Remove dependency on apparentlymart/go-cidr

Fixes #651

Replace the go-cidr library with Go's standard netip package. The
dependency was only used in pkg/tap/ip_pool.go for counting IPs and
getting the nth host address in a subnet.

Changes:
- Convert IPPool to use netip.Prefix and netip.Addr instead of
  net.IPNet and net.IP
- Replace cidr.Host() iteration with netip.Addr.Next() traversal
- Remove cidr.AddressCount() by iterating directly through the prefix
- Update callers in pkg/virtualnetwork and pkg/services/dhcp

Assisted-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Signed-off-by: Matus Skvarla <mskvarla@redhat.com>

Author: redbeam

go.mod

@@ -4,7 +4,6 @@ go 1.25.5
 
 require (
 	github.com/Microsoft/go-winio v0.6.2
-	github.com/apparentlymart/go-cidr v1.1.1
 	github.com/containers/winquit v1.1.0
 	github.com/coreos/stream-metadata-go v0.4.11
 	github.com/dustin/go-humanize v1.0.1

go.sum

@@ -1,7 +1,5 @@
 github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
 github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
-github.com/apparentlymart/go-cidr v1.1.1 h1:oEEk8CE0HP0YpHxsegk/TaOtR2FLHdWv4p3eM4ceUwg=
-github.com/apparentlymart/go-cidr v1.1.1/go.mod h1:EBcsNrHc3zQeuaeCeCtQruQm+n9/YjEn/vI25Lg7Gwc=
 github.com/armon/go-proxyproto v0.0.0-20210323213023-7e956b284f0a/go.mod h1:QmP9hvJ91BbJmGVGSbutW19IC0Q9phDCLGaomwTJbgU=
 github.com/containers/winquit v1.1.0 h1:jArun04BNDQvt2W0Y78kh9TazN2EIEMG5Im6/JY7+pE=
 github.com/containers/winquit v1.1.0/go.mod h1:PsPeZlnbkmGGIToMPHF1zhWjBUkd8aHjMOr/vFcPxw8=

pkg/services/dhcp/dhcp.go

@@ -44,7 +44,7 @@ func handler(configuration *types.Configuration, ipPool *tap.IPPool) server4.Han
 			return
 		}
 
-		reply.YourIPAddr = ip
+		reply.YourIPAddr = net.IP(ip.AsSlice())
 		reply.UpdateOption(dhcpv4.OptServerIdentifier(net.ParseIP(configuration.GatewayIP)))
 		reply.UpdateOption(dhcpv4.OptIPAddressLeaseTime(time.Hour))
 

pkg/tap/ip_pool.go

@@ -3,24 +3,19 @@ package tap
 import (
 	"errors"
 	"maps"
-	"math"
-	"net"
+	"net/netip"
 	"sync"
-
-	"github.com/apparentlymart/go-cidr/cidr"
 )
 
 type IPPool struct {
-	base   *net.IPNet
-	count  uint64
+	base   netip.Prefix
 	leases map[string]string
 	lock   sync.Mutex
 }
 
-func NewIPPool(base *net.IPNet) *IPPool {
+func NewIPPool(base netip.Prefix) *IPPool {
 	return &IPPool{
 		base:   base,
-		count:  cidr.AddressCount(base),
 		leases: make(map[string]string),
 	}
 }
@@ -34,37 +29,35 @@ func (p *IPPool) Leases() map[string]string {
 }
 
 func (p *IPPool) Mask() int {
-	ones, _ := p.base.Mask.Size()
-	return ones
+	return p.base.Bits()
 }
 
-func (p *IPPool) GetOrAssign(mac string) (net.IP, error) {
+func (p *IPPool) GetOrAssign(mac string) (netip.Addr, error) {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 
 	for ip, candidate := range p.leases {
 		if candidate == mac {
-			return net.ParseIP(ip), nil
+			return netip.ParseAddr(ip)
 		}
 	}
 
-	if p.count > math.MaxInt {
-		return nil, errors.New("IP pool exceeds maximum number of IP addresses")
-	}
-	for i := 1; i < int(p.count); i++ {
-		candidate, err := cidr.Host(p.base, i)
-		if err != nil {
-			continue
-		}
+	// Start from the first usable IP (network address + 1)
+	candidate := p.base.Masked().Addr().Next()
+
+	// Iterate through all IPs in the subnet
+	for candidate.IsValid() && p.base.Contains(candidate) {
 		if _, ok := p.leases[candidate.String()]; !ok {
 			p.leases[candidate.String()] = mac
 			return candidate, nil
 		}
+		candidate = candidate.Next()
 	}
-	return nil, errors.New("cannot find available IP")
+
+	return netip.Addr{}, errors.New("cannot find available IP")
 }
 
-func (p *IPPool) Reserve(ip net.IP, mac string) {
+func (p *IPPool) Reserve(ip netip.Addr, mac string) {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 

pkg/tap/ip_pool_test.go

@@ -1,14 +1,14 @@
 package tap
 
 import (
-	"net"
+	"net/netip"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestIPPool(t *testing.T) {
-	_, network, _ := net.ParseCIDR("10.0.0.0/8")
+	network := netip.MustParsePrefix("10.0.0.0/8")
 	pool := NewIPPool(network)
 
 	ip1, err := pool.GetOrAssign("mac1")

pkg/virtualnetwork/virtualnetwork.go

@@ -6,6 +6,7 @@ import (
 	"math"
 	"net"
 	"net/http"
+	"net/netip"
 	"os"
 
 	"github.com/containers/gvisor-tap-vsock/pkg/notification"
@@ -34,17 +35,25 @@ func (n *VirtualNetwork) SetNotificationSender(notificationSender *notification.
 }
 
 func New(configuration *types.Configuration) (*VirtualNetwork, error) {
-	_, subnet, err := net.ParseCIDR(configuration.Subnet)
+	subnet, err := netip.ParsePrefix(configuration.Subnet)
 	if err != nil {
 		return nil, fmt.Errorf("cannot parse subnet cidr: %w", err)
 	}
 
 	var endpoint stack.LinkEndpoint
 
 	ipPool := tap.NewIPPool(subnet)
-	ipPool.Reserve(net.ParseIP(configuration.GatewayIP), configuration.GatewayMacAddress)
+	gatewayIP, err := netip.ParseAddr(configuration.GatewayIP)
+	if err != nil {
+		return nil, fmt.Errorf("cannot parse gateway IP: %w", err)
+	}
+	ipPool.Reserve(gatewayIP, configuration.GatewayMacAddress)
 	for ip, mac := range configuration.DHCPStaticLeases {
-		ipPool.Reserve(net.ParseIP(ip), mac)
+		addr, err := netip.ParseAddr(ip)
+		if err != nil {
+			return nil, fmt.Errorf("cannot parse static lease IP %s: %w", ip, err)
+		}
+		ipPool.Reserve(addr, mac)
 	}
 
 	mtu := configuration.MTU