coredhcp/plugins/file/plugin.go

// Copyright 2018-present the CoreDHCP Authors. All rights reserved
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree.

// Package file enables static mapping of MAC <--> IP addresses.
// The mapping is stored in a text file, where each mapping is described by one line containing
// two fields separated by spaces: MAC address, and IP address. For example:
//
//  $ cat file_leases.txt
//  00:11:22:33:44:55 10.0.0.1
//  01:23:45:67:89:01 10.0.10.10
//
// To specify the plugin configuration in the server6/server4 sections of the config file, just
// pass the leases file name as plugin argument, e.g.:
//
//  $ cat config.yml
//
//  server6:
//     ...
//     plugins:
//       - file: "file_leases.txt"
//     ...
//
// If the file path is not absolute, it is relative to the cwd where coredhcp is run.
package file

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"net"
	"strings"

	"github.com/coredhcp/coredhcp/handler"
	"github.com/coredhcp/coredhcp/logger"
	"github.com/coredhcp/coredhcp/plugins"
	"github.com/insomniacslk/dhcp/dhcpv4"
	"github.com/insomniacslk/dhcp/dhcpv6"
)

var log = logger.GetLogger("plugins/file")

func init() {
	plugins.RegisterPlugin("file", setupFile6, setupFile4)
}

// StaticRecords holds a MAC -> IP address mapping
var StaticRecords map[string]net.IP

// DHCPv6Records and DHCPv4Records are mappings between MAC addresses in
// form of a string, to network configurations.
var (
	DHCPv6Records map[string]net.IP
	DHCPv4Records map[string]net.IP
)

// LoadDHCPv4Records loads the DHCPv4Records global map with records stored on
// the specified file. The records have to be one per line, a mac address and an
// IPv4 address.
func LoadDHCPv4Records(filename string) (map[string]net.IP, error) {
	log.Printf("reading leases from %s", filename)
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, err
	}
	records := make(map[string]net.IP)
	for _, lineBytes := range bytes.Split(data, []byte{'\n'}) {
		line := string(lineBytes)
		if len(line) == 0 {
			continue
		}
		tokens := strings.Fields(line)
		if len(tokens) != 2 {
			return nil, fmt.Errorf("malformed line, want 2 fields, got %d: %s", len(tokens), line)
		}
		hwaddr, err := net.ParseMAC(tokens[0])
		if err != nil {
			return nil, fmt.Errorf("malformed hardware address: %s", tokens[0])
		}
		ipaddr := net.ParseIP(tokens[1])
		if ipaddr.To4() == nil {
			return nil, fmt.Errorf("expected an IPv4 address, got: %v", ipaddr)
		}
		records[hwaddr.String()] = ipaddr
	}

	return records, nil
}

// LoadDHCPv6Records loads the DHCPv6Records global map with records stored on
// the specified file. The records have to be one per line, a mac address and an
// IPv6 address.
func LoadDHCPv6Records(filename string) (map[string]net.IP, error) {
	log.Printf("reading leases from %s", filename)
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, err
	}
	records := make(map[string]net.IP)
	// TODO ignore comments
	for _, lineBytes := range bytes.Split(data, []byte{'\n'}) {
		line := string(lineBytes)
		if len(line) == 0 {
			continue
		}
		tokens := strings.Fields(line)
		if len(tokens) != 2 {
			return nil, fmt.Errorf("malformed line: %s", line)
		}
		hwaddr, err := net.ParseMAC(tokens[0])
		if err != nil {
			return nil, fmt.Errorf("malformed hardware address: %s", tokens[0])
		}
		ipaddr := net.ParseIP(tokens[1])
		if ipaddr.To16() == nil {
			return nil, fmt.Errorf("expected an IPv6 address, got: %v", ipaddr)
		}
		records[hwaddr.String()] = ipaddr
	}
	return records, nil
}

// Handler6 handles DHCPv6 packets for the file plugin
func Handler6(req, resp dhcpv6.DHCPv6) (dhcpv6.DHCPv6, bool) {
	mac, err := dhcpv6.ExtractMAC(req)
	if err != nil {
		log.Warningf("Could not find client MAC, passing")
		return resp, false
	}
	log.Printf("looking up an IP address for MAC %s", mac.String())

	ipaddr, ok := StaticRecords[mac.String()]
	if !ok {
		log.Warningf("MAC address %s is unknown", mac.String())
		return resp, false
	}
	log.Printf("found IP address %s for MAC %s", ipaddr, mac.String())
	resp.AddOption(&dhcpv6.OptIANA{
		// FIXME copy this field from the client, reject/drop if missing
		IaId: [4]byte{0xaa, 0xbb, 0xcc, 0xdd},
		Options: []dhcpv6.Option{
			&dhcpv6.OptIAAddress{
				IPv6Addr:          ipaddr,
				PreferredLifetime: 3600,
				ValidLifetime:     3600,
			},
		},
	})

	decap, err := req.GetInnerMessage()
	if err != nil {
		log.Errorf("Could not decapsulate: %v", err)
		return nil, true
	}
	if oro := decap.GetOption(dhcpv6.OptionORO); len(oro) > 0 {
		for _, code := range oro[0].(*dhcpv6.OptRequestedOption).RequestedOptions() {
			if code == dhcpv6.OptionBootfileURL {
				// bootfile URL is requested
				// FIXME this field should come from the configuration, not
				// being hardcoded
				resp.AddOption(
					&dhcpv6.OptBootFileURL{BootFileURL: []byte("http://[2001:db8::0:1]/nbp")},
				)
			}
		}
	}
	// XXX: We should maybe allow other plugins to run after this to add other options/handle non-IANA requests
	return resp, true
}

// Handler4 handles DHCPv4 packets for the file plugin
func Handler4(req, resp *dhcpv4.DHCPv4) (*dhcpv4.DHCPv4, bool) {
	ipaddr, ok := StaticRecords[req.ClientHWAddr.String()]
	if !ok {
		log.Warningf("MAC address %s is unknown", req.ClientHWAddr.String())
		return resp, false
	}
	resp.YourIPAddr = ipaddr
	log.Printf("found IP address %s for MAC %s", ipaddr, req.ClientHWAddr.String())
	return resp, true
}

func setupFile6(args ...string) (handler.Handler6, error) {
	h6, _, err := setupFile(true, args...)
	return h6, err
}

func setupFile4(args ...string) (handler.Handler4, error) {
	_, h4, err := setupFile(false, args...)
	return h4, err
}

func setupFile(v6 bool, args ...string) (handler.Handler6, handler.Handler4, error) {
	var err error
	var records map[string]net.IP
	if len(args) < 1 {
		return nil, nil, errors.New("need a file name")
	}
	filename := args[0]
	if filename == "" {
		return nil, nil, errors.New("got empty file name")
	}
	if v6 {
		records, err = LoadDHCPv6Records(filename)
	} else {
		records, err = LoadDHCPv4Records(filename)
	}
	if err != nil {
		return nil, nil, fmt.Errorf("failed to load DHCPv6 records: %v", err)
	}
	StaticRecords = records
	log.Printf("loaded %d leases from %s", len(records), filename)
	return Handler6, Handler4, nil
}