBusConnection interface {
-	Auth([]godbus.Auth) error
-	Hello() error
 	Close() error
 	AddMatchSignal(...godbus.MatchOption) error
 	Signal(chan<- *godbus.Signal)
 	Object(string, godbus.ObjectPath) godbus.BusObject
 }
 
-// DBusConnector is a constructor function providing D-Bus connection.
-type DBusConnector func() (DBusConnection, error)
-
-// DBusSystemPrivateConnector is a standard update_engine connector using system bus.
-func DBusSystemPrivateConnector() (DBusConnection, error) {
-	return godbus.SystemBusPrivate()
+type caller interface {
+	Call(method string, flags godbus.Flags, args ...interface{}) *godbus.Call
 }
 
 type client struct {
 	conn   DBusConnection
-	object godbus.BusObject
+	object caller
 	ch     chan *godbus.Signal
 }
 
 // New creates new instance of Client and initializes it.
-func New(newConnection DBusConnector) (Client, error) {
-	conn, err := newConnection()
+func New(connector dbus.Connector) (Client, error) {
+	conn, err := dbus.New(connector)
 	if err != nil {
-		return nil, fmt.Errorf("opening private connection to system bus: %w", err)
-	}
-
-	methods := []godbus.Auth{godbus.AuthExternal(strconv.Itoa(os.Getuid()))}
-
-	if err := conn.Auth(methods); err != nil {
-		// Best effort closing the connection.
-		_ = conn.Close()
-
-		return nil, fmt.Errorf("authenticating to system bus: %w", err)
-	}
-
-	if err := conn.Hello(); err != nil {
-		// Best effort closing the connection.
-		_ = conn.Close()
-
-		return nil, fmt.Errorf("sending hello to system bus: %w", err)
+		return nil, fmt.Errorf("creating D-Bus client: %w", err)
 	}
 
 	matchOptions := []godbus.MatchOption{