panic: runtime at property.(*Collector).Retrieve

[amandahla]

I'm collecting vms like this:

        mgr := view.NewManager(c)

	v, err := mgr.CreateContainerView(ctx, c.ServiceContent.RootFolder, []string{"VirtualMachine"}, true)
	if err != nil {
		return nil, err
	}

	defer v.Destroy(ctx)

	// Retrieve summary property for all machines
	var vmt []mo.VirtualMachine
	err = v.Retrieve(ctx, []string{"VirtualMachine"}, []string{"summary"}, &vmt)
	if err != nil {
		return nil, err
	}

Then I want to see the network names from which VM and made like this:

        pc := property.DefaultCollector(c)

	var nets []mo.Network
	err := pc.Retrieve(ctx, vm.Network, []string{"name", "summary"}, &nets)
	if err != nil {
		return nil, err
	}

	for _, net := range nets {
		name := strings.Replace(net.Name, ".", "_", -1)
		outputNetworkNames.Put("name", name)
	}

Then I got:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x230becc]

goroutine 90 [running]:
github.com/elastic/beats/metricbeat/module/vsphere/vendor/github.com/vmware/govmomi/property.(*Collector).Retrieve(0xc420051370, 0x3714980, 0xc420346200, 0x0, 0x0, 0x0, 0xc42022e110, 0x1, 0x1, 0x2423000, ...)
	/home/user/project/beats/src/github.com/elastic/beats/metricbeat/module/vsphere/vendor/github.com/vmware/govmomi/property/collector.go:157 +0x50c
github.com/elastic/beats/metricbeat/module/vsphere/virtualmachine.getNetworkNames(0x3714980, 0xc420346200, 0xc4202ec580, 0x0, 0x0, 0x0, 0x4, 0x1000000007, 0x0)

I don't know why this is happening here. Any help?

[dougm]

Avoid the call toRetrieve if len(vm.Network) == 0. We can also change Retrieve to handle that case.

[amandahla]

Great @dougm
You made me see that I was doing wrong actually. Since I retrieved only Summary, I needed to use vm.Summary.Vm.Reference() instead vm.Network then retrieve this reference for finally get network.

        pc := property.DefaultCollector(c)

	var vm mo.VirtualMachine
	err := pc.RetrieveOne(ctx, vm.Summary.Vm.Reference(), []string{"network"}, &vm)
	if err != nil {
		return nil, err
	}

	if len(vm.Network) == 0 {
		return nil, nil
	}

	var nets []mo.Network
	err = pc.Retrieve(ctx, vm.Network, []string{"name"}, &nets)
	if err != nil {
		return nil, err
	}

	for _, net := range nets {
		name := strings.Replace(net.Name, ".", "_", -1)
		outputNetworkNames.Put("name", name)
	}