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package main
import (
func setupMdns(ctx context.Context, h host.Host) error {
// We're going to be announcing every 5 seconds
mdns, err := discovery.NewMdnsService(ctx, h, time.Second*5, "")
if err != nil {
return err
notifee := &MdnsNotifee{
h: h,
askedPeers: make(map[peer.ID]struct{}),
return nil
type MdnsNotifee struct {
lock sync.Mutex
h host.Host
askedPeers map[peer.ID]struct{}
// When a new peer is found, we run a new Stream of `SayMyAddrs` protocol where
// we receive his/her preferred multiaddrs to be dialed.
func (mh *MdnsNotifee) HandlePeerFound(ai peer.AddrInfo) {
defer mh.lock.Unlock()
// Already Ping/Pong peer?
if _, ok := mh.askedPeers[ai.ID]; ok {
mh.askedPeers[ai.ID] = struct{}{}
log.Infof("discovered unknown peer: %s", ai.ID)
// We add the discovered addrs from Mdns to the peer known addrs
mh.h.Peerstore().AddAddrs(ai.ID, ai.Addrs, peerstore.PermanentAddrTTL)
addrs := askPeerForPreferredAddrs(mh.h, ai.ID)
// We define that our discovered peer addrs are what they prefer
mh.h.Peerstore().SetAddrs(ai.ID, addrs, peerstore.PermanentAddrTTL)
// Close existing connection with the peer, so new Streams will dial from
// preferred addresses
if err := mh.h.Network().ClosePeer(ai.ID); err != nil {
log.Warning("error when closing existing connection with peer")
go playPingPong(mh.h, ai.ID)
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