operator: fix gRPC dialing over UDS (#3201)

* operator: add test for gRPC connection over UDS

operators/constellation-node-operator/internal/upgrade/upgrade_test.go

@@ -0,0 +1,52 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package upgrade
+
+import (
+	"context"
+	"net"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/edgelesssys/constellation/v2/internal/versions/components"
+	"github.com/edgelesssys/constellation/v2/upgrade-agent/upgradeproto"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+)
+
+// TestGRPCDialer is a regression test to ensure the upgrade client can connect to a UDS.
+func TestGRPCDialer(t *testing.T) {
+	require := require.New(t)
+
+	dir := t.TempDir()
+	sockAddr := filepath.Join(dir, "test.socket")
+
+	upgradeAgent := &fakeUpgradeAgent{}
+	grpcServer := grpc.NewServer()
+	upgradeproto.RegisterUpdateServer(grpcServer, upgradeAgent)
+
+	listener, err := net.Listen("unix", sockAddr)
+	require.NoError(err)
+	go grpcServer.Serve(listener)
+	t.Cleanup(grpcServer.Stop)
+
+	fileInfo, err := os.Stat(sockAddr)
+	require.NoError(err)
+	require.Equal(os.ModeSocket, fileInfo.Mode()&os.ModeType)
+
+	upgradeClient := newClientWithAddress(sockAddr)
+	require.NoError(upgradeClient.Upgrade(context.Background(), []*components.Component{}, "v1.29.6"))
+}
+
+type fakeUpgradeAgent struct {
+	upgradeproto.UnimplementedUpdateServer
+}
+
+func (s *fakeUpgradeAgent) ExecuteUpdate(_ context.Context, _ *upgradeproto.ExecuteUpdateRequest) (*upgradeproto.ExecuteUpdateResponse, error) {
+	return &upgradeproto.ExecuteUpdateResponse{}, nil
+}