Support ipv6 for mDNS Server

[TA2k]

At the moment the mDNS server is not working if other service already offer mDNS service. To allow multiple mDNS server for example in multi docker systems you have to support ipv6

Please add the option to enable mDNS server via ipv6 https://github.com/pion/ice/blob/c8227261a2b808446bf181475032c54c3b509f1c/mdns.go#L46C5-L46C5

Depends on https://github.com/pion/mdns/issues/69

[edaniels]

mdns/v2 now supports IPv6 so it can get into ICE now! Shouldn't be too difficult but we'll need to explicitly configure it

[edaniels]

@TA2k do you want to take a shot at this?

It may be as simple as in mdns.go:

func createMulticastDNS(n transport.Net, networkTypes []NetworkType, mDNSMode MulticastDNSMode, mDNSName string, log logging.LeveledLogger) (*mdns.Conn, MulticastDNSMode, error) {
    if mDNSMode == MulticastDNSModeDisabled {
        return nil, mDNSMode, nil
    }

    var wantV4, wantV6 bool
    if len(networkTypes) == 0 {
        wantV4 = true
        wantV6 = true
    }
    for _, nt := range networkTypes {
        switch nt {
        case NetworkTypeTCP4, NetworkTypeUDP4:
            wantV4 = true
        case NetworkTypeTCP6, NetworkTypeUDP6:
            wantV6 = true
        }
    }
    if !(wantV4 || wantV6) {
        return nil, mDNSMode, errMulticastDNSNoUsableNetworkType
    }

    var multicastPktConnV4 *ipv4.PacketConn
    if wantV4 {
        addr4, mdnsErr := n.ResolveUDPAddr("udp4", mdns.DefaultAddressIPv4)
        if mdnsErr != nil {
            return nil, mDNSMode, mdnsErr
        }

        l4, mdnsErr := n.ListenUDP("udp4", addr4)
        if mdnsErr != nil {
            // If ICE fails to start MulticastDNS server just warn the user and continue
            log.Errorf("Failed to enable mDNS, continuing in mDNS disabled mode: (%s)", mdnsErr)
            return nil, MulticastDNSModeDisabled, nil
        }

        multicastPktConnV4 = ipv4.NewPacketConn(l4)
    }

    var multicastPktConnV6 *ipv6.PacketConn
    if wantV6 {
        addr6, mdnsErr := n.ResolveUDPAddr("udp6", mdns.DefaultAddressIPv6)
        if mdnsErr != nil {
            return nil, mDNSMode, mdnsErr
        }

        l6, mdnsErr := n.ListenUDP("udp6", addr6)
        if mdnsErr != nil {
            // If ICE fails to start MulticastDNS server just warn the user and continue
            log.Errorf("Failed to enable mDNS, continuing in mDNS disabled mode: (%s)", mdnsErr)
            return nil, MulticastDNSModeDisabled, nil
        }

        multicastPktConnV6 = ipv6.NewPacketConn(l6)
    }

    switch mDNSMode {
    case MulticastDNSModeQueryOnly:
        conn, err := mdns.Server(multicastPktConnV4, multicastPktConnV6, &mdns.Config{})
        return conn, mDNSMode, err
    case MulticastDNSModeQueryAndGather:
        conn, err := mdns.Server(multicastPktConnV4, multicastPktConnV6, &mdns.Config{
            LocalNames: []string{mDNSName},
        })
        return conn, mDNSMode, err
    default:
        return nil, mDNSMode, nil
    }
}

but it needs some testing around interfaces that have supported ipv6 addresses https://tools.ietf.org/html/rfc8445#section-5.1.1.1 (link-local ones which are common are not allowed for security reasons of exposing the zone (I think))

[Sean-Der]

IPv6 support was added with 39c0392295a06b5cac940f7a49d61cc74ca56c6f

thank you @edaniels !