edge/pkg/module/cast/discovery.go

package cast

import (
	"context"
	"net"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"gitlab.com/wpetit/goweb/logger"

	"github.com/barnybug/go-cast"
	"github.com/barnybug/go-cast/log"
	"github.com/hashicorp/mdns"
	"github.com/pkg/errors"
)

type Service struct {
	found     chan *cast.Client
	entriesCh chan *mdns.ServiceEntry

	stopPeriodic chan struct{}
}

func NewService(ctx context.Context) *Service {
	s := &Service{
		found:     make(chan *cast.Client),
		entriesCh: make(chan *mdns.ServiceEntry, 10),
	}

	go s.listener(ctx)
	return s
}

func (d *Service) Run(ctx context.Context, interval time.Duration) error {
	ifaces, err := findMulticastInterfaces(ctx)
	if err != nil {
		return errors.WithStack(err)
	}

	var wg sync.WaitGroup

	for _, iface := range ifaces {
		hasIPv4, hasIPv6, err := retrieveSupportedProtocols(iface)
		if err != nil {
			return errors.WithStack(err)
		}

		if !hasIPv4 && !hasIPv6 {
			continue
		}

		if err := d.queryIface(iface, !hasIPv4, !hasIPv6); err != nil {
			return errors.WithStack(err)
		}

		pollCtx, cancel := context.WithCancel(ctx)
		defer cancel()

		wg.Add(1)

		go func(ctx context.Context, iface net.Interface) {
			defer wg.Done()

			if err := d.pollInterface(ctx, iface, interval, !hasIPv4, !hasIPv6); err != nil {
				if errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled) {
					return
				}

				logger.Error(
					ctx, "could not poll interface",
					logger.E(errors.WithStack(err)), logger.F("iface", iface.Name),
				)
			}
		}(pollCtx, iface)
	}

	wg.Wait()

	return nil
}

func (d *Service) queryIface(iface net.Interface, disableIPv4, disableIPv6 bool) error {
	err := mdns.Query(&mdns.QueryParam{
		Service:     "_googlecast._tcp",
		Domain:      "local",
		Timeout:     3 * time.Second,
		Entries:     d.entriesCh,
		Interface:   &iface,
		DisableIPv6: disableIPv6,
		DisableIPv4: disableIPv4,
	})
	if err != nil {
		return errors.WithStack(err)
	}

	return nil
}

func (d *Service) pollInterface(ctx context.Context, iface net.Interface, interval time.Duration, disableIPv4, disableIPv6 bool) error {
	ticker := time.NewTicker(interval)
	for {
		select {
		case <-ticker.C:
			if err := d.queryIface(iface, disableIPv4, disableIPv6); err != nil {
				return errors.WithStack(err)
			}

		case <-ctx.Done():
			if err := ctx.Err(); err != nil {
				return errors.WithStack(err)
			}

			return nil
		}
	}
}

func (d *Service) Stop() {
	if d.stopPeriodic != nil {
		close(d.stopPeriodic)
		d.stopPeriodic = nil
	}
}

func (d *Service) Found() chan *cast.Client {
	return d.found
}

func (d *Service) listener(ctx context.Context) {
	for entry := range d.entriesCh {
		name := strings.Split(entry.Name, "._googlecast")
		// Skip everything that doesn't have googlecast in the fdqn
		if len(name) < 2 {
			continue
		}

		log.Printf("New entry: %#v\n", entry)
		client := cast.NewClient(entry.AddrV4, entry.Port)
		info := decodeTxtRecord(entry.Info)
		client.SetName(info["fn"])
		client.SetInfo(info)

		select {
		case d.found <- client:
		case <-time.After(time.Second):
		case <-ctx.Done():
			break
		}
	}
}

func decodeDnsEntry(text string) string {
	text = strings.Replace(text, `\.`, ".", -1)
	text = strings.Replace(text, `\ `, " ", -1)

	re := regexp.MustCompile(`([\\][0-9][0-9][0-9])`)
	text = re.ReplaceAllStringFunc(text, func(source string) string {
		i, err := strconv.Atoi(source[1:])
		if err != nil {
			return ""
		}

		return string([]byte{byte(i)})
	})

	return text
}

func decodeTxtRecord(txt string) map[string]string {
	m := make(map[string]string)

	s := strings.Split(txt, "|")
	for _, v := range s {
		s := strings.Split(v, "=")
		if len(s) == 2 {
			m[s[0]] = s[1]
		}
	}

	return m
}

func isIPv4(ip net.IP) bool {
	return strings.Count(ip.String(), ":") < 2
}

func isIPv6(ip net.IP) bool {
	return strings.Count(ip.String(), ":") >= 2
}

func findMulticastInterfaces(ctx context.Context) ([]net.Interface, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, nil
	}

	multicastIfaces := make([]net.Interface, 0)

	for _, iface := range ifaces {
		if iface.Flags&net.FlagLoopback == net.FlagLoopback {
			continue
		}

		if iface.Flags&net.FlagRunning != net.FlagRunning {
			continue
		}

		if iface.Flags&net.FlagMulticast != net.FlagMulticast {
			continue
		}

		multicastIfaces = append(multicastIfaces, iface)
	}

	return multicastIfaces, nil
}

func retrieveSupportedProtocols(iface net.Interface) (bool, bool, error) {
	adresses, err := iface.Addrs()
	if err != nil {
		return false, false, errors.WithStack(err)
	}

	hasIPv4 := false
	hasIPv6 := false

	for _, addr := range adresses {
		ip, _, err := net.ParseCIDR(addr.String())
		if err != nil {
			return false, false, errors.WithStack(err)
		}

		if isIPv4(ip) {
			hasIPv4 = true
		}

		if isIPv6(ip) {
			hasIPv6 = true
		}

		if hasIPv4 && hasIPv6 {
			return hasIPv4, hasIPv6, nil
		}
	}

	return hasIPv4, hasIPv6, nil
}