Calling Prefix.Usage() on a child prefixes with mask size 31 or 32 panics with "negative shift amount"

[antonprokopovich]

Version: go-ipam v1.11.6

Here's the exact line that panics: https://github.com/metal-stack/go-ipam/blob/master/prefix.go#L642

The code to reproduce the issue:

package main

import (
	"context"
	"fmt"

	goipam "github.com/metal-stack/go-ipam"
)

type Subnet struct {
	cidr       string
	parentCidr string
}

var parentSubnets = []Subnet{
	{
		cidr:       "192.168.0.0/24",
		parentCidr: "",
	},
}

var subnets = []Subnet{
	{
		cidr:       "192.168.0.0/30",
		parentCidr: "192.168.0.0/24",
	},
}

var storage = map[string][]Subnet{
	"parents":  parentSubnets,
	"children": subnets,
}

func main() {
	ipam := goipam.New()

	ctx := context.Background()

	for _, parent := range storage["parents"] {
		parPrefix, err := ipam.NewPrefix(ctx, parent.cidr)
		if err != nil {
			fmt.Println(err)
		}

		for _, child := range storage["children"] {
			if child.parentCidr == parent.cidr {
				chPrefix, err := ipam.AcquireSpecificChildPrefix(ctx, parent.cidr, child.cidr)
				if err != nil {
					fmt.Println(err)
				}

                                 // This call will panic
				u := chPrefix.Usage()
				_ = u
			}
		}
	}
}

[majst01]

Nice catch, do you mind creating a PR with a unit test showing this issue ?

[antonprokopovich]

@majst01 Will try to do it today and let you know when I finish

[antonprokopovich]

@majst01 I just opened the PR: #113

I will be glad to contribute more if needed

[majst01]

Thanks, looking at it. Do you have a idea howto fix that ?

[antonprokopovich]

@majst01 Not yet but I will try to look into it later today

[majst01]

@majst01 Not yet but I will try to look into it later today

I made a fix #114