implement basic peer discovery using mdns

discovery/mdns.go

+package discovery
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	golog "log"
+	"net"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/hashicorp/mdns"
+	ma "github.com/ipfs/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr"
+	manet "github.com/ipfs/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr-net"
+
+	"github.com/ipfs/go-ipfs/p2p/host"
+	"github.com/ipfs/go-ipfs/p2p/peer"
+	u "github.com/ipfs/go-ipfs/util"
+)
+
+var log = u.Logger("mdns")
+
+const LookupFrequency = time.Second * 5
+const ServiceTag = "discovery.ipfs.io"
+
+type Service interface {
+	io.Closer
+	RegisterNotifee(Notifee)
+	UnregisterNotifee(Notifee)
+}
+
+type Notifee interface {
+	HandlePeerFound(peer.PeerInfo)
+}
+
+type mdnsService struct {
+	server  *mdns.Server
+	service *mdns.MDNSService
+	host    host.Host
+
+	lk       sync.Mutex
+	notifees []Notifee
+}
+
+func NewMdnsService(peerhost host.Host) (Service, error) {
+
+	// TODO: dont let mdns use logging...
+	golog.SetOutput(ioutil.Discard)
+
+	// determine my local swarm port
+	port := 4001
+	for _, addr := range peerhost.Addrs() {
+		parts := strings.Split(addr.String(), "/")
+		fmt.Println("parts len: ", len(parts))
+		if len(parts) == 5 && parts[3] == "tcp" {
+			n, err := strconv.Atoi(parts[4])
+			if err != nil {
+				return nil, err
+			}
+			port = n
+			break
+		}
+	}
+	fmt.Println("using port: ", port)
+
+	myid := peerhost.ID().Pretty()
+
+	info := []string{myid}
+	service, err := mdns.NewMDNSService(myid, ServiceTag, "", "", port, nil, info)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create the mDNS server, defer shutdown
+	server, err := mdns.NewServer(&mdns.Config{Zone: service})
+	if err != nil {
+		return nil, err
+	}
+
+	s := &mdnsService{
+		server:  server,
+		service: service,
+		host:    peerhost,
+	}
+
+	go s.pollForEntries()
+
+	return s, nil
+}
+
+func (m *mdnsService) Close() error {
+	return m.server.Shutdown()
+}
+
+func (m *mdnsService) pollForEntries() {
+	ticker := time.NewTicker(LookupFrequency)
+	for {
+		select {
+		case <-ticker.C:
+			entriesCh := make(chan *mdns.ServiceEntry, 16)
+			go func() {
+				for entry := range entriesCh {
+					m.handleEntry(entry)
+				}
+			}()
+
+			qp := mdns.QueryParam{}
+			qp.Domain = "local"
+			qp.Entries = entriesCh
+			qp.Service = ServiceTag
+			qp.Timeout = time.Second * 3
+
+			err := mdns.Query(&qp)
+			if err != nil {
+				log.Error("mdns lookup error: ", err)
+			}
+			close(entriesCh)
+		}
+	}
+}
+
+func (m *mdnsService) handleEntry(e *mdns.ServiceEntry) {
+	mpeer, err := peer.IDB58Decode(e.Info)
+	if err != nil {
+		log.Warning("Error parsing peer ID from mdns entry: ", err)
+		return
+	}
+
+	if mpeer == m.host.ID() {
+		return
+	}
+
+	maddr, err := manet.FromNetAddr(&net.TCPAddr{
+		IP:   e.AddrV4,
+		Port: e.Port,
+	})
+	if err != nil {
+		log.Warning("Error parsing multiaddr from mdns entry: ", err)
+		return
+	}
+
+	pi := peer.PeerInfo{
+		ID:    mpeer,
+		Addrs: []ma.Multiaddr{maddr},
+	}
+
+	m.lk.Lock()
+	for _, n := range m.notifees {
+		n.HandlePeerFound(pi)
+	}
+	m.lk.Unlock()
+}
+
+func (m *mdnsService) RegisterNotifee(n Notifee) {
+	m.lk.Lock()
+	m.notifees = append(m.notifees, n)
+	m.lk.Unlock()
+}
+
+func (m *mdnsService) UnregisterNotifee(n Notifee) {
+	m.lk.Lock()
+	found := -1
+	for i, notif := range m.notifees {
+		if notif == n {
+			found = i
+			break
+		}
+	}
+	if found != -1 {
+		m.notifees = append(m.notifees[:found], m.notifees[found+1:]...)
+	}
+	m.lk.Unlock()
+}