core/pkg/dhcp4c/lease.go

// Copyright 2020 The Monogon Project Authors.
//
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package dhcp4c

import (
	"encoding/binary"
	"net"
	"time"

	"github.com/insomniacslk/dhcp/dhcpv4"
)

// Lease represents a DHCPv4 lease. It only consists of an IP, an expiration timestamp and options as all other
// relevant parts of the message have been normalized into their respective options. It also contains some smart
// getters for commonly-used options which extract only valid information from options.
type Lease struct {
	AssignedIP net.IP
	ExpiresAt  time.Time
	Options    dhcpv4.Options
}

// SubnetMask returns the SubnetMask option or the default mask if not set or invalid.
// It returns nil if the lease is nil.
func (l *Lease) SubnetMask() net.IPMask {
	if l == nil {
		return nil
	}
	mask := net.IPMask(dhcpv4.GetIP(dhcpv4.OptionSubnetMask, l.Options))
	if _, bits := mask.Size(); bits != 32 { // If given mask is not valid, use the default mask
		mask = l.AssignedIP.DefaultMask()
	}
	return mask
}

// IPNet returns an IPNet from the assigned IP and subnet mask.
// It returns nil if the lease is nil.
func (l *Lease) IPNet() *net.IPNet {
	if l == nil {
		return nil
	}
	return &net.IPNet{
		IP:   l.AssignedIP,
		Mask: l.SubnetMask(),
	}
}

// Router returns the first valid router from the DHCP router option or nil if none such exists.
// It returns nil if the lease is nil.
func (l *Lease) Router() net.IP {
	if l == nil {
		return nil
	}
	routers := dhcpv4.GetIPs(dhcpv4.OptionRouter, l.Options)
	for _, r := range routers {
		if r.IsGlobalUnicast() || r.IsLinkLocalUnicast() {
			return r
		}
	}
	// No (valid) router found
	return nil
}

// DNSServers represents an ordered collection of DNS servers
type DNSServers []net.IP

func (a DNSServers) Equal(b DNSServers) bool {
	if len(a) == len(b) {
		if len(a) == 0 {
			return true // both are empty or nil
		}
		for i, aVal := range a {
			if !aVal.Equal(b[i]) {
				return false
			}
		}
		return true
	}
	return false

}

func ip4toInt(ip net.IP) uint32 {
	ip4 := ip.To4()
	if ip4 == nil {
		return 0
	}
	return binary.BigEndian.Uint32(ip4)
}

// DNSServers returns all unique valid DNS servers from the DHCP DomainNameServers options.
// It returns nil if the lease is nil.
func (l *Lease) DNSServers() DNSServers {
	if l == nil {
		return nil
	}
	rawServers := dhcpv4.GetIPs(dhcpv4.OptionDomainNameServer, l.Options)
	var servers DNSServers
	serversSeenMap := make(map[uint32]struct{})
	for _, s := range rawServers {
		ip4Num := ip4toInt(s)
		if s.IsGlobalUnicast() || s.IsLinkLocalUnicast() || ip4Num != 0 {
			if _, ok := serversSeenMap[ip4Num]; ok {
				continue
			}
			serversSeenMap[ip4Num] = struct{}{}
			servers = append(servers, s)
		}
	}
	return servers
}