fix: [BREAKING] Treat ip_ranges as a pointer in config interface update options

[lgarber-akamai]

📝 Description

This change resolves an issue that prevented users from updating the interface ip_ranges field with an explicitly empty list. This works by treating ip_ranges as a pointer so it will be only omitted if the pointer is nil, as opposed to if the slice is nil OR the slice is empty.

Resolves #462

✔️ How to Test

The following test steps assume you have pulled down this PR locally.

Integration Testing

make ARGS="-run TestInstance_ConfigInterface_Update" fixtures

Manual Testing

1. In a linodego sandbox environment (e.g. dx-devenv), run the following:

package main

import (
	"context"
	"fmt"
	"github.com/linode/linodego"
	"log"
	"os"
)

func main() {
	ctx := context.Background()

	client := linodego.NewClient(nil)
	client.SetToken(os.Getenv("LINODE_TOKEN"))

	vpc, err := client.CreateVPC(ctx, linodego.VPCCreateOptions{
		Label:  "test-vpc",
		Region: "us-mia",
		Subnets: []linodego.VPCSubnetCreateOptions{
			{
				Label: "test-subnet",
				IPv4:  "10.0.0.0/24",
			},
		},
	})
	if err != nil {
		log.Fatal(err)
	}

	defer func() {
		client.DeleteVPC(ctx, vpc.ID)
	}()

	inst, err := client.CreateInstance(
		ctx,
		linodego.InstanceCreateOptions{
			Region: "us-mia",
			Label:  "test-inst",
			Type:   "g6-nanode-1",
		},
	)
	if err != nil {
		log.Fatal(err)
	}
	defer func() {
		client.DeleteInstance(ctx, inst.ID)
	}()

	cfg, err := client.CreateInstanceConfig(
		ctx,
		inst.ID,
		linodego.InstanceConfigCreateOptions{
			Label:   "test-config",
			Devices: linodego.InstanceConfigDeviceMap{},
			Interfaces: []linodego.InstanceConfigInterfaceCreateOptions{
				{
					Purpose:  linodego.InterfacePurposeVPC,
					SubnetID: &vpc.Subnets[0].ID,
					IPRanges: []string{"10.0.0.5/32"},
				},
			},
		},
	)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println("ip_ranges before update:", cfg.Interfaces[0].IPRanges)

	updatedIPRanges := make([]string, 0)

	iface, err := client.UpdateInstanceConfigInterface(
		ctx,
		inst.ID,
		cfg.ID,
		cfg.Interfaces[0].ID,
		linodego.InstanceConfigInterfaceUpdateOptions{
			IPRanges: &updatedIPRanges,
		},
	)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println("ip_ranges after update: ", iface.IPRanges)
}

2. Ensure no errors are raised and the output looks similar to the following:

ip_ranges before update: [10.0.0.5/32]
ip_ranges after update:  []

[zliang-akamai]

Another option would be making IPRanges as a pointer, but that would be a breaking change for the users? I think it might be fine since we are still in the early phase of VPC? Or maybe we can schedule it to linodego v2?

[lgarber-akamai]

Another option would be making IPRanges as a pointer, but that would be a breaking change for the users? I think it might be fine since we are still in the early phase of VPC? Or maybe we can schedule it to linodego v2?

@zliang-akamai That's a good point! I wrote this with avoiding a breaking change in mind but it might make sense to transition this to a pointer now or in v2 for consistency with the rest of the codebase.

[yec-akamai]

LGTM! Tests passed locally

[jriddle-linode]

LGTM