tools/botanist/targets/ip.go

// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package targets

import (
	"context"
	"errors"
	"fmt"
	"log"
	"net"
	"time"

	"github.com/kr/pretty"

	"go.fuchsia.dev/fuchsia/tools/lib/logger"
	"go.fuchsia.dev/fuchsia/tools/net/mdns"
)

// Interval at which resolveIP will send a question packet as long as it doesn't
// receive a response. If it receives a response it may send packets more
// quickly.
const mDNSQuestionInterval = 2 * time.Second

func getLocalDomain(nodename string) string {
	return nodename + ".local"
}

// resolveIP returns the IPv4 and IPv6 addresses of a fuchsia node via mDNS.
//
// It makes a best effort at returning *both* the IPv4 and IPv6 addresses, but if
// both interfaces do not come up within a reasonable amount of time, it returns
// only the first one that it finds (and no error).
func ResolveIP(ctx context.Context, nodename string) (net.IP, net.IPAddr, error) {
	// Keep track of the start time to log the duration after which a timeout
	// occurred.
	startTime := time.Now()
	m := mdns.NewMDNS()
	defer m.Close()
	m.EnableIPv4()
	m.EnableIPv6()
	out := make(chan net.IPAddr, 1)
	domain := getLocalDomain(nodename)
	m.AddHandler(func(addr net.Addr, packet mdns.Packet) {
		logger.Debugf(ctx, "mdns packet from %s: %# v", addr, pretty.Formatter(packet))
		var zone string
		switch addr := addr.(type) {
		case *net.IPAddr:
			zone = addr.Zone
		case *net.UDPAddr:
			zone = addr.Zone
		}
		for _, records := range [][]mdns.Record{
			packet.Answers,
			packet.Additional,
		} {
			for _, record := range records {
				if record.Class == mdns.IN && record.Domain == domain {
					switch record.Type {
					case mdns.A, mdns.AAAA:
						out <- net.IPAddr{
							IP:   net.IP(record.Data),
							Zone: zone,
						}
						return
					}
				}
			}
		}
	})
	m.AddWarningHandler(func(addr net.Addr, err error) {
		logger.Infof(ctx, "from: %s; warn: %s", addr, err)
	})
	errs := make(chan error, 1)
	m.AddErrorHandler(func(err error) {
		errs <- err
	})

	ctx, cancel := context.WithCancel(ctx)
	defer cancel() // Clean up any goroutines launched by the mDNS client.
	if err := m.Start(ctx, mdns.DefaultPort); err != nil {
		return nil, net.IPAddr{}, fmt.Errorf("could not start mDNS client: %w", err)
	}

	var ipv4Addr net.IP
	var ipv6Addr net.IPAddr
	t := time.NewTicker(mDNSQuestionInterval)
	defer t.Stop()
	for {
		if err := m.Send(ctx, mdns.QuestionPacket(domain)); err != nil {
			return nil, net.IPAddr{}, fmt.Errorf("could not send mDNS question: %w", err)
		}

		for {
			select {
			case <-ctx.Done():
				// A timeout/cancelation is only considered an error if we
				// failed to resolve either address in the allotted time.
				// If we've already resolved at least one address, then we can
				// proceed since it's not the end of the world if we haven't
				// resolved both.
				if ipv4Addr == nil && ipv6Addr.IP == nil {
					err := ctx.Err()
					if errors.Is(err, context.DeadlineExceeded) {
						err = fmt.Errorf("%w after %s", err, time.Since(startTime))
					}
					return nil, net.IPAddr{}, err
				}
				return ipv4Addr, ipv6Addr, nil
			case err := <-errs:
				return ipv4Addr, ipv6Addr, err
			case addr := <-out:
				if addr.IP.To4() != nil {
					ipv4Addr = addr.IP
				} else if addr.IP.To16() != nil {
					ipv6Addr = addr
				} else {
					log.Panicf("IP address %q is neither IPv4 nor IPv6", addr)
				}

				// Got both addresses, so we're done.
				if ipv4Addr != nil && ipv6Addr.IP != nil {
					return ipv4Addr, ipv6Addr, nil
				}
				// `select` again to see if we can get the other IP address
				// without resending the question.
				continue
			case <-t.C:
				// If we already have one IP address and one more attempt didn't
				// get us the second one, we'll assume that it's not going to
				// come up (or at least not any time soon) and exit early with
				// just the first IP we resolved.
				if ipv4Addr != nil || ipv6Addr.IP != nil {
					return ipv4Addr, ipv6Addr, nil
				}
				// Fallthrough to resend the question.
			}
			break
		}
	}
}