// startListening on the network addresses
func startListening(ctx context.Context, host p2phost.Host, cfg *config.Config) error {
	listenAddrs, err := listenAddresses(cfg)
	if err != nil {
		return err
	}

	// make sure we error out if our config does not have addresses we can use
	log.Debugf("Config.Addresses.Swarm:%s", listenAddrs)
	filteredAddrs := addrutil.FilterUsableAddrs(listenAddrs)
	log.Debugf("Config.Addresses.Swarm:%s (filtered)", filteredAddrs)
	if len(filteredAddrs) < 1 {
		return fmt.Errorf("addresses in config not usable: %s", listenAddrs)
	}

	// Actually start listening:
	if err := host.Network().Listen(filteredAddrs...); err != nil {
		return err
	}

	// list out our addresses
	addrs, err := host.Network().InterfaceListenAddresses()
	if err != nil {
		return err
	}
	log.Infof("Swarm listening at: %s", addrs)
	return nil
}

// dial is the actual swarm's dial logic, gated by Dial.
func (s *Swarm) dial(ctx context.Context, p peer.ID) (*Conn, error) {
	var logdial = lgbl.Dial("swarm", s.LocalPeer(), p, nil, nil)
	if p == s.local {
		log.Event(ctx, "swarmDialDoDialSelf", logdial)
		return nil, ErrDialToSelf
	}
	defer log.EventBegin(ctx, "swarmDialDo", logdial).Done()
	logdial["dial"] = "failure" // start off with failure. set to "success" at the end.

	sk := s.peers.PrivKey(s.local)
	logdial["encrypted"] = (sk != nil) // log wether this will be an encrypted dial or not.
	if sk == nil {
		// fine for sk to be nil, just log.
		log.Debug("Dial not given PrivateKey, so WILL NOT SECURE conn.")
	}

	// get remote peer addrs
	remoteAddrs := s.peers.Addrs(p)
	// make sure we can use the addresses.
	remoteAddrs = addrutil.FilterUsableAddrs(remoteAddrs)
	// drop out any addrs that would just dial ourselves. use ListenAddresses
	// as that is a more authoritative view than localAddrs.
	ila, _ := s.InterfaceListenAddresses()
	remoteAddrs = addrutil.Subtract(remoteAddrs, ila)
	remoteAddrs = addrutil.Subtract(remoteAddrs, s.peers.Addrs(s.local))

	log.Debugf("%s swarm dialing %s -- local:%s remote:%s", s.local, p, s.ListenAddresses(), remoteAddrs)
	if len(remoteAddrs) == 0 {
		err := errors.New("peer has no addresses")
		logdial["error"] = err
		return nil, err
	}

	remoteAddrs = s.filterAddrs(remoteAddrs)
	if len(remoteAddrs) == 0 {
		err := errors.New("all adresses for peer have been filtered out")
		logdial["error"] = err
		return nil, err
	}

	// try to get a connection to any addr
	connC, err := s.dialAddrs(ctx, p, remoteAddrs)
	if err != nil {
		logdial["error"] = err
		return nil, err
	}
	logdial["netconn"] = lgbl.NetConn(connC)

	// ok try to setup the new connection.
	defer log.EventBegin(ctx, "swarmDialDoSetup", logdial, lgbl.NetConn(connC)).Done()
	swarmC, err := dialConnSetup(ctx, s, connC)
	if err != nil {
		logdial["error"] = err
		connC.Close() // close the connection. didn't work out :(
		return nil, err
	}

	logdial["dial"] = "success"
	return swarmC, nil
}

func filterAddrs(listenAddrs []ma.Multiaddr) ([]ma.Multiaddr, error) {
	if len(listenAddrs) > 0 {
		filtered := addrutil.FilterUsableAddrs(listenAddrs)
		if len(filtered) < 1 {
			return nil, fmt.Errorf("swarm cannot use any addr in: %s", listenAddrs)
		}
		listenAddrs = filtered
	}
	return listenAddrs, nil
}

func TestFilterAddrs(t *testing.T) {

	m := func(s string) ma.Multiaddr {
		maddr, err := ma.NewMultiaddr(s)
		if err != nil {
			t.Fatal(err)
		}
		return maddr
	}

	bad := []ma.Multiaddr{
		m("/ip4/1.2.3.4/udp/1234"),           // unreliable
		m("/ip4/1.2.3.4/udp/1234/sctp/1234"), // not in manet
		m("/ip4/1.2.3.4/udp/1234/utp"),       // utp is broken
		m("/ip4/1.2.3.4/udp/1234/udt"),       // udt is broken on arm
		m("/ip6/fe80::1/tcp/0"),              // link local
		m("/ip6/fe80::100/tcp/1234"),         // link local
	}

	good := []ma.Multiaddr{
		m("/ip4/127.0.0.1/tcp/0"),
		m("/ip6/::1/tcp/0"),
	}

	goodAndBad := append(good, bad...)

	// test filters

	for _, a := range bad {
		if addrutil.AddrUsable(a, true) {
			t.Errorf("addr %s should be unusable", a)
		}
	}

	for _, a := range good {
		if !addrutil.AddrUsable(a, true) {
			t.Errorf("addr %s should be usable", a)
		}
	}

	subtestAddrsEqual(t, addrutil.FilterUsableAddrs(bad), []ma.Multiaddr{})
	subtestAddrsEqual(t, addrutil.FilterUsableAddrs(good), good)
	subtestAddrsEqual(t, addrutil.FilterUsableAddrs(goodAndBad), good)

	// now test it with swarm

	id, err := testutil.RandPeerID()
	if err != nil {
		t.Fatal(err)
	}

	ps := peer.NewPeerstore()
	ctx := context.Background()

	if _, err := NewNetwork(ctx, bad, id, ps, metrics.NewBandwidthCounter()); err == nil {
		t.Fatal("should have failed to create swarm")
	}

	if _, err := NewNetwork(ctx, goodAndBad, id, ps, metrics.NewBandwidthCounter()); err != nil {
		t.Fatal("should have succeeded in creating swarm", err)
	}
}